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Thermodynamic Modeling and Experimental Analysis of Oxidation/Sulfidation of Ni-Cr-Al Model Alloy Coatings

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PAGE 1

THERMODYNAMIC MODELING AND EXPERIMENTAL ANALYSIS OF OXIDATION/ SULFIDATION OF NI-CR-AL MODEL ALLOY COATINGS By ERIK M. MUELLER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2007

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2007 Erik M. Mueller

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This dissertation is dedicated to all hard-working graduate students.

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ACKNOWLEDGMENTS I would like to thank my supervisory committee chair, Dr. Wolfgang Sigmund, for all his support and last-minute assistance on this dissertation. I would also like to thank my former advisor, Dr. Hans Seifert, for not only starting me on and supporting me with this project financially, but for the invaluable help in teaching the Thermo-Calc computational software as well as the challenging goals set to enable me to finish this project. I would like to thank Damian Cupid for his help with the thermodynamic software and his insight into unique approaches to the problems encountered in computational thermodynamics. I would also like to thank Dr. L. Amelia Dempere for her support and use of the characterization equipment at the Major Analytical Instrumentation Center. Wayne Acree should be credited with the operating the electron microprobe. Dr. Gerhard Fuchs high-temperature materials courses were also instrumental in exposing me to this subject area in metallurgy. Dr. W. Greg Sawyer and Dr. Gerald Bourne also assisted in this project by serving on my supervisory committee. Finally, I would also like to thank the University of Florida and the Materials Science and Engineering Department for use of their facilities and for affording me the opportunity to complete this degree with financial assistance. iv

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TABLE OF CONTENTS page ACKNOWLEDGMENTS .............................................................................................................iv LIST OF TABLES ........................................................................................................................vii LIST OF FIGURES .....................................................................................................................viii ABSTRACT .....................................................................................................................................1 1 INTRODUCTION ........................................................................................................................2 2 LITERATURE REVIEW .............................................................................................................5 2.1 Turbine Engine Considerations ..........................................................................................5 2.2 Turbine Blade Materials .....................................................................................................6 2.2.1 Superalloys ...............................................................................................................6 2.2.2 Coatings for Turbine Blades .....................................................................................7 2.4 The Al-Cr-Ni Ternary System ............................................................................................9 2.5 Oxidation of Al-Ni-Cr Alloys ...........................................................................................17 2.5.1 General Oxidation Mechanism ...............................................................................17 2.5.1.1 Oxidation of Ni .............................................................................................19 2.5.1.2 Oxidation of Al .............................................................................................20 2.5.1.3 Oxidation of Cr .............................................................................................22 2.5.2 Oxidation of Ni-Al Alloys ......................................................................................23 2.5.3 Oxidation in Al-Cr-Ni Ternary and NiCrAlY Coatings .........................................26 2.6 Sulfidation and Hot Corrosion ..........................................................................................28 2.6.1 Hot Corrosion .........................................................................................................28 2.6.2 Sulfidation on Metals .............................................................................................29 2.6.3 Sulfidation on Metal Oxides ...................................................................................31 2.6.4 Sulfidation in Ni-Cr-Al Coatings ...........................................................................33 2.7 Calculations of Oxidation/Sulfidation ..............................................................................34 3 METHODS AND MATERIALS ................................................................................................36 3.1 Thermodynamic Modeling and Simulations ....................................................................36 3.1.1 The CALPHAD Approach .....................................................................................36 3.1.2 Databases and Software ..........................................................................................37 3.2 Materials and Sample Preparation ....................................................................................38 3.3 Thermogravimetric Analysis ............................................................................................39 3.4 Characterization ................................................................................................................43 3.4.1 X-Ray Diffraction ...................................................................................................44 3.4.2 Scanning Electron Microscopy ...............................................................................44 3.4.3 Electron Microprobe ...............................................................................................45 4 THERMODYNAMIC CALCULATION RESULTS .................................................................46 v

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4.1 Calculations of Ni-Cr-Al Alloys and Mixtures using Phase Diagrams ............................46 4.1.1 Binary Systems .......................................................................................................46 4.1.2 Ternary Systems .....................................................................................................49 4.2 Calculations of Temperature-Potential Diagrams ............................................................53 4.2.1 Calculations with O-SO Interactions 2 2 ...................................................................53 4.2.2 Calculations of Metal-Gas Interactions ..................................................................57 4.3 Calculations of Potential Diagrams ..................................................................................58 4.4 Phase Fraction Diagrams ..................................................................................................73 5 EXPERIMENTAL RESULTS ....................................................................................................81 5.1 TGA Experiments .............................................................................................................81 5.1.1 Oxidation Experiments in Air ................................................................................81 5.1.2 Oxidation Experiments in He + 0.21 O + 0.02 SO 2 2 ..............................................88 5.1.3 Oxidation Experiments in He + 0.21 O + 0.10 SO 2 2 ..............................................91 5.2 Phase Identification ..........................................................................................................95 5.3 Surface Imaging ..............................................................................................................106 5.3.1 Untested Alloy Specimens ...................................................................................106 5.3.2 Oxidized Ni and Ni-Al Specimens .......................................................................113 5.3.3 Oxidized Ni-8Cr-6Al Specimens .........................................................................113 5.3.3.1 Ni-8Cr-6Al Oxidized in Air .......................................................................113 5.3.3.2 Ni-8Cr-6Al Oxidized in He + 0.21 O + 0.02 SO 2 2 .....................................118 5.3.3.3 Ni-8Cr-6Al Oxidized in He + 0.21 O + 0.10 SO 2 2 .....................................121 5.3.4 Oxidized Ni-22Cr-11Al Specimens .....................................................................124 5.3.4.1 Ni-22Cr-11Al Oxidized in Air ...................................................................124 5.3.4.2 Ni-22Cr-11Al Oxidized in He + 0.21 O + 0.02 SO 2 2 .................................126 5.3.4.3 Ni-8Cr-6Al Oxidized in He + 0.21 O + 0.10 SO 2 2 .....................................129 5.4 Cross-Sectional Analysis ................................................................................................131 5.4.1 Ni and Ni-Al Specimens ...............................................................................131 5.4.2 Ni-8Cr-6Al Specimens ..................................................................................133 5.4.3 Ni-22Cr-11Al Specimens ..............................................................................137 5.4.4 Electron Microprobe (EPMA) Analysis ........................................................139 6 DISCUSSION AND ANALYSIS ............................................................................................142 6.1 Mechanisms of Scale Formation ....................................................................................142 6.2 Comparison of Experimental Results and Calculations .................................................148 7 CONCLUSIONS .......................................................................................................................156 LIST OF REFERENCES .............................................................................................................158 BIOGRAPHICAL SKETCH .......................................................................................................167 vi

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LIST OF TABLES Table page 2-1. List of common alloying elements in Ni-base superalloys. ......................................................7 2-2. List of phases described in calculations of the Al-Cr-Ni ternary. ..........................................14 2-3. The phases present in the Ni-22Cr-11Al and Ni-8Cr-6Al (weight percent) alloys at room temperature and 1000C. ..........................................................................................17 2-4. Descriptions and crystallographic information on different phases of AlO [49-50]. 2 3 ..........21 3-1. List of experimental conditions performed for oxidation of alloys for 100 hr in 1 bar of gas at 25 mL/min. ..............................................................................................................43 4-1. Comparison of equilibria computed between two databases SPOT3 and SPIN4 at a pressure of 1 bar and T = 1073 K for Ni-22Cr-11Al alloy (by mass) with a P of 0.22 bar. This table compares number of moles of each phase, along with the composition (in weight fraction) of each phase. O2 ................................................................58 4-2. Comparison of gas species (at mole fractions > 10) present in the unstable equilibrium regions of Figure 4-19 at low P and high P. These mole fractions are calculated based on ideal gas behavior. -10 O2 O2 .............................................................................60 5-1. List of the parabolic rate constants obtained from steady-state oxidation of Ni, Ni-13.6Al, NiAl, Ni-8Cr-6Al, and Ni-22Cr-11Al alloys. .......................................................94 5-2. Table summarizing the phases identified using XRD for all cast, heat-treated alloys oxidized. ...........................................................................................................................107 6-1. Table showing the equilibrium partial pressures of gases that evolve upon various mixtures of O and SO at various temperatures, calculated from the SPOT3 database. 2 2 ...........................................................................................................................146 vii

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LIST OF FIGURES Figure page 2-1. Schematic of a typical turbine engine. ......................................................................................5 2-2. Schematic of coating configuration of modern turbine blades. ................................................9 2-3. Al-Ni binary phase diagram [H. Baker. ASM Handbook Vol. 3Alloy Phase Diagrams, ASM International: Materials Park, OH, p. 49 (1992)]. ....................................................10 2-4. Ni-Cr binary phase diagram [H. Baker. ASM Handbook Vol. 3Alloy Phase Diagrams, ASM International: Materials Park, OH, p. 155 (1992)]. ..................................................10 2-5. Al-Cr binary phase diagram [H. Baker. ASM Handbook Vol. 3Alloy Phase Diagrams, ASM International: Materials Park, OH, p. 43 (1992)]. ....................................................11 2-6. Liquidus projection of the Al-Ni-Cr ternary system [P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 411 (1991)]. ........................................................13 2-7. Scheil reaction scheme of the Al-Cr-Ni ternary. The -phase refers to NiAl, the to AlCr-hexagonal, to AlCr-rhombodedral, and to AlCr. The question marks represent areas of the ternary that were not investigated. 2 3 1 8 5 2 8 5 1 9 4 ..................................................13 2-8. Isothermal section of Al-Cr-Ni ternary at 1025C above the U reaction. The green areas denote regions of two-phase equilibria [P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 414 (1991)]. 4 ........................................................15 2-9. Partial Isothermal section of Al-Cr-Ni ternary at 850C below the U reaction. The green areas denote regions of two-phase equilibria [P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 413 (1991)]. 4 ........................................................15 2-10. Plot of oxidation growth kinetics versus time. .....................................................................18 2-11 Arrhenius plot of parabolic growth rates versus temperature of NiO (violet) as well as CrO and AlO (red) [J.L. Smialek, G.M. Meier, High-Temperature Oxidation, Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New York p. 295 (1987)]. 2 3 2 3 .........................................................................................................24 2-12. Dependence of oxidation mechanisms and scale type of Ni-Al alloys based on temperature and Al content [F.S. Pettit: Transactions of the AIME. 239, pp. 1296-1305 (1967)]. ......................................................................................................................25 2-13. Schematic of the stages of oxidation in Ni-Cr-Al alloys. Group I are alloys that will have a stable NiO scale, Group II will develop a stable CrO scale, and Group III 2 3 viii

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will develop a stable AlO scale [F.S. Pettit: Transactions of the AIME. 239, pp. 1296-1305 (1967)]. 2 3 ............................................................................................................27 2-24. Schematic showing the formation of metal sulfides (a) under an initial metal oxide layer (b) in simultaneous oxidizing and sulfidizing conditions. The various proposed transport mechanisms are shown. ......................................................................................32 3-1. Flowchart detailing the Calculation of Phase Diagrams approach. This study is concerned mostly with the equilibrium calculations. ........................................................37 3-2. Schematic of the Setsys Evolution (TGA only). ....................................................................41 4-1. Temperature-composition binary phase diagram of the Ni-Al system calculated from the SPIN4 database. ...........................................................................................................47 4-2. Temperature-composition binary phase diagram of the Ni-Cr system calculated from the SPIN4 database. ...........................................................................................................47 4-3. Temperature-composition binary phase diagram of the Al-Cr system calculated from the SPIN4 database. ...........................................................................................................48 4-4. Temperature-composition binary phase diagram of the Ni-Al system calculated from the SPIN4 database with the NiAl low-temperature phase restored. 3 5 ..............................48 4-5. Isothermal section of Ni-Cr-Al ternary system at 900C in weight fractions. This diagram is calculated from data in the SPIN4 database. ....................................................49 4-6. Partial isothermal section of Ni-Cr-Al ternary system at 850C in mole fractions. The axes are chosen to compare with Figure 2-9. This diagram is calculated from data in the SPIN4 database. ...........................................................................................................50 4-7. Isothermal section of Ni-Cr-Al ternary system at 1025C in mole fractions. The axes are chosen to compare with Figure 2-8. This diagram is calculated from data in the SPIN4 database. .................................................................................................................50 4-8. Ternary isothermal section of the Ni-Al-O system at 900C. The x-axis is the composition of Al in weight percent, and the y-axis is the logarithmic partial pressure of O in bar. This diagram is calculated from data in the SPIN4 database. 2 2 .......51 4-9. Ternary isothermal section of the Ni-Cr-O system at 900C. The x-axis is the composition of Cr in weight percent, and the y-axis is the logarithmic partial pressure of O in bar. This diagram is calculated from data in the SPIN4 database. 2 2 .......51 4-10. The Ni-Al-Cr-O system shown as a series of connected ternary subsystem isotherms at 900C. The outer axes are the logarithm of the partial pressure of O in bar, whereas the inner axes are the weight percents of Ni, Cr, and Al. This diagram is calculated from data in the SPIN4 database. 2 .......................................................................................52 ix

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4-11. Change in partial pressure of O, SO, and SO (in bar) with temperature using the initial gas mixture of He + 0.21 O + 0.02 SO. The P is omitted due to scale. The data used for calculations is taken from the SPOT3 database. 2 2 3 2 2 He ..........................................54 4-12. Change in partial pressure of O, SO, and SO (in bar) with temperature using the initial gas mixture of He + 0.21 O + 0.10 SO. The P is omitted due to scale. The data used for calculations is taken from the SPOT3 database. 2 2 3 2 2 He ..........................................55 4-13. The relationship between the partial pressure of SO in an O-SO gas mixture, with varying temperature. All partial pressures are in bar. 3 2 2 .......................................................55 4-14. The relationship between the partial pressure of S in an O-SO gas mixture, with varying temperature. All partial pressures are in bar. 2 2 2 .......................................................56 4-15. The relationship between the partial pressure of O in an SO-SO gas mixture, with varying temperature. All partial pressures are in bar. 2 3 2 .......................................................56 4-16. Stability diagram of Ni and its oxide with varying temperature and partial pressure of oxygen (in bar). ..................................................................................................................59 4-17. Stability diagram of Ni and its oxide with varying temperature and partial pressure of oxygen (in bar) with a constant partial pressure of sulfur dioxide at 2 mol %. .................59 4-18. Stability diagram of Ni and its oxide with varying temperature and partial pressure of oxygen (in bar) with a constant partial pressure of sulfur dioxide at 10 mol %. ...............60 4-19. Ni potential diagrams for (a) SO-Oand (b) S-Oat 800C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 2 2 2 2 .................................................................61 4-20. Ni SO-Opotential diagram at 900C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 2 2 .......................................................................................61 4-21. Ni SO-Opotential diagram at 1000C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 2 2 .......................................................................................62 4-22. Al potential diagrams for (a) SO-Oand (b) S-Oat 800C. Published in [170]. 2 2 2 2 .............63 4-23. Al SO-Opotential diagram at 900C. 2 2 .................................................................................64 4-24. Al SO-Opotential diagram at 1000C. 2 2 ...............................................................................64 4-25. Cr potential diagrams for (a) SO-Oand (b) S-Oat 800C. Published in [170]. 2 2 2 2 .............65 4-26. Cr SO-Opotential diagram at 900C. 2 2 .................................................................................65 4-27. Al SO-Opotential diagram at 900C. 2 2 .................................................................................66 4-28. Ni-13.6Al potential diagrams for (a) SO-Oand (b) S-Oat 800C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 2 2 2 2 ............................................66 x

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4-29. NiAl SO-Opotential diagram at 900C. 3 2 2 ...........................................................................67 4-30. NiAl SO-Opotential diagram at 1000C. Published in [170]. 3 2 2 .........................................67 4-31. NiAl potential diagrams for (a) SO-Oand (b) S-Oat 800C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 2 2 2 2 .................................................................68 4-32. NiAl SO-Opotential diagram at 900C. 2 2 .............................................................................68 4-33. NiAl SO-Opotential diagram at 1000C. Published in [170]. 2 2 ..........................................69 4-34. Ni-8Cr-6Al potential diagrams for (a) SO-Oand (b) S-Oat 800C. Published in [170]. 2 2 2 2 ..................................................................................................................................70 4-35. Ni-8Cr-6Al SO-Opotential diagram at 900C. Published in [170]. 2 2 .................................70 4-36. Ni-8Cr-6Al SO-Opotential diagram at 1000C. Published in [170]. 2 2 ...............................71 4-37. Ni-22Cr-11Al potential diagrams for (a) SO-Oand (b) S-Oat 800C. Published in [170]. 2 2 2 2 ..................................................................................................................................72 4-38. Ni-22Cr-11Al SO-Opotential diagram at 900C. Published in [170]. 2 2 .............................72 4-39. Ni-22Cr-11Al SO-Opotential diagram at 1000C. Published in [170]. 2 2 ...........................73 4-40. Phase fraction diagram of the Ni-O system showing the change in phase percent with varying oxygen partial pressure at 800C in air. Calculated from the SPOT3 database. .............................................................................................................................75 4-41. Phase fraction diagram of the Ni-O-S system showing the change in phase percent with varying oxygen partial pressure at 800C in an 0.21 O + 0.02 SO atmosphere. Calculated from the SPOT3 database. 2 2 ...............................................................................76 4-42. Phase fraction diagram of the Ni-O-S system showing the gas evolution (in partial pressure [bar]) with varying oxygen partial pressure at 800C in an 0.21 O + 0.02 SO atmosphere. Calculated from the SPOT3 database. 2 2 ..................................................76 4-43. Phase fraction diagram of the Ni-O-S system showing activity change of each component with varying oxygen partial pressure at 800C in an 0.21 O + 0.02 SO atmosphere. Calculated from the SPOT3 database. 2 2 ..........................................................77 4-44. Phase fraction diagram an Ni-8Cr-6Al alloy showing activity change of each component with varying oxygen partial pressure at 800C in air. Calculated from the SPIN4 database. .................................................................................................................77 4-45. Phase fraction diagram an Ni-8Cr-6Al alloy showing the change in phase percent with varying oxygen partial pressure at 800C in air. Calculated from the SPIN4 database. .............................................................................................................................78 xi

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4-46. Phase fraction diagram an Ni-8Cr-6Al alloy at 800C comparing the activity change calculated for Figure 4-38 using the SPIN4 database (black) and the SPOT3 database (teal). ..................................................................................................................................78 4-48. Phase fraction diagram of an Ni-8Cr-6Al alloy showing the change in phase percent with varying oxygen partial pressure at 800C in an 0.21 O + 0.02 SO atmosphere. Calculated from the appended SPIN4 database. 2 2 ................................................................79 4-49. Phase fraction diagram of an Ni-22Cr-11Al alloy showing activity change of each component with varying oxygen partial pressure at 800C in an 0.21 O + 0.02 SO atmosphere. Calculated from the appended SPIN4 database. 2 2 ...........................................80 4-50. Phase fraction diagram of an Ni-22Cr-11Al alloy showing the change in phase percent with varying oxygen partial pressure at 800C in an 0.21 O2 + 0.02 SO atmosphere. Calculated from the appended SPIN4 database. 2 ................................................................80 5-1. Plot of weight change versus time for Ni specimen at 800C for 24 hr in air. .......................81 5-2. Plot of weight change versus square root time for Ni specimen at 800C for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. ............82 5-3. Plot of weight change versus square root time for Ni specimen at 900C for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. ............83 5-4. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni oxidized for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. .....................................................................................................83 5-5. Plot of weight change versus square root time for a NiAl specimen at 800C for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. ....84 5-6. Arrhenius plot of the parabolic rate constant versus inverse temperature of NiAl oxidized for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. .....................................................................................................85 5-7. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 1000C for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. ............................................................................................................................86 5-8. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 900C for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. ............................................................................................................................86 5-9. Plot of weight change versus square root time for a Ni-22Cr-11Al specimen at 800C for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. .....................................................................................................87 xii

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5-10. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al oxidized for 100 hr in air. ..................................................................................................87 5-11. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-11Al oxidized for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. ................................................................................................88 5-12. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 975C for 100 hr in He + 0.21 O + 0.02 SO. The formula containing the slope and the coefficient of determination are listed. 2 2 ..............................................................................89 5-13. Plot of weight change versus square root time for a Ni-22Cr-11Al specimen at 975C for 100 hr in He + 0.21 O + 0.02 SO. The formula containing the slope and the coefficient of determination are listed. 2 2 ..............................................................................89 5-14. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al oxidized for 100 hr in He + 0.21 O + 0.02 SO. The formula containing the slope and the coefficient of determination are listed. 2 2 ..................................................................90 5-15. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-11Al oxidized for 100 hr in He + 0.21 O + 0.02 SO. The formula containing the slope and the coefficient of determination are listed. 2 2 ........................................................90 5-16. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 900C for 100 hr in He + 0.21 O + 0.10 SO. The formulas containing the slopes and the coefficients of determination are listed. 2 2 .............................................................................91 5-17. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al oxidized for 100 hr in He + 0.21 O + 0.10 SO. The blue data and regression correspond to the initial oxidation rates, whereas the red data and regression correspond to the later stage oxidation. The formulas containing the slope and the coefficients of determination are listed. 2 2 .............................................................................92 5-18. Plot of weight change versus square root time for a Ni-22Cr-11Al specimen at 800C for 100 hr in He + 0.21 O + 0.10 SO. The formula containing the slope and the coefficient of determination are listed. 2 2 ..............................................................................93 5-19. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-11Al oxidized for 100 hr in He + 0.21 O + 0.10 SO. The formula containing the slope and the coefficient of determination are listed. 2 2 ........................................................93 5-20. Arrhenius plot of alloys isothermally oxidized in this study for 100 hr. ..............................95 5-21. Histogram of the peak intensities measured from an XRD analysis of polished, heat treated Ni-8Cr-6Al. ............................................................................................................96 5-22. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in air for 100 hr at 800C. ....................................................................................96 xiii

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5-23. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in air for 100 hr at 900C. ....................................................................................97 5-24. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in air for 100 hr at 1000C. ..................................................................................97 5-25. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O + 0.02 SOfor 100 hr at 800C. 2 2 ................................................98 5-26. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O + 0.02 SOfor 100 hr at 900C. 2 2 ................................................98 5-27. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O + 0.02 SOfor 100 hr at 975C. 2 2 ................................................99 5-28. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O + 0.10 SOfor 100 hr at 800C. 2 2 ................................................99 5-29. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O + 0.10 SOfor 100 hr at 900C. 2 2 ..............................................100 5-30. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O + 0.10 SOfor 100 hr at 975C. 2 2 ..............................................100 5-31. Histogram of the peak intensities measured from an XRD analysis of polished, heat treated Ni-22Cr-11Al. ......................................................................................................101 5-32. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in air for 100 hr at 800C. ..................................................................................102 5-33. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in air for 100 hr at 900C. ..................................................................................102 5-34. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in air for 100 hr at 1000C. ................................................................................103 5-35. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O + 0.02 SOfor 100 hr at 800C. 2 2 ..............................................103 5-36. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O + 0.02 SOfor 100 hr at 900C. 2 2 ..............................................104 5-37. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O + 0.02 SOfor 100 hr at 975C. 2 2 ..............................................104 5-38. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O + 0.10 SOfor 100 hr at 800C. 2 2 ..............................................105 xiv

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5-39. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O + 0.10 SOfor 100 hr at 900C. 2 2 ..............................................105 5-40. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O + 0.10 SOfor 100 hr at 975C. 2 2 ..............................................106 5-41. Optical micrograph of as cast Ni-8Cr-6Al at 125X. ...........................................................108 5-42. Optical micrograph of heat-treated Ni-8Cr-6Al at 125X. ..................................................108 5-43. Secondary electron (SE) micrograph of as cast Ni-8Cr-6Al microstructure at 5000X. .....109 5-44. SE micrograph of heat-treated Ni-8Cr-6Al microstructure at 20000X. .............................109 5-45. Optical micrograph of as cast Ni-22Cr-11Al at 125X. .......................................................110 5-46. Optical micrograph of heat-treated Ni-22Cr-11Al at 125X. ..............................................111 5-47. Backscattered electron (BSE) micrograph of as cast Ni-22Cr-11Al microstructure at 5000X. ..............................................................................................................................111 5-48. Secondary electron (SE) micrograph of heat-treated Ni-22Cr-11Al microstructure at 15000X. ............................................................................................................................112 5-49. X-ray map of the SE micrograph in Figure 5-46. ...............................................................112 5-50. SE micrograph of NiO scale Ni oxidized in air at 800C for 24 hr. ...................................113 5-51. SE micrograph of NiAl oxidized at 800C for 36 hr at 5000X. .........................................114 5-52. SE micrograph of NiAl oxidized at 1000C for 36 hr at 20000X. .....................................114 5-53. SE micrograph of NiAl oxidized at 1000C for 36 hr at 200X. .........................................115 5-54. Backscattered electron (BSE) micrograph of Ni-8Cr-6Al oxidized in air for 100 hr at 900C. ...............................................................................................................................116 5-55. X-ray map of SE micrograph at 2500X of Ni-8Cr-6Al oxidized in air for 100 hr at 800C. ...............................................................................................................................116 5-56. SE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 100hr at 1000C at 10000X .............................................................................................................................117 5-57. BSE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 100hr at 1000C at 5000X. ..............................................................................................................................117 5-58. SE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 0.5 hr at 800C at 10000X. The light oxide is NiO and the dark oxide on the right is alumina. .................118 xv

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5-59. BSE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO at 800C for 100 hr at 4000X. 2 ..........................................................................................................................119 5-60. BSE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO at 900C for 100 hr at 1000X. 2 ..........................................................................................................................119 5-61. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO at 975C for 100 hr at 1500X. 2 ..............................................................................................................................120 5-62. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO at 975C for 100 hr at 1500X. In this area, the scale has spalled off revealing the bare metal surface. 2 .............120 5-63. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO at 800C for 100 hr at 15000X. 2 ........................................................................................................................121 5-64. SE micrograph of Ni-8Cr-6Al alloy oxidized in 10% SO at 800C for 100 hr at 1500 showing scale blisters. 2 ..................................................................................................122 5-65. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO at 900C for 100 hr at 700X. 2 ............................................................................................................................122 5-66. SE micrograph of the overlying alumina regions of Ni-8Cr-6Al oxidized in 10% SO at 900C for 100 hr at 10000X. 2 ........................................................................................123 5-67. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO at 975C for 100 hr at 5000X. 2 ..........................................................................................................................123 5-68. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO at 975C for 100 hr at 1500X where the scale (top) had spalled off and began to reoxidized (bottom). 2 ........124 5-69. SE micrograph of Ni-22Cr-11Al oxidized in air at 800C for 100 hr at 1000X. ...............125 5-70. SE micrograph of Ni-22Cr-11Al oxidized in air at 800C for 100 hr at 5000X. ...............125 5-71. BSE micrograph of Ni-22Cr-11Al oxidized in air at 1000C for 100 hr at 500X. .............126 5-72. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO gas mixture at 800C for 100 hr at 1000X. 2 ..........................................................................................................................127 5-73. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO gas mixture at 900C for 100 hr at 9000X. 2 ..........................................................................................................................127 5-74. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO gas mixture at 900C for 100 hr at 10000X. 2 ........................................................................................................................128 5-75. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO gas mixture at 1000C for 100 hr at 1900X. 2 ..........................................................................................................................128 xvi

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5-76. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO gas mixture at 800C for 100 hr at 100X. 2 ............................................................................................................................129 5-77. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO gas mixture at 800C for 100 hr at 5000X. 2 ..........................................................................................................................130 5-78. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO gas mixture at 1000C for 100 hr at 10000X. 2 ...................................................................................................................130 5-79. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO gas mixture at 900C for 100 hr at 1500X. 2 ..........................................................................................................................131 5-80. BSE micrograph of a Ni specimen oxidized at 800C for 24 hr at 1900X. The top layer is the electroless Ni layer deposited for edge retention. .........................................132 5-81. BSE micrograph of a NiAl specimen oxidized at 1000C for 36 hr at 2000X. The top layer is the electroless Ni layer deposited for edge retention. .........................................132 5-82. BSE micrograph of Ni-8Cr-6Al oxidized at 900C in cross-section. .................................133 5-83. SE micrograph of Ni-8Cr-6Al oxidized in 2% SO gas mixture at 800C for 100hr in cross-section at 10000X. 2 ..................................................................................................134 5-84. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO gas mixture at 900C for 100hr in cross-section at 3500X. 2 ....................................................................................................135 5-85. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO gas mixture at 900C for 100hr in cross-section at 3500X, showing an oxide deeply penetrating along a grain boundary. 2 .135 5-86. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO gas mixture at 900C for 100hr in cross-section at 5000X, showing sulfides along a grain boundary. 2 .................................136 5-87. SE micrograph of Ni-8Cr-6Al oxidized in 2% SO gas mixture at 800C for 100hr in cross-section, showing sulfides along grain boundaries and pores in the oxide layer. 2 ....136 5-88. BSE micrograph of Ni-22Cr-11Al oxidized in 2% SO gas mixture at 975C for 100hr in cross-section at 8000X. The top layer is a Ni-coating added for edge retention. 2 .......138 5-89. BSE micrograph of Ni-22Cr-11Al oxidized in 2% SO gas mixture at 800C for 100hr in cross-section at 800X. 2 ..................................................................................................138 5-90. BSE micrograph of Ni-22Cr-11Al matrix that was exposed to the 2% SO gas mixture at 975C for 100hr 2000X. The labeled X-numbers are areas that were probed for EDS. 2 .................................................................................................................................139 5-91. EPMA linescan across scale and interface in an Ni-8Cr-6Al alloy oxidized at 900C in He + 0.21 O + 0.02 SO gas mixture. 2 2 .............................................................................140 xvii

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5-92. EPMA linescan across scale and interface in an Ni-22Cr-11Al alloy oxidized at 800C in He + 0.21 O + 0.02 SO gas mixture. 2 2 .........................................................................141 5-93. EPMA linescan across scale and interface in a Ni-22Cr-11Al alloy oxidized at 975C in He + 0.21 O + 0.02 SO gas mixture. 2 2 .........................................................................141 6-1. Comparison of phases observed in SPIN4 calculations versus an SO-O potential diagram of Ni-8Cr-6Al at 900C. The blue dots correspond to calculated equilibria where the appended SPIN4 and SPOT3 databases agree. The green cubes correspond to disagreements. The dashed lines represent the alternate reaction lines determined by the appended SPIN4 database. 2 2 .................................................................150 6-2. Comparison of phases observed in SPIN4 calculations versus an SO-O potential diagram of Ni-22Cr-11Al at 975C. This diagram uses the same methodology as used in Figure 6-1. 2 2 ...........................................................................................................151 6-3. Comparison of the calculated activities from microprobe linescans with calculated values using the appended SPIN4 database for a Ni-8Cr-6Al alloy oxidized at 900C in 0.21 O + 0.02 SO. 2 2 .....................................................................................................154 6-4. Comparison of the calculated activities from microprobe linescans with calculated values using the appended SPIN4 database for a Ni-22Cr-11Al alloy oxidized at 975C in 0.21 O + 0.02 SO. 2 2 ..........................................................................................154 xviii

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ABSTRACT Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THERMODYNAMIC MODELING AND EXPERIMENTAL ANALYSIS OF OXIDATION/ SULFIDATION OF NI-CR-AL MODEL ALLOY COATINGS By Erik M. Mueller May 2007 Chair: Wolfgang Sigmund Major: Materials Science and Engineering With the current focus on finding future energy sources, land-based power gas turbines offer a desirable alternative to common coal-fired steam power generation. Ni-Cr-Al-X alloys are the material basis for producing overlay bond coats for the turbine blades used in sections of the turbine engine experiencing the most extreme environments. These overlay coatings are designed to provide environmental protection for the blades and vanes. While the oxidation of such alloys has been investigated and modeled in-depth, the concurrent sulfidation attack has not. This corrosion mode is now being heavily researched with the desire to use gasified coal, biomass, and other renewable fuel sources in gas turbines that often contain significant amounts of sulfur. The purpose of this dissertation was to use thermodynamic calculations to describe and predict the oxidation/sulfidation processes of two Ni-Cr-Al model alloys regarding phase evolution, composition, and component activities. These calculations, in the form of potential and phase fraction diagrams, combined with sulfidation experiments using kinetic measurements and materials characterization techniques, were able to describe and predict the simultaneous oxidation and sulfidation that occurred in these alloys. 1

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CHAPTER 1 INTRODUCTION The United States and the rest of the world today are on the verge of an energy crisis. A situation has developed in which increasing energy demands are consuming the current supply. Besides the United States, which consumes more than 25% of the worlds energy resources, the growing economies of Eastern Europe, China, India, and other developing countries are taxing world energy reserves [1]. Therefore, in order to solve this growing problem, energy supply must be increased while the demand is reduced. The solution to creating new energy supplies is not easy, especially considering the environmental and political impact of the most common source, fossil fuels [2]. Fossil fuel use has led to the production of sulfur and nitrous oxides (SO X and NO X respectively) and the byproducts of incomplete combustion, carbon monoxide and excess hydrocarbons, which were the chief environmental concerns of the Environmental Protection Agency and the Department of Energy [3]. However, with the recent recognition by the White House of manmade global climate change due to carbon dioxide (CO 2 ) emissions, the focus of new energy creation is finding carbon-neutral or less carbon-positive sources [4]. In essence, this entails the maximized reduction of carbon dioxide from not only fuel consumption, but also fuel production. Current alternatives for traditional coal, oil, and natural gas combustion to power steam turbines are wide and varied. However, many of these energy sources are not available in all regions and some do not yet process the technological development to make efficient use of their resources. Furthermore, some energy sources, such as nuclear power, have such high capital costs and political restriction, as to make them unfeasible in many regions. One currently developed and researched alternative is the use of land-based power gas turbines. The advantage of this process is that it has relatively few mechanical parts, requiring small capital investment, 2

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reaching stable power output quickly, and achieving high thermal efficiencies [5]. This high thermal efficiency translates into more power production for less fuel consumption, resulting in a reduction in CO 2 emissions compared to traditional steam turbines [5]. Furthermore, the source of fuel does not have to be limited to natural gas, but can also be synthetic combustion gases derived from biomass, gasified coal, and steam reformation of liquid hydrocarbons. However, the use of synthetic gases and even natural gas allow the inclusion of sulfur-based gases, such as SO 2 SO 3 and H 2 S, into the engine itself. In the turbine industry, research of the effects of these fuels were often overlooked since they play little role highly oxidizing conditions found in aerospace turbines. However, with the advent of fuels from less pure sources and the addition of later turbine blade stages, which operate at temperatures lower than those near the combustor chamber, this has again become a concern. The blades and vanes found in the turbine section can be attacked by these impurities, leading to catastrophic failure of the turbine and the entire engine as a whole. New research into understanding the prevention of this failure is key to making the placement of gas-based turbines in power plants more feasible and cost-effective. Experimental research and testing of the alloys in the turbine section are expensive, long, and difficult to reproduce. Therefore, efforts have been made to calculate these conditions [6-9]. However, these efforts are usually restricted to oxidation alone, or are performed on single elements, limiting their application to complex turbine alloys or their coatings. The purpose of this dissertation was to test if thermodynamic calculations can be used to describe and predict the oxidation/sulfidation processes of two Ni-Cr-Al alloys with regard to phase evolution, composition, and component activities. In addition, the oxidation of these alloys was analyzed in situ to determine the rate of corrosion in air and synthetic air mixtures 3

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with SO 2 as the sulfidizing gas. These specimens will be characterized using a variety of techniques to determine the evolution of various phases during oxidation and the mechanisms for corrosion. Information garnered from these experiments was compared and contrasted to calculations using free energy minimization software to simulate the gas corrosion conditions. The combination of these procedures was expected to determine the effects of these coatings in the environments given and suggest solutions for preventing their failure. 4

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CHAPTER 2 LITERATURE REVIEW As stated in Chapter 1, the corrosion mechanisms of overlay coatings on turbine blades are the chief concern of this dissertation. This chapter introduces the turbine blade alloys and their coatings, the thermodynamics of the coatings used, and the corrosion issues characteristic of the Ni-Cr-Al systems that are published to date. 2.1 Turbine Engine Considerations Turbines operate by using the power from the exhaust to drive the forward inlet compressor (Figure 2-1). Todays modern turbine engines comprise a fan, a compressor, a combustion region, and a turbine. The fan draws in the air required for eventual combustion, and in the case of bypass turbofan engines provides most of the thrust for commercial and military aviation uses. For industrial gas turbines used in power generation, the fan may be replaced by a generator to create electricity (more often, the generator is placed toward the rear). Figure 2-1. Schematic of a typical turbine engine. The compressor region is a series of blades, rotors, and stators that draw air in and compress it in ranges upwards of 30 to 40 bar [10]. In the combustion chamber, fuel is injected into the hot compressed air, combusting spontaneously and expanding the gas mixture toward the 5

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exhaust of the engine. This hot, expanding exhaust drives the turbine section, comprised of a series of blades and vanes, which powers the compressor and fan. As expected, the blades nearest to the combustion section experience the most severe conditions, but the later stages are greatly taxed as well. The materials contained in and the environments affecting the turbine section are the focus of this dissertation. 2.2 Turbine Blade Materials 2.2.1 Superalloys Nickel base superalloys are often used for applications that require high strength at elevated temperatures, and are the material of choice for the turbine sections because, in addition to being strong and tough, they are resistant to fatigue, creep, and environmental attack. Common yield strengths for cast polycrystalline Ni-base superalloys are on the order of 700-1000 MPa at room temperature [11]. Creep rupture strength are typically 75-300 MPa at 870C after 1000 hrs, and 60-125 MPa at 980C after 1000 hr [11]. These properties stem from the nature of the two majority phases which have a coherent interface between the FCC structure and the L1 2 structure of Ni 3 Alboth having similiar lattice parameters and coherent interfaces creating a low mismatch (less than 0.5% by length) [11-12]. The phase is a superlattice that shows long-range ordering (LRO) to its melting point. This microstructure displays an increase in flow stress with increasing temperature [11-12]. Extensive and complex heat treatments, along with careful alloying, are used to create unique microstructures that will have the desired mechanical and environmental properties. The alloying elements commonly used in superalloys are listed in Table 2-1. Each of the elements has a tendency to partition during non-equilibrium solidification causing some of the elements to remain in the dendrite cores and some to be rejected into the interdendritic fluid that solidifies last. In service, these elements have a 6

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tendency to diffuse and react with the environment. Therefore, careful balance and knowledge of the effects of each of these elements must be understood. Furthermore, complex heat treatments are employed to carefully control the microstructures, and mitigate these effects. Table 2-1. List of common alloying elements in Ni-base superalloys. Alloying Element Alloying Properties Partitioning Behavior Al former; increases anti-phase boundary energy ( APB ), increases oxidation resistance Interdendritic / C Carbide former; oxygen getter; grain boundary strengthener n/a Co Lowers stacking fault energy ( SFE ); increases melting point; strengthens phase Dendrite Core / Cr Oxidation/corrosion protection, lowers APB ; can form topologically close-packed (TCP) phases Dendrite Core / Mo Increase creep strength, strength in ; decrease oxidation/corrosion resistance; forms TCP Dendrite Core / Nb former; increases coherency strain, peak strength, room temperature strength Interdendritic / / Re Increases creep strength, strength in modulus; decrease oxidation/corrosion resistance, forms TCP Dendrite Core / Ru Reduces Re partitioning; delays TCP formation; increase creep strength; decreases oxidation/corrosion resistance Dendrite Core / Ta former; increase APB coherency strain, creep strength, peak strength; improves castability Interdendritic / Ti former; increases APB coherency strain Interdendritic / W Increases creep strength, strength in modulus; decrease oxidation/corrosion resistance, forms TCP Dendrite Core / 2.2.2Coatings for Turbine Blades There are a variety of coatings for superalloy blades and vanes, and they are applied to increase environmental stability and/or reduce the heat transmitted to the blade. Figure 2-2 shows the common coating configuration used in aerospace and industrial gas turbine (IGT) engines [16]: 7

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The substrate (superalloy turbine blades) The bond coat, which provides an environmental barrier for the substrate and a better bonding surface for the exterior coating The thermally grown oxide (TGO), which is sometimes manufactured before service The thermal barrier coating (TBC), which is a porous, columnar ceramic coating usually consisting of ZrO 2 designed to reduce the heat seen by the layers underneath The TBC effectiveness of the TBC is the change in temperature (T) which controlled by TBC thickness (), thermal conductivity (k), and the thermal flux (Q) through the blade wall, via: kQT (2-1) The T values obtained can be as high as 150C [10]. The focus of this study will be on bond coats, which are generally of the MCrAlY composition design, where M is a metal base usually Ni, Co, or both. This layer, which is higher in Cr and Al than the substrate, is designed to oxidize first and protect the superalloy. This is because, even though the TBC is the outer coating, it is porous and the oxidizing/corroding elements of the atmosphere directly contact and react with the bond coat. Ni-base superalloys generally oxidize to form nickel-based oxides, which do not adhere to the substrate and cause spallation of TBC layer [13]. The layer of protection formed on the bond coat is generally designed to grow as aluminum oxide, -Al 2 O 3 since it has the lowest oxygen diffusivity of the oxide of any of the elements listed in Table 2-1 [14]. The TGO is sometimes pre-grown before the coated blade is put into service but, regardless, is present upon usage in the highly oxidizing high temperature conditions. Co is can be used to increase the coating ductility, but the formation of CoO reduces the oxidation resistance because this oxide grows at a faster rate than NiO, Al 2 O 3 or Cr 2 O 3 [10,13,15]. The thermal barrier coating is said to fail when the TGO grows to a thickness so large that it spalls. Spallation can also occur from buckling due to cyclic thermal stresses [16]. 8

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Figure 2-2. Schematic of coating configuration of modern turbine blades. 2.4 The Al-Cr-Ni Ternary System The bond coats that are examined here are of the NiCrAl-type. In order to understand these coatings, the Al-Cr-Ni ternary should be discussed. The Al-Cr-Ni ternary has been studied through both experiments [17-22] and thermodynamic calculations [23-29]. Figures 2-3, 2-4, and 2-5 refer to the ASM Handbook binary phase diagrams of Al-Ni, Al-Cr, and Cr-Ni, respectively [30]. Studies of the Al-Cr-Ni ternary were undertakenfirst using powder X-ray diffraction techniques [17], which were integrated with other techniques to determine thermodynamic data such as the Gibbs free energies of formation (G f ) [18]. These other methods included diffusion couples [19-20], differential thermal analysis (DTA) [21], and electron microprobe (EPMA) [21]. The data were optimized to enable calculations of the ternary system. Since the Ni-rich area (X Ni > 0.5) is of more importance for practical applications, it has been studied in more depth than the Al or Cr-rich regions [19-20, 23, 25, 27]. 9

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Figure 2-3. Al-Ni binary phase diagram [H. Baker. ASM Handbook Vol. 3Alloy Phase Diagrams, ASM International: Materials Park, OH, p. 49 (1992)]. Figure 2-4. Ni-Cr binary phase diagram [H. Baker. ASM Handbook Vol. 3Alloy Phase Diagrams, ASM International: Materials Park, OH, p. 155 (1992)]. 10

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Figure 2-5. Al-Cr binary phase diagram [H. Baker. ASM Handbook Vol. 3Alloy Phase Diagrams, ASM International: Materials Park, OH, p. 43 (1992)]. A recent retooling of the G f descriptions of several of the important phases has been performed. Earlier studies described the and phases as having separate Gibbs energy functions [23-24], but more recent studies by using new data [25] describe the and as ordered and disordered versions of the same phase, transforming via a second-order reaction [27]. The -Cr and -NiAl are also treated as having the same Gibbs energy function [26-27] as can be described by the compound energy formalism, which attempt to simplify descriptions of intermetallics and oxides using sublattices that can substitute multiple elements and vacancies [31]. This methodology is used for one of the databases accessed for ternary calculations (see Chapter 4). Debate has occurred over the exact descriptions of this sublattice model, as to whether there should be a single sublattice [23-25] or multiple [26-27]. The most recent 11

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publications, though, [27-29, 32] agree that multiple sublattice models best describe the ordered and disordered phases present in the Al-Cr-Ni system. The phases present in the Al-Cr-Ni ternary are listed in Table 2-2. Figure 2-6 shows the liquidus projection taken from a review of a compilation of calculated and experimental data [32]. The Scheil reaction scheme is shown in Figure 2-7. At 1445C (labeled e 1 ), a eutectic occurs in which -Cr and -NiAl solidify. Eutectics also occur for and at 1380C (e 2 ) and for and at 1345C (e 3 ). Peritectics are observed for L + at 1385C (p 1 ) and 1350C for L + 1 (Al 8 Cr 5 -hexagonal) (p 2 ). At 1340C, L and L tie-triangles react in a ternary invariant reaction (Class II) to form L and b three-phase equilibria (U 1 ). The L then reacts with the L and L tie-triangles at a ternary eutectic reaction (Class I) to solidify to + + at 1320C (E 1 ). At 990C, a ternary invariant reaction (U 4 ) occurs in which the reacts with to form and three-phase equilibria. Figures 2-8 and 2-9 show isothermal sections of the ternary before and after reaction U 4 respectively. Other invariant reactions occur in the Cr-rich and Al-rich areas of the ternary, but these are ignored as they are not applicable to this study nor the one referenced [32]. The importance of studying this ternary is to construct model alloys of Ni-Cr-Al that can be modeled and studied as opposed to multicomponent alloys [28-29]. Results from experiments with these model alloys can be directly correlated to bond coats containing more elements such as rare-earths and Y (typically less than or equal to 1 wt%) and be to related to their microstructures and corrosion results. Overlay coatings are those in which interdiffusion is not required so that the coatings are laid onto the substrate. The MCrAlY compositions are designed to provide optimum oxidation or hot corrosion resistance, as well as strength, ductility, and thermal expansion match with the 12

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Figure 2-6. Liquidus projection of the Al-Ni-Cr ternary system [P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 411 (1991)]. Figure 2-7. Scheil reaction scheme of the Al-Cr-Ni ternary. The -phase refers to Ni 2 Al 3 the 1 to Al 8 Cr 5 -hexagonal, 2 to Al 8 Cr 5 -rhombodedral, and 1 to Al 9 Cr 4 The question marks represent areas of the ternary that were not investigated. 13

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Table 2-2. List of phases described in calculations of the Al-Cr-Ni ternary. Phase Temperature Range (C) Lattice Parameter () Space Group Pearson Symbol (Al) < 660.45 4.049 Fm 3 m cF4 -Cr < 1863 2.884 Im 3 m cI2 -Ni < 1455 3.524 Fm 3 m cF4 (Ni3Al) < 1372 3.566 Pm 3 m cP4 (NiAl) < 1638 2.886 Pm 3 m cP2 Ni 2 Al 3 < 1133 a = 4.036 c = 4.900 P 3 m1 hP5 NiAl 3 < 854 a = 6.611 b = 7.366 c = 4.8112 Pnma oP16 Al 13 Cr 2 < 791 a = 25.19 b = 7.574 c = 10.95 = 128.7 C2/m mC104 Al 11 Cr 2 < 941 a = 12.88 b = 7.652 c = 10.639 = 119.3 P2 mP48 Al 4 Cr < 1031 a = 8.716 b = 23.95 c = 16.39 = 119.33 P2/m mP180 Al 9 Cr 4 1172 1061 a = 9.123 Unknown cI52 Al 9 Cr 4 < 1050 Unknown Unknown [Monoclinic] Al 8 Cr 5 1352 1127 a = 9.047 Unknown cI52 Al 8 Cr 5 < 1127 a = 12.733 c = 7.944 R3m hR26 AlCr 2 < 911 a = 0.3004 c = 0.8648 I4/mmm tI6 Ni 2 Cr < 590 a = 2.524 b = 7.571 c = 3.568 oI6 14

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Figure 2-8. Isothermal section of Al-Cr-Ni ternary at 1025C above the U 4 reaction. The green areas denote regions of two-phase equilibria [P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 414 (1991)]. Figure 2-9. Partial Isothermal section of Al-Cr-Ni ternary at 850C below the U 4 reaction. The green areas denote regions of two-phase equilibria [P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 413 (1991)]. 15

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given substrate. One application method is through electron beam physical vapor deposition (EB-PVD). This method allows direct deposition from a metal source to a heated metal substrate without a chemical reaction and forms a columnar structure [33]. This can also be accomplished using an electric arc [34]. Another common method, plasma spraying, involves injecting a prefabricated powder into a plasma-gas stream, which deposits melted pellets as splats on the surface [35]. This leaves few voids, but the coating has a rougher surface finish than EB-PVD. The surfaces of both coatings are often mechanically machined to create a smooth exterior and heat-treated to better bond to the substrate. Oxidative heat treatments are sometimes employed to begin TGO formation in a controlled manner in order to stabilize the coating system. Overlays can also be applied by a high-velocity oxide furnace (HVOF) in which liquid fuel and oxygen are fed at high pressure into a combustion chamber where they burn to produce a hot gas stream that accelerates powder particles onto the substrate [36]. The phases present in the overlay coating vary with the composition of the coating and can be approximated by the Ni-Cr-Al or Co-Cr-Al ternaries. Many of the coating processes do not create an equilibrium microstructure due to the rapid solidification, so they heat-treated to obtain the desired microstructure [37]. For the coatings to be used in this project, Ni-22Cr-11Al and Ni-8Cr-6Al, the phases present are shown in Table 2-3 [37]. Upon proper heat-treatment, the Ni-8Cr-6Al shows a microstructure of cubiodal surrounded by a matrix of [28], whereas Ni-22Cr-11Al alloys show large globular phases containing small surrounded by a matrix of with small irregular [37]. At increasing temperature, the solubility of the alloying elements in the and phases increase, reducing the number of stable phases. In this respect, there is more compositional homogeneity to more easily form a stable -Al 2 O 3 oxide film. The oxidation mechanisms and behavior of these coatings is discussed in the next section. 16

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Table 2-3. The phases present in the Ni-22Cr-11Al and Ni-8Cr-6Al (weight percent) alloys at room temperature and 1000C. Alloy Composition Phases Present (Room Temperature) Phases Present (1000C) Ni-8Cr-6Al Ni-22Cr-11Al , , 2.5 Oxidation of Al-Ni-Cr Alloys 2.5.1 General Oxidation Mechanism In general, the oxidation of a metal in a gaseous environment involves several stages. First, the O 2 molecule must adsorb (by physisorbtion) and dissociate onto two sites on the metal surface [39-40]. The molecule then chemisorbs with the surface, at which one or more of several processes may take place: Active oxidationan M x O y molecule may desorb leaving a bare metal surface [40] Dissolutionthe oxygen may diffuse into the metal, where it may later form internal oxides [38] Nucleationoxides islands may nucleate and grow [38] Thin film formationa thin film layer of oxide may form, passivating the metal [38-40] This general mechanism is the mechanism of oxide growth expected for the alloys in this study. The reaction on the surface )()(22sOMOsxMxyy (2-2) can be rate-limited by [38] Desorption (in the case of active oxidation) Diffusion of species through a film Gas transport in the substrate Ion transport in the substrate Oxide growth Oxide nucleation Surface adsorption In the case of the formation of a thin film at lower temperatures, the rate-limiting step has been shown to be cation transfer from metal to oxide surface driven by an electric potential 17

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across the film, as described by Mott and Cabrera [39]. The kinetics of thin film growth can be described as logarithmic ) log( tkxl (2-3) or inverse logarithmic tkBlxlog1 (2-4) where x is film thickness, k l is the rate constant, t is time, and B and are constants. Figure 2-10 shows an example of logarithmic and inverse logarithmic growth. Figure 2-10. Plot of oxidation growth kinetics versus time. At higher temperatures, and in thicknesses large enough where electric field effects are negligible (x > 10 nm), parabolic kinetics usually govern film growth (Figure 2-10): (2-5) Ctkxp2 As described by Wagners theory of passive oxidation of Si, thermal diffusion of cations and anions is generally the rate-limiting step in parabolic growth [40]. As the film thickness increases, the diffusion length increases slowing the growth. This observation, however, assumes a compact, adherent scale. If the oxide is porous or has poor adhesion with the metal surface, then bulk parabolic growth may not apply as short-circuit surface O 2 diffusion paths 18

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become prevalent. Bulk diffusion is usually bypassed by diffusion along grain boundaries, stacking faults, and dislocations, which increase the film growth rate [41]. Other kinetic oxidation models relevant to this study include linear growth: kdtdx (2-6) Linear kinetics are also observed if the oxide is volatile or above its melting point. This occurs in oxides where the film is not protective, and is often porous. Other kinetic models include paralinear, cubic, and subparabolic, which describe mixed growth. These models attempt to describe transitions from one kinetic model to another (e.g. linear to parabolic) or growth limited by several simultaneous mechanisms. The oxidation described in this section and the rest of this report deals with isothermal oxidation. Cyclic oxidation, where the temperature is varied (usually from room temperature to a maximum temperature), is not covered here as thermal expansion and residual stress factors must be taken into account, leading to more rapid failure than in isothermal conditions. For more information on cyclic oxidation, the interested reader is referred to references 10, 14, and 15. 2.5.1.1 Oxidation of Ni The oxidation of Ni is governed by gas absorption, oxide nucleation, and film growth as per the chemical reaction 2Ni + O 2 2NiO (2-7) NiO, or busenite, has an NaCl-type structure and appears as a black oxide (or green in high Ni contents). The oxide grows with a (111) Ni ||(001) Ni [ 011 ] NiO ||[ 011 ] Ni orientation relationship, although (100) NiO and (211) NiO are grown in epitaxy as well [36]. NiO is a p-type metal deficient oxide, where every cation vacancy has two Ni 3+ pairs. In p-type metal deficient oxides, cations diffuse via vacancies in the cation sublattice to the oxide/gas surface while electrons migrate via 19

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electron holes back toward the oxide/metal interface as determined by tracer experiments [38, 43]. Ni oxidation has been described by parabolic kinetics [43-46]. However, a recent study with pure Ni in various oxygen-argon atmospheres showed that between 700C and 1000C, NiO could grow subparabolically [44]; above 1000C and below 600C, parabolic growth is observed. The reason for this is that above 1000C, bulk diffusion via cation vacancies dominates, and the scale exhibits columnar grains [47]. In the subparabolic regime, the scale exhibits a duplex structure with outer columnar grains having outward Ni cation diffusion, and inner equiaxed grains with short-circuit O 2(g) diffusion inward [48]. 2.5.1.2 Oxidation of Al Al oxidation has been widely characterized for a variety of applications. Al is highly reactive and readily ionizes at -1.662 eV [38]: Al Al 3+ + 3e (2-8) Al 2 O 3 is considered an excellent passivating film due to its good Pilling-Bedworth (P-B) ratio (1.28) [38] and having a low O 2diffusivity at sufficient thicknesses [49]. Alumina is most prevalent in the -Al 2 O 3 corundum R3c phase, although other phases exist, as outlined in Table 2-4. The initial stages of Al oxidation have been described using Al substrates in ultra-high vacuums. In the initial stages, O 2 molecules approaching an Al surface physisorb, dissociate, and chemisorb onto the surface. This then allows for the inward diffusion of O 2and the formation of Al 2 O 3 tetrahedra [51]. The adsorption sites are different based on the orientation of the metal surface. Initially, these original formula units of Al 2 O 3 exist as amorphous islands, which grow laterally, eventually covering most of the metal surface [52]. Initially cation20

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Table 2-4. Descriptions and crystallographic information on different phases of Al 2 O 3 [49-50]. -Al 2 O 3 -Al 2 O 3 -Al 2 O 3 -Al 2 O 3 -Al 2 O 3 Crystal system Trigonal Orthorhombic Cubic Monoclinic Tetragonal Space group R3c Pna2 1 Fd 3 m C2/m P 4 m2 Lattice parameters () a=4.7587 c= 12.9929 a=4.8351 b=8.3109 c=8.9363 a=7.92 a=11.8545 b=2.9041 c=5.6622 =103.837 A=5.599 c=23.657 Al atoms in unit cell 12 16 63/3 n/a 14 O atoms in unit cell 18 24 32 n/a 12 Al-co-ordination Octahedral 75% octahedral 25% tetrahedral n/a n/a n/a deficient, the amorphous film grows outward via interstitial Al 3+ transport [49,52] driven by the Al concentration gradient [49,53] and E-field effects [40]. At several nanometers, when stoichiometry in the oxide is achieved [54], the amorphous alumina crystallizes into -Al 2 O 3 (sometimes preceded by a -Al 2 O 3 [55]) due to a close orientation relationship between the oxide and the substrate (111) Al ||(111) -Al2O3 as determined by a rigorous TEM analysis [56-57]. The -Al 2 O 3 is an anion-deficient n-type semiconductor, growing via inward chemical bulk O diffusion [58]. Short-circuit paths play a role at larger thicknesses. The growth kinetics are logarithmic at lower temperatures, and parabolic at higher temperatures. The -phase is metastable and rarely seen above 800C [58]. It will usually transition to the stable -phase at sufficient thicknesses, times, and temperatures. The and phases are sometimes seen as intermediates with whisker morphologies [58-59] and generally grow by outward cation diffusion, as determined by tracer and inert marker tests [58-60]. These transition 21

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phases are undesirable compared to the -phase because stable -phase has a parabolic rate constant an order of magnitude lower [61] due to slow anion-diffusion along grain boundaries [56, 62]. This growth mechanism depletes the substrate less (in the case of Al-X alloys) than the cation-diffusing transition aluminas. Furthermore, the k P of -Al 2 O 3 is higher than that of NiO or Cr 2 O 3 defeating the use of Al 2 O 3 as an impediment to oxidation in Ni-Cr-Al alloys [63]. 2.5.1.3 Oxidation of Cr The oxidation of Cr has been studied extensively due to its use as the major alloying protectant in stainless steels [64-66]. As found with tests in steels or in elemental form, Cr reacts with O 2 to form Cr 2 O 3 via a similar reaction as Al does with O 2 : 4Cr + 3O 2 2Cr 2 O 3 (2-9) Cr 2 O 3 or chromia, like NiO is a p-type metal deficient semiconductor [67], and therefore grows by outward cation transport through the scale lattice [67-68] at temperatures less than 1250C. Cr 2 O 3 is commonly used because it reacts faster with O than the elements it is alloyed with and has a low O 2 diffusivity, thereby allowing a slow growth rate [69-70]. Cr oxidation is described by parabolic kinetics above 700C, and shows initial logarithmic growth at lower temperatures. Above this temperature, chromia can become amphoteric, or able to transport in both directions simultaneously, and the growth rate increases rapidly [67]. Due to this defect structure, the Cr 2 O 3 can form a duplex structure with an inner layer where interstitial Cr 3+ diffusion also takes place. This tends to increase the diffusion of Cr 3+ in the inner region, which is highly dependent on the oxygen partial pressure [70]. As validated by tracer tests and diffusion coefficient findings, short-circuit diffusion through grain boundaries, cracks, and pores dominate and increase the scale growth rate [64, 69-70]. One oxidation study showed that this was the primary growth mechanism [71]. 22

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One of the problems with Cr 2 O 3 is the ability for the Cr cations to become hexavalent at higher O 2 partial pressures, forming CrO 3 such as can be experienced in gas turbine conditions by these reactions [72]: 2Cr + 3O 2 2CrO 3 (2-10) 2Cr 2 O 3 + 3O 2 4CrO 3 (2-11) The formation of this gas species removes the protective chromia layer thereby making the Cr 2 O 3 ineffective. Volatilization also increases the Cr alloyed in the substrate, decreasing the time-to-fail of the Cr 2 O 3 scale. Other gas species have been studied, but are less likely to be major contributors at high temperatures and high oxygen partial pressures [72-73]. Hexavalent Cr gas species have been classified as carcinogens and the use of Cr coatings in some industries has been restricted [74]. 2.5.2 Oxidation of Ni-Al Alloys Al 2 O 3 (as well as Cr 2 O 3 ) has a slower growth rate (Figure 2-11) and higher affinity for O 2 than Ni [15]. Therefore, Al is commonly used as an alloying agent with Ni to provide an environmental protection in lieu of the unprotective NiO scale. As mentioned in Section 2.2, Al is also used to form and stabilize the intermetallics and (). With Ni-Al alloys, the corundum -alumina phase is the desired TGO for its slow-growth rate, low anion diffusivity, and overall smooth morphology. The -alumina phase has been shown in studies to appear first, especially at lower temperatures (T < 850C) due to a lower activation energy to form on Ni-Al alloys [75-77]. The oxidation of dilute Ni-Al alloys begins with the formation of NiO. The formation of this oxide, though, depletes the alloy at the alloy/gas interface of Ni and reduces the P O2 in relation to the gas/scale interface. This leads then to the formation of Al 2 O 3 [63]. Scanning 23

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Figure 2-11 Arrhenius plot of parabolic growth rates versus temperature of NiO (violet) as well as Cr 2 O 3 and Al 2 O 3 (red) [J.L. Smialek, G.M. Meier, High-Temperature Oxidation, Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New York p. 295 (1987)]. electron microscopy (SEM) cross-sections found that alumina scale formation will develop fastest at the grain boundaries, since these are fast diffusion paths for Al 3+ and O 2transport [77]. Hindam and Smeltzer decribed the formation of Al 2 O 3 in the presence of NiO or Ni will lead to breakdown oxidation of the alumina scale in which spinel is formed via [78]: NiO + Al 2 O 3 NiAl 2 O 4 (2-12) If the amount of Al present in the alloy is too little, a stable alumina scale may not be formed [78]. As graphically described by Pettit in Figure 2-12, too little Al will prevent the internal oxides of Al 2 O 3 from coalescing to form a continuous scale [76]. Furthermore, even if a stable scale is formed, the alloy must have enough Al to continually feed the oxide growth, and the flux of Al in the alloy must exceed that in the oxide. If not, the alumina scale will break down, and NiO and NiAl 2 O 4 will stabilize [76, 78-79]. 24

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Figure 2-12. Dependence of oxidation mechanisms and scale type of Ni-Al alloys based on temperature and Al content [F.S. Pettit: Transactions of the AIME. 239, pp. 1296-1305 (1967)]. In two-phase alloys, oxidation rates and oxide phases can differ over a range of compositions. The addition of any Al to Ni will cause an increase in the rate of oxide growth, and a decrease in activation energy [58, 79]. This fast oxidation is due to Al 3+ doping of the NiO and the formation of the open NiAl 2 O 4 spinel that allows for rapid cation diffusion [79]. In + mixtures, the kinetics are more complex, showing a parabolic-linear-parabolic procedure whose growth rate is less than alloys with Al < 6 wt% [76]. This occurs because the initial -Al 2 O 3 scale is being overtaken by NiO growth, and eventually reaches steady-state nickel oxide parabolic growth [80]. For those oxides growing over -Ni, the only alumina seen is -Al 2 O 3 and can be mixed with NiO and spinel. Transient and alumina phases are often seen growing first over Ni 3 Al [81-82]. This is also observed on + mixtures, but kinetics are always parabolic [76, 83-84]. The presence of causes the faster formation of -Al 2 O 3 and a slower growth rate than with more dilute Ni-Al alloys. Transient alumina phases have been observed over NiAl as well [85]. 25

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2.5.3 Oxidation in Al-Cr-Ni Ternary and NiCrAlY Coatings Oxidation of Ni-Cr-Al alloys involves a complex competition of the formation and growth of NiO, Cr 2 O 3 and Al 2 O 3 In addition, the nickel-chromium and nickel-aluminum spinels often play a role. In general, the addition of Cr to Ni-Al alloys stabilizes the Al 2 O 3 phase [85-86]. This overall process, was first described by Pettit [76] and is shown in Figure 2-13. Upon initial oxidation, the activities of oxygen and nickel are high enough that NiO forms [87]. Any Al or Cr that oxidizes reacts with NiO to form spinel. NiCr 2 O 4 and NiAl 2 O 4 allow for faster transport of O 2anions in and Ni 2+ anions out. As the initial scale grows, the P O2 at the scale/alloy interface diminishes due to scale thickening, and the activity of Ni decreases due to Ni-depletion in the alloy below the interface [88]. This causes internal oxidation of Cr and Al in the alloy. If there are insufficient amounts of alloying elements, the Al and Cr oxides will remain as small spherical and/or rodlike internal phases (Group I). If, however, there is enough Cr, a continuous scale of Cr 2 O 3 will form and grow at the scale/alloy interface (Group II). This has the effect of further lowering the oxygen activity at the interface, which, if there is enough Al to sustain it, will form a continuous Al 2 O 3 scale that becomes rate-controlling (Group III) [86, 89-90]. In effect, Cr getters O 2 allowing the Al 2 O 3 scale to stabilize. If there is not enough Al, though, the steady-state scale that grows will be chromia (Group II) [90-92]. Kinetically, as with Ni-Al alloys, increasing the alloying elements Al and Cr in Ni-Cr-Al will cause a decrease in the parabolic growth rate [93-94]. The exception to this is in the case of dilute alloys wherein the alloying elements actually dope the oxide increasing ionic mobility by introducing lattice vacancies [88, 95]. 26

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Figure 2-13. Schematic of the stages of oxidation in Ni-Cr-Al alloys. Group I are alloys that will have a stable NiO scale, Group II will develop a stable Cr 2 O 3 scale, and Group III will develop a stable Al 2 O 3 scale [F.S. Pettit: Transactions of the AIME. 239, pp. 1296-1305 (1967)]. The microstructure of the scale shows orientation relationships between the initial oxides formed and the metal. Similar to that of -Al 2 O 3 and Al, the relationship of the spinel and -Al 2 O 3 that forms on the alloy is (111) Spinel ||(111) NiCrAl <110> Spinel ||<110> NiCrAl [58]. The Cr 2 O 3 that grows is (0001) Cr2O3 ||(111) NiCrAl < 0211 > Cr2O3 ||<110> NiCrAl However, TEM studies showed that the steady-state alumina that grows has a random orientation with the alloy and the other oxide layers [58, 61, 96]. Over time, the Cr in the alloy tends to segregate out of the NiAl into the and . Cr 2 O 3 is seen on top of those Cr-rich regions, whereas Al 2 O 3 forms faster above the [57]. As with Ni-Al with high Al contents, and -Al 2 O 3 are observed having a needle-like morphology [57, 97-98] that transforms to during continuous exposure to an oxidizing gas 27

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mixture [56]. A study by Levi et. al. observed these transient aluminas formed as lumps or hills on top of the whereas the oxides over / were seen as a smooth scale [97]. The -alumina that forms underneath (over all alloy phases) is columnar [93, 96-97]. The absence of these transient aluminas again shows a lower oxidation rate [98]. 2.6 Sulfidation and Hot Corrosion 2.6.1 Hot Corrosion Hot corrosion is an accelerated corrosive attack of molten salts that often occurs in the later stages of turbine engines where the pressure is less than those near the combustor, and when salt or ash deposits accrue on the alloy or coating surface [99]. Even for applications typically operating above 1000C, hot corrosion can be a problem during thermal cyclingfrequently occurring in salty marine areas or in operations with fuels containing S, V, and/or P. This mechanism occurs when temperatures enable molten salts such as Na 2 SO 4 K 2 SO 4 and/or NaCl to be in their liquid state, in which they attack the oxide scale, and eventually penetrate into the substrate itself [99-101]. This type of corrosion can be categorized into two stages: an initiation stage, and a propagation stage. The initiation stage is marked by either parabolic growth or slow weight loss. The mechanism is similar to oxidation, except that sulfides form in the oxide from an influx of sulfur anions or SO X gases. Once the propagation stage begins, severe weight loss is observed and rapid attack of the oxide and alloy begins. The chief reaction(s) governing this process is Na 2 SO 4 Na 2 O + SO 3 (g) (2-13) SO 4 2O 2+ SO 3 (g) (2-14) 28

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These are the basis for the fluxing reactions in which basic fluxing MO + O 2MO 2 2(2-15) or acidic fluxing MO M 2+ + O 2(2-16) occurs [102]. This attack can be categorized into either Type I, which occurs between 850 and 1000C and is governed by basic fluxing, and Type II that occurs between 680 and 750C [97] and is governed by acidic fluxing [103-104]. Type II corrosion displays characteristic pits can be avoided through higher Cr contents, higher temperatures, and larger gas flow velocities in the engine. The partial pressure of SO 3 is critical for the reaction where the sulfate dissolves the metal oxide at the scale/salt interface, which then reacts with SO 3 to form oxide (low P SO3 ) or sulfate (high P SO3 ), which then repeats the process [103-105]. Type I hot corrosion is of more concern for this study, in which the formation of metal sulfides from reactions with the sulfate create a free oxygen anion that reacts with the metal oxide to form a metal oxyanion that dissolves in the salt [105-106]. This MO X 2then can react with SO 2 (or SO X ) to form oxide particulates at the salt/gas interface that frees up oxygen anions to repeat the process [106-107]. While originally thought to be self-sustaining, other research by Goebel and Shores has shown that a constant supply of Na 2 SO 4 (l) is required to prolong the reaction [100, 108] One of the chief drivers for this corrosive attack is the production of sulfides, and the diffusion of sulfur into the oxide itself [109]. The last sections of this chapter will examine the role of sulfidation, which is the mechanism for the initiation stage of Type I hot corrosion [103-105]. 2.6.2 Sulfidation on Metals Sulfidation in metallic systems has been studied in oxygen and oxygen-free environments. Sulfur is present in unclean fuels, coal, and salts in marine environments, and behaves differently 29

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depending on whether it is present in oxidizing environments, or those devoid of oxygen (reducing environments). Reducing environments of sulfur are often modeled in H 2 S atmospheres with low oxygen partial pressures and a fixed H 2 /H 2 S ratio in order to fix the partial pressure of S 2 Studies involving this have shown that Ni in H 2 /H 2 S environments form almost exclusively -Ni 3 S 2 which exhibits linear sulfidation behavior initially (or at lower temperatures) and then grows parabolically [110-111] due to rapid sulfur diffusion along grain boundaries [112]. In Cr-containing alloys, the sulfides come closer to a 1:1 ratio of CrS as the temperature increases as determined by XRD and TEM, with a layered structure exhibiting inward anion diffusion, and an outer layer exhibiting outward cation diffusion [113]. This duplex sulfide layer is also seen in alloys where the rate-limiting mechanisms are similar with an outer layer of Ni 3 S 2 and an inner layer mix of nickel, chromium, and aluminum sulfides [114-115] due to decreased the sulfur activity. In sulfidation experiments performed in oxidizing conditions, which are the focus of this study, either SO 2 is mixed with the oxidizing atmosphere (usually air or O 2 ), SO 2 is used alone, or H 2 S is added to oxygen. In all these situations, the P O2 is usually high enough to begin initial oxidation of the metal, and sulfides are absent since these conditions are above their dissolution pressure [116-117]. In oxidation, the role of S is initially one of an impurity dopant that accelerates oxidation through the creation of vacancies [118-119]. Sulfur can diffuse rapidly through grain boundaries, pores, and other high surface energy defects and stabilize them, allowing fast transport of other ions [122-124]. This can be accelerated by the dissociation of SO 2 in these defects, which increases the oxygen and sulfur partial pressures [125-127]. However, sulfur can build up at sufficient scale thicknesses to cause sulfide formation. This will be elaborated upon in section 2.6.3. 30

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Whenever SO 2 and O 2 are present below 700C, they can react to form SO 3 [125], a gas above 45C, via the reaction 2SO 2 + O 2 2SO 3 (2-17) The formation of SO 3 causes different reactions with the metal, as it is more oxidizing [128] and therefore sulfidizing [129] than its dioxide counterpart. These conditions make it more likely to form sulfates, which, as with hot corrosion, can rapidly attack the oxide or metal [130-131]. However, the effects of SO 3 are minimal above 800C in that it becomes unstable and will readily decompose into SO 2 and O 2 SO 3 also chemisorbs on the oxide surface slower than SO 2 [128]. Furthermore, the reaction on Equation 2-16 occurs at slow rates, requiring a platinum catalyst to stabilize the reaction at higher temperatures [128]. Therefore, the effects of SO 3 may only be relevant in specific service conditions in modeling Type I hot corrosion. 2.6.3 Sulfidation on Metal Oxides In metal oxide scales adherent to metal alloys, sulfur has been shown to migrate towards the scale/alloy interface. Sulfur is also present in pores, cracks, and grain boundaries [127, 132-135]. At the scale/alloy interface at extended times, the amount of sulfur continues to build up while the scale/gas interface moves further away relative to the scale/alloy interface due to oxide growth [136-139]. This reduces the amount of oxygen near the interface [140]. When the P S2 is high enough, and the P O2 is low enough, sulfide phases begin to stabilize and their growth becomes faster than that of the oxide [126-127, 130-131, 139, 140-146]. The formation of these sulfides destabilizes the scale adherence to the substrate [135], causing the formation of cracks and pores, which leads to scale spallation [120, 127, 133, 138, 140]. These cracks allow the gas species to migrate faster to the interface, accelerating corrosion. Due to the complex and open structures of these sulfides, ionic species are able to diffuse faster though the sulfide, which also increases the oxidation rate [111, 121, 126, 133, 147]. This mechanism of premature oxide 31

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failure because of sulfur buildup at the oxide/alloy interface has been dubbed the sulfur effect by Lees and Fox and is illustrated in Figure 2-14 [120, 139]. If enough Ni 3 S 2 is present, it can react with Ni to form a low melting liquid eutectic, exacerbating the situation [130, 146]. Figure 2-14. Schematic showing the formation of metal sulfides (a) under an initial metal oxide layer (b) in simultaneous oxidizing and sulfidizing conditions. The various proposed transport mechanisms are shown. While it is clear that sulfur migrates towards the scale/alloy interface, the mechanism behind this process is not entirely agreed upon. Two schools of thought have developed as drawn in Figure 2-14. Originally, it was believed that sulfur diffused as S 2anions through the lattice, accumulating at the interface [119, 122, 142, 144, 148-149]. However, other studies have rejected this notion stating that diffusion rate is too slow for this to be seen in experiments [118, 130] and, with Cr 2 O 3 the solubility of S or S 2 is too low [134]. Furthermore, the S 2anions would eventually have to climb up a concentration gradient as the P S2 required to form sulfides is significantly higher that of the corrosive gas at the gas/scale interface [138, 141]. The other theory is that the sulfur migrates by gaseous diffusion of SO 2 [118, 123-124, 130, 132, 134, 138, 140-141]. The SO 2 would flow via cracks and pores, or along high-angle grain boundaries to the scale/alloy interface where one of three reactions are possible [150]: 2yM + SO 2 = 2M y O + S 2 (2-18) xM + SO 2 = M x S + O 2 (2-19) 32

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(2x+y)M + SO 2 = 2M y O + M x S (2-20) This third reaction is unlikely to occur, while the first allows for the formation of free sulfur, which increases the P S2 and the second causes sulfide formation (although it does raise the P O2 which is generally counteractive to sulfide formation). Indeed, in SEM studies with Cr and Ni-Cr alloys exposed to SO 2 that developed compact chromia scales, no sulfide formation took place at the scale/alloy interface, while porous scales developed sulfides [117, 134]. This mechanism is disputed by other studies stating that gaseous diffusion is unlikely due to the size of the SO 2 molecule [142], and studies with high S contents at grain boundaries absent of voids still formed sulfides at the scale/alloy interface [122, 139]. 2.6.4 Sulfidation in Ni-Cr-Al Coatings As has been shown, sulfur can reduce the effectiveness of bond coats, even in highly oxidizing conditions. As described by previous publications, sulfidation processes for these coatings resemble the initiation stage of Type I hot corrosion [90, 99, 107, 130]. Ni-Cr-Al alloys have been designed to resist against sulfidation attack and are relatively high in Al and Cr, mainly because the S and O diffusivities in Al 2 O 3 and Cr 2 O 3 are lower than in NiO [120, 143, 148, 151]. In sulfidation attacks, Al 2 O 3 is slightly more susceptible to SO 2 attack [99] by 3SO 2 + Al 2 O 3 2Al 3+ + 3S 2+ 3O 2(2-21) Therefore, some applications, especially those experiencing hot corrosion, are designed to allow for Cr 2 O 3 protective scales rather than Al 2 O 3 to grow, even though chromia grows faster [73]. In addition, rare earth elements, yttrium, and silicon are commonly added as getters for O and S. These elements have been shown to decrease corrosion rates as well as spallation and scale degradation in sulfidizing environments [124, 133, 151]. This occurs when reactive-element grain boundaries phases such as Ni 5 Y, which react with S first [152], prevent the sulfidation of the other alloying elements. 33

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2.7 Calculations of Oxidation/Sulfidation Thermodynamic calculations have been used to describe and predict a variety of materials applications, especially the development of phase diagrams. Calculations of the Al-Cr-Ni ternary have already been performed (see Section 2.4). The study of oxidation by calculations for this system was limited until recent publications compiled and optimized thermodynamic data. Previous studies of the Al 2 O 3 -Cr 2 O 3 system used the quasichemical model for non-gaseous phases and modeled the phases as a single solid solution with a miscibility gap [153]. The quasichemical model was used for the Cr-Ni-O system [154], and, combined with the sublattice model descriptions of the Cr-Ni-O and Al-Ni-O systems [43, 155], an Al 2 O 3 -Cr 2 O 3 -NiO ternary was constructed [6]. Saltykovs analysis of these ternaries allowed one of the more comprehensive descriptions of the Al-Ni-Cr-O quaternary system using free energy minimization [156] software to produce multiple plots that graphically described the system [6]. This approach was also used by Seifert et. al. to assess the AlNi-Cr-Ni-O system [7]. However, little work has been done to model sulfidation attacks of this system. M-O-S systems for Fe, Ni, Co, and Cr were developed using Gibbs energy minimization techniques with CO 2 /H 2 and H 2 S/H 2 ratios to set the P O2 and P S2 respectively [8]. The idea of using M-O-S type diagrams was also approached in previous publications [127, 142]. An attempt to produce Na-M-O-S quaternaries of Fe, Cr, and Al for Type II hot corrosion applications was also performed by Li and Gesmundo [157] based on previous techniques of overlaying quasi-ternaries and finding stable quadruple points [158-159]. Through all these publications, no work has been done to attempt to describe alloys or even their mechanical mixtures. This dissertation will fill these gaps by calculating the stability of Ni-Cr-Al alloys and their mechanical mixtures in oxidizing and sulfidizing atmospheres. These diagrams will be plotted as potential diagrams, described by Yokokawa [160], which plot chemical potential 34

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instead of composition (a traditional phase diagram). Potential diagrams are useful for showing diffusion paths, which are straight lines on potential diagrams, and for visualizing phases present based on the changing activities of various reacting elements of an oxidizing and/or sulfidizing system [160]. The chemical potentials can also be plotted as activities or partial pressures, for easier interpretation. The exact methodology of these calculations will be described in Section 3.1. 35

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CHAPTER 3 METHODS AND MATERIALS This chapter discusses the methods and materials used in this study. This includes the calculation of phase diagrams approach (CALPHAD) for the development of potential diagrams, as well as the experimental design for the kinetic tests and the characterization of the materials of this study. 3.1 Thermodynamic Modeling and Simulations 3.1.1 The CALPHAD Approach In performing simulations by thermodynamic modeling, the CALPHAD approach was used. This approach is shown as a flowchart in Figure 3-1. Here, one combines the information obtained by theoretical development with that of experimental measurements and estimates to create data that are stored as analytical expressions of thermodynamic functions with adjustable parameters [156]. These descriptions are then optimized using a least squares regression to get the best possible thermodynamic data [156]. From this, the data are compiled into stored databases, from which the desired information for a particular study can be obtained. This method prevents the use of a black box design and allows the data to be adjusted, as opposed to some other calculation methodologies [161]. From these databases, one can then use a thermodynamic software program to obtain the desired information. This is done by computing an equilibrium and then graphically presenting the phase diagram from the initial equilibrium. These diagrams are then compared and contrasted with the existing experimental data to determine if database adjusting is needed. Lastly, the calculated diagrams are utilized for developing and designing applications in industry and research. This study will stress this last part of the CALPHAD approachthe calculation of diagrams from previously developed databases. 36

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Figure 3-1. Flowchart detailing the Calculation of Phase Diagrams approach. This study is concerned mostly with the equilibrium calculations. 3.1.2 Databases and Software The databases used in this particular study were the Scientific Group Thermodata Europe (SGTE) Standard Potential Database (SPOT3) obtained from the Russian Academy of Sciences (TCRAS) and other sources [162-165], as well as the SPIN4 database, developed from previous Ni-Cr-Al-O studies [6-7]. Both databases contain thermodynamic descriptions of Ni, Cr, Al, and O. However, only the SPOT3 database contained descriptions for S and its sulfide and sulfate phases. The SPOT3 database, though, only takes into account thermochemical reactions between stoichiometric compounds that allow for no solutionsa mechanical mixturewhereas 37

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the SPIN4 database allows for solution phases. The use of mechanical mixtures to model a system has been previously published [166]. An attempt was made to append the SPIN4 database with the SPOT3 descriptions for the sulfur, sulfide, and sulfates phases. The Gibbs free energy minimization software used for this study is Thermo-Calc version Q. Using this software, the desired phase or potential diagrams was obtained by: 1. Selecting the desired elements 2. Accessing the relevant thermodynamic information on each element and compound formed between each element 3. Setting conditions for each degree of freedom (eg. temperature, pressure, composition) so as to satisfy Gibbs Phase Rule: P + F = C + 2 (3-1) 4. Computing an equilibrium using Gibbs free energy minimization algorithms 5. Assigning one condition per axis of the desired diagram 6. Mapping from the initial computed equilibrium along each axis to determine phase stability regions. From this method, graphical plots of phase and potential diagrams were created. 3.2 Materials and Sample Preparation The materials used for the experimental aspects of this dissertation were obtained from Alfa Aesar with the purity determined by chemical analyses from the company. The metals used are Ni slugs: 99.98% metals basis Al shot: 99.999% metals basis Cr granules: 99.999% metals basis These metals were measured by weight and combined into either the Ni-8Cr-6Al or Ni-22Cr-11Al alloys, which were approximately 12.5 g for Ni-8Cr-6Al and 7.5 g for the Ni-22Cr-11Al alloys. The mixtures were placed in a Centorr chilled-copper arc-melter that used a non-consumable tungsten electrode. The chamber was evacuated and backfilled with argon gas three times. Titanium getters were melted initially, followed by the mixture of interest. The melted 38

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and solidified button was flipped and remelted four times in order to ensure homogeneity. These arc-melted buttons were then heat-treated at 1200C for 4 hours in vacuum (better than 10 -4 torr) using an Elatec Technology Corporation vacuum furnace, using a He(g) quench. In addition, some of the Ni slugs as well as arc-melted Ni-13.6Al and NiAl were used in the oxidation studies. The compositions were checked by energy dispersive spectroscopy. The specimens were then sliced using an Allied Techcut 4 diamond saw at low speeds (< 300 RPM). The slices, approximately 0.7 mm in thickness, were ground with SiC abrasive paper of 60, 180, 320, 600, 800, and 1200 grit on all sides. They were then polished on velcloth with 1 m polycrystalline diamond suspension. The polished slices were measured using calipers to measure the various dimensions of each specimen to determine the surface area of each specimen. The surface area was approximately 1.7 to 2.8 cm 2 Each polished sample was ultrasonically cleaned in acetone and then methanol for 10 minutes each. Some specimens to be characterized were etched with aqua regia for macroetching and/or equal parts HCl and ethanol for microetching. Some specimens had a strip of Pt paint applied to one surface. This is to allow for the classic Pt-marker experiment to be conducted in which the movement of the scale/alloy interface can be measured [41]. 3.3 Thermogravimetric Analysis The thermogravimetric analysis (TGA) was performed using a Setaram Setsys Evolution. Figure 3-2 shows a schematic of the TGA used for this study. The Setsys TGA works by having a balance whose deflection in either direction was measured using a laser. Each cleaned, polished specimen was placed in a silica crucible suspended by a series of quartz hooks from the balance. A counterweight is used to balance the weight. The following gas mixtures were used: 39

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Air He + 0.21 O 2 + 0.02 SO 2 He + 0.21 O 2 + 0.10 SO 2 In the case of air, the gas flowed over the specimen chamber and the instrument head. In the case of the O 2 + SO 2 mixtures, ultra-high purity (4.5 Grade) He was passed through the instrumentation head and into the specimen chamber via the anti-convection tube. The O 2 + SO 2 mixture was made possible by using analog volumetric flowmeters, which were then flowed through the auxiliary gas inlet to the specimen chamber and mixed with the He. The Setsys had its own digital flow controllers, so the desired gas mixture could be established. The total gas flow used was 25 mL/min, which is the Setaram recommended flow rate for this instrument. This flow rate was selected to prevent turbulence in the furnace chamber. The flow of the He carrier gas was also greater than that of the corrosive auxiliary gas to prevent attack of the instrumentation head. The gas then passed out of the chamber through an exhaust outlet. A type S thermocouple, encased in alumina was inserted into the chamber adjacent to the specimen crucible in order to measure the temperature of the specimen. Each sample run was performed by flowing only carrier gas (He) through the entire chamber at 200 mL/min for 10 minutes to remove most of the reacting oxygen and other species in air. The flow was then decreased to 20 mL/min to allow for the measure weight of the specimen to equilibrate for 10 minutes. The chamber, with the carrier gas still flowing, was then raised to the desired temperature for the experimental run (either 800, 900, or 975C) at 50C/min. Those samples not exposed to sulfidizing gases did not require a silica crucible and 40

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Figure 3-2. Schematic of the Setsys Evolution (TGA only). were heated to 1000C instead of 975C in a Pt crucible. Upon reaching the desired temperature, the chamber was held for 2 minutes to allow the specimen to reach the temperature of the furnace, and to allow for the buoyancy of the carrier gas to equilibrate for the specimen. After this, the desired auxiliary gas was added. In the case of those specimens in air, the carrier and auxiliary gases were both switched to air. Each experiment was run this way for 100 hr. At the conclusion of the test, the auxiliary gas was shut off, and the chamber was cooled at 99C/min. 41

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No baseline calculations were performed since the desired measurement was a weight change at a constant temperature. In addition, some oxidation tests were carried out in a Lindberg/Blue 1200C tube furnace to test specimens for less than 100 hr. The data obtained from the TGA experiments were analyzed to determine the parabolic, or other rate constants, gained from the growth of oxides and/or sulfides on each specimen. In the previous publications on high temperature oxidation discussed in Chapter 2, the weight change of the specimen is normalized by dividing by the surface area exposed. This way, sample of different size and surface area can be properly compared. The specimens used in this study were made from arc-melted buttons, as described in Section 3.2. Each specimen cut from each button was elliptical in nature, and the resulting surface area being tPbaA 2 (3-2) where A is the surface area, a is the half-length of the longer dimension, b is the half-length of the shorter dimension, t is the thickness, and P is the perimeter of the specimen as described by )(22221baP (3-3) In analyzing the growth rate constants of any oxidation study, the normalized weight change is plotted on one axis and the time on the other so that the slope of a linear regression of the experimental data is growth rate constant. If growth is occurring linearly, plotting normalized weight change over time will yield a straight line with a slope equal to k L In most studies of oxidation and sulfidation, normalized weight change is plotted squared against time, revealing k P However, a study by Pieraggi argues that this method can only be used for pure metals or simple alloys [167]. His study plots normalized weight change over the square root of time to determine the initial kinetics and differentiate that from the steady-state k P which is desired. This study follows Pieraggis method. Lastly, the parabolic rate constants for each 42

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composition and condition were plotted Arrheniusly in order to determine what, if any, activation energy could be garnered from these experiments. Table 3-1 lists the experiments for the alloys in this study. Table 3-1. List of experimental conditions performed for oxidation of alloys for 100 hr in 1 bar of gas at 25 mL/min. Alloy (Weight Percent) Atmosphere (bar) Temperature (C) Ni Air 800 Ni Air 900 Ni Air 1000 Ni Air 1100 Ni-13.6Al Air 800 Ni-13.6Al Air 900 Ni-13.6Al Air 1000 Ni-22Cr-11Al Air 800 Ni-22Cr-11Al Air 900 Ni-22Cr-11Al Air 1000 Ni-22Cr-11Al He + 0.21 O 2 + 0.02 SO 2 800 Ni-22Cr-11Al He + 0.21 O 2 + 0.02 SO 2 900 Ni-22Cr-11Al He + 0.21 O 2 + 0.02 SO 2 975 Ni-22Cr-11Al He + 0.21 O 2 + 0.10 SO 2 800 Ni-22Cr-11Al He + 0.21 O 2 + 0.10 SO 2 900 Ni-22Cr-11Al He + 0.21 O 2 + 0.10 SO 2 975 Ni-31Al Air 800 Ni-31Al Air 900 Ni-31Al Air 1000 Ni-8Cr-6Al Air 800 Ni-8Cr-6Al Air 900 Ni-8Cr-6Al Air 1000 Ni-8Cr-6Al He + 0.21 O 2 + 0.02 SO 2 800 Ni-8Cr-6Al He + 0.21 O 2 + 0.02 SO 2 900 Ni-8Cr-6Al He + 0.21 O 2 + 0.02 SO 2 975 Ni-8Cr-6Al He + 0.21 O 2 + 0.10 SO 2 800 Ni-8Cr-6Al He + 0.21 O 2 + 0.10 SO 2 900 Ni-8Cr-6Al He + 0.21 O 2 + 0.10 SO 2 975 3.4 Characterization This section details the methods and procedures of materials characterization for each specimen. Data obtained from these various techniques was used to identify the microstructures formed from and mechanisms of oxidation and sulfidation on these alloys. 43

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3.4.1 X-Ray Diffraction Each polished and oxidized specimen was analyzed using X-Ray diffraction (XRD). The specimens were adhered to a glass slide using double-sided tape and placed in a Philips APD 3720 XRD. The specimens were exposed from 10 to 90 2 at a rate of 0.5 s per step using 40 kV and 20 mA from a Cu K radiation source. The patterns were then treated according to the software protocol of the APD 3720 to determine the d-spacings detected. These were then compared to the files from the JCPDS International Center for Diffraction database to determine the phases diffracting at those 2 angles. 3.4.2 Scanning Electron Microscopy After XRD, the specimens were then analyzed using Scanning Electron Microscopy (SEM). First, each sample, whether oxidized or not, was affixed onto an aluminum mount using a small amount of carbon paint and analyzed from the top of the surface. The SEM used was a JEOL SEM 6400 equipped with Oxford Link ISIS energy dispersive spectroscopy (EDS) and Oxford OPAL electron backscattered secondary electron detector (EBSD), operated at 15 kV. Semi-quantitative analysis was performed using correction matrices for atomic number, absorption, and fluorescence (ZAF) [166]. The grain size of the substrate materials was determined by using line-intercept stereology methods from optical light micrographs taken from a Leco Neophot 21 optical microscope. After this analysis, the specimens were viewed in cross-section. This was performed applying an electroless Ni layer between 1 and 5 m thick using Buehler Edgemet chemical system for scale adhesion and edge retention. Next, the specimens were help upright using stainless steel clips, cast into an epoxy mixture, and allowed to cure overnight at room temperature. These epoxy-mounted specimens were then sectioned using the Allied TechCut 4 44

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and ground using 600, 800, and 1200 grit SiC abrasive paper on the Allied MetPrep3 with an AP-3 autopolisher. They were then polished using 3 m diamond suspension on nylon, 1 m diamond suspension on velcloth, and 0.1 m diamond suspension on Chem-Pol B cloth. Lastly, the specimens were thermally carbon coated in order to make the surface electrically conductive, and were analyzed on the SEM. 3.4.3 Electron Microprobe Some of the cross-sectioned epoxy-mounted specimens were analyzed using wavelength dispersive spectroscopy (WDS) in a JEOL Superprobe 733 electron microprobe (EPMA). These were performed using a 1 m size beam at approximately 1 nA that was scanned at various intervals (usually 1 m) to detect the change in composition, not only from phase to phase, but across the scale and alloy depletion zones. The compositions were calculated using the ZAF correction technique also used for EDS. The activities of the elements from each of the line scan were calculated from the Thermo-Calc software using the appended SPIN4 database with S descriptions. This was performed by entering the microprobe data from each point of a line scan into the software at the temperature the sample was oxidized and computing an equilibrium to determine the equilibrium activities at each probe. 45

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CHAPTER 4 THERMODYNAMIC CALCULATION RESULTS This section shows the diagrams created using the Thermo-Calc software. This chapter is divided into three sections that detail the development of various phase diagrams of the Ni-Cr-Al system, the temperature-potential diagrams, and potential diagrams at fixed temperatures and pressures. Phase fraction diagrams are also included throughout the chapter to give a better visual understanding of mechanisms and reactions occurring. 4.1 Calculations of Ni-Cr-Al Alloys and Mixtures using Phase Diagrams 4.1.1 Binary Systems Before attempting to analyze the more complex systems, it is important to validate the simpler binary systems that will be the basis for later calculations. Using the SPIN4 database, the Ni-Al, Ni-Cr, and Al-Cr binaries were calculated as shown in Figures 4-1, 4-2, and 4-3, respectively. The green lines represent various tie lines of two-phase equilibria. These diagrams agree with those found in the ASM Handbooks as seen in Figures 2-3, 2-4, and 2-5 for Al-Ni, Cr-Ni, and Al-Cr, respectively [30]. Differences include some of the solubility ranges for several phases including the Al-Cr diagram, where all the intermetallic phases are stoichiometric compounds with no solubility, unlike in Figure 2-5. It should be noted that the Al 13 Cr 2 and Al 11 Cr 2 intermetallics in Figure 4-3 are the same as Al 7 Cr and Al 5 Cr, respectively, in Figure 2-5. It should also be noted that the Ni-Al diagram calculated in Figure 4-4 was done without the low-temperature Ni 3 Al 5 phase. In Figure 4-4, this is restored. However, its position differs from that of Figure 2-3. Since this phase is only stable at temperatures lower than the experiments to be performed in this study, and since it is rarely discussed in literature, it will not be used for further calculations. Lastly, the SPOT3 database was not used to describe these binaries since each phase has no solubility for other elements, the liquids of each element are immiscible, and 46

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the diagrams merely show a series of lines. However, the SPOT3 potential database contains information on the solid-gas reactions that will be elaborated upon in Sections 4.2 and 4.3. Figure 4-1. Temperature-composition binary phase diagram of the Ni-Al system calculated from the SPIN4 database. Figure 4-2. Temperature-composition binary phase diagram of the Ni-Cr system calculated from the SPIN4 database. 47

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Figure 4-3. Temperature-composition binary phase diagram of the Al-Cr system calculated from the SPIN4 database. Figure 4-4. Temperature-composition binary phase diagram of the Ni-Al system calculated from the SPIN4 database with the Ni 3 Al 5 low-temperature phase restored. 48

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4.1.2 Ternary Systems The ternary phase diagrams were calculated using the thermodynamic data in the SPIN4 database. Figure 4-5 shows the complete Ni-Cr-Al ternary isothermal section for 900C, where the weight percents of the Cr and Al elements are plotted. This can be compared to the ternary calculated by Dupin in Figures 2-9 and 2-8 with that calculated in Figure 4-6, which is in mole percent at 850C and in Figure 4-7 in weight percent at 1025C. The fields of stability are often different in size and shape in comparing the isotherms, and Figure 4-7 is more complete in showing the Al rich regions of the phase diagram. Figure 4-5. Isothermal section of Ni-Cr-Al ternary system at 900C in weight fractions. This diagram is calculated from data in the SPIN4 database. 49

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Figure 4-6. Partial isothermal section of Ni-Cr-Al ternary system at 850C in mole fractions. The axes are chosen to compare with Figure 2-9. This diagram is calculated from data in the SPIN4 database. Figure 4-7. Isothermal section of Ni-Cr-Al ternary system at 1025C in mole fractions. The axes are chosen to compare with Figure 2-8. This diagram is calculated from data in the SPIN4 database. 50

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Figure 4-8. Ternary isothermal section of the Ni-Al-O 2 system at 900C. The x-axis is the composition of Al in weight percent, and the y-axis is the logarithmic partial pressure of O 2 in bar. This diagram is calculated from data in the SPIN4 database. Figure 4-9. Ternary isothermal section of the Ni-Cr-O 2 system at 900C. The x-axis is the composition of Cr in weight percent, and the y-axis is the logarithmic partial pressure of O 2 in bar. This diagram is calculated from data in the SPIN4 database. 51

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Figure 4-10. The Ni-Al-Cr-O system shown as a series of connected ternary subsystem isotherms at 900C. The outer axes are the logarithm of the partial pressure of O 2 in bar, whereas the inner axes are the weight percents of Ni, Cr, and Al. This diagram is calculated from data in the SPIN4 database. In addition to the Ni-Cr-Al ternary, the Ni-Al-O 2 and Ni-Cr-O 2 ternaries were calculated and are shown as isotherms at 900C in Figure 4-8 and 4-9, respectively. Here the partial pressure of oxygen gas (in bar) was used to plot the oxygen axes. These ternary subsystems were then combined with the Al-Cr-O 2 and Ni-Cr-Al isotherms to help depict the Ni-Cr-Al-O system at 900C in Figure 4-10. In this figure, the inner axes are in weight percent, while the outer axes are the logarithms (base 10) of the partial pressure of O 2 (in bar). 52

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4.2. Calculations of Temperature-Potential Diagrams Calculations were performed using the SPOT3 database to develop diagrams that would show the reactions occurring with change in temperature and the chemical potential (or activity). These and all further diagrams show axes labeled as the partial pressure of a certain gas, in bar. This is found by converting either the natural log of activity or chemical potential into units of log 10 bar by 10ln)ln(XXaP (4-1) )10ln()(TRXPX (4-2) where a is the activity of a certain gas species X, P is the partial pressure of the gas species, (X) is the chemical potential of a gas species (in J/mol), R is the gas constant of 8.314 J/mol K, and T is the temperature in K. 4.2.1 Calculations with O 2 -SO 2 Interactions For the physical experiments used in this study, the reacting gases used were air, oxygen (O 2 ) and sulfur dioxide (SO 2 ). These results are discussed in Chapter 5, but in this section are dealt with by thermodynamic calculations. As discussed in Chapter 2, an environment mixing O 2 and SO 2 will cause a reaction that can create sulfur trioxide (SO 3 ) and other products. Using the conditions for the experiments 1. He + 0.21 O 2 + 0.02 SO 2 2. He + 0.21 O 2 + 0.10 SO 2 calculations were performed to determine how the gases react with change in temperature. The calculations for condition 1 are shown in Figure 4-11, and condition 2 are shown in Figure 4-12. These are shown in a similar manner to CO 2 /CO diagrams illustrating isobars of O 2 [167]. With both diagrams, at temperatures below approximately 600C, the reaction 53

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O 2 + 2SO 2 = 2SO 3 (4-3) occurs readily and SO 3 is the more stable sulfur-based gas species. However, it is of much less consequence above 900C. Between the two temperatures, the stability of SO 2 and SO 3 change rapidly with a major vapor transition point occurring at 707C. He is used in the calculations as filler so that the total number of moles can remain constant at unity. However, due to scale its partial pressure is omitted. Figure 4-11. Change in partial pressure of O 2 SO 2 and SO 3 (in bar) with temperature using the initial gas mixture of He + 0.21 O 2 + 0.02 SO 2 The P He is omitted due to scale. The data used for calculations is taken from the SPOT3 database. As well as these calculations, diagrams were calculated of isobaric lines of one gas in relation to a ratio of the partial pressures of two other gases with changing temperature. For example, Figure 4-13 shows lines of constant partial pressure of sulfur trioxide based of the ratio of partial pressure of oxygen over sulfur dioxide. The region labeled as unstable gas, occurring at high SO 2 and low O 2 at higher temperatures, could not be calculated due to the 54

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Figure 4-12. Change in partial pressure of O 2 SO 2 and SO 3 (in bar) with temperature using the initial gas mixture of He + 0.21 O 2 + 0.10 SO 2 The P He is omitted due to scale. The data used for calculations is taken from the SPOT3 database. Figure 4-13. The relationship between the partial pressure of SO 3 in an O 2 -SO 2 gas mixture, with varying temperature. All partial pressures are in bar. 55

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Figure 4-14. The relationship between the partial pressure of S 2 in an O 2 -SO 2 gas mixture, with varying temperature. All partial pressures are in bar. Figure 4-15. The relationship between the partial pressure of O 2 in an SO 3 -SO 2 gas mixture, with varying temperature. All partial pressures are in bar. 56

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evolution of more than three phases in equilibrium. In CO/CO 2 /O 2 systems, this corresponds with the deposition of graphite [157]. Here, it may correspond with the deposition of liquid sulfur, but this could not be calculated and was not confirmed by any experiments. This is continued in Figures 4-14 and 4-15, which show the isobars of S 2 and O 2 based on ratios of O 2 /SO 2 and SO 3 /SO 2 respectively. 4.2.2 Calculations of Metal-Gas Interactions Thermodynamic equilibria were calculated for several metal mechanical mixtures (meant to represent specific phases or alloys) between 800 and 1000C by fixing the number of conditions so that the degrees of freedom were zero. Then, a range of activities or chemical potentials of the components O 2 and SO 2 were defined, and the diagrams were mapped in that range. The diagrams are plotted at various temperatures using the partial pressures of either O 2 and SO 2 or O 2 and S 2 which can be defined from their activities or chemical potentials, as axes. The mixtures for which calculations were performed are: Ni Ni 3 Al () NiAl () Ni-8Cr-6Al Ni-22Cr-11Al Since no solubility in the solid state is described per the SPOT3 database, the equilibria calculated were compared to a proprietary database that allows for solubility, SPIN4. This database was not accessed for this study because it has no description for S. However, in using a Ni-Cr-Al-O system, the calculated equilibria are in good agreement between the two databases and are shown in Table 4-1. Figure 4-16 shows the temperature-potential diagram of Ni in an environment with only oxygen and some inert gas. Here, one can see that at higher partial pressures of O 2 NiO becomes more stable than Ni. However, this oxide stability decreases with increasing 57

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Table 4-1. Comparison of equilibria computed between two databases SPOT3 and SPIN4 at a pressure of 1 bar and T = 1073 K for Ni-22Cr-11Al alloy (by mass) with a P O2 of 0.22 bar. This table compares number of moles of each phase, along with the composition (in weight fraction) of each phase. Database Phases Moles W(Ni) W(Cr) W(Al) W(O 2 ) NiO 0.134 0.786 0 0 0.214 NiAl 2 O 4 0.424 0.332 0 0.305 0.362 SPOT3 NiCr 2 O 4 0.441 0.259 0.459 0 0.362 Halite (NiO) 0.138 0.777 9.87e-4 4.75e-3 0.217 SPIN4 Spin3 Ni[Cr,Al] 2 O 4 ) 0.862 0.290 0.263 0.131 0.216 temperature. Figures 4-17 and 4-18 show the same conditions as that for 4.16, except for the addition of 2 mol % SO 2 and 10 mol % SO 2 respectively. It is plain to see that the stability of the Ni and the nickel oxide decrease dramatically with even small sulfur dioxide additions. At higher partial pressures of oxygen at lower temperatures, the nickel sulfate becomes stable, and at lower oxygen partial pressures, the nickel sulfides become stableNi 3 S 2 is the most stable, but NiS, Ni 3 S 4 and NiS 2 can also be present. The areas labeled unstable equilibrium are areas where the software could not calculate, and therefore not map, a stable equilibrium. This is likely due to the evolution of some gas, which creates too many phases to calculate a stable equilibrium. These conditions are mostly observed at high P O2 at low temperatures, or high P SO2 at high temperatures. Diagrams for mixtures of Ni, O 2 and other metals (Al and/or Cr) were not able to be calculated and are not shown. 4.3 Calculations of Potential Diagrams The results for the calculations of Ni in SO 2 /O 2 environments at 800, 900, and 1000C are show in Figures 4-19a, 4-20, and 4-21, respectively. Figure 4-19b also shows the S 2 -O 2 potential diagram for Ni at 800C for comparison with Figure 4-19a. As with section 4.2, all calculations were performed using data from the SPOT3 database unless otherwise noted. At high P O2 and low P SO2 the NiO becomes stable from the oxidation of Ni. Increasing SO 2 can cause the 58

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Figure 4-16. Stability diagram of Ni and its oxide with varying temperature and partial pressure of oxygen (in bar). Figure 4-17. Stability diagram of Ni and its oxide with varying temperature and partial pressure of oxygen (in bar) with a constant partial pressure of sulfur dioxide at 2 mol %. 59

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Figure 4-18. Stability diagram of Ni and its oxide with varying temperature and partial pressure of oxygen (in bar) with a constant partial pressure of sulfur dioxide at 10 mol %. formation of NiSO 4 Decreasing O 2 at higher SO 2 contents cause the formation of Ni sulfidesNi 3 S 2 NiS, Ni 3 S 4 and NiS 2 at increasing P SO2 The Ni 3 S 2 is a liquid at these temperatures. At high P SO2 and high or low P O2 no stable equilibrium could be calculated. It is possible that this is a gas phase, which at low P O2 is almost entirely SO 2 whereas the gas at high P O2 is a mixture of SO 2 O 2 and SO 3 (see Table 4-2). As temperature is increased, the resistance of Ni to oxidize decreases, but attack by sulfur species is more prevalent. Table 4-2. Comparison of gas species (at mole fractions > 10 -10 ) present in the unstable equilibrium regions of Figure 4-19 at low P O2 and high P O2 These mole fractions are calculated based on ideal gas behavior. Gas Species (low P O2 ) Mole Fraction Gas Species (High P O2 ) Mole Fraction SO 2 0.999 SO 2 0.356 SO 4.59e-6 O 2 0.356 SO 3 4.14e-6 SO 3 0.288 S 2 O 8.92e-7 S 2 3.84e-7 60

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Figure 4-19. Ni potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. Figure 4-20. Ni SO 2 -O 2 potential diagram at 900C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 61

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Figure 4-21. Ni SO 2 -O 2 potential diagram at 1000C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. Figures 4-22a, 4-23, and 4-24 show the SO 2 -O 2 potential diagrams for Al at 800, 900, and 1000C, respectively. Figures 4-25a, 4-26, and 4-27 show the SO 2 -O 2 potential diagrams for Cr at the same respective temperatures. Figures 4-22b and 4-25b show the S 2 -O 2 potential diagrams for Al and Cr, respectively. Comparing these diagrams with those for Ni, one can tell that Cr and especially Al have greater affinities for O 2 as they will oxidize at a lower P O2 than Ni. In addition, Al and Cr will also sulfidize at lower S activities, and these sulfides will oxidize at lower P O2 Al and Cr were calculated as having only one sulfidation product each, as opposed to the four exhibited by Ni at these temperatures. Figures 4-28, 4-29, and 4-30 show calculations of Ni 3 Al, or , at 800, 900, and 1000C, respectively. Due to the Gibbs Phase Rule (Equation 3-1), each phase field contains two phases. At low partial pressures of both gases, the phase was calculated and, to satisfy the phase rule, Al is in equilibrium as excess in the intermetallic. In this system, Al is the more reactive element, and reacts with S and/or O at lower partial 62

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pressures. In all cases, the Al 2 O 3 phase is Increasing the O 2 eventually depletes the phase of Al, causing it to form the (Ni) phase. Further increasing P O2 causes the alumina to react with the to form a spinel phase (NiAl 2 O 4 ). Al forms only an Al 2 S 3 sulfide, and similar to what is shown in Figures 4-19-4-21, the Ni forms a variety of sulfides depending on the P SO2 At 900 and 1000C, the Ni 3 S 2 becomes the most stable sulfide, as the others become degenerate cases. Figures 4-31, 4-32, and 4-33 show calculations of NiAl, or at 800, 900, and 1000C, respectively. These diagrams are similar to those for Ni 3 Al, except that is the stable phase, and that there is enough Al present to keep Al 2 O 3 stable up to 1 bar P O2 Also, the phase was shown to have a larger stability range than Figure 4-22. Al potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. Published in [170]. 63

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Figure 4-23. Al SO 2 -O 2 potential diagram at 900C. Figure 4-24. Al SO 2 -O 2 potential diagram at 1000C. 64

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Figure 4-25. Cr potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. Published in [170]. Figure 4-26. Cr SO 2 -O 2 potential diagram at 900C. 65

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Figure 4-27. Al SO 2 -O 2 potential diagram at 900C. Figure 4-28. Ni-13.6Al potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. 66

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Figure 4-29. Ni 3 Al SO 2 -O 2 potential diagram at 900C. Figure 4-30. Ni 3 Al SO 2 -O 2 potential diagram at 1000C. Published in [170]. 67

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Figure 4-31. NiAl potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. U.E. is an abbreviation for undefined equilibrium. Published in [170]. Figure 4-32. NiAl SO 2 -O 2 potential diagram at 900C. 68

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Figure 4-33. NiAl SO 2 -O 2 potential diagram at 1000C. Published in [170]. Figures 4-34, 4-35, and 4-36 show calculations of the Ni-8Cr-6Al mixture at 800, 900, and 1000C, respectively. As per the Gibbs Phase Rule, each phase field must now have three phases in equilibrium. The base metal at low partial pressures is shown as a mixture of -Ni, , and Crin reality the alloy should have -Ni as the only stable phase at these temperatures. However, the other phase fields agree with studies that show alumina and chromia stable at lower partial pressures of O 2 whereas NiO and spinel are stable at higher partial pressures. While Al has a higher affinity for O, Cr is the element that forms sulfides (CrS) at the lowest P SO2 At higher temperatures, Ni 3 S 2 again becomes the dominant Ni sulfide, whereas NiO and spinel become less stable. 69

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Figure 4-34. Ni-8Cr-6Al potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. Published in [170]. Figure 4-35. Ni-8Cr-6Al SO 2 -O 2 potential diagram at 900C. Published in [170]. 70

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Figure 4-36. Ni-8Cr-6Al SO 2 -O 2 potential diagram at 1000C. Published in [170]. In the composition with higher concentrations of Cr and Al, the mixture oxidizes at lower P O2 The potential diagrams for the Ni-22Cr-11Al mechanical mixture are shown in for 800, 900, and 1000C in Figures 4-37, 4-38, and 4-39, respectively. Here, the substrate alloy is shown as a combination of , and -Cr. This composition reacts more readily with O 2 and SO 2 than the other two as shown with the addition Al 2 O 3 -Cr- and --CrS phase fields. Again, as with the other two mixtures, Ni 3 S 2 becomes the predominant Ni sulfide at higher temperatures, alumina and chromia are more resilient against sulfidation, and NiO and spinel become less stable at higher temperatures. 71

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Figure 4-37. Ni-22Cr-11Al potential diagrams for (a) SO 2 -O 2 and (b) S 2 -O 2 at 800C. Published in [170]. Figure 4-38. Ni-22Cr-11Al SO 2 -O 2 potential diagram at 900C. Published in [170]. 72

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Figure 4-39. Ni-22Cr-11Al SO 2 -O 2 potential diagram at 1000C. Published in [170]. 4.4 Phase Fraction Diagrams This section shows the calculations in the form of phase fraction diagrams, which are diagrams with a potential, temperature, or composition of the x-axis, and a quantity on the y-axis. This quantity can be a generic term such as phase fraction, or can be more specific like partial pressure or composition. Figure 4-40 shows a phase fraction diagram of the Ni-O system calculated using the SPOT3 database at 800C with varying oxygen partial pressure. As predicted from Figure 4-16, the Ni phase is stable below a P O2 of 10-14, whereas the NiO is stable above this partial pressure. In essence, Figure 4-40 is slice of Figure 4-16 at a constant temperature. Figure 4-41 shows the phase fraction diagram of Ni at 800C if 2% SO 2 is added. The partial pressure of S 2 is derived using the same methods to obtain Figures 4-11 and 4-14. The addition of S to the system causes the formation of Ni 3 S 2 at lower PO 2 and NiSO 4 at higher PO 2 In between is a gas that stabilizes (mostly SO 2 ), consisting of the species shown in Figure 4-42. In this calculation, Ar was added 73

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as a component to the system to add as filler to keep the total system pressure 1 bar. An attempt was made to use the appended SPIN4 database to calculate these diagrams, but no stable equilibrium could be calculated. This was likely due to the equilibrium converging to two stable phases, which would violate the Gibbs Phase Rule for a three-component Ni-O-S system. Figure 4-43 shows the change in component activity where there is an increase in S 2 activity at the oxide/metal interface. On either side of this peak, the P S2 drops, especially toward increasing O 2 where the S is oxidized into SO 2 and SO 3 Figure 4-44 shows the phase fraction diagram of changing activity of the constituents of the Ni-8Cr-6Al alloy in air calculated using the SPIN4 database. This diagram shows the drop in metal activities with increasing P O2 starting with the most reactive, Al, then Cr and finally Ni. Figure 4-45 shows the different phases that are stable over this range of P O2 Figure 4-46 shows a comparison of the activities obtained for this system with the SPOT3 and SPIN4 database. The two calculations agree perfectly with component activities in the (Al,Cr) 2 O 3 oxide and NiO. However, there is disagreement where the component are dissolved in and the spinel phase, due to the interaction parameters of elements in solution, which is not accounted for in the SPOT3 database. The addition of sulfur to the above system and Ni-22Cr-11Al are of the most interest for this dissertation. Figure 4-47 shows the Ni-8Cr-6Al alloy in a 2% SO 2 atmosphere, as calculated by the appended SPIN4 database. As with Figure 4-43, there is again a spike in S 2 activity near the boundary of oxide/alloy stability. The phase fraction diagram in Figure 4-48 shows stabilization of sulfurous phasesfrom CrS at low P O2 to Ni 3 S 2 at higher P O2 and finally a gas consisting mostly of SO 2 and O 2 Figure 4-49 shows the activity change for Ni-22Cr-11Al in the same environment and temperature, and Figure 4-50 shows the phase quantities. The activity 74

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profile is similar to that of Ni-8Cr-6Al. In addition, similar phases evolve with the Ni-22Cr-11Al alloy, except with the formation of an -Cr phase at low P O2 Spinel is now the most predominant oxide at high P O2 and at intermediate partial pressures of oxygen, the oxide dominates instead of the alloy. Figure 4-40. Phase fraction diagram of the Ni-O system showing the change in phase percent with varying oxygen partial pressure at 800C in air. Calculated from the SPOT3 database. 75

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Figure 4-41. Phase fraction diagram of the Ni-O-S system showing the change in phase percent with varying oxygen partial pressure at 800C in an 0.21 O 2 + 0.02 SO 2 atmosphere. Calculated from the SPOT3 database. Figure 4-42. Phase fraction diagram of the Ni-O-S system showing the gas evolution (in partial pressure [bar]) with varying oxygen partial pressure at 800C in an 0.21 O 2 + 0.02 SO 2 atmosphere. Calculated from the SPOT3 database. 76

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Figure 4-43. Phase fraction diagram of the Ni-O-S system showing activity change of each component with varying oxygen partial pressure at 800C in an 0.21 O 2 + 0.02 SO 2 atmosphere. Calculated from the SPOT3 database. Figure 4-44. Phase fraction diagram an Ni-8Cr-6Al alloy showing activity change of each component with varying oxygen partial pressure at 800C in air. Calculated from the SPIN4 database. 77

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Figure 4-45. Phase fraction diagram an Ni-8Cr-6Al alloy showing the change in phase percent with varying oxygen partial pressure at 800C in air. Calculated from the SPIN4 database. Figure 4-46. Phase fraction diagram an Ni-8Cr-6Al alloy at 800C comparing the activity change calculated for Figure 4-38 using the SPIN4 database (black) and the SPOT3 database (teal). 78

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Figure 4-47. Phase fraction diagram of an Ni-8Cr-6Al alloy showing activity change of each component with varying oxygen partial pressure at 800C in an 0.21 O 2 + 0.02 SO 2 atmosphere. Calculated from the appended SPIN4 database. Figure 4-48. Phase fraction diagram of an Ni-8Cr-6Al alloy showing the change in phase percent with varying oxygen partial pressure at 800C in an 0.21 O 2 + 0.02 SO 2 atmosphere. Calculated from the appended SPIN4 database. 79

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Figure 4-49. Phase fraction diagram of an Ni-22Cr-11Al alloy showing activity change of each component with varying oxygen partial pressure at 800C in an 0.21 O 2 + 0.02 SO 2 atmosphere. Calculated from the appended SPIN4 database. Figure 4-50. Phase fraction diagram of an Ni-22Cr-11Al alloy showing the change in phase percent with varying oxygen partial pressure at 800C in an 0.21 O2 + 0.02 SO 2 atmosphere. Calculated from the appended SPIN4 database. 80

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CHAPTER 5 EXPERIMENTAL RESULTS This chapter will discuss the results of the kinetic experiments conducted using the methodology described in Chapter 3. The results of the kinetic analyses will be shown, and then the characterization data of the oxidized specimens will be presented. 5.1 TGA Experiments 5.1.1 Oxidation Experiments in Air The TG experiments were carried out as outlined in Chapter 3. Figure 5-1 shows the results of a typical oxidation runa Ni specimen in air at 800C for 24 hr. Here, the weight change divided by surface area (in mg/cm 2 ) is plotted against the time in seconds. However, for the purpose of brevity, further results will be given to best visualize and derive the parabolic rate constant(s) of each sample run. Figure 5-2 is similar to Figure 5-1 except that the x-axis plots the square root of time, in s From this figure, one can derive the parabolic rate constant, k P in mg/cm 2 s from the slope of the linear regression which is plotted on the graph. The R 2 coefficient of determination is plotted as well to show the global fit of the parabolic rate model. Figure 5-1. Plot of weight change versus time for Ni specimen at 800C for 24 hr in air. 81

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Figure 5-2. Plot of weight change versus square root time for Ni specimen at 800C for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. Figure 5-3 shows the TG data collected for Ni oxidized at 900C. This data is noteworthy because the oxidation growth at the beginning of the test takes on the subparabolic behavior described by Haugsrud [44]. This is also observed in the Ni specimen oxidized at 1100C. However, it is not seen at 1000C. To compare the growth constants for this study with those of most every other oxidation study, which plot the weight change squared versus time yielding units of mg 2 /cm 4 s, the k P values obtain were squared, and then plotted Arrheniusly against the inverse absolute temperature to determine an activation energy, as shown in Figure 5-4. The activation energy, Q A can be derived from the slope by: RmQA (5.1) where m is the slope of the linear regression obtained from the Arrhenius plot (in K) and R is the ideal gas constant of 8.314 J/molK. The oxidation of Ni specimens in this study had an activation energy of 150.74 kJ/mol. 82

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Figure 5-3. Plot of weight change versus square root time for Ni specimen at 900C for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. Figure 5-4. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni oxidized for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. Unlike the TG curves for pure Ni, the oxidation growth for all the other alloys was more complex. In Figure 5-5, the oxidation of NiAl at 800C for 24 hr is plotted. This plot shows an incubation time with possibly some minor weight loss until approximately 3 hours into the test 83

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(105 s on Figure 5-5), when parabolic grows occurs. This same behavior was seen for all three NiAl oxidation tests, which had incubation times of 3.1 hr, 1.5 hr, and 1.2 hr respectively for tests at 800, 900, and 1000C. This incubation time was chosen by taking a tangent to the parabolic region of the curve, as outlined by the method developed by Pieraggi [167]. Where the slope changed there was a deviation defined by Equation 2-5 and was not considered steady-state. The parabolic rate constants for the NiAl specimens are graphed on an Arrhenius plot in Figure 5-6. The activation energy for the oxidation of NiAl, excluding the incubation time, was found to be 161.69 kJ/mol. No activation energies for these materials were calculated by literature Figure 5-5. Plot of weight change versus square root time for a NiAl specimen at 800C for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. 84

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Figure 5-6. Arrhenius plot of the parabolic rate constant versus inverse temperature of NiAl oxidized for 24 hr in air. The formula containing the slope and the coefficient of determination are listed. For the Ni-Cr-Al alloys, the TG curves were even more complex. One of the Ni-8Cr-6Al, like Figure 5-7, had a similar shape to that of Figure 5-5. Others, like Figure 5-8 had an initial oxidation growth rate that was faster than the steady-state parabolic growth. The oxidation plots for Ni-8Cr-6Al at 800C has the same shape as that for 1000C (Figure 5-7), although the initial oxidation stages are much less pronounced. The curves for the Ni-22Cr-11Al alloys were all similar to those for 100 hr at 800C, as shown in Figure 5-9. In the experiments with these alloys, there was an initial weight gain, then a slight weight loss, and finally steady parabolic growth. The steady-state parabolic rate constants for Ni-8Cr-6Al and Ni-22Cr-11Al are plotted versus inverse absolute temperature as Arrhenius plots in Figures 5-10 and 5-11, respectively. No activation energy could be calculated for the Ni-8Cr-6Al alloy because there was not an Arrhenius dependency. An activation energy of 25.07 kJ/mol was calculated for the the oxidation of Ni-22Cr-11Al. However, the amount of variance here cannot be explained by the Arrhenius model making this is statistic unsound. 85

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Figure 5-7. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 1000C for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. Figure 5-8. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 900C for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. 86

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Figure 5-9. Plot of weight change versus square root time for a Ni-22Cr-11Al specimen at 800C for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. Figure 5-10. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al oxidized for 100 hr in air. 87

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Figure 5-11. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-11Al oxidized for 100 hr in air. The formula containing the slope and the coefficient of determination are listed. 5.1.2 Oxidation Experiments in He + 0.21 O 2 + 0.02 SO 2 The TG experiments with 2% SO 2 showed more scatter in the collected data, but there appeared to be less change in mechanism during the oxidation process. For Ni-8Cr-6Al, there appeared to be a faster initial stage of oxidation before transitioning to the steady parabolic rate (Figure 5-12). For all other conditions though, with this alloy and with Ni-22Cr-11Al, there appeared to be no pronounced initial oxidation stage, as shown in Figure 5-13. The Arrhenius plots for Ni-8Cr-6Al and Ni-22Cr-11Al are shown in Figures 5-14 and 5-15, respectively. The activation energy for oxidation of Ni-8Cr-6Al in He + 0.21 O 2 + 0.02 SO 2 is 415.14 kJ/mol, and for Ni-22Cr-11Al is 157.83 kJ/mol. This shows a higher activation energy for steady-state oxidation in the Ni-8Cr-6Al specimens than the Ni-22Cr-11Al. No previous literature discusses activation energies for the oxidation of these alloys. 88

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Figure 5-12. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 975C for 100 hr in He + 0.21 O 2 + 0.02 SO 2 The formula containing the slope and the coefficient of determination are listed. Figure 5-13. Plot of weight change versus square root time for a Ni-22Cr-11Al specimen at 975C for 100 hr in He + 0.21 O 2 + 0.02 SO 2 The formula containing the slope and the coefficient of determination are listed. 89

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Figure 5-14. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al oxidized for 100 hr in He + 0.21 O 2 + 0.02 SO 2 The formula containing the slope and the coefficient of determination are listed. Figure 5-15. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-11Al oxidized for 100 hr in He + 0.21 O 2 + 0.02 SO 2 The formula containing the slope and the coefficient of determination are listed. 90

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5.1.3 Oxidation Experiments in He + 0.21 O 2 + 0.10 SO 2 The oxidation/sulfidation TG plots of all the Ni-8Cr-6Al alloys in He + 0.21 O 2 + 0.10 SO 2 had the same shape as the plot in Figure 5-16 for 900C. There was an initial parabolic growth rate, which at a certain time would enter a transition stage, which would then the growth would proceed at a faster parabolic rate. Therefore, there are two parabolic rate constants for each experimental temperatureone for the initial oxidation, and one for the later, steady-state oxidation. Figure 5-17 shows the Arrhenius plots for both oxidation stages. The activation energy for the initial oxidation in He + 0.21 O 2 + 0.10 SO 2 is 140 kJ/mol, while that of the later stage is 120 kJ/mol. Figure 5-16. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 900C for 100 hr in He + 0.21 O 2 + 0.10 SO 2 The formulas containing the slopes and the coefficients of determination are listed. 91

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Figure 5-17. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al oxidized for 100 hr in He + 0.21 O 2 + 0.10 SO 2 The blue data and regression correspond to the initial oxidation rates, whereas the red data and regression correspond to the later stage oxidation. The formulas containing the slope and the coefficients of determination are listed. The oxidation curves of Ni-22Cr-11Al alloy in He + 0.21 O 2 + 0.10 SO 2 followed that of the one recorded at 800C (Figure 5-18)fast growth that eventually decreases until steady-state parabolic kinetics is observed. An Arrhenius plot of the parabolic rate constants for these experiments is shown in Figure 5-19. The activation energy for the oxidation of Ni-22Cr-11Al in He + 0.21 O 2 + 0.10 SO 2 could be 152.52 kJ/mol, although it is not statistically significant. Table 5-1 lists the mean parabolic rate constants for all the oxidation and oxidation/sulfidation experiments. Figure 5-20 shows an Arrhenius plot of all the experiments. 92

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Figure 5-18. Plot of weight change versus square root time for a Ni-22Cr-11Al specimen at 800C for 100 hr in He + 0.21 O 2 + 0.10 SO 2 The formula containing the slope and the coefficient of determination are listed. Figure 5-19. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-11Al oxidized for 100 hr in He + 0.21 O 2 + 0.10 SO 2 The formula containing the slope and the coefficient of determination are listed. 93

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Table 5-1. List of the parabolic rate constants obtained from steady-state oxidation of Ni, Ni-13.6Al, NiAl, Ni-8Cr-6Al, and Ni-22Cr-11Al alloys. Alloy Name Atmosphere (bar) Temperature (C) k P (mg/cm 2 s ) k P (mg 2 /cm 4 s) Ni Air 800 3.13E-03 9.82E-06 Ni Air 900 6.42E-03 4.12E-05 Ni Air 1000 1.20E-02 1.43E-04 Ni Air 1100 1.97E-02 3.89E-04 Ni-13.6Al Air 800 1.15E-04 1.31E-08 Ni-13.6Al Air 900 3.20E-04 1.02E-07 Ni-13.6Al Air 1000 2.45E-04 6.02E-08 Ni-22Cr-11Al Air 800 4.08E-04 1.66E-07 Ni-22Cr-11Al Air 900 6.10E-04 3.72E-07 Ni-22Cr-11Al Air 1000 5.05E-04 2.55E-07 Ni-22Cr-11Al He + 0.21 O 2 + 0.02 SO 2 800 2.28E-04 5.20E-08 Ni-22Cr-11Al He + 0.21 O 2 + 0.02 SO 2 900 4.00E-04 1.60E-07 Ni-22Cr-11Al He + 0.21 O 2 + 0.02 SO 2 975 5.39E-04 2.91E-07 Ni-22Cr-11Al He + 0.21 O 2 + 0.10 SO 2 800 1.68E-04 2.82E-08 Ni-22Cr-11Al He + 0.21 O 2 + 0.10 SO 2 900 7.05E-04 4.97E-07 Ni-22Cr-11Al He + 0.21 O 2 + 0.10 SO 2 975 5.19E-04 2.69E-07 Ni-31Al Air 800 4.83E-04 2.33E-07 Ni-31Al Air 900 1.10E-03 1.20E-06 Ni-31Al Air 1000 1.95E-03 3.82E-06 Ni-8Cr-6Al Air 800 1.58E-03 2.50E-06 Ni-8Cr-6Al Air 900 5.31E-04 2.82E-07 Ni-8Cr-6Al Air 1000 1.94E-03 3.76E-06 Ni-8Cr-6Al He + 0.21 O 2 + 0.02 SO 2 800 1.24E-04 1.54E-08 Ni-8Cr-6Al He + 0.21 O 2 + 0.02 SO 2 900 1.32E-03 1.74E-06 Ni-8Cr-6Al He + 0.21 O 2 + 0.02 SO 2 975 3.14E-03 9.86E-06 Ni-8Cr-6Al He + 0.21 O 2 + 0.10 SO 2 800 9.33E-04 8.70E-07 Ni-8Cr-6Al He + 0.21 O 2 + 0.10 SO 2 900 4.54E-03 2.06E-05 Ni-8Cr-6Al He + 0.21 O 2 + 0.10 SO 2 975 6.82E-03 4.64E-05 94

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Figure 5-20. Arrhenius plot of alloys isothermally oxidized in this study for 100 hr. 5.2 Phase Identification The identification of phases was performed using the APD3720 XRD and compared the d-spacings of the peak intensities with those of cataloged JCPDS files. This section shows the XRD results from the tests described in Section 5.1 on the Ni-8Cr-6Al and Ni-22Cr-11 Al alloys. Figure 5-21 shows the XRD results of a polished, heat-treated specimen of Ni-8Cr-6Al. The peaks identified show the presence of Ni, Ni 3 Al, and possibly some Al 2 O 3 This oxide might be residual from the alumina polished used in sample preparation, as it is not expected. Figures 5-22, 5-23, and 5-24 show the XRD results of Ni-8Cr-6Al oxidized in air for 100 hr at 800, 900, and 1000C, respectively. Comparing these with Figure 5-21, one can see the emergence of NiO and Al 2 O 3 All Al 2 O 3 identified from these XRD studies is the stable phase. At 800C, some chromia is seen, and at 1000C, NiAl 2 O 4 spinel is present. The peak heights of the Ni and fluctuate between all four figures, but they will not be used in this study to 95

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determine the phase percentages. The figures with higher alumina peaks have corresponding higher Ni peaks, and those with lower alumina and/or higher NiO have higher Ni 3 Al peaks. This is likely due to a depletion of one element near the surface if one oxide is more prevalent, and would thus show more of either or accordingly. Figure 5-21. Histogram of the peak intensities measured from an XRD analysis of polished, heat treated Ni-8Cr-6Al. Figure 5-22. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in air for 100 hr at 800C. 96

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Figure 5-23. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in air for 100 hr at 900C. Figure 5-24. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in air for 100 hr at 1000C. Figures 5-25, 5-26, and 5-27 show the XRD data for Ni-8Cr-6Al oxidized in 2% SO 2 for 800, 900, and 975C, respectively. As with the samples oxidized in air, alumina and NiO are present. However, chromia is present at all temperatures, not just at 800C. The spinel phase is also shown for the higher temperatures of 900 and 975C. Those specimens oxidized in 10% 97

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SO 2 show similar results with those oxidized in 2% SO 2 as shown in Figures 5-28, 5-29, and 5-30 for 800, 900, and 975C, respectively. However, spinel is only seen on the 900C sample, and it is the NiCr 2 O 4 (not NiAl 2 O 4 ) phase. NiO was found at the lowest temperature, but not at the others. In addition, a sulfide peak (Ni 3 S 2 ) may have been detected from the 800C sample, likely from a spot where the oxide had spalled revealing the interface underneath. Figure 5-25. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O 2 + 0.02 SO 2 for 100 hr at 800C. Figure 5-26. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O 2 + 0.02 SO 2 for 100 hr at 900C. 98

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Figure 5-27. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O 2 + 0.02 SO 2 for 100 hr at 975C. Figure 5-28. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O 2 + 0.10 SO 2 for 100 hr at 800C. 99

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Figure 5-29. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O 2 + 0.10 SO 2 for 100 hr at 900C. Figure 5-30. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al oxidized in He + 0.21 O 2 + 0.10 SO 2 for 100 hr at 975C. The XRD data of polished, heat-treated Ni-22Cr-11Al is shown in Figure 5-31, and the samples oxidized in air at 800, 900, and 1000C are shown in Figures 5-32, 5-33, and 5-34, respectively. The unoxidized specimen of Ni-22Cr-11Al contains Ni, Ni 3 Al, NiAl, and Cr, as well as the one alumina peak. Upon oxidation, chromia and alumina are formed. NiAl 2 O 4 spinel 100

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was also identified for the sample oxidized at 900C. The formation of Al 2 O 3 corresponded with the loss of NiAl peaks, as this phase was likely consumed during the experiments. Also, the amount of present decreased relative to Ni (except at 1000C). The addition of 2% SO 2 showed little difference with the XRD data of the oxidized samples, as seen in Figures 5-35, 5-36, and 5-37 for 800, 900, and 975C, respectively. Two Ni 3 S 2 peaks were observed on the specimen exposed at 975C, likely from areas of oxide spallation, which was observed on this sample. At 10% SO 2 (as seen in Figures 5-38, 5-39, and 5-40 for 800, 900, and 975C, respectively), more sulfide peaks were observed. As with the 2%, some Ni 3 S 2 was observed at 800C, but was a different phase at 900CNi 3 S 4 At 975C, Cr sulfide in the form of Cr 3 S 4 was identified. Not all of these samples showed spallation, so some of the sulfides may be present in the oxide or in larger amounts than other sample runs. Table 5-2 summarizes the phases identified from the XRD measurements. Figure 5-31. Histogram of the peak intensities measured from an XRD analysis of polished, heat treated Ni-22Cr-11Al. 101

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Figure 5-32. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in air for 100 hr at 800C. Figure 5-33. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in air for 100 hr at 900C. 102

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Figure 5-34. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in air for 100 hr at 1000C. Figure 5-35. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O 2 + 0.02 SO 2 for 100 hr at 800C. 103

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Figure 5-36. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O 2 + 0.02 SO 2 for 100 hr at 900C. Figure 5-37. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O 2 + 0.02 SO 2 for 100 hr at 975C. 104

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Figure 5-38. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O 2 + 0.10 SO 2 for 100 hr at 800C. Figure 5-39. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O 2 + 0.10 SO 2 for 100 hr at 900C. 105

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Figure 5-40. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-11Al oxidized in He + 0.21 O 2 + 0.10 SO 2 for 100 hr at 975C. 5.3 Surface Imaging 5.3.1 Untested Alloy Specimens After casting, some of the specimens were inspected using optical and scanning electron microscopy. Figure 5-41 shows an optical micrograph of the microstructure of the Ni-8Cr-6Al composition as cast. Figure 5-42 shows the microstructure of the same composition, but after the 4 hr heat treatment at 1200C in vacuum. It is clear that the grain size increased due to the heat treatment. Analysis of the grain size showed that the as cast material had a size of 260 91 m, and after heat treatment was 432 90 m. In addition, there was less porosity seen after heat treatment. From Figures 5-41 and 5-42, it appears as though there the grains are single-phase However, SEM reveals that there are randomly sized precipitates of throughout the microstructure (Figure 5-43), which decreased in size and become cuboidal after heat treatment (Figure 5-44). 106

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Table 5-2. Table summarizing the phases identified using XRD for all cast, heat-treated alloys oxidized. Alloy Environment Temperature (C) Metallic Phases Oxides Sulfides? Ni-8Cr-6Al None None Ni, Al 2 O 3 Air 800 , Ni Al 2 O 3 NiO, Cr 2 O 3 Air 900 , Ni Al 2 O 3 NiO Air 1000 , Ni Al 2 O 3 NiAl 2 O 4 21% O 2 + 2% SO 2 800 Al 2 O 3 NiO, Cr 2 O 3 21% O 2 + 2% SO 2 900 , Ni Al 2 O 3 NiO, NiAl 2 O 4, Cr 2 O 3 Cr 3 S 4 21% O 2 + 2% SO 2 975 , Ni Cr 2 O 3, NiCr 2 O 4, Al 2 O 3 21% O 2 + 10% SO 2 800 , Ni Al 2 O 3 NiO Ni 3 S 2 21% O 2 + 10% SO 2 900 , Ni Al 2 O 3 Cr 2 O 3, NiCr 2 O 4 21% O 2 + 10% SO 2 975 , Ni Al 2 O 3 Cr 2 O 3 Ni-22Cr-11Al None None , Ni, Cr Al 2 O 3 Air 800 Ni, Cr Al 2 O 3 Cr 2 O 3 Air 900 Ni, Cr Al 2 O 3 Cr 2 O 3 Air 1000 , Ni, Cr Al 2 O 3 Cr 2 O 3 21% O 2 + 2% SO 2 800 , Ni, Cr Al 2 O 3 Cr 2 O 3 21% O 2 + 2% SO 2 900 , Ni, Cr Al 2 O 3 Cr 2 O 3 21% O 2 + 2% SO 2 975 , Ni, Cr Al 2 O 3 Cr 2 O 3 Ni 3 S 2 21% O 2 + 10% SO 2 800 Ni, Cr Al 2 O 3 Cr 2 O 3 Ni 3 S 2 21% O 2 + 10% SO 2 900 Ni, Cr Al 2 O 3 Cr 2 O 3 Ni 3 S 4 21% O 2 + 10% SO 2 975 , Ni, Cr Al 2 O 3 Cr 2 O 3 Cr 3 S 4 107

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Figure 5-41. Optical micrograph of as cast Ni-8Cr-6Al at 125X. Figure 5-42. Optical micrograph of heat-treated Ni-8Cr-6Al at 125X. 108

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Figure 5-43. Secondary electron (SE) micrograph of as cast Ni-8Cr-6Al microstructure at 5000X. Figure 5-44. SE micrograph of heat-treated Ni-8Cr-6Al microstructure at 20000X. Figure 5-45 shows the as-cast microstructure of the Ni-22Cr-11Al composition, and Figure 5-46 shows the same alloy composition after heat-treatment. Both figures show a variety of 109

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phases present with a dendritic structure in the as cast specimen. This is ameliorated in the heat-treated specimens and grain growth is observed 32 m in the as cast versus 329 92 m in the heat-treated. From the SE micrographs in Figures 5-47 and 5-48, one can see circular regions with small precipitates surrounded by phase with a different morphology. Heat treatment increased the size of these circular phase regions. As shown by the X-Ray map in Figure 5-49, the circular regions were rich in Ni and Al, while the surrounding phase was rich in Cr. Comparing these results with the XRD micrograph in Figure 5-31 with those obtained from EDS probes of each region, the heat-treated microstructure is one of circular -NiAl regions containing small, cuboidal Ni 3 Al phases surrounded by a Cr-rich -Ni matrix. Figure 5-45. Optical micrograph of as cast Ni-22Cr-11Al at 125X. 110

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Figure 5-46. Optical micrograph of heat-treated Ni-22Cr-11Al at 125X. Figure 5-47. Backscattered electron (BSE) micrograph of as cast Ni-22Cr-11Al microstructure at 5000X. 111

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Figure 5-48. Secondary electron (SE) micrograph of heat-treated Ni-22Cr-11Al microstructure at 15000X. Figure 5-49. X-ray map of the SE micrograph in Figure 5-46. 112

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5.3.2 Oxidized Ni and Ni-Al Specimens The oxide formed on all the Ni specimens was similar to that in Figure 5-50a triangular shaped layered oxide. The NiAl specimens showed only an external alumina scale that had the appearance of the one showed in Figure 5-51. However, at 1000C, the morphology changed to a needleor plate-like pattern (see Figure 5-52). This could indicate transient or Al 2 O 3 The amount of these aluminas was increased above the grain boundaries of the substrate, indicating faster Al transport along the substrate grain boundaries (see Figure 5-53). Figure 5-50. SE micrograph of NiO scale Ni oxidized in air at 800C for 24 hr. 5.3.3 Oxidized Ni-8Cr-6Al Specimens 5.3.3.1 Ni-8Cr-6Al Oxidized in Air The specimens oxidized in air were analyzed using SEM for analysis. All three samples exhibited adherent scales. The specimens oxidized at 800 and 900C exhibited an almost identical microstructure. Figure 5-54 shows a backscattered electron (BSE) micrograph of one oxidized specimen. The high-Z (atomic number) phase was shown to be NiO, and the low-Z 113

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Figure 5-51. SE micrograph of NiAl oxidized at 800C for 36 hr at 5000X. Figure 5-52. SE micrograph of NiAl oxidized at 1000C for 36 hr at 20000X. 114

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Figure 5-53. SE micrograph of NiAl oxidized at 1000C for 36 hr at 200X. phase underneath was alumina (see Figure 5-55). Even though XRD identified chromia in the 800C specimen, it was not observed on the surface in the SEM. At 1000C, a different morphology was seenone with whiskers as seen with the NiAl (see Figures 5-56 and 5-57). BSE imaging, EDS, and XRD showed these whiskers to be -Al 2 O 3 (when compared with Figure 5-24) near flaky NiO on top of a mixture of Al 2 O 3 and Ni 2 AlO 4 Whiskers are not the normal morphology of -Al 2 O 3 but it is likely that prolonged exposure at elevated temperatures converted them from a transient phase to the more stable Oxidation of this alloy for 30 min showed that there had developed a similar scale morphology as shown in Figure 5-51 (see Figure 5-58). The NiO morphology was similar the NiO that grew on pure Ni (see Figure 5-50). 115

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Figure 5-54. Backscattered electron (BSE) micrograph of Ni-8Cr-6Al oxidized in air for 100 hr at 900C. Figure 5-55. X-ray map of SE micrograph at 2500X of Ni-8Cr-6Al oxidized in air for 100 hr at 800C. 116

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Figure 5-56. SE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 100hr at 1000C at 10000X Figure 5-57. BSE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 100hr at 1000C at 5000X. 117

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Figure 5-58. SE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 0.5 hr at 800C at 10000X. The light oxide is NiO and the dark oxide on the right is alumina. 5.3.3.2 Ni-8Cr-6Al Oxidized in He + 0.21 O 2 + 0.02 SO 2 Exposure to SO 2 appeared to stabilize Cr 2 O 3 on Ni-8Cr-6Al samples during oxidation, which was not seen with those oxidized in air. At 800C, the surface was Al 2 O 3 covered by small rounded Cr 2 O 3 bumps about 2 m wide with an occasional blocky NiO protrusion on the order of 20 m wide (see Figure 5-59). At 900C, there was more NiO coverage of the underlying alumina scale (see Figure 5-60). No spinel or chromia phases were identified from EDS of this specimen, as the low-Z phase was almost all Al and O, while the high-Z was Ni and O. As shown in Figure 5-61, at 975C the outer scale coverage increased, and it was revealed as an oxide with a mixture of Ni and Cr (corresponding with Figure 5-27). This outer scale tended to spall, and left a bare surface with some small Al oxides, as shown by Figure 5-62. No indication was seen of sulfide or sulfur-bearing phases from the EDS probes of any of these specimens. 118

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Figure 5-59. BSE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO 2 at 800C for 100 hr at 4000X. Figure 5-60. BSE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO 2 at 900C for 100 hr at 1000X. 119

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Figure 5-61. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO 2 at 975C for 100 hr at 1500X. Figure 5-62. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO 2 at 975C for 100 hr at 1500X. In this area, the scale has spalled off revealing the bare metal surface. 120

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5.3.3.3 Ni-8Cr-6Al Oxidized in He + 0.21 O 2 + 0.10 SO 2 Analysis of the specimens treated in 10% SO 2 at 800C showed a continuous Al 2 O 3 oxide covered by small NiO particles with script morphology (see Figure 5-63). In addition, much of the scale had blistered, as can be seen in Figure 5-64. At 900C, a small script NiO was identified instead of the larger, flat plates of NiCr 2 O 4 spinel (see Figure 5-65) on top of an Al 2 O 3 /Cr 2 O 3 underlying oxide. Also on top of the underlying oxide, was a layer of Al 2 O 3 (the small, lighter phase in Figure 5-65), which showed a small, needlelike morphology, as seen in Figure 5-66. At 975C, no Ni-oxide phases were observed, and as seen in Figure 5-67, the surface had an Al 2 O 3 oxide covered by intermittent Cr 2 O 3 This scale combination spalled often, which revealed the underlying metal that that was shown to reoxidize as Al 2 O 3 (see Figure 5-68). Sulfur was detected at levels under 2 wt% where the scale had spalled. Figure 5-63. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO 2 at 800C for 100 hr at 15000X. 121

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Figure 5-64. SE micrograph of Ni-8Cr-6Al alloy oxidized in 10% SO 2 at 800C for 100 hr at 1500 showing scale blisters. Figure 5-65. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO 2 at 900C for 100 hr at 700X. 122

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Figure 5-66. SE micrograph of the overlying alumina regions of Ni-8Cr-6Al oxidized in 10% SO 2 at 900C for 100 hr at 10000X. Figure 5-67. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO 2 at 975C for 100 hr at 5000X. 123

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Figure 5-68. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO 2 at 975C for 100 hr at 1500X where the scale (top) had spalled off and began to reoxidized (bottom). 5.3.4 Oxidized Ni-22Cr-11Al Specimens 5.3.4.1 Ni-22Cr-11Al Oxidized in Air The scale observed on the Ni-22Cr-11Al alloy consisted of a two-phase microstructure, each in a separate region for all three temperatures (see Figures 5-69, 5-70). The lighter oxide was found to be Cr 2 O 3 while the darker was Al 2 O 3 The chromia scale appeared to have grown first, over the regions rich in Cr as seen in Figure 5-49, while the alumina grew over the regions of and . It cannot be determined from this analysis if the Cr 2 O 3 scale is on top of the Al 2 O 3 or if it is continuous to the scale metal interface. The specimens oxidized at 1000C exhibited a different surface morphology than the other two (Figure 5-71). In this situation, an outer scale (shown as dark) was flaking off. This scale was determined to be a mixture of Cr 2 O 3 (lighter on scale) and Al 2 O 3 (darker on scale) with the same pattern as Figure 5-69. This scale flaked off, however, leaving a bare metal surface that grew a thin layer of Al 2 O 3 (the lighter phase). 124

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Figure 5-69. SE micrograph of Ni-22Cr-11Al oxidized in air at 800C for 100 hr at 1000X. Figure 5-70. SE micrograph of Ni-22Cr-11Al oxidized in air at 800C for 100 hr at 5000X. 125

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Figure 5-71. BSE micrograph of Ni-22Cr-11Al oxidized in air at 1000C for 100 hr at 500X. 5.3.4.2 Ni-22Cr-11Al Oxidized in He + 0.21 O 2 + 0.02 SO 2 The specimens exposed to 2% SO 2 exhibited a similar surface oxide structure with those of the oxidized specimensAl 2 O 3 was shown to grow over the areas and Cr 2 O 3 grew over the regions (see Figure 5-72). However, on these samples, the Cr 2 O 3 was not a continuous layer, but rather small, spherical blobs between 0.5 and 5 m in size (see Figure 5-73). Figure 5-74 shows that while the alumina scale was mostly flat, some regions did show a small, needlelike morphology that was also observed on the Ni-8Cr-6Al specimens exposed to 10% SO 2 (see Figure 5-66). Overall, the surface scale for all samples was the same, except for 1000C, which showed some cracking of the scale (Figure 5-75). Sulfur was detected in these regions of bare metal. 126

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Figure 5-72. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO 2 gas mixture at 800C for 100 hr at 1000X. Figure 5-73. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO 2 gas mixture at 900C for 100 hr at 9000X. 127

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Figure 5-74. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO 2 gas mixture at 900C for 100 hr at 10000X. Figure 5-75. SE micrograph of Ni-22Cr-11Al oxidized in 2% SO 2 gas mixture at 1000C for 100 hr at 1900X. 128

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5.3.4.3 Ni-8Cr-6Al Oxidized in He + 0.21 O 2 + 0.10 SO 2 The specimens oxidized in 10% SO 2 had a similar morphology with that of those in 2% (see Figure 5-76). The amount and size of the Cr 2 O 3 particles was reduced when compared to the 2% samples, and some of the Cr 2 O 3 spheres had Cr 2 O 3 whiskers, as shown in Figure 5-77. The alumina either had a smoother blocky morphology (Figure 5-76) or would appear as needlelike whiskers (Figure 5-78). All three specimens showed areas of spallation (Figure 5-79), where the metal was exposed. Sulfur-based phases were detected by EDS analyses of these regions and, as detected by XRD (Table 5-2), were found to be Ni-sulfides at 800 and 900C, and Cr-sulfides at 1000C. Figure 5-76. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO 2 gas mixture at 800C for 100 hr at 100X. 129

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Figure 5-77. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO 2 gas mixture at 800C for 100 hr at 5000X. Figure 5-78. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO 2 gas mixture at 1000C for 100 hr at 10000X. 130

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Figure 5-79. SE micrograph of Ni-22Cr-11Al oxidized in 10% SO 2 gas mixture at 900C for 100 hr at 1500X. 5.4 Cross-Sectional Analysis 5.4.1 Ni and Ni-Al Specimens Figure 5-80 shows a cross-section SEM micrograph of an oxidized Ni specimen. The NiO takes a columnar morphology. There appeared to some layers of internal oxidation that may have cracked during sample preparation. Figure 5-81 shows a NiAl sample in cross-section, revealing a layer of Al 2 O 3 alone. There was no depletion layer detected on these samples beneath the scale/alloy interface. However, some Ni-metal areas were observed surrounded by the alumina scale. Due to the lack of phosphorus in these regions, it was concluded that these regions were not from the electroless Ni deposited for edge retention. 131

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Figure 5-80. BSE micrograph of a Ni specimen oxidized at 800C for 24 hr at 1900X. The top layer is the electroless Ni layer deposited for edge retention. Figure 5-81. BSE micrograph of a NiAl specimen oxidized at 1000C for 36 hr at 2000X. The top layer is the electroless Ni layer deposited for edge retention. 132

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5.4.2 Ni-8Cr-6Al Specimens Figure 5-82 shows the cross-section of Ni-8Cr-6Al oxidized at 900C, in which the oxide likely cracked during sample preparation. The outermost oxide was shown to be NiO by EDS, with no solubility for other elements. Beneath that, a mixed Al/Cr oxide was identified with generally the same atomic percent of both Al and Cr. The darker oxide is Al 2 O 3 with only trace amounts of Ni and no other elements. There were small amounts of spinel detected, as well as some of the -Ni alloy in oxide itself. This indicates that at least part of the oxide grew into the alloy. Platinum marker tests confirm this, and show that the NiO grew outward from the original alloy/gas interface, while the (Al,Cr) 2 O 3 grew inward. The oxide was approximately 5 to 8 m thick, on average. Figure 5-82. BSE micrograph of Ni-8Cr-6Al oxidized at 900C in cross-section. Figure 5-83 shows the cross-section of the same alloy oxidized in 2% SO 2 at 800C. The oxide layer, as with most of the specimens showed a columnar grain morphology. Figure 5-84 133

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shows a 900C sample and, in contrast with Figure 5-82, there seemed to be no detectable NiO (even though it was seen in XRD), but a nominal amount of Cr 2 O 3 was detected. The top oxide was again (Al,Cr) 2 O 3 with nearly equal amounts of Cr and Al (by mole). Below this layer was a mix of Cr 2 O 3 and Al 2 O 3 each closer to stoichiometry with solubility for the other elements less than 8 at%. Some Ni(Cr,Al) 2 O 4 spinel phase was observed, particularly at the alloy/scale interface, which had between 1 and 2 at% sulfur. Internally (below the oxide/alloy interface) some Cr sulfides were detected. From the semi-quantitative EDS analyses, their composition was observed as closest to the CrS stoichiometry, as compared to other Cr x S y sulfides. At a grain boundary, deep penetration of oxide was observed (Figure 5-85). In addition, there were sulfides observed along the grain boundary, which continued into the alloy (see Figure 5-86). These sulfides were also seen at 800C, which appeared as a mix of Ni and Cr sulfides (se Figure 5-87). Pores were also observed in the oxide and at the oxide/alloy interface. While these could be artifacts, they are likely actual pores due to the observation of good scale adhesion on this specimen. Figure 5-83. SE micrograph of Ni-8Cr-6Al oxidized in 2% SO 2 gas mixture at 800C for 100hr in cross-section at 10000X. 134

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Figure 5-84. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO 2 gas mixture at 900C for 100hr in cross-section at 3500X. Figure 5-85. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO 2 gas mixture at 900C for 100hr in cross-section at 3500X, showing an oxide deeply penetrating along a grain boundary. 135

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Figure 5-86. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO 2 gas mixture at 900C for 100hr in cross-section at 5000X, showing sulfides along a grain boundary. Figure 5-87. SE micrograph of Ni-8Cr-6Al oxidized in 2% SO 2 gas mixture at 800C for 100hr in cross-section, showing sulfides along grain boundaries and pores in the oxide layer. 136

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As shown in Figure 5-84, several depletion layers existed in the alloy below the scale/alloy interface. The first layer, approximately 1-2m, showed a Ni phase with small (less than 4 wt%) amounts of each alloying element, and 6 wt% O, likely from irresolvable internal oxides. The second layer, which was 5 m thick, was an Al-depletion layer with less than 1 wt% S and 3 wt% O. Lastly, the third layer (5-8 m thick) was also depleted of Al, but had no S or O. Below that (~12-15 m under the interface) was the nominal alloy composition with the + microstructure. 5.4.3 Ni-22Cr-11Al Specimens The Ni-22Cr-11Al oxidized samples showed thinner oxide layers than Ni-8Cr-6Al (between 1-3 m versus 5-8 m for the Ni-8Cr-6Al) (see Figure 5-88). The oxide, though showed a similar pattern in that there was an outer layer of (Al,Cr) 2 O 3 and an inner layer of Al 2 O 3 At 2% SO 2 no sulfides were detected at the oxide/alloy interface, or anywhere else (see Figure 5-89). Low-Z phases were present beneath the interface, which consisted of mostly Al with approximately 11 at% Ni. This would indicate a NiAl 3 + (Al) phase, which would be liquid at these oxidizing temperatures. In addition, NiAl 2 O 4 was often seen near these phases. The most striking difference in the change in microstructure from the unoxidized specimens. If compared to Figure 5-48, there are large areas of -NiAl and small 2-4 m precipitates of -Cr (see Figure 5-90) surrounded now by a matrix of . However, closest to the surface, was less likely to be found and there were usually only and present. As shown with the surface SEM images, more Cr 2 O 3 was present above the scale/alloy interface at the lower testing temperatures. One of these samples is shown in Figure 5-89. Beneath this oxide is the (Cr,Al) 2 O 3 which has been seen before, as well as NiAl 2 O 4 spinel. In all the oxides characterized that were exposed to 2% SO 2 no sulfur or sulfide phases were found. 137

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Figure 5-88. BSE micrograph of Ni-22Cr-11Al oxidized in 2% SO 2 gas mixture at 975C for 100hr in cross-section at 8000X. The top layer is a Ni-coating added for edge retention. Figure 5-89. BSE micrograph of Ni-22Cr-11Al oxidized in 2% SO 2 gas mixture at 800C for 100hr in cross-section at 800X. 138

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Figure 5-90. BSE micrograph of Ni-22Cr-11Al matrix that was exposed to the 2% SO 2 gas mixture at 975C for 100hr 2000X. The labeled X-numbers are areas that were probed for EDS. 5.4.4 Electron Microprobe (EPMA) Analysis The EPMA scans of the cross-sections shown in the previous two sections were performed to determine the extent of sulfur at the scale/alloy interface, as well as the amount of internal oxidation and composition changes in the scale. The major drawback to the EPMA probes, though, were that the X-ray interaction volumes were on the order of 1 m, and so could not be used accurately for individual phase analysis. However, EPMA was useful in determining the composition changes across a line scanned, as shown in Figures 5-91 through 5-93. In all three EPMA linescans shown here, the oxide layer is on the left. The interface is located at 5.5 m, 5.9 m, and 7.0 m for Figures 5-91, 5-92, and 5-93, respectively. In Figure 5-86, the outermost layer is Cr 2 O 3 followed by a spinel phase, and then (Al,Cr) 2 O 3 which becomes leaner in Cr closer to the interface. At the interface, S was detected, upwards of 3.5 139

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wt%. S continued to be found in the alloy, which was depleted in Al up to around 18 m. With Figure 5-92, the oxide was overall uniformly (Cr,Al) 2 O 3 except towards the surface which may have been spinel. An -Cr precipitate in the matrix near the interface was included in this linescan. This could account for the higher Cr in the oxide since the was so close to the interface. The last scan shown here (Figure 5-93) reveals a mostly Al oxide, with one NiCr 2 O 4 spinel phase in the scan. In both Ni-22Cr-11Al alloy scans show here, the maximum S detected at the interface was 0.3 wt%. Figure 5-91. EPMA linescan across scale and interface in an Ni-8Cr-6Al alloy oxidized at 900C in He + 0.21 O 2 + 0.02 SO 2 gas mixture. 140

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Figure 5-92. EPMA linescan across scale and interface in an Ni-22Cr-11Al alloy oxidized at 800C in He + 0.21 O 2 + 0.02 SO 2 gas mixture. Figure 5-93. EPMA linescan across scale and interface in a Ni-22Cr-11Al alloy oxidized at 975C in He + 0.21 O 2 + 0.02 SO 2 gas mixture. 141

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CHAPTER 6 DISCUSSION AND ANALYSIS 6.1 Mechanisms of Scale Formation From the kinetic plot of Figure 5-20, the addition of alloying elements lessens the scale growth in all the oxidizing environments examined. From the XRD and SEM analysis, the following occurred during oxidation: Ni oxidized to form NiO Ni-8Cr-6Al oxidized to form NiO, NiAl 2 O 4 Al 2 O 3 and some (Al,Cr) 2 O 3 Ni-8Cr-6Al oxidized with SO 2 to form the same oxides in addition to stabilizing chromia as well as Ni and Cr sulfides Ni-22Cr-11Al oxidized to form pure Al 2 O 3 and Cr 2 O 3 as well as an inner layer of (Al,Cr) 2 O 3 Some spinel was also observed. Ni-22Cr-11Al oxidized with SO 2 produced the same oxides and sulfide were detected by XRD but not found from EDS/EPMA analyses. With the Ni-8Cr-6Al alloys, NiO, spinel, and Al 2 O 3 were observed in SEM. Layers of NiO were observed on top of the Al 2 O 3 scale that lay underneath. This alumina layer with NiO clusters on top was uniform on all specimens tested. The heat-treated samples showed a uniform + microstructure and this oxidation pattern appears valid, at least on the magnifications afforded via SEM. In addition, it is apparent that the reaction of Ni and O 2 occurs first, and the NiO scale begins to grow by outward cation diffusion of NiO [42-44]. This oxide took triangular plate-like morphology which grew laterally rather than transversely. This structure became layered as new nucleates would form on the transverse surfaces and, matching the substrate coherency, would also grow laterally although no texture was found in the oxides from EBSD. In addition, Al 2 O 3 would also nucleate on the surface along side the formation of NiO. Spinel was also formed via Equation 2-12, or from Al substituting on the Ni lattice or vice-versa. Previous studies have show that a spinel phase will often form in Ni-Al alloys [76, 78] and from interactions of the NiO and alumina, especially in the initial oxidation [79]. The surface alumina 142

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often appeared, on this alloy and others, as needles or thin plates in random orientations, especially at high temperatures. Previous research has shown that transient aluminas, such as or which are tetragonal and monoclinic respectively, often evolve initially on Al, Ni-Al, and Ni-Cr-Al specimens and grow by outward cation transport [58-59]. However, XRD scans of Ni-8Cr-6Al oxidized at 0.5, 16, and 100 hrs show only the corundum phase, which was been shown to grow by inward anion transport [55, 60-61, 89]. Previous publications demonstrated that the transient aluminas will often transform to after the formation of a continuous -Al 2 O 3 scale [55, 89, 97-98], due to lattice mismatch strains at the differing alumina interfaces [55-56]. This would explain why, if they existed, that the transient alumina phases were not detected. Cr 2 O 3 or Cr-containing oxides and spinels were not detected on the surface of oxidized Ni-8Cr-6Al specimens. Previous studies of compositions similar to this one by Giggins, Pettit, and other show the formation of NiO and NiCr 2 O 4 at the surface at high oxygen partial pressures (0.2-1 bar) [90, 93, 127]. If not, Cr 2 O 3 stabilized [93, 127]. Cross-sections, however, revealed a (Cr,Al) 2 O 3 layer present underneath, which has been previously observed [86, 97-98]. This would agree with generally accepted mechanism that the formation of NiO (and Al 2 O 3 ) on the surface caused the transport of O 2anions and metal cations, not the surface metal/chemisorbed oxygen reaction, to be rate limiting, causing a decrease in oxygen activity [48-40]. This allowed for the stabilization of Cr 2 O 3 and Al 2 O 3 which coalesced into a continuous scale and grew in a steady-state manner, which would be described by the parabolic, steady state growth recorded by the TGA. Since the anion diffusion through alumina scales is slow, it would be rate-limiting [49, 88], and short-circuit processes would dominate at sufficient scale thicknesses [41]. Previous studies, though, commented that this alloy composition might not develop a continuous alumina scale below 1000C [76, 90, 127], but here was able to form a stable, adherent Al 2 O 3 scale for 143

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100 hrs of isothermal oxidation. There was, however, spallation observed in scales at higher temperatures and in SO 2 gas mixtures. However, TG tests could not confirm an Arrhenius dependence to oxidation in air for either Ni-Cr-Al alloys. Either this is due to measurement/preparation error, steady-state scale growth not being achieved, or complex/competing mechanisms that vary with temperature. The Ni-22Cr-11Al specimens oxidized and showed only Al 2 O 3 and Cr 2 O 3 on the surface during oxidation. As shown by Figure 5-64, chromia would develop over the Cr-rich regions, while Al 2 O 3 would develop over the Al-rich + regions, as had been previously observed in + alloys [96-97]. Comparing Figure 5-48 and 5-49 to the microstructure of the center of the oxidized samples, it can be assumed that the heat-treatment meant to homogenize the Ni-22Cr-11Al arc-melted buttons did not achieve its goal. Unlike the Ni-8Cr-6Al composition, which would solidify as -Ni first and then precipitate the , the Ni-22Cr-11Al would solidify as dendrites, rejecting Cr due to constitutional supercooling. This would push the interdendritic liquid composition closer to the e 3 reaction (see Figures 2-6 and 2-7) in which the liquid would solidify as and If the center microstructure of the Ni-22Cr-11Al oxidized specimen is an indication of an equilibrium microstructure, then the heat treatment of 4 hr at 1200C was neither long enough nor at a high enough temperature to fully equilibriate the microstructure. The oxidized specimens showed, at distances far away from O-penetration, that the equilibrium microstructure is a + matrix, with semi-spherical and phases dispersed throughout. Regardless, the Ni-22Cr-11Al specimens that were oxidized showed a faster, outward growing Cr 2 O 3 and a smoother Al 2 O 3 This oxidation stage was likely shown as initial parabolic rates of the TG curves for this alloy, which last between two and ten hours, depending on the temperature. No dependence could be found between temperature and this transition time. At 144

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the transition in growth kinetics, spinel may have grown underneath these phases due to the initial depletion of Cr and Al from oxidation. Spinel was detected in some of the samples exposed to SO 2 but not in the oxidized samples, so it cannot be said whether it existed during this process. This transition process could also indicate the internal oxidation of Cr, which would catalyze the internal oxidation of Al. Like with Ni-8Cr-6Al, and most Ni-Cr-Al alloys with high enough concentrations of Cr and Al, the activity of O was reduced due to the gettering effect of Cr, and a continuous alumina scale formed [85-90]. Cross-sections of the alloy showed this in which the Cr 2 O 3 would appear closest to the gas/scale interface, growing by outward Cr 3+ transport. Underneath a semi-duplex layer of (Al,Cr) 2 O 3 and Al 2 O 3 closest to the scale/alloy interface was observed, which likely grew from internal anion diffusion as it was shown to penetrate into the alloy. Like the Ni-8Cr-6Al specimens, the amount of Cr in the (Al,Cr) 2 O 3 region generally decreased the closer one traced towards the scale/alloy interface, which contained alumina with less than 3 wt% Cr. The effect of sulfur was one that enhanced the oxidative effects of the atmosphere on the alloys (see Figure 5-20). At the higher temperatures (900 and 975C), the rate of oxidation increased when SO 2 was added to the gas mixture. This was in spite of the fact that the partial pressure of O 2 may have been decreased due to the formation of SO 3 via Equation 2-16. The partial pressures of O 2 SO 2 and SO 3 for the mixed gas experiments are shown in Table 6-1. However, as stated by Luthra, the SO 3 formation is extremely slow and takes extended times to developupwards of 90-100 hr, near the length of these tests [128]. No catalyst was used in this test to attempt to have SO 2 and not SO 3 be the majority sulfidizing gas. Even with equilibrium achieved, SO 2 was the major sulfidizing gas, particularly at 900 and 975C. Furthermore, studies have shown that SO 2 is more likely to adsorb on oxide surfaces than SO 3 [128], making 145

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its the reaction-controlling sulfidizing agent. SO 3 though, was found condensed in the TGA further down the gas stream past the furnace where the gas reached room temperature. SO 3 may have had an effect beyond just lowering the oxygen partial pressure at 800C (the growth rate was less for SO 2 exposed samples at this temperature). However, no NiSO 4 or any other sulfates were detected, which are usually signs of an SO 3 -dependent reaction [127, 130-131, 145]. Table 6-1. Table showing the equilibrium partial pressures of gases that evolve upon various mixtures of O 2 and SO 2 at various temperatures, calculated from the SPOT3 database. Mixture (bar) Temperature (C) P O2 (bar) P SO2 (bar) P SO3 (bar) He + 0.21 O 2 + 0.02 SO 2 800 0.208 0.015 5.43e-3 He + 0.21 O 2 + 0.02 SO 2 900 0.209 0.018 2.57e-3 He + 0.21 O 2 + 0.02 SO 2 975 0.209 0.019 1.50e-3 He + 0.21 O 2 + 0.10 SO 2 800 0.199 0.074 0.027 He + 0.21 O 2 + 0.10 SO 2 900 0.205 0.088 0.013 He + 0.21 O 2 + 0.10 SO 2 975 0.207 0.093 7.49e-3 As stated previously, the effect sulfur plays in the oxidation tests of this study is one of accelerating the oxidation process. This appears to occur in two ways. First, the SO 2 reacts with the metal to form an oxide and free up sulfur in the form of S 2 as per Equation 2-17 [150]. The second is the faster diffusion of ions through the oxide lattice due to defects created from S impurities [111]. This has been shown to occur from S 2 substituting on the anion lattice, creating cation vacancies [121, 171]: 221221OShOSOO (6-1) This free oxygen then creates more cation vacancies (in this case a Ni vacancy) which increases the overall cation diffusion rate: hVOONiO2221 (6-2) 146

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Similar reactions also occur in Cr 2 O 3 These vacancies could migrate and be more prevalent at the grain boundaries, increasing diffusion there. In addition, with the Ni-8Cr-6Al samples, cross-sectional analysis showed the presence of Cr and Ni sulfides along the grain boundaries and phase boundaries in the alloy. There was also a higher concentration of S at the scale/alloy interface than in the matrix or scale. Studies have shown that sulfur and SO 2 are attracted to grain boundaries, pores, and surfaces with higher surface energies [138, 142, 144-145, 151]. In studies with polycrystalline Cr [140] and superalloys [124, 151], at these surfaces, when the P S2 is high enough, the SO 2 reacts with Cr in solution to form chromium sulfides beneath the interface (Equation 2-18). The high defect structure of these sulfides affords rapid transport of S 2, O 2, and cations [119, 148]. Next, with the increasing P O2 from the anion influx, the sulfide oxidizes via: 2M x S y + yO 2 = 2M x O y + yS 2 (6-3) leaving free sulfur to further migrate into the alloy forming more sulfides and repeating this process. This proposed mechanism can explain Figures 5-85 through 5-87 and was observed in previous mixed oxidation/sulfidation studies [115, 133, 137, 140]. In all the SO 2 -exposed samples, Cr 2 O 3 and/or NiCr 2 O 4 were found, and were often more prevalent than NiO. It appears that the presence of sulfur, at these levels, stabilizes the formation of Cr 2 O 3 This can be attributed to the fact that the presence of sulfur may cause the more rapid growth diffusion of Cr, allowing its oxide to stabilize faster [119]. The mechanism for transport of sulfur through the oxide scale seems more likely to be better described by the transport of sulfur gas molecules. The major criticism to this theory is the inability of the SO 2 molecule to diffuse through a compact scale [117, 122]. However, images of these scales in cross-section show them to be anything but compact: they display pores, cracks, 147

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and scale buckling. It should be noted, though, that some of these observed defects could be preparation artifacts. SO 2 would easily be able to travel through these paths and react by Equation 2-18 to release S at the scale/alloy interface. While bulk diffusion of S 2may be occuring, in these experiments, bulk transport processes would be orders of magnitude slower than grain boundary or free surface diffusion of SO 2 [112, 117, 133]. Furthermore, the presence of S has been shown to increase the amount of voids present in an oxide scale, which would increase SO 2 transport [135, 137]. Sulfides were not observed in the Ni-22Cr-11Al samples, although one specimen did show a small sulfur concentration at the scale/metal interface. This is likely due to the fact that the increased concentration of Al and Cr stabilized the protective oxides faster, reducing the rate of sulfur influx. For the length of these tests, the sulfur activity may never reached high enough levels to begin sulfide stabilization. In addition, the grain size of the Ni-22Cr-11Al specimens was smaller than the Ni-8Cr-6Al. Previous research of cast and forged Ni-base superalloys has shown that a finer grain size reduces sulfidation in oxidizing environments [133]. This is due to the faster diffusion of Al and Cr outward along more grain boundary surface area, which forms a protective (Al,Cr) 2 O 3 layer more rapidly. 6.2 Comparison of Experimental Results and Calculations As shown in Chapter 4, calculations were performed to help predict and explain the processes occurring during the oxidation and sulfidation of the Ni-Cr-Al alloys used in this study. The diagrams calculated for the ternary subsystems of the Ni-Cr-Al-O quaternary system appear to agree well with previous literature, except for one point [6-7, 32]. In previous calculations by Saltykov, the Ni-Al-O and Ni-Cr-O systems produced showed that in the Ni-lean, O-rich sections (Al/Cr) 2 O 3 would always be a two-phase mixture with spinel [6]. However, the results of the calculations (see Figures 4-8, 4-9, and 4-10) in this study show that there is a point 148

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of stoichiometric spinel that decomposes via a peritectoid reaction into (Al/Cr) 2 O 3 and NiO at around 10-14 bar of O 2 This decomposition reaction is supported by previous studies [121, 171], which were not contradicted by the experiments of this dissertation. In calculations involving alloys, temperature increases corresponded to the stabilization of oxides that were more stable at lower partial pressures of oxygen. As shown from analysis of the Ni-8Cr-6Al alloy in all environments, NiO was not detected at higher temperatures whereas spinel and chromia (or Cr-rich aluminas) were. This shows that the stability of these oxides increased, causing them to form faster, reducing the amount of NiO that could form. While thermodynamics may play a role, it should be noted that the increase in temperature would have a kinetic effect, allowing faster cation transport that may have aided in the faster formation of the non-Ni oxides. For most of the calculations involving S, the SPOT3 database was accessed since it had the S descriptions that are unavailable in the SPIN4 database as well as gas phase descriptions for all the S and O gas species. However, the SPOT3 only simulates mechanical mixtures of solid solutions and not the actual alloys (no mixing parameters). In spite of this, the phases, activities, and reactions were close in the calculations involving SPIN4 and SPOT3 comparisons (see Table 4-1 and Figure 4-40). The results appeared nearly identical for regions where the (Al,Cr) 2 O 3 oxide was predominant (described as two stoichiometric oxides by SPOT3). Furthermore, the reactions occurring at the scale/alloy interface are stoichiometric themselves and proceed whether the material is an alloy or mechanical mixture. For example, for the formation of Al 2 O 3 from a Ni-Al mixture, the software calculates either: Alloy: Ni + 4Al(soln) + 3O 2 Ni + 2Al 2 O 3 Mixture: 4Ni 3 Al + 3O 2 12Ni + 2Al 2 O 3 149

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In either case, the net reaction is still that of Al reacting with O 2 to form Al 2 O 3 with the Ni having no net contribution. Therefore, for the calculation purposes of this dissertation, it is immaterial whether the reacting element is part of a solution or a mechanical mixture, so long as it is the only element reacting with either O 2 or SO 2 The calculations of SO 2 -O 2 diagrams from this dissertation using this reasoning have already been presented and published [170]. The main discrepancy involves the activity of a component in a particular phase. In addition, the reactions on the potential diagrams calculated for the alloys are identical for the appended SPIN4 database and the SPOT3 database, except were noted on Figures 6-1 and 6-2. This difference is due to an alternate spinel phase description in the SPIN4 database. Figure 6-1. Comparison of phases observed in SPIN4 calculations versus an SO 2 -O 2 potential diagram of Ni-8Cr-6Al at 900C. The blue dots correspond to calculated equilibria where the appended SPIN4 and SPOT3 databases agree. The green cubes correspond to disagreements. The dashed lines represent the alternate reaction lines determined by the appended SPIN4 database. 150

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Figure 6-2. Comparison of phases observed in SPIN4 calculations versus an SO 2 -O 2 potential diagram of Ni-22Cr-11Al at 975C. This diagram uses the same methodology as used in Figure 6-1. The results of the oxidation experiments for both Ni-8Cr-6Al and Ni-22Cr-11Al were described qualitatively by calculations. The SO 2 -O 2 potential diagrams showed the progression of oxidation across the scale in the same manner as obtained from varying the oxygen partial pressure. Closest to the gas/scale interface was NiO and spinel, which was stable at the highest P O2 Underneath, the scale became a mix of Al 2 O 3 and Cr 2 O 3 (here described as separate phases, but were often found in solution as described by the SPIN4 descriptions), as well as spinel phases. There was generally not a second Ni phase detected in SEM (exception: Figure 5-85), but according to Figure 4-8, is able to be in solution with (Al,Cr) 2 O 3 up to around 25 wt%less than detected in the oxide by EPMA. At lower P O2 only Al 2 O 3 was calculated to be stable using SPOT3. All the cross-section SEM micrographs of both alloys showed this at the scale/alloy interface. In this calculated phase region, Cr is depicted as a separate phase. While Cr was in solution in -Ni in Ni-8Cr-6Al, it manifested itself as a separate phase -Cr phase in the Ni151

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22Cr-11Al as predicted by a previous work [37]. Lastly, for the Ni-22Cr-11Al alloy, at low enough P O2 the -NiAl phase is stable. The data in this dissertation showed no near the scale/alloy interface. It should be noted that the oxidation processes described here are ones of a coating in direct contact with a gas atmosphere, and partial pressures of the gas species decreasing as the oxide grows (at the scale/alloy interface). In common service conditions, though, the application of a TBC reduces the P O2 seen at the scale/alloy interface, causing the (desired) formation of (Al,Cr) 2 O 3 Only after longer service times and more oxygen penetration do spinel and NiO begin to form as part of the TGO [91, 155]. The diagrams calculated and shown in Figures 4-13 through 4-15 were useful in determining the stability of the O 2 + SO 2 gas mixture at various temperatures. The diagrams showed the significance of SO 3 formation and how much of a factor it could be in the sulfidation corrosion observed in the results. Figure 4-14 was also helpful in showing the partial pressure of S 2 in relation to the gas mixture not only at the surface, but also at the scale/alloy interface, where higher sulfur concentrations were discovered from microprobe analyses. In addition, the high temperatures allowed for sulfide stabilization at higher oxygen partial pressures. The minimal activities of SO 2 gas required to form sulfides varied with the alloy composition, temperature, and oxygen partial pressure. However, the calculations did show that Cr sulfides could form in equilibrium with Ni and Al 2 O 3 (at the scale/alloy interface) or in equilibrium with Ni and , which was seen at the grain boundaries in the alloy in Figure 5-86 for the Ni-8Cr-6Al alloy. The Ni-22Cr-11Al alloy, however, showed no real sulfidation at all, being absent of sulfides. The only sulfur found present was at the scale/alloy interface, in amounts of less than 0.30 wt%. From Figures 4-41 and 4-43, the P S2 required to stabilize sulfides in the oxides could be calculated. At high P O2 in these alloys, if the P S2 is too low, the SO 2 will remain 152

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as a gas, or form oxides. Once the P S2 is high enough, as shown by the P S2 spikes in Figures 4-41 and 4.43, sulfidation of the alloy can begin. Clearly, the lower the P O2 the lower the P S2 required to for sulfide formation/stabilization. This may explain why, in the Ni-8Cr-6Al alloys oxidized in SO 2 only Cr-sulfides were observed (see Figures 5-85 through 5-87). Where Ni 3 S 2 is stable, the P O2 may have been too high and the P S2 too low. However, deeper into the substrate, along the grain boundaries, the P S2 was adequate to allow for sulfide formation in a lower P O2 environment. Figures 6-3 and 6-4 show how activity values calculated from EPMA line scans compared to calculated activities from Section 4.4. In both Figures, there is close agreement between the activities Ni. However, there are discrepancies between the other components. Qualitatively, they all follow the trends calculatedthe lowering of a Cr and a Al as P O2 increases. In addition, the activity of S 2 is shown to increase at the scale/alloy interface. Experimentally, activity of S 2 decreases as one moves into the alloy away from the scale/alloy interface. This was not as calculated because the calculations assumed a constant mole fraction of SO 2 gas in the system, which is not the case experimentally. There is also a higher Al activity than calculated. This could be due to the depletion of reacting elements from the alloy near the interface, or the linescans probing certain phases instead of the bulk such a probe of instead of The error in correlating the experiments and calculations can come from several sources. First, the activities calculated for the calculations and from the experimental EPMA data are both assumed to be at some equilibrium. The activities calculated from the experimental data assume local equilibrium at the one point, which is likely. However, the calculated diagrams assume equilibrium across a range of P O2 This can be problematic, especially when interpreting these diagrams in relation to the actual observed cross-sections. In Figures 5-83 to 5-89, spinel was 153

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Figure 6-3. Comparison of the calculated activities from microprobe linescans with calculated values using the appended SPIN4 database for a Ni-8Cr-6Al alloy oxidized at 900C in 0.21 O 2 + 0.02 SO 2 Figure 6-4. Comparison of the calculated activities from microprobe linescans with calculated values using the appended SPIN4 database for a Ni-22Cr-11Al alloy oxidized at 975C in 0.21 O 2 + 0.02 SO 2 154

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only once found in contact with the alloy substrate (usually, this was Al-rich Al 2 O 3 ). However, the calculations from the SPIN4, as well as SPOT3, databases show a mixture of and (Al,Cr) 2 O 3 bounded by and spinel. It has been established that the scale/alloy interface is not usually at equilibrium due to slow rate-limiting ion transport that stabilizes (Al,Cr) 2 O 3 or sulfides in the case of SO 2 diffusion. Nevertheless, the calculations performed in this dissertation show promise that the Ni-Cr-Al-O-S system can be successfully modeled using thermodynamic calculations. In the future, refinement of the SPIN4 database to allow solution phases of sulfides and sulfates, as well as a sulfur contribution to the ionic liquid phase description and the addition of the additional gas species, will greatly advance the calculations completed here. 155

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CHAPTER 7 CONCLUSIONS The purpose of this research study was to calculate the stability of Ni-Cr-Al alloys and their mechanical mixtures in oxidizing and sulfidizing atmospheres. Experiments were also conducted to examine the impact of sulfur on the oxidation of two Ni-Cr-Al alloys. The following conclusions can be drawn from this study: The oxidation, and even the simultaneous oxidation/sulfidation, kinetics can be generally described as parabolic in nature. This is due to the nature of this growth mechanism in that the rate of the oxidation reaction is dependent on ionic transport through the oxide scale, which decreases over time as the scale thickens. Higher temperatures showed the growth of less NiO and more Al 2 O 3 /Cr 2 O 3 initially, as predicted by thermodynamic calculations of Ni-8Cr-6Al alloys. While the morphology of and -Al 2 O 3 was observed, particularly on the surface, XRD could not detect any alumina phases except It is possible that even at short oxidation times, the transient aluminas transform to corundum quickly at these temperatures. The addition of SO 2 caused sulfur to accumulate at the scale/alloy interface. In the Ni-8Cr-6Al, SO 2 migrated to the scale/alloy interface and oxidized the alloy releasing free sulfur. This sulfur reacted with Cr in solution to form Cr-sulfides at the alloy grain boundaries. These sulfides allowed rapid ion transport due to their high-defect structures, and oxidized themselves allowing sulfur to move further into the alloy, sulfidizing more Cr and repeating the process. Cr-containing oxides, which were not detected on Ni-8Cr-6Al in oxidation-only experiments, were detected on the surface when exposed to SO 2 This was attributed to the vacancy creation of S in the oxide lattice, as well as SO 2 at cracks and grain boundaries allowing faster diffusion of Cr 3+ and was observed as a decreased activation energy. For the extent of these tests, the scale formed by the Ni-22Cr-11Al alloys was protective against the formation of internal sulfides. The thermodynamic calculations were able to predict the progression of oxidation as well as confirm the phases in equilibrium at various oxygen and sulfur dioxide partial pressures. In (Al,Cr) 2 O 3 and NiO, the activities and compositions of the elements were nearly identical for calculations from each database. There were small differences in spinel and the alloy. The activities calculated from the experiments showed qualitative trends with the calculations. 156

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Combining the results from the two databases used in this dissertation, a more representative SO 2 -O 2 potential diagram could be calculated. This dissertation is a first step in being able to calculate the Al-Cr-Ni-O-S quinary system for describing sulfidation and hot corrosion problems affecting NiCrAlY bond coats. 157

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LIST OF REFERENCES 1. Department of Energy. International Energy Outlook 2006. Report #DOE/EIA-0484 (2006) 2. International Energy Agency. Monthly Electricity Statistics: November 2006. (2007) 3. J.P. Longwell, E.S. Rubin, J. Wilson. Progress in Energy and Combustion Science. 21 pp. 209-360 (1995) 4. Department of Energy. Annual Energy Outlook 2007 with Projections to 2030. Report #DOE/EIA-0383 (2007) 5. H.M. Kvamsel, K. Jordal, O. Bollard. Energy. 32 pp. 10-24 (2007) 6. P. Saltykov, O. Fabrichnaya, J. Golczewski, F. Aldinger. Journal of Alloys and Compounds. 381 pp. 99-113 (2004) 7. H.J. Seifert, H. Mozaffari, H.L. Lukas, F. Aldinger. The Oxidation of Ni-Base AlloysThermodynamic Modeling and Calculations. High Temperature Corrosion and Materials Chemistry V: Proceedings of the International Symposium. E. Opila, J. Fergus, Y. Maruyama, J. Mizusaki, T. Narita, D. Shifler, E. Wuchina, eds. ECS: Pennington, NJ pp. 347-360 (2005) 8. D.J. Srolovitz, T.A. Ramanarayanan. Oxidation of Metals. 22 pp. 247-275 (1984) 9. P. Berthod, S. Michon, J. Di Martino, S. Mathieu, S. Nol, R. Podor, C. Rapin. Calphad. 27 pp. 279-288 (2003) 10. Y. Tamarin: Protective Coatings for Turbine Blades, ASM International, Materials Park, OH (1992) pp. 5-23 11. J.R. Davis, ed. Heat Resistant Materials, ASM International: Materials Park, OH (1997) pp. 221-254 12. E. Ross, C.T. Sims, Nickel-base Alloys, Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New York (1987) pp. 97-133 13. G.H. Meier, F.S. Pettit. Materials Science and Engineering A. 153, pp. 548-560 (1992) 14. P. Kofstad. High Temperature Oxidation of Metals. John Wiley & Sons: New York, NY pp. 88-111 (1988) 15. J.L. Smialek, G.M. Meier, High-Temperature Oxidation, Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New York pp. 293-326 (1987) 16. D.R. Clarke, C.G. Levi. Annual Review of Materials Research. 33 pp. 383-417 (2003) 17. A. Taylor, R.W. Floyd. Journal of Institute of Metals. 81 pp. 451-464 (1952) 158

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18. N.C. Oforka, B.B. Argent, Journal of Less-Common Metals. 114 pp. 97-109 (1985) 19. J.A. Nesbitt, R.W. Heckel. Metallurgical Transactions A. 18A pp. 2061-2073 (1987) 20. J.A. Nesbitt, R.W. Heckel. Metallurgical Transactions A. 18A pp. 2087-2094 (1987) 21. Y.M. Hong, Y. Mishima, T. Suzuki. DTA Measurements of the Ni-Cr-Al Ternary System, Materials Research Society Symposium Proceedings. 133 C.T. Liu, A.I. Taub, N.S. Stoloff, C.C. Koch. eds., MRS: Pittsburg, PA pp. 429-440 (1989) 22. C.C. Jia, K. Ishida, T. Nishizawa. Metallurgical and Materials Transactions A. 25A pp. 473-485 (1994) 23. L. Kaufman, H. Nesor. Metallurgical Transactions. 5 pp. 1623-1629 (1974) 24. S. Ochiai, Y. Oya, T. Suzuki. Acta Metallurgica. 32 pp. 289-298 (1984) 25. I. Ansara, B. Sundman, P. Willemin. Acta Metallurgica. 36 pp. 977-982 (1988) 26. I. Ansara, N. Dupin, H. L. Lukas, B. Sundman Journal of Alloys and Compounds. 247 p. 20-30 (1997) 27. N. Dupin, I. Ansara, B. Sundman. Calphad. 25 pp. 279-298 (2001) 28. D.R.G. Achar, R. Munoz-Arroyo, L. Singheiser, W.J. Quadakkers, Surface & Coatings Technology. 187 pp. 272 (2004) 29. P.K. Sung, D.R. Poirier, Metallurgical and Materials Transactions A. 30A, pp. 2173-2182 (1999) 30. H. Baker. ASM Handbook Volume 3Alloy Phase Diagrams, ASM International: Materials Park, OH, pp. 43-155 (1992) 31. M. Hillert. Journal of Alloys and Compounds. 320 pp. 161-171 (2001) 32. P. Rogl. Al-Cr-Ni, Ternary Alloys: A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 pp. 400-415 (1991) 33. R. Bakish, ed. Introduction to Electron Beam Technology. John Wiley and Sons: New York, NY (1962) p. 395-422 34. A.M. Dorodnov. Journal Technical Physics. 51 pp. 504-524 (1981) 35. R.C. Dykhuizen, M.F. Smith. Surface and Coatings Technology. 37 pp. 349-358 (1989) 36. K.G. Schmitt-Thomas, H. Haindl, D. Fu. Surface and Coatings Technology. 94-95. pp. 149-154 (1997) 159

PAGE 178

37. Y. Tamarin: Protective Coatings for Turbine Blades, ASM International, Materials Park, OH p. 65-67 (1992) 38. S.A. Bradford. Fundamentals of Corrosion of Gases, ASM Handbook Volume 13Corrosion. ASM International: Materials Park, OH. pp. 61-76 (1992) 39. N. Cabrera, N.F. Mott. Reports on the Progress of Physics. 12 pp. 163-184 (1948-1949) 40. C. Wagner. Zeitschrift fr Physikalische Chemie. B21 pp. 25-41 (1933) 41. D.A. Porter, K.E. Easterling. Phase Transformations in Metals and Alloys, 2 nd Ed. Chapman & Hall: London pp. 98-103 (1993) 42. T. Homma, N.N. Khoi, W.W. Smeltzer, J.D. Embury. Oxidation of Metals. 3 pp. 463-473 (1971) 43. J.R. Taylor, A.T. Dinsdale. Zeitschrift fr Metallkunde. Vol 81, pp. 354-366 (1990) 44. R. Haugsrud. Corrosion Science. 45. pp 211-235 (2003) 45. H. Hindam, D.P. Whittle. Oxidation of Metals. 18 p. 245-284 (1982) 46. M. Schuetze. Oxidation of Metals. 44 p. 29-61 (1995) 47. H.V. Atkinson. Materials Science and Technology. 4 pp. 1052-1063 (1988) 48. A.W. Harris, A. Atkinson. Oxidation of Metals. 34 pp. 229-258 (1990) 49. L.P.H. Jeurgens, W.G. Sloof, F.D. Tichelaar, E.J. Mittemeijer: Journal of Applied Physics. 92 pp. 1649-1656 (2002) 50. P. Villars. Pearsons Handbook: Desk Edition: Crystallographic Data for Intermetallic Phases. ASM International: Materials Park, OH. (1998) 51. Y.F. Zhukovskii, P.W.M. Jacobs, M. Causa. Journal of Physics and Chemistry of Solids. 64 pp. 1317 (2003) 52. L.P.H. Jeurgens, W.G. Sloof, F.D. Tichelaar, E.J. Mittemeijer. Thin Solid Films. 418 p. 89-101 (2002) 53. S.R. Pollack, C.E. Morris. Journal of Applied Physics. 35 p. 1503-1512 (1964) 54. L.P.H. Jeurgens, W.G. Sloof, F.D. Tichelaar, E.J. Mittemeijer. Surface Science. 506 pp. 313 (2002) 55. H.J. van Beek, E.J. Mittemeijer. Thin Solid Films. 122-151 p. 131 (1984) 56. D. Clemens, V.R. Vosberg, L.W. Hobbs, U. Breuer, W.J. Quadakkers, H. Nickel. Fresenius. Fresenius Journal of Analytical Chemistry. 355 p. 703-706 (1996) 160

PAGE 179

57. D. Clemens, V.R. Vosberg, H.J. Penkella, U. Breuer, W.J. Quadakkers, H. Nickel. Fresenius. Fresenius Journal of Analytical Chemistry. 358 p. 122-126 (1997) 58. J.L. Smialek, R. Gibala. Metallurgical Transactions A. 14A pp. 2143-2164 (1983) 59. G.C. Rybicki, J.L. Smialek. Oxidation of Metals. 31 p. 275-304 (1989) 60. J. Doychak, J.L. Smialek, T.E. Mitchell. Metallurgical Transactions A. 20A p. 499-518 (1989) 61. A. Ul-Hamid. Corrosion Science. 46 p. 27-36 (2004) 62. R. Prescott, M.J. Graham. Oxidation of Metals. 38 p. 223-254 (1992) 63. B. Chattopadhyay, G.C. Wood. Oxidation of Metals. 2 p. 373-399 (1970) 64. M.T. Shim, W.J. Moore. Journal of Chemistry and Physics. 26 p. 802-832 (1957) 65. D. Caplan, G.I. Sproule. Oxidation of Metals. 9 p. 459-472 (1975) 66. A.U. Seybolt. Journal of the Electrochemical Society. 107 pp. 147-156 (1960) 67. W.C. Hagel, A.U. Seybolt. Journal of the Electrochemical Society. 108 pp. 1146-1152 (1961) 68. S.C. Tsai, A.M. Huntz, C. Dolin. Oxidation of Metals. 43 pp. 581-596 (1995) 69. K.P. Lillerud, P. Kofstad. Journal of the Electrochemical Society. 127 pp. 2397-2409 (1980) 70. P. Kofstad, K.P. Lillerud. Journal of the Electrochemical Society. 127 pp. 2410-2419 (1980) 71. D. Caplan, G.I. Sproule, R.J. Hussey. Corrosion Science. 10 pp. 9-17 (1970) 72. M. Skeldon, J.M. Calvert, D.G. Lees. Oxidation of Metals. 28 pp. 109-125 (1987) 73. D. Caplan, M. Cohen. Journal of the Electrochemical Society. 108 pp. 438-442 (1961) 74. C.A. Stearns, F.J. Kohl, G.C. Fryburg. Journal of the Electrochemical Society. 121 pp. 952-961 (1974) 75. T. Sorahan, D.C.L. Burges, L. Hamilton, J.M. Harrington, Occupational Environmental Medicine. 55 pp. 236 (1998) 76. F.S. Pettit: Transactions of the AIME. 239, pp. 1296-1305 (1967) 77. G.C. Wood, F.H. Stott: British Corrosion Journal. 6, pp. 247-256 (1971) 161

PAGE 180

78. H.M. Hindam, W.W. Smeltzer. Journal of the Electrochemical Society. 127 pp. 1622-1630 (1980) 79. K. Fueki, H. Ishibashi. Journal of the Electrochemical Society. 108 pp. 306-311 (1961) 80. R.T. Haasch, A.M. Venezia, C.M. Loxton: Journal of Materials Research. 7, pp. 1341-1349 (1992) 81. H.C. Yi, W.W. Smeltzer, A. Petric. Oxidation of Metals. 45 pp. 281-299 (1996) 82. S.C. Choi, H.J. Cho, Y.J. Kim, D.B. Lee. Oxidation of Metals. 46 pp. 51-72 (1996) 83. H.M. Hindam, W.W. Smeltzer. Journal of the Electrochemical Society. 127 pp. 1630-1635 (1980) 84. P.Y. Hou, K. Priimak. Oxidation of Metals. 63 pp. 113-130 (2005) 85. J.L. Smialek. Metallurgical Transactions A. 9A pp. 309-320 (1978) 86. B.H. Kear, F.S. Pettit, D.E. Fornwalt, L.P. Lemaire. Oxidation of Metals. 3 pp. 557-569 (1971) 87. P. Sarrazin, A. Galerie, M. Caillet. Oxidation of Metals. 46 pp. 299-312 (1996) 88. S.W. Guan, W.W. Smeltzer. Oxidation of Metals. 42 pp. 375-391 (1994) 89. P. Sarrazin, A. Galerie, M. Caillet. Oxidation of Metals. 46 pp. 1-17 (1996) 90. C.S. Giggins, F.S. Pettit. Journal of the Electrochemical Society. 118 pp. 1782-1790 (1971) 91. F.H. Stott, G.C. Wood, M.G. Hobby. Oxidation of Metals. 3 pp. 103-113 (1971) 92. F. Gesmundo, F. Vianni, Y. Niu. Oxidation of Metals. 42 pp. 285-301 (1994) 93. G.J. Santoro, D.L. Deadmore, C.E. Lowell. NASA Technical Note. TN D-6414 (1971) 94. C.E. Lowell, G.J. Santoro. NASA Technical Note. TN D-6838 (1972) 95. F.H. Stott, I.G. Wright, T. Hodgkiess, G.C. Wood. Oxidation of Metals. 11 pp. 141-150 (1977) 96. J.L. Gonzlez Carrasco, P. Adeva, M. Aballe. Oxidation of Metals. 33 pp. 1-17 (1990) 97. C.G. Levi, E. Sommer, S.G. Terry, A. Catanoiu, M. Rhle. Journal of the American Ceramic Society. 86 pp. 676-685 (2003) 98. W. Brandl, D. Toma, H.J. Grabke. Surface and Coatings Technology. 108-109 pp. 10-15 (1998) 162

PAGE 181

99. F.S. Pettit, C.S. Giggins. Hot Corrosion, Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New York (1987) pp. 327-358 100. J.A. Goebel, F.S. Pettit. Metallurgical Transactions. 1 pp. 1943-1954 (1970) 101. N.S. Bornstein, M.A. DeCrescente. Metallurgical Transactions. 2 pp. 2875-2892 (1971) 102. A. Rahmel. Materials Science and Engineering. 87 pp. 345-352 (1987) 103. K.L. Luthra, D.A. Shores. Journal of the Electrochemical Society. 127 pp. 2202-2210 (1980) 104. K.L. Luthra, O.H. LeBlanc. Materials Science and Engineering. 87 pp. 329-335 (1987) 105. D.K. Gupta, R.A. Rapp. Journal of the Electochemical Society. 127 pp. 2194-2202 (1980) 106. R.A. Rapp. Materials Science and Engineering. 87 pp. 319-327 (1987) 107. R.A. Rapp. Corrosion Science. 44 pp. 209-221 (2002) 108. D.A. Shores. New Perspectives on Hot Corrosion Mechanisms, High Temperature Corrosion. R.A. Rapp, ed. NACE: Houston, TX. p. 493-511 (1983) 109. A.K. Roslik, V.N. Konev, A.M. Maltsev. Oxidation of Metals. 43 pp. 59-82 (1995) 110. A. Stokosa, J. Stringer. Oxidation of Metals. 11 pp. 263-276 (1977) 111. A. Stokosa, J. Stringer. Oxidation of Metals. 11 pp. 277-288 (1977) 112. J. Stringer, M.E. El-Dahshan, I.G. Wright. Oxidation of Metals. 8 pp. 361-377 (1974) 113. T. Narita, T. Ishikawa, K. Nishida. Oxidation of Metals. 27 pp. 221-237 (1987) 114. W. Kai, Y.T. Lin, C.C. Yu, P.C. Chen, C.H. Wu. Oxidation of Metals. 61 pp. 507-527 (2004) 115. C.J. Spengler, R. Viswanathan. Metallurgical Transactions. 3 pp. 161-166 (1972) 116. P. Singh, N. Birks. Oxidation of Metals. 13 pp. 457-474 (1979) 117. C. de Asumndis, F. Gesmundo, C. Bottino. Oxidation of Metals. 14 pp. 351-361 (1980) 118. P. Kofstad, G. kesson. Oxidation of Metals. 13 pp. 57-76 (1979) 119. D.G. Lees. Oxidation of Metals. 27 pp. 75-81 (1987) 120. K. Natesan. Oxidation of Metals. 30 pp. 53-83 (1988) 121. W.H. Lee. Materials Chemistry and Physics. 76 pp. 26-37 (2002) 163

PAGE 182

122. P. Fox, D.G. Lees, G.W. Lorimer. Oxidation of Metals. 36 pp. 491-503 (1991) 123. H.J. Grabke, G. Kustonov, H.J. Schmultzer. Oxidation of Metals. 43 pp. 97-114 (1995) 124. Z. Zurek, J. Jedlinski, K. Kowalski, K. Kowalska. Solid State Ionics. 101-103 pp. 743-747 (1997) 125. J. Gawel. Oxidation of Metals. 30 pp. 139-140 (1988) 126. C. Mathieu, J.P. Larpin, S. Toesca. Oxidation of Metals. 39 pp. 211-220 (1993) 127. C.S. Giggins, F.S. Pettit. Oxidation of Metals. 14 pp. 363-413 (1980) 128. K.L. Luthra, W.L. Worrell. Metallurgical Transactions A. 10A pp. 621-631 (1979) 129. F. Gesmundo, C. de Asumndis, P. Nanni. Oxidation of Metals. 20 pp. 217-240 (1983) 130. K.P. Lillerud, B. Haflan, P. Kofstad. Oxidation of Metals. 21 pp. 119-134 (1984) 131. A.K. Misra, D.P. Whittle. Oxidation of Metals. 22 pp. 1-33 (1984) 132. K.L. Luthra, W.L. Worell. Metallurgical Transactions A. 9A pp. 1055-1061 (1978) 133. A.S. Khanna, W.J. Quadakkers, X. Yang, H. Schuster. Oxidation of Metals. 40 pp. 275-294 (1993) 134. R.E. Lobnig, H.J. Grabke, H.R. Schmidt, K. Hennessen. Oxidation of Metals. 39 pp. 353-370 (1993) 135. P.Y. Hou, K. Priimak. Oxidation of Metals. 63 pp. 113-130 (2005) 136. P. Kofstad, G. kesson. Oxidation of Metals. 12 pp. 503-526 (1978) 137. M.H. LaBranche, G.J. Yurek. Oxidation of Metals. 28 pp. 78-98 (1987) 138. Z. El-Majid, M. Lambertin. Oxidation of Metals. 27 pp. 333-345 (1987) 139. P. Fox, D.G. Lees, G.W. Lorimer. Oxidation of Metals. 36 pp. 491-503 (1991) 140. A.G. Andersen, P. Kofstad. Oxidation of Metals. 43 pp. 301-315 (1995) 141. P. Singh, N. Birks. Oxidation of Metals. 19 pp. 37-52 (1982) 142. D. Wang, D.L. Douglass. Oxidation of Metals. 20 pp. 111-146 (1983) 143. M.F. Chen, D.L. Douglass, F. Gesmundo. Oxidation of Metals. 33 pp. 399-423 (1990) 144. S.W. Kim, K. Ohla, H. Fischmeister, E. Fromm. Oxidation of Metals. 36 pp. 395-407 (1991) 164

PAGE 183

145. A.K. Roslik, V.N. Koner, A.M. Maltsev. Oxidation of Metals. 43 pp. 83-95 (1995) 146. Y.R. He, D.L. Douglass. Oxidation of Metals. 40, pp. 337-371 (1993) 147. S. Mrowec. Oxidation of Metals. 44 pp. 177-209 (1995) 148. E.J. Vineberg, D.L. Douglass. Oxidation of Metals. 25 pp. 1-28 (1986) 149. P.Y. Hou, J. Stringer. Oxidation of Metals. 38 pp. 323-345 (1992) 150. F. Gesmundo. Oxidation of Metals. 13 pp. 237-244 (1979) 151. K. Natesan. Materials Science and Engineering. 87 pp. 99-106 (1987) 152. J.H. Wood, E.H. Goldman. Protective Coatings, Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New York pp. 359-383 (1987) 153. S. Degterov, A. Pelton. Journal of Phase Equilibria. 17 pp. 476-488 (1996) 154. A.D. Pelton, H. Schmalzried, J. Strichner. Journal of Physics and Chemistry of Solids. 40 pp. 1103-1122 (1979) 155. H. Mozaffari. Ph.D. Dissertation. Universitt Stuttgart (2002) 156. H.L. Lukas, S.G. Fries. Journal of Phase Equilibria. 13 pp. 532-541 (1992) 157. L.C. Li, F. Gesmundo, F. Vianni. Oxidation of Metals. 40 pp. 395-419 (1993) 158. J.M. Quets, W.H. Dresher. Journal of Materials. 4 pp. 583-599 (1969) 159. L.C. Li, F. Gesmundo, F. Vianni, Materials Engineering. 4 p. 133-148 (1993) 160. H. Yokokawa, Journal of Phase Equilibria. 20 pp. 258-287 (1999) 161. N. Saunders, Z. Guo, X. Li, A.P. Miodownik, J-Ph. Schill. Modeling the Materials Properties and Behavior of Ni-Based Superalloys, Superalloys 2004. K.A. Green, T.M. Pollock, H. Harada, T.E. Howson, R.C. Reed, J.J. Schirra, S. Watson, eds., TMS: Materials Park, OH. pp. 849-858 (2004) 162. JANAF Thermochemical Tables, 2 nd ed. National Bureau of Standards: Washington, D.C., (1986) 163. B. Bergman, J. Agren. Journal of the American Ceramics Society. 68 pp. 444-450 (1985) 164. K.K. Sunil, K.D. Jordan. Journal of Physical Chemistry. 92-101 p. 2774 (1988) 165. O. Kubaschewski, C.B. Alcock. Metallurgical Thermochemistry, 6 th ed. Oxford, UK: Pergamon Press (1979) 165

PAGE 184

166. J.M. Larrain. Calphad. 4 pp. 155-171 (1980) 167. B. Pieraggi. Oxidation of Metals. 64 pp. 397-403 (2005) 168. G.I. Goldstein, D.E. Newbury, P. Echlin, D.C. Joy, A.D. Romig Jr, C.E. Lyman, C. Fiori, E. Lifshin. Scanning Electron Microscopy and X-Ray Microanalysis, 2 nd Ed. Plenum: New York pp. 417-524 (1994) 169. D.V. Ragone. Thermodynamics of Materials. J. Wiley & Sons, Inc.: New York (1994) 170. E. Mueller, H. Seifert. Thermodynamic Calculations of Mixed Sulfidation and Oxidation of Ni-Cr-Al Alloys, Materials Science and Technology (MS&T) 2006: Fundamentals and Characterization: Vol 2. Z. Liu, C.E. Campbell, L.Q. Chen, E.B. Damm, J.E. Morral, J.L. Murray, eds. pp. 125-136 (2006) 171. M.C. Pope, N. Birks. Oxidation of Metals. 12 pp. 191-204 (1978) 166

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BIOGRAPHICAL SKETCH Erik Michael Matthew Mueller was born on July 7, 1978, to Michael J. and Sally Leona Mueller in Jacksonville, FL. There he attended Sacred Heart Elementary and Bishop Kenny High School, where he started at defensive line for the football team and threw shotput and discus for the track team, lettering in both. After graduating in 1996, Erik moved to Gainesville, FL, where he attended the University of Florida. In May 2000, he graduated cum laude with a Bachelor of Science in materials science and engineering with a focus in engineering ceramics, and began an internship at American Technical Ceramics. He entered graduate school later that year at the University of Florida and redirected his focus to metallurgy, electron microscopy, and high-temperature corrosion. He received a Master of Science degree in May 2003, and was admitted to doctoral candidacy in December of 2005. He is currently also captain of University of Florida mascots, who perform at various Gator sporting events, commercial appearances, and charitable festivities. He is also a 3rd degree knight and recorder for the local Knights of Columbus Chapter 13207. In the future, Erik plans to earn his professional engineering license in metallurgical engineering, and to explore the fields of consulting and politics. 167


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THERMODYNAMIC MODELING AND EXPERIMENTAL ANALYSIS OF OXIDATION/
SULFIDATION OF NI-CR-AL MODEL ALLOY COATINGS


















By

ERIK M. MUELLER


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2007







































O 2007 Erik M. Mueller
































This dissertation is dedicated to all hard-working graduate students.









ACKNOWLEDGMENTS

I would like to thank my supervisory committee chair, Dr. Wolfgang Sigmund, for all his

support and last-minute assistance on this dissertation. I would also like to thank my former

advisor, Dr. Hans Seifert, for not only starting me on and supporting me with this proj ect

financially, but for the invaluable help in teaching the Thermo-Calc computational software as

well as the challenging goals set to enable me to finish this proj ect. I would like to thank

Damian Cupid for his help with the thermodynamic software and his insight into unique

approaches to the problems encountered in computational thermodynamics.

I would also like to thank Dr. L. Amelia Dempere for her support and use of the

characterization equipment at the Major Analytical Instrumentation Center. Wayne Acree

should be credited with the operating the electron microprobe. Dr. Gerhard Fuchs' high-

temperature materials courses were also instrumental in exposing me to this subj ect area in

metallurgy. Dr. W. Greg Sawyer and Dr. Gerald Bourne also assisted in this project by serving

on my supervisory committee.

Finally, I would also like to thank the University of Florida and the Materials Science and

Engineering Department for use of their facilities and for affording me the opportunity to

complete this degree with financial assistance.












TABLE OF CONTENTS


page

ACKNOWLEDGMENT S ............_...... .............. iv...


LIST OF TABLES ............_...... ..............vii...


LI ST OF FIGURE S ............_...... .............. viii..


AB S TRAC T ............._. .......... ..............._ 1...


1 INTRODUCTION .............. ...............2.....


2 LITERATURE REVIEW .............. ...............5.....


2.1 Turbine Engine Considerations .............. ...............5.....
2.2 Turbine Blade Materials .............. ...............6.....
2.2.1 Superalloys .............. ........ ...............6.
2.2.2 Coatings for Turbine Blades ................. ...............7............ ...
2.4 The Al-Cr-Ni Ternary System ................. ...............9............ ...
2.5 Oxidation of Al-Ni-Cr Alloys. ................ ................... .........................17
2.5.1 General Oxidation Mechanism ................. ...............17........... ..
2.5.1.1 Oxidation of Ni............... ...............19..
2.5.1.2 Oxidation of Al ................. ...............20........... ..
2.5.1.3 Oxidation of Cr ................. ...............22........... ..
2.5.2 Oxidation of Ni-Al Alloys................................ ...........2
2.5.3 Oxidation in Al-Cr-Ni Ternary and NiCrAlY Coatings ................. ................ ...26
2.6 Sulfidation and Hot Corrosion............... ...............2
2.6.1 Hot Corrosion .............. ...............28....
2.6.2 Sulfidation on Metals .............. ...............29....
2.6.3 Sulfidation on Metal Oxides............... ...............31.
2.6.4 Sulfidation in Ni-Cr-Al Coatings .............. ...............33....
2.7 Calculations of Oxidation/Sulfidation ................ ...............34...............


3 METHODS AND MATERIALS................ ..............3


3.1 Thermodynamic Modeling and Simulations .............. ...............36....
3.1.1 The CALPHAD Approach ................... ...............3
3.1.2 Databases and Software .............. ...............37.__. ...
3.2 Materials and Sample Preparation .............. ...............38.__. ...
3.3 Thermogravimetric Analysis .............. ...............39....
3.4 Characterization............... ............4
3.4.1 X-Ray Diffraction............... ..............4
3.4.2 Scanning Electron Microscopy............... ...............4
3.4.3 Electron Microprobe............... ...............4

4 THERMODYNAMIC CALCULATION RESULTS ................. ................................46












4. 1 Calculations of Ni-Cr-Al Alloys and Mixtures using Phase Diagrams ................... .........46
4. 1.1 Binary Systems ........._._ ...... .... ...............46.
4. 1.2 Ternary Systems ....................... ... ..............4
4.2 Calculations of Temperature-Potential Diagrams .............. ...............53....
4.2.1 Calculations with 02-SO2 Interactions .............. ...............53....
4.2.2 Calculations of Metal-Gas Interactions ........._._.......___ .......___.........5
4.3 Calculations of Potential Diagrams .............. ...............58....
4.4 Phase Fraction Diagrams .............. ...............73....

5 EXPERIMENTAL RESULTS................ ...............81


5.1 TGA Experiments ................. ........... ...............81.....
5.1.1 Oxidation Experiments in Air ............... .. ........ ..... ............8
5.1.2 Oxidation Experiments in He + 0.21 02 + 0.02 SO2 ........._.__...... ..._._..........88
5.1.3 Oxidation Experiments in He + 0.21 02 + 0. 10 SO2 ................. ......._._. ........91
5.2 Phase Identification .............. ...............95....
5.3 Surface Imaging............... ...............106
5.3.1 Untested Alloy Specimens .............. ...............106....
5.3.2 Oxidized Ni and Ni-Al Specimens ....._.._._ ........_.. ...._.. .........13
5.3.3 Oxidized Ni-8Cr-6Al Specimens ........._._........__. ....__. ..........13
5.3.3.1 Ni-8Cr-6Al Oxidized in Air .........._.... .. ..... ..... ...............113..
5.3.3.2 Ni-8Cr-6Al Oxidized in He + 0.21 02 + 0.02 SO2................... ...............11
5.3.3.3 Ni-8Cr-6Al Oxidized in He + 0.21 02 + 0.10 SO2................... ...............12
5.3.4 Oxidized Ni-22Cr-11Al Specimens .............. ...............124....
5.3.4. 1 Ni-22Cr-11Al Oxidized in Air .........._..._.. .. ..... ......._ ...............124
5.3.4.2 Ni-22Cr-11Al Oxidized in He + 0.21 02 + 0.02 SO2................. ...............126
5.3.4.3 Ni-8Cr-6Al Oxidized in He + 0.21 02 + 0.10 SO2................... ...............12
5.4 Cross-Sectional Analysis............... ...............13
5.4.1 Ni and Ni-Al Specimens .............. ...............131....
5.4.2 Ni-8Cr-6Al Specimens ........._... .....___ ...............133..
5.4.3 Ni-22Cr-11Al Specimens .........._..__ ......__. ....._.._ ..........13
5.4.4 Electron Microprobe (EPMA) Analysis............... ...............13

6 DISCUSSION AND ANALYSIS .............. ...............142....


6.1 Mechanisms of Scale Formation ............................ .............14
6.2 Comparison of Experimental Results and Calculations ................. .......................148

7 CONCLUSIONS................ .............15


LIST OF REFERENCES ......._................. ...............158 .....


BIOGRAPHICAL SKETCH ................. ...............167......... ......










LIST OF TABLES


Table page

2-1. List of common alloying elements in Ni-base superalloys............... ...............

2-2. List of phases described in calculations of the Al-Cr-Ni ternary. ................ ................ ...14

2-3. The phases present in the Ni-22Cr-11Al and Ni-8Cr-6Al (weight percent) alloys at
room temperature and 1000oC. ............. ...............17.....

2-4. Descriptions and crystallographic information on different phases of Al203 [49-50]. ..........21

3-1. List of experimental conditions performed for oxidation of alloys for 100 hr in 1 bar of
gas at 25 mL/min. ............. ...............43.....

4-1. Comparison of equilibria computed between two databases SPOT3 and SPIN4 at a
pressure of 1 bar and T = 1073 K for Ni-22Cr-11Al alloy (by mass) with a PO2 Of
0.22 bar. This table compares number of moles of each phase, along with the
composition (in weight fraction) of each phase. ........._.._. ......_. ......._.. .......5

4-2. Comparison of gas species (at mole fractions > 10-10) present in the unstable
equilibrium regions of Figure 4-19 at low PO2 and high PO2. These mole fractions are
calculated based on ideal gas behavior. .............. ...............60....

5-1. List of the parabolic rate constants obtained from steady-state oxidation of Ni, Ni-
13.6Al, NiAl, Ni-8Cr-6Al, and Ni-22Cr-11Al alloys. .........._... ......... ..........._....94

5-2. Table summarizing the phases identified using XRD for all cast, heat-treated alloys
oxidized ................. ...............107................

6-1. Table showing the equilibrium partial pressures of gases that evolve upon various
mixtures of 02 and SO2 at various temperatures, calculated from the SPOT3
database ................. ...............146................










LIST OF FIGURES


Figure page

2-1. Schematic of a typical turbine engine............... ...............5.

2-2. Schematic of coating configuration of modern turbine blades. ........._._.... .....__...........9

2-3. Al-Ni binary phase diagram [H. Baker. ASM~Handbook Vol. 3--Alloy Phase Diagrams,
ASM Intemnational: Materials Park, OH, p. 49 (1992)] ......._._._ ......... ...............10

2-4. Ni-Cr binary phase diagram [H. Baker. ASM~Handbook Vol. 3--Alloy Phase Diagramns,
ASM Intemnational: Materials Park, OH, p. 155 (1992)] ............... .......... .............10

2-5. Al-Cr binary phase diagram [H. Baker. ASM~Handbook Vol. 3--Alloy Phase Diagramns,
ASM Intemnational: Materials Park, OH, p. 43 (1992)] ........___ ......... ...............11

2-6. Liquidus projection of the Al-Ni-Cr ternary system [P. Rogl. "Al-Cr-Ni," Ternary
Alloys: A Comprehensive Compendium of~valuated Constitutional Data and Phase
Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 411 (1991)] ........___ ..... .. ...............1

2-7. Scheil reaction scheme of the Al-Cr-Ni ternary. The 6-phase refers to Ni2Al3, the rl to
AlsCrs-hexagonal, T2 to AlsCrs-rhombodedral, and at to Al9 4. The question marks
represent areas of the ternary that were not investigated. ................. ....__ .............13

2-8. Isothermal section of Al-Cr-Ni ternary at 1025oC above the U4 reaction. The green
areas denote regions of two-phase equilibria [P. Rogl. "Al-Cr-Ni," Ternary Alloys: A
Comprehensive Compendium of~valuated Constitutional Data and Phase
Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 414 (1991)]. ............. ...............15.....

2-9. Partial Isothermal section of Al-Cr-Ni ternary at 850.C below the U4 reaction. The
green areas denote regions of two-phase equilibria [P. Rogl. "Al-Cr-Ni," Ternary
Alloys: A Comprehensive Compendium of~valuated Constitutional Data and Phase
Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 413 (1991)]. ............. ...............15.....

2-10. Plot of oxidation growth kinetics versus time. ............. .....................18

2-1 1 Arrhenius plot of parabolic growth rates versus temperature of NiO (violet) as well as
Cr203 and Al203 (red) [J.L. Smialek, G.M. Meier, "High-Temperature Oxidation,"
SuperalloysHI. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New
York p. 295 (1987)]. ................ ...............24.......... ....

2-12. Dependence of oxidation mechanisms and scale type of Ni-Al alloys based on
temperature and Al content [F.S. Pettit: Transactions of the AIM~E. 239, pp. 1296-
13 05 (1967) ]..........._...._ ...............25...._... ...

2-13. Schematic of the stages of oxidation in Ni-Cr-Al alloys. Group I are alloys that will
have a stable NiO scale, Group II will develop a stable Cr203 Scale, and Group III










will develop a stable Al203 Scale [F.S. Pettit: Transactions of the AIM~E. 239, pp.
1296-13 05 (1967)1 ]........._.__ ........... ...............27.

2-24. Schematic showing the formation of metal sulfides (a) under an initial metal oxide
layer (b) in simultaneous oxidizing and sulfidizing conditions. The various proposed
transport mechanisms are shown. ............. ...............32.....

3-1. Flowchart detailing the Calculation of Phase Diagrams approach. This study is
concerned mostly with the equilibrium calculations. ............. ...... ............... 3

3-2. Schematic of the Setsys Evolution (TGA only). ................ ................ ......... ...._41

4-1. Temperature-composition binary phase diagram of the Ni-Al system calculated from
the SPINT4 database. ............. ...............47.....

4-2. Temperature-composition binary phase diagram of the Ni-Cr system calculated from
the SPINT4 database. ............. ...............47.....

4-3. Temperature-composition binary phase diagram of the Al-Cr system calculated from
the SPINT4 database. ............. ...............48.....

4-4. Temperature-composition binary phase diagram of the Ni-Al system calculated from
the SPINT4 database with the Ni3Als low-temperature phase restored. ............. ................48

4-5. Isothermal section of Ni-Cr-Al ternary system at 900oC in weight fractions. This
diagram is calculated from data in the SPIN4 database ................. ............... ...._...49

4-6. Partial isothermal section of Ni-Cr-Al ternary system at 850.C in mole fractions. The
axes are chosen to compare with Figure 2-9. This diagram is calculated from data in
the SPINT4 database. ............. ...............50.....

4-7. Isothermal section ofNi-Cr-Al ternary system at 1025oC in mole fractions. The axes
are chosen to compare with Figure 2-8. This diagram is calculated from data in the
S PIN4 d database. ............. ...............50.....

4-8. Ternary isothermal section of the Ni-Al-O2 System at 900oC. The x-axis is the
composition of Al in weight percent, and the y-axis is the logarithmic partial
pressure of 02 in bar. This diagram is calculated from data in the SPINT4 database. .......51

4-9. Ternary isothermal section of the Ni-Cr-O2 System at 900oC. The x-axis is the
composition of Cr in weight percent, and the y-axis is the logarithmic partial
pressure of 02 in bar. This diagram is calculated from data in the SPINT4 database. .......51

4-10. The Ni-Al-Cr-O system shown as a series of connected ternary subsystem isotherms at
900oC. The outer axes are the logarithm of the partial pressure of 02 in bar, whereas
the inner axes are the weight percent of Ni, Cr, and Al. This diagram is calculated
from data in the SPINT4 database ................. ...............52...............










4-11. Change in partial pressure of Oz, SO2, and SO3 (in bar) with temperature using the
initial gas mixture of He + 0.21 02 + 0.02 SO2. The PHe is omitted due to scale. The
data used for calculations is taken from the SPOT3 database. ............. .....................5

4-12. Change in partial pressure of Oz, SO2, and SO3 (in bar) with temperature using the
initial gas mixture of He + 0.21 02 + 0.10 SO2. The PHe is omitted due to scale. The
data used for calculations is taken from the SPOT3 database. ............. .....................5

4-13. The relationship between the partial pressure of SO3 in an 02-SO2 gaS mixture, with
varying temperature. All partial pressures are in bar. ................... ... ............5

4-14. The relationship between the partial pressure of S2 in an 02-SO2 gaS mixture, with
varying temperature. All partial pressures are in bar. ................... ... ............5

4-15. The relationship between the partial pressure of 02 in an SO3-SO2 gaS mixture, with
varying temperature. All partial pressures are in bar. ................... ... ............5

4-16. Stability diagram of Ni and its oxide with varying temperature and partial pressure of
oxygen (in bar) ................. ...............59........... ....

4-17. Stability diagram of Ni and its oxide with varying temperature and partial pressure of
oxygen (in bar) with a constant partial pressure of sulfur dioxide at 2 mol %. ................59

4-18. Stability diagram of Ni and its oxide with varying temperature and partial pressure of
oxygen (in bar) with a constant partial pressure of sulfur dioxide at 10 mol %................60

4-19. Ni potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. U.E. is an abbreviation
for undefined equilibrium. Published in [170] ....._.._.. .... ... .... ... .._._........6

4-20. Ni SO2-O2 pOtential diagram at 900oC. U.E. is an abbreviation for undefined
equilibrium. Published in [ 170]. ............. ...............61.....

4-21. Ni SO2-O2 pOtential diagram at 1000.C. U.E. is an abbreviation for undefined
equilibrium. Published in [ 170]. ............. ...............62.....

4-22. Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in [170]......_......63

4-23. Al SO2-O2 pOtential diagram at 900oC. ................ ...................... ..................64

4-24. Al SO2-O2 pOtential diagram at 1000.C ........._._.. ...._.__ ...............64

4-25. Cr potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in [170]......_......65

4-26. Cr SO2-O2 pOtential diagram at 900oC............... ...............65.

4-27. Al SO2-O2 pOtential diagram at 900oC............... ...............66.

4-28. Ni-13.6Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. U.E. is an
abbreviation for undefined equilibrium. Published in [170]..........._._... ......._._.......66










4-29. Ni3Al SO2-O2 pOtential diagram at 900oC. ............. ...............67.....

4-30. Ni3Al SO2-O2 pOtential diagram at 1000.C. Published in [170]............_._. .........._._. ...67

4-31. NiAl potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. U.E. is an abbreviation
for undefined equilibrium. Published in [170] .....__.....___ ..............__........6

4-32. NiAl SO2-O2 pOtential diagram at 900oC............... ...............68.

4-33. NiAl SO2-O2 pOtential diagram at 1000.C. Published in [170]..........._._._ ........_._. .....69

4-34. Ni-8Cr-6Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in
[ 170] ....__ ................ .......__ .........7

4-35. Ni-8Cr-6Al SO2-O2 pOtential diagram at 900oC. Published in [170]. ............. .................70

4-36. Ni-8Cr-6Al SO2-O2 pOtential diagram at 1000.C. Published in [170]. ............. ..... ...........71

4-37. Ni-22Cr-11Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in
[ 170] ...._._. ................ ......._._. .........7

4-3 8. Ni-22Cr-11Al SO2-O2 pOtential diagram at 900oC. Published in [170]. ........._.._.. .............72

4-39. Ni-22Cr-11Al SO2-O2 pOtential diagram at 1000.C. Published in [170]. ........._................73

4-40. Phase fraction diagram of the Ni-O system showing the change in phase percent with
varying oxygen partial pressure at 800.C in air. Calculated from the SPOT3
database ................. ...............75.................

4-41. Phase fraction diagram of the Ni-O-S system showing the change in phase percent
with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2 atmosphere.
Calculated from the SPOT3 database. ............. ...............76.....

4-42. Phase fraction diagram of the Ni-O-S system showing the gas evolution (in partial
pressure [bar]) with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02
SO2 atmosphere. Calculated from the SPOT3 database. ............. .....................7

4-43. Phase fraction diagram of the Ni-O-S system showing activity change of each
component with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2
atmosphere. Calculated from the SPOT3 database............... ...............77

4-44. Phase fraction diagram an Ni-8Cr-6Al alloy showing activity change of each
component with varying oxygen partial pressure at 800.C in air. Calculated from the
S PIN4 d database. ............. ...............77.....

4-45. Phase fraction diagram an Ni-8Cr-6Al alloy showing the change in phase percent with
varying oxygen partial pressure at 800.C in air. Calculated from the SPIN4
database ................. ...............78.................










4-46. Phase fraction diagram an Ni-8Cr-6Al alloy at 800.C comparing the activity change
calculated for Figure 4-3 8 using the SPIN4 database (black) and the SPOT3 database
(teal). ............. ...............78.....

4-48. Phase fraction diagram of an Ni-8Cr-6Al alloy showing the change in phase percent
with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2 atmosphere.
Calculated from the appended SPIN4 database. .............. ...............79....

4-49. Phase fraction diagram of an Ni-22Cr-1 1Al alloy showing activity change of each
component with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2
atmosphere. Calculated from the appended SPIN4 database............... ................8

4-50. Phase fraction diagram of an Ni-22Cr-1 1Al alloy showing the change in phase percent
with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2 atmosphere.
Calculated from the appended SPIN4 database. .............. ...............80....

5-1. Plot of weight change versus time for Ni specimen at 800.C for 24 hr in air. ....................81

5-2. Plot of weight change versus square root time for Ni specimen at 800.C for 24 hr in air.
The formula containing the slope and the coeffcient of determination are listed.............82

5-3. Plot of weight change versus square root time for Ni specimen at 900oC for 24 hr in air.
The formula containing the slope and the coeffcient of determination are listed.............83

5-4. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni oxidized
for 24 hr in air. The formula containing the slope and the coeffcient of
determination are listed............... ...............83.

5-5. Plot of weight change versus square root time for a NiAl specimen at 800.C for 24 hr in
air. The formula containing the slope and the coeffcient of determination are listed. ....84

5-6. Arrhenius plot of the parabolic rate constant versus inverse temperature of NiAl
oxidized for 24 hr in air. The formula containing the slope and the coeffcient of
determination are listed............... ...............85.

5-7. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 1000.C for
100 hr in air. The formula containing the slope and the coeffcient of determination
are listed. .............. ...............86....

5-8. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 900oC for
100 hr in air. The formula containing the slope and the coeffcient of determination
are listed. .............. ...............86....

5-9. Plot of weight change versus square root time for a Ni-22Cr-1 1Al specimen at 800.C
for 100 hr in air. The formula containing the slope and the coeffcient of
determination are listed............... ...............87.










5-10. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al
oxidized for 100 hr in air. ............. ...............87.....

5-11i. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-
11Al oxidized for 100 hr in air. The formula containing the slope and the coeffcient
of determination are listed. ............. ...............88.....

5-12. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 975 oC for
100 hr in He + 0.21 02 + 0.02 SO2. The formula containing the slope and the
coeffcient of determination are listed. ............. ...............89.....

5-13. Plot of weight change versus square root time for a Ni-22Cr-1 1Al specimen at 975 oC
for 100 hr in He + 0.21 02 + 0.02 SO2. The formula containing the slope and the
coeffcient of determination are listed. ............. ...............89.....

5-14. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al
oxidized for 100 hr in He + 0.21 02 + 0.02 SO2. The formula containing the slope
and the coeffcient of determination are listed ................. ...............90........... ..

5-15. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-
11Al oxidized for 100 hr in He + 0.21 02 + 0.02 SO2. The formula containing the
slope and the coeffcient of determination are listed. ............. ...... ............... 9

5-16. Plot of weight change versus square root time for a Ni-8Cr-6Al specimen at 900oC for
100 hr in He + 0.21 02 + 0.10 SO2. The formulas containing the slopes and the
coeffcients of determination are listed ................. ...............91...............

5-17. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-8Cr-6Al
oxidized for 100 hr in He + 0.21 02 + 0.10 SO2. The blue data and regression
correspond to the initial oxidation rates, whereas the red data and regression
correspond to the later stage oxidation. The formulas containing the slope and the
coeffcients of determination are listed ................. ...............92...............

5-18. Plot of weight change versus square root time for a Ni-22Cr-1 1Al specimen at 800.C
for 100 hr in He + 0.21 02 + 0.10 SO2. The formula containing the slope and the
coeffcient of determination are listed. ............. ...............93.....

5-19. Arrhenius plot of the parabolic rate constant versus inverse temperature of Ni-22Cr-
11Al oxidized for 100 hr in He + 0.21 02 + 0.10 SO2. The formula containing the
slope and the coeffcient of determination are listed. ............. ...... ............... 9

5-20. Arrhenius plot of alloys isothermally oxidized in this study for 100 hr............... ...... ........._95

5-21. Histogram of the peak intensities measured from an XRD analysis of polished, heat
treated Ni-8Cr-6Al ................ ...............96.................

5-22. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in air for 100 hr at 800.C............... ...............96.










5-23. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in air for 100 hr at 900oC............... ...............97.

5-24. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in air for 100 hr at 1000"C.C................ ...............97...........

5-25. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in He + 0.21 02 + 0.02 SO2 for 100 hr at 800.C. ............. .....................9

5-26. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in He + 0.21 02 + 0.02 SO2 for 100 hr at 900oC. ............. .....................9

5-27. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in He + 0.21 02 + 0.02 SO2 for 100 hr at 975oC. ............. .....................9

5-28. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in He + 0.21 02 + 0. 10 SO2 for 100 hr at 800.C. ............. .....................9

5-29. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in He + 0.21 02 + 0. 10 SO2 for 100 hr at 900oC. ............. ......................0

5-30. Histogram of the peak intensities measured from an XRD analysis of Ni-8Cr-6Al
oxidized in He + 0.21 02 + 0. 10 SO2 for 100 hr at 975oC. ............. ......................0

5-31i. Histogram of the peak intensities measured from an XRD analysis of polished, heat
treated Ni-22Cr-11A l. ........._..._._ ...............101...._._ .....

5-32. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in air for 100 hr at 800.C............... ...............102.

5-33. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in air for 100 hr at 900oC............... ...............102.

5-34. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in air for 100 hr at 1000"C.C................ ...............103...........

5-3 5. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in He + 0.21 02 + 0.02 SO2 for 100 hr at 800.C. ............. ......................0

5-36. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in He + 0.21 02 + 0.02 SO2 for 100 hr at 900oC. ............. ......................0

5-37. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in He + 0.21 02 + 0.02 SO2 for 100 hr at 975oC. ............. ......................0

5-3 8. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in He + 0.21 02 + 0. 10 SO2 for 100 hr at 800.C. ............. ......................0











5-39. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in He + 0.21 02 + 0. 10 SO2 for 100 hr at 900oC. ............. .....................10

5-40. Histogram of the peak intensities measured from an XRD analysis of Ni-22Cr-1 1Al
oxidized in He + 0.21 02 + 0. 10 SO2 for 100 hr at 975oC. ............. .....................10

5-41. Optical micrograph of as cast Ni-8Cr-6Al at 125X ................. ...............108...........

5-42. Optical micrograph of heat-treated Ni-8Cr-6Al at 125X. ................ ............... ...._..108

5-43. Secondary electron (SE) micrograph of as cast Ni-8Cr-6Al microstructure at 5000X......109

5-44. SE micrograph of heat-treated Ni-8Cr-6Al microstructure at 20000X. ............. ..... ..........109

5-45. Optical micrograph of as cast Ni-22Cr-1 1Al at 125X ................. ......... ................1 10

5-46. Optical micrograph of heat-treated Ni-22Cr-1 1Al at 125X. ................ ......................11 1

5-47. Backscattered electron (BSE) micrograph of as cast Ni-22Cr-1 1Al microstructure at
5000X ................. ...............111................

5-48. Secondary electron (SE) micrograph of heat-treated Ni-22Cr-1 1Al microstructure at
15000X ................. ...............112................

5-49. X-ray map of the SE micrograph in Figure 5-46 ................. ...............112............

5-50. SE micrograph of NiO scale Ni oxidized in air at 800.C for 24 hr ................. ................1 13

5-51i. SE micrograph of NiAl oxidized at 800.C for 36 hr at 5000X. ................ ................. ..1 14

5-52. SE micrograph of NiAl oxidized at 1000.C for 36 hr at 20000X. ................ .................1 14

5-53. SE micrograph of NiAl oxidized at 1000.C for 36 hr at 200X. ................ ................. ..11 5

5-54. Backscattered electron (BSE) micrograph ofNi-8Cr-6Al oxidized in air for 100 hr at
900oC............... ...............116.

5-55. X-ray map of SE micrograph at 2500X of Ni-8Cr-6Al oxidized in air for 100 hr at
800oC............... ...............116.

5-56. SE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 100hr at 1000.C at
10000X ................. ...............117................

5-57. BSE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 100hr at 1000.C at
5000X ................. ...............117................

5-58. SE micrograph of surface of Ni-8Cr-6Al after oxidation in air for 0.5 hr at 800.C at
10000X. The light oxide is NiO and the dark oxide on the right is alumina. .................11 8











5-59. BSE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO2 at 800.C for 100 hr
at 4000X ................. ...............119................

5-60. BSE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO2 at 900oC for 100 hr
at 1000X ................. ...............119................

5-61. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO2 at 975oC for 100 hr at
1500X ................. ...............120................

5-62. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 2% SO2 at 975oC for 100 hr at
1500X. In this area, the scale has spalled off revealing the bare metal surface. .............120

5-63. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO2 at 800.C for 100 hr
at 15000X ................. ...............121................

5-64. SE micrograph of Ni-8Cr-6Al alloy oxidized in 10% SO2 at 800.C for 100 hr at 1500
showing scale "blisters." ................ ...............122...............

5-65. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO2 at 900oC for 100 hr
at 700X ................. ...............122................

5-66. SE micrograph of the overlying alumina regions of Ni-8Cr-6Al oxidized in 10% SO2
at 900oC for 100 hr at 10000X ................. ...............123........... .

5-67. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO2 at 975oC for 100 hr
at 5000X ................. ...............123................

5-68. SE micrograph of the surface of Ni-8Cr-6Al oxidized in 10% SO2 at 975oC for 100 hr
at 1500X where the scale (top) had spalled off and began to reoxidized (bottom). ........124

5-69. SE micrograph of Ni-22Cr-1 1Al oxidized in air at 800.C for 100 hr at 1000X. ...............125

5-70. SE micrograph of Ni-22Cr-1 1Al oxidized in air at 800.C for 100 hr at 5000X. ...............125

5-71. BSE micrograph of Ni-22Cr-1 1Al oxidized in air at 1000.C for 100 hr at 500X.............. 126

5-72. SE micrograph of Ni-22Cr-1 1Al oxidized in 2% SO2 gaS mixture at 800.C for 100 hr
at 1000X ................. ...............127................

5-73. SE micrograph of Ni-22Cr-1 1Al oxidized in 2% SO2 gaS mixture at 900oC for 100 hr
at 9000X ................. ...............127................

5-74. SE micrograph of Ni-22Cr-1 1Al oxidized in 2% SO2 gaS mixture at 900oC for 100 hr
at 10000X ................. ...............128................

5-75. SE micrograph of Ni-22Cr-1 1Al oxidized in 2% SO2 gaS mixture at 1000.C for 100 hr
at 1900X. ................ .............128.................










5-76. SE micrograph of Ni-22Cr-1 1Al oxidized in 10% SO2 gaS mixture at 800.C for 100 hr
at 100OX ................. ...............129................

5-77. SE micrograph of Ni-22Cr-1 1Al oxidized in 10% SO2 gaS mixture at 800.C for 100 hr
at 5000X ................. ...............130................

5-78. SE micrograph of Ni-22Cr-1 1Al oxidized in 10% SO2 gaS mixture at 1000.C for 100
hr at 10000X. ............. ...............130....

5-79. SE micrograph of Ni-22Cr-1 1Al oxidized in 10% SO2 gaS mixture at 900oC for 100 hr
at 1500X ................. ...............13. 1......... ....

5-80. BSE micrograph of a Ni specimen oxidized at 800.C for 24 hr at 1900X. The top
layer is the electroless Ni layer deposited for edge retention. ............. ....................13

5-81. BSE micrograph of a NiAl specimen oxidized at 1000.C for 36 hr at 2000X. The top
layer is the electroless Ni layer deposited for edge retention. ............. ....................13

5-82. BSE micrograph of Ni-8Cr-6Al oxidized at 900oC in cross-section. .............. .... ............133

5-83. SE micrograph of Ni-8Cr-6Al oxidized in 2% SO2 gaS mixture at 800.C for 100hr in
cross-section at 10000X ................. ...............134...............

5-84. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO2 gaS mixture at 900oC for 100hr in
cross-section at 3500X ................. ...............135...............

5-85. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO2 gaS mixture at 900oC for 100hr in
cross-section at 3500X, showing an oxide deeply penetrating along a grain boundary..135

5-86. BSE micrograph of Ni-8Cr-6Al oxidized in 2% SO2 gaS mixture at 900oC for 100hr in
cross-section at 5000X, showing sulfides along a grain boundary ................. ...............136

5-87. SE micrograph of Ni-8Cr-6Al oxidized in 2% SO2 gaS mixture at 800.C for 100hr in
cross-section, showing sulfides along grain boundaries and pores in the oxide layer.....136

5-88. BSE micrograph of Ni-22Cr-1 1Al oxidized in 2% SO2 gaS mixture at 975 oC for 100~hr
in cross-section at 8000X. The top layer is a Ni-coating added for edge retention. .......138

5-89. BSE micrograph of Ni-22Cr-1 1Al oxidized in 2% SO2 gaS mixture at 800.C for 100~hr
in cross-section at 800X ................. ...............138...............

5-90. BSE micrograph of Ni-22Cr-1 1Al matrix that was exposed to the 2% SO2 gaS mixture
at 975oC for 100hr 2000X. The labeled X-numbers are areas that were probed for
ED S. ............. ...............139....

5-91. EPMA linescan across scale and interface in an Ni-8Cr-6Al alloy oxidized at 900oC in
He + 0.21 02 + 0.02 SO2 gaS mixture. .............. ...............140....


XV11










5-92. EPMA linescan across scale and interface in an Ni-22Cr-11Al alloy oxidized at 800.C
in He + 0.21 02 + 0.02 SO2 gaS mixture ................. ...............141...........

5-93. EPMA linescan across scale and interface in a Ni-22Cr-11Al alloy oxidized at 975oC
in He + 0.21 02 + 0.02 SO2 gaS mixture ................. ...............141...........

6-1. Comparison of phases observed in SPIN4 calculations versus an SO2-O2 pOtential
diagram of Ni-8Cr-6Al at 900oC. The blue dots correspond to calculated equilibria
where the appended SPIN4 and SPOT3 databases agree. The green cubes
correspond to disagreements. The dashed lines represent the alternate reaction lines
determined by the appended SPIN4 database ................. ...............150..............

6-2. Comparison of phases observed in SPIN4 calculations versus an SO2-O2 pOtential
diagram of Ni-22Cr-1 1Al at 975oC. This diagram uses the same methodology as
used in Figure 6-1. ............. ...............151....

6-3. Comparison of the calculated activities from microprobe linescans with calculated
values using the appended SPIN4 database for a Ni-8Cr-6Al alloy oxidized at 900oC
in 0.21 02 + 0.02 SO2. ............. ...............154....

6-4. Comparison of the calculated activities from microprobe linescans with calculated
values using the appended SPIN4 database for a Ni-22Cr-11Al alloy oxidized at
975oC in 0.21 02 + 0.02 SO2. ............. ...............154....


XV111










Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

THERMODYNAMIC MODELING AND EXPERIMENTAL ANALYSIS OF OXIDATION/
SULFIDATION OF NI-CR-AL MODEL ALLOY COATINGS

By

Erik M. Mueller

May 2007

Chair: Wolfgang Sigmund
Major: Materials Science and Engineering

With the current focus on finding future energy sources, land-based power gas turbines

offer a desirable alternative to common coal-fired steam power generation. Ni-Cr-Al-X alloys

are the material basis for producing overlay bond coats for the turbine blades used in sections of

the turbine engine experiencing the most extreme environments. These overlay coatings are

designed to provide environmental protection for the blades and vanes. While the oxidation of

such alloys has been investigated and modeled in-depth, the concurrent sulfidation attack has

not. This corrosion mode is now being heavily researched with the desire to use gasified coal,

biomass, and other renewable fuel sources in gas turbines that often contain significant amounts

of sulfur. The purpose of this dissertation was to use thermodynamic calculations to describe

and predict the oxidation/sulfidation processes of two Ni-Cr-Al model alloys regarding phase

evolution, composition, and component activities. These calculations, in the form of potential

and phase fraction diagrams, combined with sulfidation experiments using kinetic measurements

and materials characterization techniques, were able to describe and predict the simultaneous

oxidation and sulfidation that occurred in these alloys.









CHAPTER 1
INTTRODUCTION

The United States and the rest of the world today are on the verge of an energy crisis. A

situation has developed in which increasing energy demands are consuming the current supply.

Besides the United States, which consumes more than 25% of the world' s energy resources, the

growing economies of Eastern Europe, China, India, and other developing countries are taxing

world energy reserves [1]. Therefore, in order to solve this growing problem, energy supply

must be increased while the demand is reduced.

The solution to creating new energy supplies is not easy, especially considering the

environmental and political impact of the most common source, fossil fuels [2]. Fossil fuel use

has led to the production of sulfur and nitrous oxides (SOx and NOx, respectively) and the

byproducts of incomplete combustion, carbon monoxide and excess hydrocarbons, which were

the chief environmental concerns of the Environmental Protection Agency and the Department of

Energy [3]. However, with the recent recognition by the White House of manmade global

climate change due to carbon dioxide (CO2) emiSsions, the focus of new energy creation is

finding carbon-neutral or less carbon-positive sources [4]. In essence, this entails the maximized

reduction of carbon dioxide from not only fuel consumption, but also fuel production.

Current alternatives for traditional coal, oil, and natural gas combustion to power steam

turbines are wide and varied. However, many of these energy sources are not available in all

regions and some do not yet process the technological development to make efficient use of their

resources. Furthermore, some energy sources, such as nuclear power, have such high capital

costs and political restriction, as to make them unfeasible in many regions. One currently

developed and researched alternative is the use of land-based power gas turbines. The advantage

of this process is that it has relatively few mechanical parts, requiring small capital investment,









reaching stable power output quickly, and achieving high thermal efficiencies [5]. This high

thermal efficiency translates into more power production for less fuel consumption, resulting in a

reduction in CO2 emiSSIOnS compared to traditional steam turbines [5]. Furthermore, the source

of fuel does not have to be limited to natural gas, but can also be synthetic combustion gases

derived from biomass, gasified coal, and steam reformation of liquid hydrocarbons.

However, the use of synthetic gases and even natural gas allow the inclusion of sulfur-

based gases, such as SO2, SO3, and H2S, into the engine itself. In the turbine industry, research

of the effects of these fuels were often overlooked since they play little role highly oxidizing

conditions found in aerospace turbines. However, with the advent of fuels from less pure

sources and the addition of later turbine blade stages, which operate at temperatures lower than

those near the combustor chamber, this has again become a concern. The blades and vanes

found in the turbine section can be attacked by these impurities, leading to catastrophic failure of

the turbine and the entire engine as a whole. New research into understanding the prevention of

this failure is key to making the placement of gas-based turbines in power plants more feasible

and cost-effective. Experimental research and testing of the alloys in the turbine section are

expensive, long, and difficult to reproduce. Therefore, efforts have been made to calculate these

conditions [6-9]. However, these efforts are usually restricted to oxidation alone, or are

performed on single elements, limiting their application to complex turbine alloys or their

coatings.

The purpose of this dissertation was to test if thermodynamic calculations can be used to

describe and predict the oxidation/sulfidation processes of two Ni-Cr-Al alloys with regard to

phase evolution, composition, and component activities. In addition, the oxidation of these

alloys was analyzed in situ to determine the rate of corrosion in air and synthetic air mixtures









with SO2 aS the sulfidizing gas. These specimens will be characterized using a variety of

techniques to determine the evolution of various phases during oxidation and the mechanisms for

corrosion. Information garnered from these experiments was compared and contrasted to

calculations using free energy minimization software to simulate the gas corrosion conditions.

The combination of these procedures was expected to determine the effects of these coatings in

the environments given and suggest solutions for preventing their failure.









CHAPTER 2
LITERATURE REVIEW

As stated in Chapter 1, the corrosion mechanisms of overlay coatings on turbine blades are

the chief concern of this dissertation. This chapter introduces the turbine blade alloys and their

coatings, the thermodynamics of the coatings used, and the corrosion issues characteristic of the

Ni-Cr-Al systems that are published to date.

2.1 Turbine Engine Considerations

Turbines operate by using the power from the exhaust to drive the forward inlet

compressor (Figure 2-1). Today's modern turbine engines comprise a fan, a compressor, a

combustion region, and a turbine. The fan draws in the air required for eventual combustion, and

in the case of bypass turbofan engines provides most of the thrust for commercial and military

aviation uses. For industrial gas turbines used in power generation, the fan may be replaced by a

generator to create electricity (more often, the generator is placed toward the rear).


Compressor Turbine


Inlet st~







Combustor

Figure 2-1. Schematic of a typical turbine engine.

The compressor region is a series of blades, rotors, and stators that draw air in and

compress it in ranges upwards of 30 to 40 bar [10]. In the combustion chamber, fuel is inj ected

into the hot compressed air, combusting spontaneously and expanding the gas mixture toward the










exhaust of the engine. This hot, expanding exhaust drives the turbine section, comprised of a

series of blades and vanes, which powers the compressor and fan. As expected, the blades

nearest to the combustion section experience the most severe conditions, but the later stages are

greatly taxed as well. The materials contained in and the environments affecting the turbine

section are the focus of this dissertation.

2.2 Turbine Blade Materials

2.2.1 Superalloys

Nickel base superalloys are often used for applications that require high strength at

elevated temperatures, and are the material of choice for the turbine sections because, in addition

to being strong and tough, they are resistant to fatigue, creep, and environmental attack.

Common yield strengths for cast polycrystalline Ni-base superalloys are on the order of 700-

1000 MPa at room temperature [l l]. Creep rupture strength are typically 75-300 MPa at 870oC

after 1000 hrs, and 60-125 MPa at 980oC after 1000 hr [1l]. These properties stem from the

nature of the two maj ority phases which have a coherent interface between the FCC y structure

and the L12 y' Structure of Ni3Al--both having similar lattice parameters and coherent interfaces

creating a low mismatch (less than 0.5% by length) [11-12]. The y' phase is a superlattice that

shows long-range ordering (LRO) to its melting point. This microstructure displays an increase

in flow stress with increasing temperature [11-12]. Extensive and complex heat treatments,

along with careful alloying, are used to create unique microstructures that will have the desired

mechanical and environmental properties. The alloying elements commonly used in superalloys

are listed in Table 2-1. Each of the elements has a tendency to partition during non-equilibrium

solidification causing some of the elements to remain in the dendrite cores and some to be

rejected into the interdendritic fluid that solidifies last. In service, these elements have a









tendency to diffuse and react with the environment. Therefore, careful balance and knowledge

of the effects of each of these elements must be understood. Furthermore, complex heat

treatments are employed to carefully control the microstructures, and mitigate these effects.

Table 2-1. List of common allowing elements in Ni-base superalloys.
Alloying Alloying Properties Partitioning
Eleme Behavior

Al y' former; increases anti-phase boundary energy (yAPB), Interdendritic /
increases oxidation resistance Y'
C Carbide former; oxygen getter; grain boundary strengthener n/a
Co Lowers stacking fault energy (YSFE); inCreaSCS y' melting Dendrite Core / y
pint; strengthens y phase
Cr Oxidation/corrosion protection, lowers yAPB; Can form Dendrite Core / y
topologically close-packed (TCP) phases
Mo Increase creep strength, strength in y; decrease Dendrite Core / y
oxidation/corrosion resistance; forms TCP
Nb y" former; increases coherency strain, peak strength, room Interdendritic /
temperature strength Y' / Y"
Re Increases creep strength, strength in y, modulus; decrease Dendrite Core / y
oxidation/corrosion resistance, forms TCP
Ru Reduces Re partitioning; delays TCP formation; increase Dendrite Core / y
creep strength; decreases oxidation/corrosion resistance
Ta y' former; increase YAPB, COherency strain, creep strength, peak Interdendritic /
strength; improves castability Y'
Ti y' former; increases yAPB, COherency strain Interdendritic /

W Increases creep strength, strength in y, modulus; decrease Dendrite Core / y
oxidation/corrosion resistance, forms TCP


2.2.2Coatings for Turbine Blades

There are a variety of coatings for superalloy blades and vanes, and they are applied to

increase environmental stability and/or reduce the heat transmitted to the blade. Figure 2-2

shows the common coating configuration used in aerospace and industrial gas turbine (IGT)

engines [16]:










* The substrate (superalloy turbine blades)
* The bond coat, which provides an environmental barrier for the substrate and a better
bonding surface for the exterior coating
* The thermally grown oxide (TGO), which is sometimes manufactured before service
* The thermal barrier coating (TBC), which is a porous, columnar ceramic coating usually
consisting of ZrO2 designed to reduce the heat seen by the layers underneath

The TBC effectiveness of the TBC is the change in temperature (AT) which controlled by

TBC thickness (6), thermal conductivity (k), and the thermal flux (Q) through the blade wall, via:


AT = O (2-1)


The AT values obtained can be as high as 150oC [10]. The focus of this study will be on bond

coats, which are generally of the MCrAlY composition design, where M is a metal base usually

Ni, Co, or both. This layer, which is higher in Cr and Al than the substrate, is designed to

oxidize first and protect the superalloy. This is because, even though the TBC is the outer

coating, it is porous and the oxidizing/corroding elements of the atmosphere directly contact and

react with the bond coat. Ni-base superalloys generally oxidize to form nickel-based oxides,

which do not adhere to the substrate and cause spallation of TBC layer [13]. The layer of

protection formed on the bond coat is generally designed to grow as aluminum oxide, ot-Al203,

since it has the lowest oxygen diffusivity of the oxide of any of the elements listed in Table 2-1

[14]. The TGO is sometimes pre-grown before the coated blade is put into service but,

regardless, is present upon usage in the highly oxidizing high temperature conditions. Co is can

be used to increase the coating ductility, but the formation of CoO reduces the oxidation

resistance because this oxide grows at a faster rate than NiO, Al203, Of CT203 [10, 13,15]. The

thermal barrier coating is said to fail when the TGO grows to a thickness so large that it spalls.

Spallation can also occur from buckling due to cyclic thermal stresses [16].










Thermal Barrier Coating







TGO
Bond Coa~t







Figure 2-2. Schematic of coating configuration of modern turbine blades.

2.4 The Al-Cr-Ni Ternary System

The bond coats that are examined here are of the NiCrAl-type. In order to understand

these coatings, the Al-Cr-Ni ternary should be discussed. The Al-Cr-Ni ternary has been studied

through both experiments [17-22] and thermodynamic calculations [23-29]. Figures 2-3, 2-4,

and 2-5 refer to the ASM Handbook binary phase diagrams of Al-Ni, Al-Cr, and Cr-Ni,

respectively [30]. Studies of the Al-Cr-Ni ternary were undertaken--first using powder X-ray

diffraction techniques [17], which were integrated with other techniques to determine

thermodynamic data such as the Gibbs free energies of formation (AGr) [18]. These other

methods included diffusion couples [19-20], differential thermal analysis (DTA) [21], and

electron microprobe (EPMA) [21]. The data were optimized to enable calculations of the ternary

sy stem. Since the Ni-rich area (XNi > 0.5) is of more importance for practical applications, it has

been studied in more depth than the Al or Cr-rich regions [19-20, 23, 25, 27].















































































,I' I II1- -
D 10 20 So 4~ 0 5 70 80 0o 100
Ni Weight PeTrcen Chromiumn Cr

Figure 2-4. Ni-Cr binary phase diagram [H. Baker. ASM~Handbook Vol. 3--Alloy Pha~se
Diagrams, ASM International: Materials Park, OH, p. 155 (1992)].


Atomi1c Fjl~LF[FFIN~k
0 10 20 30 40



1500 -

1400-

13100 L
o to~




1100




700-



EDD



0 o 20 30 40 B0 AU
A Weight Percent Nicket

Figure 2-3. Al-Ni binary phase diagram [H. Baker. AS
Diagrams, ASM International: Materials P

Atomic Percent Chromiul
ri 10 30 40 50 00 70




L



145o*C



2100


MIHandbook Vol. 3--Alloy Pha~se
ark, OH, p. 49 (1992)].


m










Atamic t)ril~e ril Chromium
as aa ~a sa


Figure 2-5. Al-Cr binary phase diagram [H. Baker. ASM~Handbook Vol. 3--Alloy Pha~se
Diagrams, ASM International: Materials Park, OH, p. 43 (1992)].

A recent retooling of the AGr descriptions of several of the important phases has been

performed. Earlier studies described the y and y' phases as having separate Gibbs energy

functions [23-24], but more recent studies by using new data [25] describe the y and y' as ordered

and disordered versions of the same phase, transforming via a second-order reaction [27]. The

co-Cr and P-NiAl are also treated as having the same Gibbs energy function [26-27] as can be

described by the compound energy formalism, which attempt to simplify descriptions of

intermetallics and oxides using sublattices that can substitute multiple elements and vacancies

[31i]. This methodology is used for one of the databases accessed for ternary calculations (see

Chapter 4). Debate has occurred over the exact descriptions of this sublattice model, as to

whether there should be a single sublattice [23-25] or multiple [26-27]. The most recent










publications, though, [27-29, 32] agree that multiple sublattice models best describe the ordered

and disordered phases present in the Al-Cr-Ni system.

The phases present in the Al-Cr-Ni ternary are listed in Table 2-2. Figure 2-6 shows the

liquidus projection taken from a review of a compilation of calculated and experimental data

[32]. The Scheil reaction scheme is shown in Figure 2-7. At 1445oC (labeled el), a eutectic

occurs in which a-Cr and P-NiAl solidify. Eutectics also occur for y and y' at 1380oC (e2) and

for y and a at 1345oC (e3). Peritectics are observed for L + P + y' at 1385oC (pl) and 1350oC

for L + a + rl (AlsCrs-hexagonal) (p2). At 1340oC, LPy' and Lyy' tie-triangles react in a ternary

invariant reaction (Class II) to form L~y and byy' three-phase equilibria (U1). The L~y then

reacts with the LaP and Lya tie-triangles at a ternary eutectic reaction (Class I) to solidify to a +

p + y at 1320oC (El). At 990oC, a ternary invariant reaction (U4) Occurs in which the upy reacts

with pyy' to form myy' and upy' three-phase equilibria. Figures 2-8 and 2-9 show isothermal

sections of the ternary before and after reaction U4, TOSpectively. Other invariant reactions occur

in the Cr-rich and Al-rich areas of the ternary, but these are ignored as they are not applicable to

this study nor the one referenced [32].

The importance of studying this ternary is to construct model alloys ofNi-Cr-Al that can

be modeled and studied as opposed to multicomponent alloys [28-29]. Results from experiments

with these model alloys can be directly correlated to bond coats containing more elements such

as rare-earths and Y (typically less than or equal to 1 wt%) and be to related to their

microstructures and corrosion results.

Overlay coatings are those in which interdiffusion is not required so that the coatings are

"laid onto" the substrate. The MCrAlY compositions are designed to provide optimum oxidation

or hot corrosion resistance, as well as strength, ductility, and thermal expansion match with the










Al grid in aL, %
axes in mass %






















Cr Ni

Figure 2-6. Liquidus projection of the Al-Ni-Cr ternary system [P. Rogl. "Al-Cr-Ni," Ternary
Alloys: A Comprehensive Compendium of~valuated Constitutional Data and Phase
Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 411 (1991)].
Cr -G Al A Ni Tersnar i-C

113851 P1 ] t +p





113a p I IL+B-1- I ?? I.u-I |11.4
i 1111LtY--- ~l I


t~, i I r~-~ r
99 01 ~llP-y + 7 Y + U


Fiur 2-7 Scheil J recto sceeo h lCrN enr.Te -hs eestoN2lte
tAl-tr-hxgnl 2t Als+r-rhoboedal an tt l 4.Teqeto
mak ersn aeso h enayta eeno netgtd










Table 2-2. List of phases described in calculations of the Al-Cr-Ni tray
Phase Temperature Lattice Parameter Space Group Pearson Symbol
Range (oC) (A)
(Al) < 660.45 4.049 Fm 3 m cF4
co-Cr < 1863 2.884 Im 3 m cl2
y-Ni < 1455 3.524 Fm 3 m cF4
y' (Ni3Al) < 1372 3.566 Pm 3 m cP4
P (NiAl) < 1638 2.886 Pm 3 m cP2
Ni2Al3 < 1133 a = 4.036 P 3 ml hP5
c = 4.900
NiAl3 < 854 a = 6.611 Pnma oPl6
b = 7.366
c= 4.8112
All3 2 < 791 a = 25.19 C2/m mC104
b = 7.574
c =10.95
S= 128.7o
AlliCr2 < 941 a = 12.88 P2 mP48
b = 7.652
c =10.639
S= 119.3o
Al4Cr < 1031 a = 8.716 P2/m mPl80
b = 23.95
c =16.39
S= 119.33o
Al9 4 1172 1061 a = 9.123 Unknown cl52
Al9 4 < 1050 Unknown Unknown [ Monoclinic]
AlsCrs 1352 1127 a = 9.047 Unknown cl52
AlsCrs < 1127 a =12.733 R3m hR26
c = 7.944
AlCr2 < 911 a = 0.3004 I4/mmm tl6
c = 0.8648
Ni2Cr < 590 a = 2.524 ol6
b = 7.571
c =3.568










grid in at. %
axes in mass %


Figure 2-8. Isothermal section of Al-Cr-Ni ternary at 1025oC above the U4 reaction. The green
areas denote regions of two-phase equilibria [P. Rogl. "Al-Cr-Ni," Ternary Alloys: A
Comprehensive Conspendium of~vaheated Constitutional Data and Phase Diagrams:
Al-Cd-Ce to Al-Cu-Ru. 4 p. 414 (1991)].


0,0 Cr grid in at.%
50.0 Al axes in at.9h


50,0 Cr Ni
50.0 Ni
Figure 2-9. Partial Isothermal section of Al-Cr-Ni ternary at 850.C below the U4 reaction. The
green areas denote regions of two-phase equilibria [P. Rogl. "Al-Cr-Ni," Ternary
Alloys: A Comprehensive Conspendium of~vaheated Constitutional Data and Phase
Diagrams: Al-Cd-Ce to Al-Cu-Ru. 4 p. 413 (1991)].










given substrate. One application method is through electron beam physical vapor deposition

(EB-PVD). This method allows direct deposition from a metal source to a heated metal substrate

without a chemical reaction and forms a columnar structure [33]. This can also be accomplished

using an electric arc [34]. Another common method, plasma spraying, involves injecting a

prefabricated powder into a plasma-gas stream, which deposits melted pellets as splats on the

surface [35]. This leaves few voids, but the coating has a rougher surface finish than EB-PVD.

The surfaces of both coatings are often mechanically machined to create a smooth exterior and

heat-treated to better bond to the substrate. Oxidative heat treatments are sometimes employed

to begin TGO formation in a controlled manner in order to stabilize the coating system.

Overlays can also be applied by a high-velocity oxide furnace (HVOF) in which liquid fuel and

oxygen are fed at high pressure into a combustion chamber where they burn to produce a hot gas

stream that accelerates powder particles onto the substrate [36].

The phases present in the overlay coating vary with the composition of the coating and can

be approximated by the Ni-Cr-Al or Co-Cr-Al ternaries. Many of the coating processes do not

create an equilibrium microstructure due to the rapid solidification, so they heat-treated to obtain

the desired microstructure [37]. For the coatings to be used in this proj ect, Ni-22Cr-1 1Al and

Ni-8Cr-6Al, the phases present are shown in Table 2-3 [37]. Upon proper heat-treatment, the Ni-

8Cr-6Al shows a microstructure of cubiodal y' surrounded by a matrix of y [28], whereas Ni-

22Cr-1 1Al alloys show large globular P phases containing small y' surrounded by a matrix of y

with small irregular a [37]. At increasing temperature, the solubility of the alloying elements in

the y and y' phases increase, reducing the number of stable phases. In this respect, there is more

compositional homogeneity to more easily form a stable a-Al203 Oxide film. The oxidation

mechanisms and behavior of these coatings is discussed in the next section.










Table 2-3. The phases present in the Ni-22Cr-11Al and Ni-8Cr-6Al (weight percent) alloys at
room temperature and 1000.C.
Alloy Composition Phases Present Phases Present
(Room Tempeature) (1000oC)
Ni-8Cr-6Al Y, Y' Y
Ni-22Cr-11Al Y, Y', P, a Y, Y'


2.5 Oxidation of Al-Ni-Cr Alloys

2.5.1 General Oxidation Mechanism

In general, the oxidation of a metal in a gaseous environment involves several stages.

First, the Ol mOlecule must adsorb (by physisorbtion) and dissociate onto two sites on the metal

surface [39-40]. The molecule then chemisorbs with the surface, at which one or more of several

processes may take place:

* Active oxidation--an MxO, molecule may desorb leaving a bare metal surface [40]
* Dissolution--the oxygen may diffuse into the metal, where it may later form internal
oxides [38]
* Nucleation--oxides "islands" may nucleate and grow [38]
* Thin film formation--a thin film layer of oxide may form, passivating the metal [38-40]

This general mechanism is the mechanism of oxide growth expected for the alloys in this study.

The reaction on the surface


xM~(s) + 0, RM~y,O(s) (2-2)

can be rate-limited by [38]

* Desorption (in the case of active oxidation)
* Diffusion of species through a film
* Gas transport in the substrate
* Ion transport in the substrate
* Oxide growth
* Oxide nucleation
* Surface adsorption

In the case of the formation of a thin film at lower temperatures, the rate-limiting step has

been shown to be cation transfer from metal to oxide surface driven by an electric potential









across the film, as described by Mott and Cabrera [39]. The kinetics of thin film growth can be

described as logarithmic

x = k, log(t + r) (2-3)

or inverse logarithmic

S= B k, log t (2-4)

where x is film thickness, kl is the rate constant, t is time, and B and z are constants. Figure 2-10

shows an example of logarithmic and inverse logarithmic growth.




t ~Inverse log
Parabol icLo





Linear


Tirne (1) ->
Figure 2-10. Plot of oxidation growth kinetics versus time.

At higher temperatures, and in thicknesses large enough where electric Hield effects are

negligible (x > 10 nm), parabolic kinetics usually govern film growth (Figure 2-10):

xZ kp t + C1 (2-5)

As described by Wagner' s theory of passive oxidation of Si, thermal diffusion of cations and

anions is generally the rate-limiting step in parabolic growth [40]. As the fi1m thickness

increases, the diffusion length increases slowing the growth. This observation, however,

assumes a compact, adherent scale. If the oxide is porous or has poor adhesion with the metal

surface, then bulk parabolic growth may not apply as short-circuit surface Oz diffusion paths









become prevalent. Bulk diffusion is usually bypassed by diffusion along grain boundaries,

stacking faults, and dislocations, which increase the film growth rate [41].

Other kinetic oxidation models relevant to this study include linear growth:


= k (2-6)


Linear kinetics are also observed if the oxide is volatile or above its melting point. This occurs

in oxides where the film is not protective, and is often porous. Other kinetic models include

paralinear, cubic, and subparabolic, which describe mixed growth. These models attempt to

describe transitions from one kinetic model to another (e.g. linear to parabolic) or growth limited

by several simultaneous mechanisms.

The oxidation described in this section and the rest of this report deals with isothermal

oxidation. Cyclic oxidation, where the temperature is varied (usually from room temperature to

a maximum temperature), is not covered here as thermal expansion and residual stress factors

must be taken into account, leading to more rapid failure than in isothermal conditions. For more

information on cyclic oxidation, the interested reader is referred to references 10, 14, and 15.

2.5.1.1 Oxidation of Ni

The oxidation ofNi is governed by gas absorption, oxide nucleation, and film growth as

per the chemical reaction

2Ni + 02 + 2NiO (2-7)

NiO, or busenite, has an NaCl-type structure and appears as a black oxide (or green in high Ni

contents). The oxide grows with a (111)Ni||(001)Ni, [1 10]Nio||[1 10 ]Ni orientation relationship,

although (100)Nio and (211)Nio are grown in epitaxy as well [36]. NiO is a p-type metal deficient

oxide, where every cation vacancy has two Ni3+ pairs. In p-type metal deficient oxides, cations

diffuse via vacancies in the cation sublattice to the oxide/gas surface while electrons migrate via









electron holes back toward the oxide/metal interface as determined by tracer experiments [38,

43].

Ni oxidation has been described by parabolic kinetics [43-46]. However, a recent study

with pure Ni in various oxygen-argon atmospheres showed that between 7000C and 10000C,

NiO could grow "subparabolically" [44]; above 10000C and below 6000C, parabolic growth is

observed. The reason for this is that above 10000C, bulk diffusion via cation vacancies

dominates, and the scale exhibits columnar grains [47]. In the subparabolic regime, the scale

exhibits a duplex structure with outer columnar grains having outward Ni cation diffusion, and

inner equiaxed grains with short-circuit 02(g) diffusion inward [48].

2.5.1.2 Oxidation of Al

Al oxidation has been widely characterized for a variety of applications. Al is highly

reactive and readily ionizes at -1.662 eV [38]:

Al & Al3+ + 3e- (2-8)

Al203 is considered an excellent passivating film due to its good Pilling-Bedworth (P-B) ratio

(1.28) [38] and having a low 02- diffusivity at sufficient thicknesses [49]. Alumina is most

prevalent in the ot-Al203 COrundum R3c phase, although other phases exist, as outlined in Table

2-4.

The initial stages of Al oxidation have been described using Al substrates in ultra-high

vacuums. In the initial stages, Ol mOlecules approaching an Al surface physisorb, dissociate,

and chemisorb onto the surface. This then allows for the inward diffusion of Ol- and the

formation of Al203 tetrahedra [51]. The adsorption sites are different based on the orientation of

the metal surface. Initially, these original formula units of Al203 eXiSt as amorphous "islands,"

which grow laterally, eventually covering most of the metal surface [52]. Initially cation-









Table 2-4. Descriptions and crystallographic information on different phases cf Al203 [49-50].
a-Al203 K-Al203 y-Al203 6-Al203 6-Al203
Crystal system Trigonal Orthorhombic Cubic Monoclinic Tetragonal

Space group R3c Pna21 Fd 3 m C2/m P 4 m2

Lattice parameters a=4.7587 a=4.8351 a=7.92 a=11.8545 A=5.599
(A) c= 12.9929 b=8.3109 b=2.9041 c=23.657
c=8.9363 c=5.6622
P=103.837
Al atoms in unit 12 16 63/3 n/a 14
cell

O atoms in unit 18 24 32 n/a 12
cell

Al-co-ordination Octahedral 75% octahedral n/a n/a n/a
25% tetrahedral



defieient, the amorphous film grows outward via interstitial Al3+ transport [49,52] driven by the

Al concentration gradient [49,53] and E-Hield effects [40]. At several nanometers, when

stoichiometry in the oxide is achieved [54], the amorphous alumina crystallizes into y-Al203

(sometimes preceded by a y'-Al203 [55]) due to a close orientation relationship between the

oxide and the substrate (111)A1||(111 )y-Al203 aS determined by a rigorous TEM analysis [56-57].

The y-Al203 is an anion-defieient n-type semiconductor, growing via inward chemical bulk O

diffusion [58]. Short-circuit paths play a role at larger thicknesses. The growth kinetics are

logarithmic at lower temperatures, and parabolic at higher temperatures.

The y-phase is metastable and rarely seen above 8000C [58]. It will usually transition to

the stable a-phase at sufficient thicknesses, times, and temperatures. The 6 and 6 phases are

sometimes seen as intermediates with whisker morphologies [58-59] and generally grow by

outward cation diffusion, as determined by tracer and inert marker tests [58-60]. These transition










phases are undesirable compared to the a-phase because stable a-phase has a parabolic rate

constant an order of magnitude lower [61] due to slow anion-diffusion along grain boundaries

[56, 62]. This growth mechanism depletes the substrate less (in the case of Al-X alloys) than the

cation-diffusing transition aluminas. Furthermore, the kP Of y-Al203 is higher than that of NiO or

Cr203, defeating the use of Al203 aS an impediment to oxidation in Ni-Cr-Al alloys [63].

2.5.1.3 Oxidation of Cr

The oxidation of Cr has been studied extensively due to its use as the maj or alloying

protectant in stainless steels [64-66]. As found with tests in steels or in elemental form, Cr reacts

with 02 to form Cr203 Via a Similar reaction as Al does with Oz-

4Cr + 302 + 2Cr203 (2-9)

Cr203, Or chromia, like NiO is a p-type metal deficient semiconductor [67], and therefore grows

by outward cation transport through the scale lattice [67-68] at temperatures less than 1250oC.

Cr203 is commonly used because it reacts faster with O than the elements it is alloyed with and

has a low 02 diffusivity, thereby allowing a slow growth rate [69-70]. Cr oxidation is described

by parabolic kinetics above 700oC, and shows initial logarithmic growth at lower temperatures.

Above this temperature, chromia can become amphoteric, or able to transport in both directions

simultaneously, and the growth rate increases rapidly [67]. Due to this defect structure, the

Cr203 Can form a duplex structure with an inner layer where interstitial Cr3+ diffusion also takes

place. This tends to increase the diffusion of Cr3+ in the inner region, which is highly dependent

on the oxygen partial pressure [70]. As validated by tracer tests and diffusion coefficient

findings, short-circuit diffusion through grain boundaries, cracks, and pores dominate and

increase the scale growth rate [64, 69-70]. One oxidation study showed that this was the primary

growth mechanism [71].









One of the problems with Cr203 is the ability for the Cr cations to become hexavalent at

higher Oz partial pressures, forming CrO3, Such as can be experienced in gas turbine conditions

by these reactions [72]:

2Cr + 302 + 2CrO3 (2-10)

2Cr203 + 302 & 4CrO3 (2-11)

The formation of this gas species removes the protective chromia layer thereby making the Cr203

ineffective. Volatilization also increases the Cr alloyed in the substrate, decreasing the time-to-

fail of the Cr203 Scale. Other gas species have been studied, but are less likely to be major

contributors at high temperatures and high oxygen partial pressures [72-73]. Hexavalent Cr gas

species have been classified as carcinogens and the use of Cr coatings in some industries has

been restricted [74].

2.5.2 Oxidation of Ni-Al Alloys

Al203 laS well as Cr203) has a slower growth rate (Figure 2-11) and higher affinity for Oz

than Ni [15]. Therefore, Al is commonly used as an alloying agent with Ni to provide an

environmental protection in lieu of the unprotective NiO scale. As mentioned in Section 2.2, Al

is also used to form and stabilize the intermetallics y' and (P).

With Ni-Al alloys, the corundum ot-alumina phase is the desired TGO for its slow-growth

rate, low anion diffusivity, and overall smooth morphology. The y-alumina phase has been

shown in studies to appear first, especially at lower temperatures (T < 850.C) due to a lower

activation energy to form on Ni-Al alloys [75-77].

The oxidation of dilute Ni-Al alloys begins with the formation of NiO. The formation of

this oxide, though, depletes the alloy at the alloy/gas interface of Ni and reduces the Po2 i

relation to the gas/scale interface. This leads then to the formation of Al203 [63]. Scanning











Temperature (T), *C
1150 1100 1050 1000 950








Cr O




-12 -1~
SiO,


-14 I I
7.0 7.4 7.8 8.2
104/T(1/K)
Figure 2-1 1 Arrhenius plot of parabolic growth rates versus temperature of NiO (violet) as well
as Cr203 and Al203 (red) [J.L. Smialek, G.M. Meier, "High-Temperature Oxidation,"
Superalloys II. C.T. Sims, N.S. Stolff, W.C. Hagel, eds., John Wiley & Sons: New
York p. 295 (1987)].

electron microscopy (SEM) cross-sections found that alumina scale formation will develop

fastest at the grain boundaries, since these are fast diffusion paths for Al3+ and Ol- transport [77].

Hindam and Smeltzer described the formation of Al203 in the presence of NiO or Ni will lead to

"breakdown oxidation" of the alumina scale in which spinel is formed via [78]:

NiO + Al203 9NiAl204 (2-12)

If the amount of Al present in the alloy is too little, a stable alumina scale may not be formed

[78]. As graphically described by Pettit in Figure 2-12, too little Al will prevent the internal

oxides of Al203 fTOm coalescing to form a continuous scale [76]. Furthermore, even if a stable

scale is formed, the alloy must have enough Al to continually feed the oxide growth, and the flux

of Al in the alloy must exceed that in the oxide. If not, the alumina scale will break down, and

NiO and NiAl204 Will Stabilize [76, 78-79].










at. soC
10 20 30 40


AlAl
2200 aff~\\\\\\\\\~ \Jlo/oxide 1200

E / AAl Steady state
3~ 2000Jatl & 3 N2 max -10
,* Exterrnal Al 31
< NA@3 overtaken y
NIO +NIAlZO 041
External NIO,
Internal Alg03


Figure 2-12. Dependence of oxidation mechanisms and scale type ofNi-Al alloys based on
temperature and Al content [F.S. Pettit: Transactions of the AIM~E. 239, pp. 1296-
1305 (1967)].

In two-phase alloys, oxidation rates and oxide phases can differ over a range of

compositions. The addition of any Al to Ni will cause an increase in the rate of oxide growth,

and a decrease in activation energy [58, 79]. This fast oxidation is due to Al3+ doping of the NiO

and the formation of the open NiAl204 Spinel that allows for rapid cation diffusion [79]. In y + y'

mixtures, the kinetics are more complex, showing a parabolic-linear-parabolic procedure whose

growth rate is less than alloys with Al < 6 wt% [76]. This occurs because the initial a-Al203

scale is being overtaken by NiO growth, and eventually reaches steady-state nickel oxide

parabolic growth [80]. For those oxides growing over y-Ni, the only alumina seen is a-Al203,

and can be mixed with NiO and spinel. Transient 6 and 6 alumina phases are often seen growing

first over Ni3Al [81-82]. This is also observed on y' + P mixtures, but kinetics are always

parabolic [76, 83-84]. The presence of P causes the faster formation of a-Al203 and a slower

growth rate than with more dilute Ni-Al alloys. Transient alumina phases have been observed

over NiAl as well [85].









2.5.3 Oxidation in Al-Cr-Ni Ternary and NiCrAlY Coatings

Oxidation of Ni-Cr-Al alloys involves a complex competition of the formation and growth

of NiO, Cr203, and Al203. In addition, the nickel-chromium and nickel-aluminum spinels often

play a role. In general, the addition of Cr to Ni-Al alloys stabilizes the Al203 phase [85-86].

This overall process, was first described by Pettit [76] and is shown in Figure 2-13. Upon initial

oxidation, the activities of oxygen and nickel are high enough that NiO forms [87]. Any Al or Cr

that oxidizes reacts with NiO to form spinel. NiCr204 and NiAl204 allOw for faster transport of

Ol- anions in and Ni2+ anions out. As the initial scale grows, the Po2 at the scale/alloy interface

diminishes due to scale thickening, and the activity of Ni decreases due to Ni-depletion in the

alloy below the interface [88]. This causes internal oxidation of Cr and Al in the alloy. If there

are insufficient amounts of alloying elements, the Al and Cr oxides will remain as small

spherical and/or rodlike internal phases (Group I). If, however, there is enough Cr, a continuous

scale of Cr203 Will form and grow at the scale/alloy interface (Group II). This has the effect of

further lowering the oxygen activity at the interface, which, if there is enough Al to sustain it,

will form a continuous Al203 Scale that becomes rate-controlling (Group III) [86, 89-90]. In

effect, Cr "getters" 02 allOwing the Al203 Scale to stabilize. If there is not enough Al, though,

the steady-state scale that grows will be chromia (Group II) [90-92].

Kinetically, as with Ni-Al alloys, increasing the alloying elements Al and Cr in Ni-Cr-Al

will cause a decrease in the parabolic growth rate [93-94]. The exception to this is in the case of

dilute alloys wherein the alloying elements actually dope the oxide increasing ionic mobility by

introducing lattice vacancies [88, 95].

































5: NHCr,Alr04
e: c ra o

Figure 2-13. Schematic of the stages of oxidation in Ni-Cr-Al alloys. Group I are alloys that will
have a stable NiO scale, Group II will develop a stable Cr203 Scale, and Group III
will develop a stable Al203 Scale [F.S. Pettit: Transactions of the AIM~E. 239, pp.
1296-1305 (1967)].

The microstructure of the scale shows orientation relationships between the initial oxides

formed and the metal. Similar to that of y-Al203 and Al, the relationship of the spinel and y-

Al203 that forms on the alloy is (1 11)Spinelll 1NiCrAl, <1 10>Spinel||<1 10>NiCrAl [5 8]. The Cr203

that grows is (0001)cl-os||l( 111)NiCrAl, <1 120 >c os||<1:=l10>NiCrAl. However, TEM studies showed

that the steady-state alumina that grows has a random orientation with the alloy and the other

oxide layers [58, 61, 96]. Over time, the Cr in the alloy tends to segregate out of the NiAl into

the y and y'. Cr203 is seen on top of those Cr-rich regions, whereas Al203 forms faster above the

p [57]. As with Ni-Al with high Al contents, 6 and 6-Al203 are Observed having a needle-like

morphology [57, 97-98] that transforms to oc during continuous exposure to an oxidizing gas










mixture [56]. A study by Levi et. al. observed these transient aluminas formed as lumps or hills

on top of the P, whereas the oxides over y/y' were seen as a smooth scale [97]. The ot-alumina

that forms underneath (over all alloy phases) is columnar [93, 96-97]. The absence of these

transient aluminas again shows a lower oxidation rate [98].

2.6 Sulfidation and Hot Corrosion

2.6.1 Hot Corrosion

Hot corrosion is an accelerated corrosive attack of molten salts that often occurs in the later

stages of turbine engines where the pressure is less than those near the combustor, and when salt

or ash deposits accrue on the alloy or coating surface [99]. Even for applications typically

operating above 10000C, hot corrosion can be a problem during thermal cycling--frequently

occurring in salty marine areas or in operations with fuels containing S, V, and/or P. This

mechanism occurs when temperatures enable molten salts such as Na2SO4, K2SO4, and/or NaCl

to be in their liquid state, in which they attack the oxide scale, and eventually penetrate into the

substrate itself [99-101]. This type of corrosion can be categorized into two stages: an initiation

stage, and a propagation stage. The initiation stage is marked by either parabolic growth or slow

weight loss. The mechanism is similar to oxidation, except that sulfides form in the oxide from

an influx of sulfur anions or SOx gases. Once the propagation stage begins, severe weight loss is

observed and rapid attack of the oxide and alloy begins. The chief reactions) governing this

process is

Na2SO4 4 Na20 + SO3(g) (2-13)

SO42- + 02- + SO3(g) (2-14)









These are the basis for the fluxing reactions in which basic fluxing

MO + 02- + MO22- (2-15)

or acidic fluxing

MO + M2+ + 02- (2-16)

occurs [102]. This attack can be categorized into either Type I, which occurs between 850 and

10000C and is governed by basic fluxing, and Type II that occurs between 680 and 7500C [97]

and is governed by acidic fluxing [103-104]. Type II corrosion displays characteristic pits can be

avoided through higher Cr contents, higher temperatures, and larger gas flow velocities in the

engine. The partial pressure of SO3 is critical for the reaction where the sulfate dissolves the

metal oxide at the scale/salt interface, which then reacts with SO3 to form oxide (low PSO3) Of

sulfate (high PSO3), which then repeats the process [103-105].

Type I hot corrosion is of more concern for this study, in which the formation of metal

sulfides from reactions with the sulfate create a free oxygen anion that reacts with the metal

oxide to form a metal oxyanion that dissolves in the salt [105-106]. This MOX2- then can react

with SO2 (Or SOx) to form oxide particulates at the salt/gas interface that frees up oxygen anions

to repeat the process [106-107]. While originally thought to be self-sustaining, other research by

Goebel and Shores has shown that a constant supply of Na2SO4(1) is required to prolong the

reaction [100, 108] One of the chief drivers for this corrosive attack is the production of

sulfides, and the diffusion of sulfur into the oxide itself [109]. The last sections of this chapter

will examine the role of sulfidation, which is the mechanism for the initiation stage of Type I hot

corrosion [103-105].

2.6.2 Sulfidation on Metals

Sulfidation in metallic systems has been studied in oxygen and oxygen-free environments.

Sulfur is present in unclean fuels, coal, and salts in marine environments, and behaves differently










depending on whether it is present in oxidizing environments, or those devoid of oxygen

(reducing environments). Reducing environments of sulfur are often modeled in H2S

atmospheres with low oxygen partial pressures and a fixed H2 H2S ratio in order to Eix the partial

pressure of S2. Studies involving this have shown that Ni in H2 H2S environments form almost

exclusively P-Ni3S2 which exhibits linear sulfidation behavior initially (or at lower temperatures)

and then grows parabolically [110-111] due to rapid sulfur diffusion along grain boundaries

[112]. In Cr-containing alloys, the sulfides come closer to a 1:1 ratio of CrS as the temperature

increases as determined by XRD and TEM, with a layered structure exhibiting inward anion

diffusion, and an outer layer exhibiting outward cation diffusion [113]. This duplex sulfide layer

is also seen in alloys where the rate-limiting mechanisms are similar with an outer layer of Ni3S2

and an inner layer mix of nickel, chromium, and aluminum sulfides [1 14-1 15] due to decreased

the sulfur activity.

In sulfidation experiments performed in oxidizing conditions, which are the focus of this

study, either SO2 is mixed with the oxidizing atmosphere (usually air or Oz), SO2 is used alone,

or H2S is added to oxygen. In all these situations, the Po2 is usually high enough to begin initial

oxidation of the metal, and sulfides are absent since these conditions are above their dissolution

pressure [116-117]. In oxidation, the role of S is initially one of an impurity dopant that

accelerates oxidation through the creation of vacancies [1 18-1 19]. Sulfur can diffuse rapidly

through grain boundaries, pores, and other high surface energy defects and stabilize them,

allowing fast transport of other ions [122-124]. This can be accelerated by the dissociation of

SO2 in these defects, which increases the oxygen and sulfur partial pressures [125-127].

However, sulfur can build up at sufficient scale thicknesses to cause sulfide formation. This will

be elaborated upon in section 2.6.3.









Whenever SO2 and 02 are preSent below 700oC, they can react to form SO3 [125], a gas

above 45oC, via the reaction

2SO2 + 02 + 2SO3 (2-17)

The formation of SO3 CauSes different reactions with the metal, as it is more oxidizing [128] and

therefore sulfidizing [129] than its dioxide counterpart. These conditions make it more likely to

form sulfates, which, as with hot corrosion, can rapidly attack the oxide or metal [130-131].

However, the effects of SO3 are minimal above 800oC in that it becomes unstable and will

readily decompose into SO2 and Oz. SO3 alSo chemisorbs on the oxide surface slower than SO2

[128]. Furthermore, the reaction on Equation 2-16 occurs at slow rates, requiring a platinum

catalyst to stabilize the reaction at higher temperatures [128]. Therefore, the effects of SO3 may

only be relevant in specific service conditions in modeling Type I hot corrosion.

2.6.3 Sulfidation on Metal Oxides

In metal oxide scales adherent to metal alloys, sulfur has been shown to migrate towards

the scale/alloy interface. Sulfur is also present in pores, cracks, and grain boundaries [127, 132-

135]. At the scale/alloy interface at extended times, the amount of sulfur continues to build up

while the scale/gas interface moves further away relative to the scale/alloy interface due to oxide

growth [136-139]. This reduces the amount of oxygen near the interface [140]. When the Ps2 is

high enough, and the Po2 is low enough, sulfide phases begin to stabilize and their growth

becomes faster than that of the oxide [126-127, 130-131, 139, 140-146]. The formation of these

sulfides destabilizes the scale adherence to the substrate [135], causing the formation of cracks

and pores, which leads to scale spallation [120, 127, 133, 138, 140]. These cracks allow the gas

species to migrate faster to the interface, accelerating corrosion. Due to the complex and open

structures of these sulfides, ionic species are able to diffuse faster though the sulfide, which also

increases the oxidation rate [1 11, 121, 126, 133, 147]. This mechanism of premature oxide









failure because of sulfur buildup at the oxide/alloy interface has been dubbed the "sulfur effect"

by Lees and Fox and is illustrated in Figure 2-14 [120, 139]. If enough Ni3S2 is present, it can

react with Ni to form a low melting liquid eutectic, exacerbating the situation [130, 146].



MIOx so02 \1 02 OS2 MOx ~jso2 M' 02-S2









Figure 2-14. Schematic showing the formation of metal sulfides (a) under an initial metal oxide
layer (b) in simultaneous oxidizing and sulfidizing conditions. The various proposed
transport mechanisms are shown.

While it is clear that sulfur migrates towards the scale/alloy interface, the mechanism

behind this process is not entirely agreed upon. Two schools of thought have developed as

drawn in Figure 2-14. Originally, it was believed that sulfur diffused as S2- anions through the

lattice, accumulating at the interface [119, 122, 142, 144, 148-149]. However, other studies have

rej ected this notion stating that diffusion rate is too slow for this to be seen in experiments [1 18,

130] and, with Cr203, the solubility of S or S2 is too low [134]. Furthermore, the S2- anions

would eventually have to climb up a concentration gradient as the Ps2 required to form sulfides is

significantly higher that of the corrosive gas at the gas/scale interface [13 8, 141].

The other theory is that the sulfur migrates by gaseous diffusion of SO2 [118, 123-124,

130, 132, 134, 138, 140-141]. The SO2 WOuld flow via cracks and pores, or along high-angle

grain boundaries to the scale/alloy interface where one of three reactions are possible [150]:

2yM + SO2 = 2MO + V/2 S2 (2-18)

xM + SO2 = MxS + 02 (2-19)









(2x+y)M + SO2 = 2MO + MxS (2-20)

This third reaction is unlikely to occur, while the first allows for the formation of free sulfur,

which increases the Ps2, and the second causes sulfide formation (although it does raise the Po2,

which is generally counteractive to sulfide formation). Indeed, in SEM studies with Cr and Ni-

Cr alloys exposed to SO2 that developed compact chromia scales, no sulfide formation took

place at the scale/alloy interface, while porous scales developed sulfides [117, 134]. This

mechanism is disputed by other studies stating that gaseous diffusion is unlikely due to the size

of the SO2 mOlecule [142], and studies with high S contents at grain boundaries absent of voids

still formed sulfides at the scale/alloy interface [122, 139].

2.6.4 Sulfidation in Ni-Cr-Al Coatings

As has been shown, sulfur can reduce the effectiveness of bond coats, even in highly

oxidizing conditions. As described by previous publications, sulfidation processes for these

coatings resemble the initiation stage of Type I hot corrosion [90, 99, 107, 130]. Ni-Cr-Al alloys

have been designed to resist against sulfidation attack and are relatively high in Al and Cr,

mainly because the S and O diffusivities in Al203 and Cr203 are l0wer than in NiO [120, 143,

148, 151]. In sulfidation attacks, Al203 is slightly more susceptible to SO2 attack [99] by

3 SO2 + Al203 + 2Al3+ + 3 S2- + 302- (2-21)

Therefore, some applications, especially those experiencing hot corrosion, are designed to allow

for Cr203 prOtective scales rather than Al203 to grow, even though chromia grows faster [73].

In addition, rare earth elements, yttrium, and silicon are commonly added as getters for O

and S. These elements have been shown to decrease corrosion rates as well as spallation and

scale degradation in sulfidizing environments [124, 133, 151]. This occurs when reactive-

element grain boundaries phases such as NiSY, which react with S first [152], prevent the

sulfidation of the other alloying elements.









2.7 Calculations of Oxidation/Sulfidation

Thermodynamic calculations have been used to describe and predict a variety of materials

applications, especially the development of phase diagrams. Calculations of the Al-Cr-Ni

ternary have already been performed (see Section 2.4). The study of oxidation by calculations

for this system was limited until recent publications compiled and optimized thermodynamic

data. Previous studies of the Al203- 203 System used the quasichemical model for non-gaseous

phases and modeled the phases as a single solid solution with a miscibility gap [153]. The

quasichemical model was used for the Cr-Ni-O system [154], and, combined with the sublattice

model descriptions of the Cr-Ni-O and Al-Ni-O systems [43, 155], an Al203- 203-NiO ternary

was constructed [6]. Saltykov' s analysis of these ternaries allowed one of the more

comprehensive descriptions of the Al-Ni-Cr-O quaternary system using free energy minimization

[156] software to produce multiple plots that graphically described the system [6]. This

approach was also used by Seifert et. al. to assess the AINi-Cr-Ni-O system [7]. However, little

work has been done to model sulfidation attacks of this system.

M-O-S systems for Fe, Ni, Co, and Cr were developed using Gibbs energy minimization

techniques with CO2 H2 and H2S/H2 ratios to set the Po2 and Ps2, respectively [8]. The idea of

using M-O-S type diagrams was also approached in previous publications [127, 142]. An

attempt to produce Na-M-O-S quaternaries of Fe, Cr, and Al for Type II hot corrosion

applications was also performed by Li and Gesmundo [157] based on previous techniques of

overlaying "quasi-ternaries" and finding stable quadruple points [158-159]. Through all these

publications, no work has been done to attempt to describe alloys or even their mechanical

mixtures. This dissertation will fill these gaps by calculating the stability ofNi-Cr-Al alloys and

their mechanical mixtures in oxidizing and sulfidizing atmospheres. These diagrams will be

plotted as potential diagrams, described by Yokokawa [160], which plot chemical potential










instead of composition (a traditional phase diagram). Potential diagrams are useful for showing

diffusion paths, which are straight lines on potential diagrams, and for visualizing phases present

based on the changing activities of various reacting elements of an oxidizing and/or sulfidizing

system [160]. The chemical potentials can also be plotted as activities or partial pressures, for

easier interpretation. The exact methodology of these calculations will be described in Section

3.1.









CHAPTER 3
METHODS AND MATERIALS

This chapter discusses the methods and materials used in this study. This includes the

calculation of phase diagrams approach (CALPHAD) for the development of potential diagrams,

as well as the experimental design for the kinetic tests and the characterization of the materials of

this study.

3.1 Thermodynamic Modeling and Simulations

3.1.1 The CALPHAD Approach

In performing simulations by thermodynamic modeling, the CALPHAD approach was

used. This approach is shown as a flowchart in Figure 3-1. Here, one combines the information

obtained by theoretical development with that of experimental measurements and estimates to

create data that are stored as analytical expressions of thermodynamic functions with adjustable

parameters [156]. These descriptions are then optimized using a least squares regression to get

the best possible thermodynamic data [156]. From this, the data are compiled into stored

databases, from which the desired information for a particular study can be obtained. This

method prevents the use of a "black box" design and allows the data to be adjusted, as opposed

to some other calculation methodologies [161].

From these databases, one can then use a thermodynamic software program to obtain the

desired information. This is done by computing an equilibrium and then graphically presenting

the phase diagram from the initial equilibrium. These diagrams are then compared and

contrasted with the existing experimental data to determine if database adjusting is needed.

Lastly, the calculated diagrams are utilized for developing and designing applications in industry

and research. This study will stress this last part of the CALPHAD approach--the calculation of

diagrams from previously developed databases.


















I I









Databalse~s
Publicatlilons







Applications

Figure 3-1. Flowchart detailing the Calculation of Phase Diagrams approach. This study is
concerned mostly with the equilibrium calculations.

3.1.2 Databases and Software

The databases used in this particular study were the Scientific Group Thermodata Europe

(SGTE) Standard Potential Database (SPOT3) obtained from the Russian Academy of Sciences

(TCRAS) and other sources [162-165], as well as the SPINT4 database, developed from previous

Ni-Cr-Al-O studies [6-7]. Both databases contain thermodynamic descriptions of Ni, Cr, Al, and

O. However, only the SPOT3 database contained descriptions for S and its sulfide and sulfate

phases. The SPOT3 database, though, only takes into account thermochemical reactions

between stoichiometric compounds that allow for no solutions--a mechanical mixture--whereas










the SPIN4 database allows for solution phases. The use of mechanical mixtures to model a

system has been previously published [166]. An attempt was made to append the SPIN4

database with the SPOT3 descriptions for the sulfur, sulfide, and sulfates phases.

The Gibbs' free energy minimization software used for this study is Thermo-Calc version

Q. Using this software, the desired phase or potential diagrams was obtained by:

1. Selecting the desired elements
2. Accessing the relevant thermodynamic information on each element and compound formed
between each element
3. Setting conditions for each degree of freedom (eg. temperature, pressure, composition) so
as to satisfy Gibbs' Phase Rule:

P+F= C+2 (3-1)

4. Computing an equilibrium using Gibbs' free energy minimization algorithms
5. Assigning one condition per axis of the desired diagram
6. Mapping from the initial computed equilibrium along each axis to determine phase
stability regions.

From this method, graphical plots of phase and potential diagrams were created.

3.2 Materials and Sample Preparation

The materials used for the experimental aspects of this dissertation were obtained from

Alfa Aesar with the purity determined by chemical analyses from the company. The metals used

are

* Ni slugs: 99.98% metals basis
* Al shot: 99.999% metals basis
* Cr granules: 99.999% metals basis

These metals were measured by weight and combined into either the Ni-8Cr-6Al or Ni-22Cr-

11Al alloys, which were approximately 12.5 g for Ni-8Cr-6Al and 7.5 g for the Ni-22Cr-11Al

alloys. The mixtures were placed in a Centorr chilled-copper arc-melter that used a non-

consumable tungsten electrode. The chamber was evacuated and backfilled with argon gas three

times. Titanium getters were melted initially, followed by the mixture of interest. The melted









and solidified button was flipped and remelted four times in order to ensure homogeneity. These

arc-melted buttons were then heat-treated at 1200oC for 4 hours in vacuum (better than 10-4 torr)

using an Elatec Technology Corporation vacuum furnace, using a He(g) quench. In addition,

some of the Ni slugs as well as arc-melted Ni-1 3.6Al and NiAl were used in the oxidation

studies. The compositions were checked by energy dispersive spectroscopy.

The specimens were then sliced using an Allied Techcut 4 diamond saw at low speeds (<

300 RPM). The slices, approximately 0.7 mm in thickness, were ground with SiC abrasive paper

of 60, 180, 320, 600, 800, and 1200 grit on all sides. They were then polished on velcloth with 1

Clm polycrystalline diamond suspension. The polished slices were measured using calipers to

measure the various dimensions of each specimen to determine the surface area of each

specimen. The surface area was approximately 1.7 to 2.8 cm2. Each polished sample was

ultrasonically cleaned in acetone and then methanol for 10 minutes each. Some specimens to be

characterized were etched with aqua regia for macroetching and/or equal parts HCI and ethanol

for microetching.

Some specimens had a strip of Pt paint applied to one surface. This is to allow for the

classic Pt-marker experiment to be conducted in which the movement of the scale/alloy interface

can be measured [41].

3.3 Thermogravimetric Analysis

The thermogravimetric analysis (TGA) was performed using a Setaram Setsys Evolution.

Figure 3-2 shows a schematic of the TGA used for this study. The Setsys TGA works by having

a balance whose deflection in either direction was measured using a laser. Each cleaned,

polished specimen was placed in a silica crucible suspended by a series of quartz hooks from the

balance. A counterweight is used to balance the weight. The following gas mixtures were used:










* Air
* He + 0.21 02 + 0.02 SO2
* He + 0.21 02 + 0.10 SO2

In the case of air, the gas flowed over the specimen chamber and the instrument head. In the

case of the Ol + SO2 mixtures, ultra-high purity (4.5 Grade) He was passed through the

instrumentation head and into the specimen chamber via the anti-convection tube. The Oz + SO2

mixture was made possible by using analog volumetric flowmeters, which were then flowed

through the auxiliary gas inlet to the specimen chamber and mixed with the He. The Setsys had

its own digital flow controllers, so the desired gas mixture could be established. The total gas

flow used was 25 mL/min, which is the Setaram recommended flow rate for this instrument.

This flow rate was selected to prevent turbulence in the furnace chamber. The flow of the He

carrier gas was also greater than that of the corrosive auxiliary gas to prevent attack of the

instrumentation head. The gas then passed out of the chamber through an exhaust outlet. A type

S thermocouple, encased in alumina was inserted into the chamber adj acent to the specimen

crucible in order to measure the temperature of the specimen.

Each sample run was performed by flowing only carrier gas (He) through the entire

chamber at 200 mL/min for 10 minutes to remove most of the reacting oxygen and other species

in air. The flow was then decreased to 20 mL/min to allow for the measure weight of the

specimen to equilibrate for 10 minutes. The chamber, with the carrier gas still flowing, was then

raised to the desired temperature for the experimental run (either 800, 900, or 975oC) at

50.C/min. Those samples not exposed to sulfidizing gases did not require a silica crucible and











DIGR ArL DISPLAY
Furnae temnpeamture
Carrier g as flowr rate
Auxiliary g as flow~ rate
Pressur in the anallysis chamber
DTB, DSC TGA or ~TMAP signal


Alurr r--tut-e ........--


Colingii~ wateriiii








Figue 3-. Scemaic o theSetss Eoluton (GA oly)

wereheaed o 100. intea of975C i a t cucile.Upo reacingte eirdtepraue

the chmber ws heldfor 2 inute to alow thespecimn to rach te tmeaueoh

furnace,~ ~ ~ ~~~~~- and--- toalwfrteboac ftecrirgst qiirateforthespcme.Afe

thi, he esredauilaryga wa aded I t e ase oftoeseiesi ar h are n


aluxilriary gase weebt wthdt i.Ec xeien a hswyfr10h.A h

concluso ftetsteaxlaygswssu of n h hme a olda9Cmn









No baseline calculations were performed since the desired measurement was a weight change at

a constant temperature. In addition, some oxidation tests were carried out in a Lindberg/Blue

1200oC tube furnace to test specimens for less than 100 hr.

The data obtained from the TGA experiments were analyzed to determine the parabolic, or

other rate constants, gained from the growth of oxides and/or sulfides on each specimen. In the

previous publications on high temperature oxidation discussed in Chapter 2, the weight change

of the specimen is normalized by dividing by the surface area exposed. This way, sample of

different size and surface area can be properly compared. The specimens used in this study were

made from arc-melted buttons, as described in Section 3.2. Each specimen cut from each button

was elliptical in nature, and the resulting surface area being

A = 2x-a b +P- t (3 -2)

where A is the surface area, a is the half-length of the longer dimension, b is the half-length of

the shorter dimension, t is the thickness, and P is the perimeter of the specimen as described by

P =2 i M (a + b (3-3)

In analyzing the growth rate constants of any oxidation study, the normalized weight

change is plotted on one axis and the time on the other so that the slope of a linear regression of

the experimental data is growth rate constant. If growth is occurring linearly, plotting

normalized weight change over time will yield a straight line with a slope equal to kL. In mOst

studies of oxidation and sulfidation, normalized weight change is plotted squared against time,

revealing kP. However, a study by Pieraggi argues that this method can only be used for pure

metals or simple alloys [167]. His study plots normalized weight change over the square root of

time to determine the initial kinetics and differentiate that from the steady-state kP, which is

desired. This study follows Pieraggi's method. Lastly, the parabolic rate constants for each










composition and condition were plotted Arrheniusly in order to determine what, if any,

activation energy could be garnered from these experiments. Table 3-1 lists the experiments for

the alloys in this study.

Table 3-1. List of experimental conditions performed for oxidation of alloys for 100 hr in 1 bar
of gas at 25 mL/min.
Allow (Weight Percent) Atmosphere (ar) Tempeature (oC)
Ni Air 800
Ni Air 900
Ni Air 1000
Ni Air 1100
Ni-13.6Al Air 800
Ni-13.6Al Air 900
Ni-13.6Al Air 1000
Ni-22Cr-11Al Air 800
Ni-22Cr-11Al Air 900
Ni-22Cr-11Al Air 1000
Ni-22Cr-11Al He + 0.21 02 + 0.02 SO2 800
Ni-22Cr-11Al He + 0.21 02 + 0.02 SO2 900
Ni-22Cr-11Al He + 0.21 02 + 0.02 SO2 975
Ni-22Cr-11Al He + 0.21 02 + 0.10 SO2 800
Ni-22Cr-11Al He + 0.21 02 + 0.10 SO2 900
Ni-22Cr-11Al He + 0.21 02 + 0.10 SO2 975
Ni-31Al Air 800
Ni-31Al Air 900
Ni-31Al Air 1000
Ni-8Cr-6Al Air 800
Ni-8Cr-6Al Air 900
Ni-8Cr-6Al Air 1000
Ni-8Cr-6Al He + 0.21 02 + 0.02 SO2 800
Ni-8Cr-6Al He + 0.21 02 + 0.02 SO2 900
Ni-8Cr-6Al He + 0.21 02 + 0.02 SO2 975
Ni-8Cr-6Al He + 0.21 02 + 0.10 SO2 800
Ni-8Cr-6Al He + 0.21 02 + 0.10 SO2 900
Ni-8Cr-6Al He + 0.21 02 + 0.10 SO2 975


3.4 Characterization

This section details the methods and procedures of materials characterization for each

specimen. Data obtained from these various techniques was used to identify the microstructures

formed from and mechanisms of oxidation and sulfidation on these alloys.









3.4.1 X-Ray Diffraction

Each polished and oxidized specimen was analyzed using X-Ray diffraction (XRD). The

specimens were adhered to a glass slide using double-sided tape and placed in a Philips APD

3720 XRD. The specimens were exposed from 10 to 90o 26 at a rate of 0.5 s per step using 40

kV and 20 mA from a Cu Koc radiation source. The patterns were then treated according to the

software protocol of the APD 3720 to determine the d-spacings detected. These were then

compared to the files from the JCPDS International Center for Diffraction database to determine

the phases diffracting at those 26 angles.

3.4.2 Scanning Electron Microscopy

After XRD, the specimens were then analyzed using Scanning Electron Microscopy

(SEM). First, each sample, whether oxidized or not, was affixed onto an aluminum mount using

a small amount of carbon paint and analyzed from the top of the surface. The SEM used was a

JEOL SEM 6400 equipped with Oxford Link ISIS energy dispersive spectroscopy (EDS) and

Oxford OPAL electron backscattered secondary electron detector (EBSD), operated at 15 kV.

Semi-quantitative analysis was performed using correction matrices for atomic number,

absorption, and fluorescence (ZAF) [166]. The grain size of the substrate materials was

determined by using line-intercept stereology methods from optical light micrographs taken from

a Leco Neophot 21 optical microscope.

After this analysis, the specimens were viewed in cross-section. This was performed

applying an electroless Ni layer between 1 and 5 Clm thick using Buehler Edgemet chemical

system for scale adhesion and edge retention. Next, the specimens were help upright using

stainless steel clips, cast into an epoxy mixture, and allowed to cure overnight at room

temperature. These epoxy-mounted specimens were then sectioned using the Allied TechCut 4










and ground using 600, 800, and 1200 grit SiC abrasive paper on the Allied MetPrep3 with an

AP-3 autopolisher. They were then polished using 3 Clm diamond suspension on nylon, 1 Clm

diamond suspension on velcloth, and 0.1 Clm diamond suspension on Chem-Pol B cloth. Lastly,

the specimens were thermally carbon coated in order to make the surface electrically conductive,

and were analyzed on the SEM.

3.4.3 Electron Microprobe

Some of the cross-sectioned epoxy-mounted specimens were analyzed using wavelength

dispersive spectroscopy (WDS) in a JEOL Superprobe 733 electron microprobe (EPMA). These

were performed using a 1 Clm size beam at approximately 1 nA that was scanned at various

intervals (usually 1 Clm) to detect the change in composition, not only from phase to phase, but

across the scale and alloy depletion zones. The compositions were calculated using the ZAF

correction technique also used for EDS.

The activities of the elements from each of the line scan were calculated from the Thermo-

Calc software using the appended SPIN4 database with S descriptions. This was performed by

entering the microprobe data from each point of a line scan into the software at the temperature

the sample was oxidized and computing an equilibrium to determine the equilibrium activities at

each probe.









CHAPTER 4
THERMODYNAMIC CALCULATION RESULTS

This section shows the diagrams created using the Thermo-Calc software. This chapter is

divided into three sections that detail the development of various phase diagrams of the Ni-Cr-Al

system, the temperature-potential diagrams, and potential diagrams at fixed temperatures and

pressures. Phase fraction diagrams are also included throughout the chapter to give a better

visual understanding of mechanisms and reactions occurring.

4.1 Calculations of Ni-Cr-Al Alloys and Mixtures using Phase Diagrams

4.1.1 Binary Systems

Before attempting to analyze the more complex systems, it is important to validate the

simpler binary systems that will be the basis for later calculations. Using the SPIN4 database,

the Ni-Al, Ni-Cr, and Al-Cr binaries were calculated as shown in Figures 4-1, 4-2, and 4-3,

respectively. The green lines represent various tie lines of two-phase equilibria. These diagrams

agree with those found in the ASM Handbooks as seen in Figures 2-3, 2-4, and 2-5 for Al-Ni,

Cr-Ni, and Al-Cr, respectively [30]. Differences include some of the solubility ranges for

several phases including the Al-Cr diagram, where all the intermetallic phases are stoichiometric

compounds with no solubility, unlike in Figure 2-5. It should be noted that the All3 2 and

AlliCr2 intermetallics in Figure 4-3 are the same as AlzCr and AlSCr, respectively, in Figure 2-5.

It should also be noted that the Ni-Al diagram calculated in Figure 4-4 was done without the

low-temperature Ni3Als phase. In Figure 4-4, this is restored. However, its position differs from

that of Figure 2-3. Since this phase is only stable at temperatures lower than the experiments to

be performed in this study, and since it is rarely discussed in literature, it will not be used for

further calculations. Lastly, the SPOT3 database was not used to describe these binaries since

each phase has no solubility for other elements, the liquids of each element are immiscible, and










the diagrams merely show a series of lines. However, the SPOT3 potential database contains

information on the solid-gas reactions that will be elaborated upon in Sections 4.2 and 4.3.

1800

;1600-

1400 -lonic Liquid


E 1200 -

1000




200-

40


0 0.2 0.4 0.6 0.8 1.0
Weight F~raction Al

Figure 4-1. Temperature-composition binary phase diagram of the Ni-Al system calculated from
the SPIN4 database.

2000

1800
1600 -lonic Liquid

1400-



6100-



400-/



0 0.2: 0.4 0.6 0.8 1.0
Weight Fraction Cr

Figure 4-2. Temperature-composition binary phase diagram of the Ni-Cr system calculated from
the SPIN4 database.

















-1400

i 1200-

S1000 ,-



600 --


200 --

20

0 0.2 0.4 0.6 0.8 1.0
Weight Fraction Cr

Figure 4-3. Temperature-composition binary phase diagram of the Al-Cr system calculated from
the SPIN4 database.

1800

1600-
1400 -Ionic Liquid




1400-





200-

20

0 0.2 0.4 0.6 0.8 1.0
Weight Fraction Al

Figure 4-4. Temperature-composition binary phase diagram of the Ni-Al system calculated from
the SPIN4 database with the Ni3Als low-temperature phase restored.









4.1.2 Ternary Systems

The ternary phase diagrams were calculated using the thermodynamic data in the SPIN4

database. Figure 4-5 shows the complete Ni-Cr-Al ternary isothermal section for 900oC, where

the weight percent of the Cr and Al elements are plotted. This can be compared to the ternary

calculated by Dupin in Figures 2-9 and 2-8 with that calculated in Figure 4-6, which is in mole

percent at 850.C and in Figure 4-7 in weight percent at 1025oC. The fields of stability are often

different in size and shape in comparing the isotherms, and Figure 4-7 is more complete in

showing the Al rich regions of the phase diagram.


Cr
1.0

0.9 -d

0.8 \ .Alr
0.7
0.6 -V
AlgCr5
0.5 j'
Alger4
0.4 '
AI4Cr
0.3 /J
Ain'




Ni 0 Y0.2 0.4 ial0.6 0.8 1.0A


Figure 4-5. Isothermal section of Ni-Cr-Al ternary system at 900oC in weight fractions. This
diagram is calculated from data in the SPIN4 database.























0.15
0.10


0.5 Cr 0
o~ i0.5


1.0


0.6 0.7 0.8 0.9


Figure 4-6. Partial isothermal section of Ni-Cr-Al ternary system at 850.C in mole fractions.
The axes are chosen to compare with Figure 2-9. This diagram is calculated from
data in the SPIN4 database.

Al


0.6


0.49'/


Cr 0


1 i~


0.2 0.4 0.6


Figure 4-7. Isothermal section of Ni-Cr-Al ternary system at 1025oC in mole fractions. The axes
are chosen to compare with Figure 2-8. This diagram is calculated from data in the
SPIN4 database.



















-20








II(I
0 0.2 0.4 0.6 0.8 1.0
Mass Fraction Al

Figure 4-8. Ternary isothermal section of the Ni-Al-O2 System at 900oC. The x-axis is the
composition of Al in weight percent, and the y-axis is the logarithmic partial pressure
of 02 in bar. This diagram is calculated from data in the SPIN4 database.




NiO -













-40-


0 0 2 0.4 0.6 0,8 1.0
Mass Fraction Cr

Figure 4-9. Ternary isothermal section of the Ni-Cr-O2 System at 900oC. The x-axis is the
composition of Cr in weight percent, and the y-axis is the logarithmic partial pressure
of 02 in bar. This diagram is calculated from data in the SPIN4 database.






















cr11 I
-40 ~ ." -








-10 ~



Fiur 410 T~heN-lC-sytmsonaaseisoconcetenrsustmiohrs
at 90oC Th ue xsae h oaih f h ata rssr f0 nbr
whereas~ ~ ~ L th inr xs rete egh prensofN, CranA.Thsdgami
caclae ro aai in h PN aaae
In aditon o te N-Cr-Al11 tenay th iA-2adNiC-2trais eecluae

and ae shwn a isoherm at 0 0o nFgr n -,rsetvl.Hr h ata






presure of10 oxyen a i ba-r)O wase used owa plot the oxygenaes.These ternary subsystem stems

were~a thenC cobndwthe othe Al-C- andth Noai-Cr-A io the prmstoa hepdepictte Nfzi-Cbr-A-

syte a 90C n igr 410 I hi fgue the inner axes are ine weight percent, whi r ndA.Ti ilea the




outerxs are th yen lgarihs (in bar se d 10) of the partial presu es of es 02 in ar). usytm









4.2. Calculations of Temperature-Potential Diagrams

Calculations were performed using the SPOT3 database to develop diagrams that would

show the reactions occurring with change in temperature and the chemical potential (or activity).

These and all further diagrams show axes labeled as the partial pressure of a certain gas, in bar.

This is found by converting either the natural log of activity or chemical potential into units of

loglo bar by

In(ax)
Px =(4 -1)
In l0

pu(X)
Pr = (4-2)
x R -T n(10)

where a is the activity of a certain gas species X, P is the partial pressure of the gas species, C1(X)

is the chemical potential of a gas species (in J/mol), R is the gas constant of 8.314 J/mol K, and T

is the temperature in K.

4.2.1 Calculations with 02-SO2 Interactions

For the physical experiments used in this study, the reacting gases used were air, oxygen

(Ol) and sulfur dioxide (SO2). These results are discussed in Chapter 5, but in this section are

dealt with by thermodynamic calculations. As discussed in Chapter 2, an environment mixing

02 and SO2 Will CaUSe a reaction that can create sulfur trioxide (SO3) and other products. Using

the conditions for the experiments

1. He + 0.21 02 + 0.02 SO2
2. He + 0.21 02 + 0.10 SO2
calculations were performed to determine how the gases react with change in temperature. The

calculations for condition 1 are shown in Figure 4-11, and condition 2 are shown in Figure 4-12.

These are shown in a similar manner to CO2/CO diagrams illustrating isobars of 02 [167]. With

both diagrams, at temperatures below approximately 600oC, the reaction










02 + 2SO2 = 2SO3 (4-3)

occurs readily and SO3 is the more stable sulfur-based gas species. However, it is of much less

consequence above 900oC. Between the two temperatures, the stability of SO2 and SO3 change

rapidly with a maj or vapor transition point occurring at 707oC. He is used in the calculations as

"filler" so that the total number of moles can remain constant at unity. However, due to scale its

partial pressure is omitted.




0.25


0.20 0


0.15-


0.10-


0.05-
SO3 SO2


O 200 400 600 800 1000 1230
T (oC)

Figure 4-11. Change in partial pressure of Oz, SO2, and SO3 (in bar) with temperature using the
initial gas mixture of He + 0.21 02 + 0.02 SO2. The PHe is omitted due to scale. The
data used for calculations is taken from the SPOT3 database.

As well as these calculations, diagrams were calculated of isobaric lines of one gas in

relation to a ratio of the partial pressures of two other gases with changing temperature. For

example, Figure 4-13 shows lines of constant partial pressure of sulfur trioxide based of the ratio

of partial pressure of oxygen over sulfur dioxide. The region labeled as "unstable gas,"

occurring at high SO2 and low 02 at higher temperatures, could not be calculated due to the












0.25


0.20


0.15


0.10


0.05-


0 \.
0 200 400 600 800 1000 1200
T (OC)

Figure 4-12. Change in partial pressure of Oz, SO2, and SO3 (in bar) with temperature using the
initial gas mixture of He + 0.21 02 + 0.10 SO2. The PHe is omitted due to scale. The
data used for calculations is taken from the SPOT3 database.





-5-


o -10-





10~8 Unstable Gas
-20-


-25
400 600 800 1000 1200 1430
Temperature (oe)

Figure 4-13. The relationship between the partial pressure of SO3 in an 02-SO2 gaS mixture, with
varying temperature. All partial pressures are in bar.

















-lU
N
S-15


800 1000 1200
Temperature (oC)


Figure 4-14. The relationship between the partial pressure of S2 in an 02-SO2 gaS mixture, with
varying temperature. All partial pressures are in bar.


300 600 900 1200
Temperature (:C')


1500


Figure 4-15. The relationship between the partial pressure of 02 in an SO3-SO2 gaS mixture, with
varying temperature. All partial pressures are in bar.










evolution of more than three phases in equilibrium. In CO/CO2/02 Systems, this corresponds

with the deposition of graphite [157]. Here, it may correspond with the deposition of liquid

sulfur, but this could not be calculated and was not confirmed by any experiments. This is

continued in Figures 4-14 and 4-15, which show the isobars of S2 and 02 based on ratios of

02/SO2 and SO3/SO2, TOSpectively.

4.2.2 Calculations of Metal-Gas Interactions

Thermodynamic equilibria were calculated for several metal mechanical mixtures (meant

to represent specific phases or alloys) between 800 and 1000.C by Eixing the number of

conditions so that the degrees of freedom were zero. Then, a range of activities or chemical

potentials of the components 02 and SO2 were defined, and the diagrams were mapped in that

range. The diagrams are plotted at various temperatures using the partial pressures of either Oz

and SO2, Or Ol and S2, which can be defined from their activities or chemical potentials, as axes.

The mixtures for which calculations were performed are:

* Ni
* Ni3Al (y')
* NiAl (P)
* Ni-8Cr-6Al
* Ni-22Cr-11Al
Since no solubility in the solid state is described per the SPOT3 database, the equilibria

calculated were compared to a proprietary database that allows for solubility, SPIN4. This

database was not accessed for this study because it has no description for S. However, in using a

Ni-Cr-Al-O system, the calculated equilibria are in good agreement between the two databases

and are shown in Table 4-1.

Figure 4-16 shows the temperature-potential diagram of Ni in an environment with only

oxygen and some inert gas. Here, one can see that at higher partial pressures of Oz, NiO

becomes more stable than Ni. However, this oxide stability decreases with increasing









Table 4-1. Comparison of equilibria computed between two databases SPOT3 and SPIN4 at a
pressure of 1 bar and T = 1073 K for Ni-22Cr-1 1Al alloy (by mass) with a PO2 Of 0.22
bar. This table compares number of moles of each phase, along with the composition
(in weight fraction) of each phase.
Database Phases Moles W(Ni) W(Cr) W(Al) W(O2)
NiO 0.134 0.786 0 0 0.214
SPOT3 NiAl204 0.424 0.332 0 0.305 0.362
NiCr204 0.441 0.259 0.459 0 0.362
Halite (NiO) 0.138 0.777 9.87e-4 4.75e-3 0.217
SPIN4 Spin3 0.862 0.290 0.263 0.131 0.216
Ni [Cr,Al]204)


temperature. Figures 4-17 and 4-18 show the same conditions as that for 4. 16, except for the

addition of 2 mol % SO2 and 10 mol % SO2, TOSpectively. It is plain to see that the stability of

the Ni and the nickel oxide decrease dramatically with even small sulfur dioxide additions. At

higher partial pressures of oxygen at lower temperatures, the nickel sulfate becomes stable, and

at lower oxygen partial pressures, the nickel sulfides become stable--Ni3S2 is the most stable,

but NiS, Ni3S4, and NiS2 Can alSo be present. The areas labeled "unstable equilibrium" are areas

where the software could not calculate, and therefore not map, a stable equilibrium. This is

likely due to the evolution of some gas, which creates too many phases to calculate a stable

equilibrium. These conditions are mostly observed at high Po2 at low temperatures, or high Pso2

at high temperatures. Diagrams for mixtures of Ni, Ol, and other metals (Al and/or Cr) were not

able to be calculated and are not shown.

4.3 Calculations of Potential Diagrams

The results for the calculations of Ni in SO2/02 CHVITOnments at 800, 900, and 1000.C are show

in Figures 4-19a, 4-20, and 4-21, respectively. Figure 4-19b also shows the S2-O2 pOtential

diagram for Ni at 800.C for comparison with Figure 4-19a. As with section 4.2, all calculations

were performed using data from the SPOT3 database unless otherwise noted. At high Po2 and

low Pso2, the NiO becomes stable from the oxidation of Ni. Increasing SO2 Can CaUSe the










2000


1800

1600

1400

1200


8000 I/I

-16 -14 -12 -10 -8 -6 -41 -2 0
log PO2 (bar)

Figure 4-16. Stability diagram of Ni and its oxide with varying temperature and partial pressure
of oxygen (in bar).


2000
1800
1600
S1400
1200


S800


400
200


-30 -25 -20 -15 -10 -5 0
log PO2 (bar)
Figure 4-17. Stability diagram of Ni and its oxide with varying temperature and partial pressure
of oxygen (in bar) with a constant partial pressure of sulfur dioxide at 2 mol %.










2000

1800 -Na

1600 -1 Undefined Nq
Equilibrium
^1400-
o u
1200-


6 00 "'
400 Niso



200 -r ~Undefined
Equilibrium
-30 -25 -20 -15 -10 -5 0
log PO2 (bar)
Figure 4-18. Stability diagram of Ni and its oxide with varying temperature and partial pressure
of oxygen (in bar) with a constant partial pressure of sulfur dioxide at 10 mol %.

formation of NiSO4. Decreasing 02 at higher SO2 COntents cause the formation of Ni sulfides--

Ni3S2, NiS, Ni3S4, and NiS2 at increasing Pso2. The Ni3S2 1S a liquid at these temperatures. At

high Pso2 and high or low Po2, HO stable equilibrium could be calculated. It is possible that this is

a gas phase, which at low Po2 is almost entirely SO2, whereas the gas at high Po2 is a mixture of

SO2, Oz, and SO3 (See Table 4-2). As temperature is increased, the resistance of Ni to oxidize

decreases, but attack by sulfur species is more prevalent.

Table 4-2. Comparison of gas species (at mole fractions > 10-10) present in the unstable
equilibrium regions of Figure 4-19 at low PO2 and high PO2. These mole fractions are
calculated based on ideal gas behavior.
Gas Species (low PO2) Mole Fraction Gas Species (High PO2) Mole Fraction
SO2 0.999 SO2 0.356
SO 4.59e-6 02 0.356
SO3 4.14e-6 SO3 0.288
S20 8.92e-7
S2 3.84e-7














-10-
-10-
-15- NiS
NilS~ -15-
S-20 -NiS2- Ni352 -2-0-
-25 e
S3: ;;-25 NiSO4

oP a -30-
S-35 -Ni NiO
-40 I -35 -( Ni NiO
-45 1 -40-
-50 -45
-50 -40 -30 -20 -10 0 -45 -40 -35 -30 -25 -20 -15 -10 -5
(a) log PO2 (bar) (b) log PO2(bar)
Figure 4-19. Ni potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. U.E. is an
abbreviation for undefined equilibrium. Published in [170].


-50 -40 -30 -20 -10 0
log PO2 (bar)
Figure 4-20. Ni SO2-O2 pOtential diagram at 900oC. U.E. is an abbreviation for undefined
equilibrium. Published in [170].













-- Undefined iO -
-10 Equilibrium

-15-

9 -20 NiS -NCi3S2

~-25 NiS2
S-30-
,9 -35
-4 -Ni NiO

-45-

-50
-50 -40 -30 -20 -10 0
log PO2 br
Figure 4-21. Ni SO2-O2 pOtential diagram at 1000.C. U.E. is an abbreviation for undefined
equilibrium. Published in [170].


Figures 4-22a, 4-23, and 4-24 show the SO2-O2 pOtential diagrams for Al at 800, 900, and

1000"C, respectively. Figures 4-25a, 4-26, and 4-27 show the SO2-O2 pOtential diagrams for Cr

at the same respective temperatures. Figures 4-22b and 4-25b show the S2-O2 pOtential diagrams

for Al and Cr, respectively. Comparing these diagrams with those for Ni, one can tell that Cr

and especially Al have greater affinities for Oz aS they will oxidize at a lower Po, than Ni. In

addition, Al and Cr will also sulfidize at lower S activities, and these sulfides will oxidize at

lower Po,. Al and Cr were calculated as having only one sulfidation product each, as opposed to

the four exhibited by Ni at these temperatures. Figures 4-28, 4-29, and 4-30 show calculations of

Ni3Al, or y', at 800, 900, and 1000"C, respectively. Due to the Gibbs' Phase Rule (Equation 3-

1), each phase field contains two phases. At low partial pressures of both gases, the y' phase was

calculated and, to satisfy the phase rule, Al is in equilibrium as excess in the intermetallic. In

this system, Al is the more reactive element, and reacts with S and/or O at lower partial










pressures. In all cases, the Al203 phase is oc. Increasing the Oz eventually depletes the y' phase

of Al, causing it to form the y (Ni) phase. Further increasing Po, causes the alumina to react with

the y to form a spinel phase (NiAl204). Al forms only an Al2S3 Sulfide, and similar to what is

shown in Figures 4-19-4-21, the Ni forms a variety of sulfides depending on the Pson. At 900

and 1000"C, the Ni3Sz becomes the most stable sulfide, as the others become degenerate cases.

Figures 4-31, 4-32, and 4-33 show calculations of NiAl, or P, at 800, 900, and 1000"C,

respectively. These diagrams are similar to those for Ni3Al, except that P is the stable phase, and

that there is enough Al present to keep Al203 Stable up to 1 bar Po,. Also, the y' phase was

shown to have a larger stability range than P.



(J.E 0Unstable
-5 Unstable -5 A2S3 Equilibrium
-10 Equilibrium C1 -l
-15 -~ -15

-2 5 -25 l0


-40 -40
-45 -'- -4

5 -0 A a 530

-40 -40 -30 C2 1 -40 3 -2 -1 0


(a) log POz (bar) (b) log Po2 (bar)

Figure 4-22. Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in [170].












-5 Unstable
-10 Equilibrium

-15-

S-20
-25-



3 -35 lzS/ Al203
-40-

-45 Al(1)
-50
-E 0 -40 -30 -20 -10
log PO2 (bar)
Figure 4-23. Al SO2-O2 pOtential diagram at 900oC.



-10-
Gas
-20-

S-30
t3 I /,IAl2S3
S-40-

bD-50-
30 Al203
-60-

-70 -1 Al~l)

-80
-E 0 -70 -60 -50 -40 -30 -20 -10
og PO2 (har)
Figure 4-24. Al SO2-O2 pOtential diagram at 1000.C.













-5- Unstable -5- CrSb
-10 Fquilibtrinni -10-
-15- -15-

S-20 rS 9-20-


S-30- -30 -1 Cr Cr203
co CrzO3 ~
.2-35- -35-
-40 r-40-
-45 -1 -45
-50 a50
-50 -40 -30 -20 -10 0 -50 -40 -30 -20 -10
(a) log POt (bar) (b) log Po2 (bar)

Figure 4-25. Cr potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in [170].


-50 -40 -30 -20 -10
log PO2 (bar)

Figure 4-26. Cr SO2-O2 pOtential diagram at 900oC.


















~-20-


Icl -30-

-35

-40-

-45-

-50
0


Figure 4-27. Al



Undef
5-Equili
-10
-15-1 Al,.S
NiS


-40 -30 -20 -10
log PO2 (bar)
SO2-O2 pOtential diagram at 900oC.


(a) log PO7 (bar) (b) log PO2 (ar)
Figure 4-28. Ni-13.6Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. U.E. is an
abbreviation for undefined equilibrium. Published in [170].












05
-5- Undefined

-0-Equilibrium

-15 **

S-20-

-25 AI S3
NiO
-3 NiAlgO4

-35 v Ap
AleS
-40- -
-45 -1 u' ,,N;ri -


-50
-50 -40 -30 -20 -10 0

log PO2 (bar)

Figure 4-29. Ni3Al SO2-O2 pOtential diagram at 900oC.





/ iAlpL
-5- Naiss,,
Undefined
-10 Equilibrium ity,,
-15- is


S-25

Oj Niss,,,
AlgS3\ NiO
-30 N, NiAlp4 -

-35 lAlzO3

-40-

-45 Al nlo Ni
-50
-8 0 -40 -30 -20 -10 0
log PO2 (bar)

Figure 4-30. Ni3Al SO2-O2 pOtential diagram at 1000.C. Published in [170].












0Undefin~ed Al: L Ni5pAl20 ,
-5- Equilibrium /TSO 5- AlgS3 Niz5,,
-10 AlgS -10
A12S3 NiS j0 1
-15- Ni 84 Ni S,, P 15
m -20- -20

-25 A1283~ y & -25 _Al201
Al23 AS A 20zi
S-30 i y-3 Nso

-35 -Al2S3 N Alg~z -35-
-40 l03A NiAl204 40 -4N l
-45 --Y' -45 -A l~ ilO
Al Alz
-50 -50
-5O -40 -30 -20 -10 0 -50 -40 -30 -20 -110 0b
(a) log PO2 (bar) (b) log PO2(bar)
Figure 4-31. NiAl potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. U.E. is an
abbreviation for undefined equilibrium. Published in [170].



-5- neie
-10 Equilibrium
AlaO3
-15- is



-25- AI)
O /I Nilp

$ -35-
AlzSI
-40 I -- a
Al4;,
-45 r'
Alpg,
-50
-8 0 -40 -30 -20 -10 0
log PO2 (bar)
Figure 4-32. NiAl SO2-O2 pOtential diagram at 900oC.











-5-
U~nde~tined
-10 Equilibrium '4' -
-15-


S-25-
-30 Ni Alp3




41-350 -40~ -30-2 -0




log POz (bar)
Figure 4-33. NiAl SO2-O2 pOtential diagram at 1000.C. Published in [170].

Figures 4-34, 4-35, and 4-36 show calculations of the Ni-8Cr-6Al mixture at 800, 900,

and 1000"C, respectively. As per the Gibbs' Phase Rule, each phase Hield must now have three

phases in equilibrium. The base metal at low partial pressures is shown as a mixture of y-Ni, y',

and Cr--in reality the alloy should have y-Ni as the only stable phase at these temperatures.

However, the other phase fields agree with studies that show alumina and chromia stable at

lower partial pressures of 02 whereas NiO and spinel are stable at higher partial pressures.

While Al has a higher affinity for O, Cr is the element that forms sulfides (CrS) at the lowest

Pson. At higher temperatures, Ni3S2 again becomes the dominant Ni sulfide, whereas NiO and

spinel become less stable.





























































-40 c

CrS Ni
-45- v'

-50
-50 -40


Figure 4-35. Ni-8Cr-6Al


-30 -20 -10 0

log PO2 (bar)
SO2-O2 pOtential diagram at 900oC. Published in [170].


* -


I


U ~-------


Ildln I lI:l.J ~:~

Equilibriumi .Lo =\ '


Al2S3
NSC A 203
All,



Ni Ni(Cr.Al O,
AIP NiO
.11 S, Cr Cr 03

-! Ni

Nia I I Ilcha


Undenined

/AlgO Cr,03


Ala, Cr

crs y' Ni









Cr


U


-10-

-15-

~--20-


-30 -

-35 -

-40 -

-465-

-50
-t
(b)


50


-20

-25

-30

-35

-40

-45

-50


Nio


-40 -30 -20 -10
log PO, ( ball


-40 -30 -20
log PO, ( bar)


Figure 4-34. Ni-8Cr-6Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published in
[170].


2 -20

S-25
O
S-30












-5 -Ninlp -
Undefined c 0,~
-10 Equilibrium

-15 lfo
Crs

-20 -




-4 -21 -j


Ns ,03 N i CiA )

540


-50 -40 -30 -20 -10 0

log PO2 (bar)
Figure 4-36. Ni-8Cr-6Al SO2-O2 pOtential diagram at 1000.C. Published in [170].

In the composition with higher concentrations of Cr and Al, the mixture oxidizes at lower

Po,. The potential diagrams for the Ni-22Cr-11Al mechanical mixture are shown in for 800,

900, and 1000.C in Figures 4-37, 4-38, and 4-39, respectively. Here, the substrate alloy is shown

as a combination of y', p, and ot-Cr. This composition reacts more readily with 02 and SO2 than

the other two as shown with the addition Al203-Cr-y' and P-y'-CrS phase fields. Again, as with

the other two mixtures, Ni3Sz becomes the predominant Ni sulfide at higher temperatures,

alumina and chromia are more resilient against sulfidation, and Nio and spinel become less

stable at higher temperatures.













v Undefined






5 -1 i ":





5 A ,Ni(Cr,AlIO,-
Cr AI20s Crp3 NI


-
5

0-
_e


-1






-2!



-3!

-41

-4!

-51


-40 -30 -20 -10


-30 -20


logPg~bar I) log PO2 (bar)
Figure 4-37. Ni-22Cr-11Al potential diagrams for (a) SO2-O2 and (b) S2-O2 at 800.C. Published
in [170].


-50 -40 -30 -20 -10 0

log PO2 (bar)

Figure 4-38. Ni-22Cr-11Al SO2-O2 pOtential diagram at 900oC. Published in [170].












-5- Undefined o.
10- Equilibrium e

-15-








-E 0 -40 -3 -0 -1
lo PO (ar
Figr 4-39. Ni2C-1lO-2pteta igrma 00..Pbihe n[7]
4. PhseFrctonDigrm
Thi s ctinsos th :Icaluain ntefr fpaefato iga s hc r
diga m wihaptnil eprtre rcmoiino h -xiadaqatt ntey


partia prssr orcmpstin

Fiur 4-0sosapaefatondarmo h iOsstmcluae sn h
SPO3 atbae t 00C it vryn oxgn prilpesr.A rdce rmFgr -6
the ~ ~ ~ ~ N Nipaei tbebeo o f1-4,weesteNOissal bv hs ata rsue

In sseceFiure4-4 i s ic ofp Figureo 4-6 t onsattmeaue iue44 hw h
phase~ frcindarmo i a 0. f2 O S de.Teprilpesueo 2I eie
usingy th aemtost banFgrs41 n 41.Teadto fSt h ytmcue
the fomto of NiS tlwe O n NiSlO4 thge O.I eweni a htsaiie
(mst y SOc rssigo teseissonin Figr4-2InticaulioA wsade









as a component to the system to add as filler to keep the total system pressure 1 bar. An attempt

was made to use the appended SPIN4 database to calculate these diagrams, but no stable

equilibrium could be calculated. This was likely due to the equilibrium converging to two stable

phases, which would violate the Gibbs Phase Rule for a three-component Ni-O-S system. Figure

4-43 shows the change in component activity where there is an increase in S2 activity at the

oxide/metal interface. On either side of this peak, the Ps2 drops, especially toward increasing 02

where the S is oxidized into SO2 and SO3.

Figure 4-44 shows the phase fraction diagram of changing activity of the constituents of

the Ni-8Cr-6Al alloy in air calculated using the SPIN4 database. This diagram shows the drop in

metal activities with increasing Po2, Starting with the most reactive, Al, then Cr and finally Ni.

Figure 4-45 shows the different phases that are stable over this range of Po2. Figure 4-46 shows

a comparison of the activities obtained for this system with the SPOT3 and SPIN4 database. The

two calculations agree perfectly with component activities in the (Al,Cr)203 Oxide and Nio.

However, there is disagreement where the component are dissolved in y and the spinel phase, due

to the interaction parameters of elements in solution, which is not accounted for in the SPOT3

database.

The addition of sulfur to the above system and Ni-22Cr-1 1Al are of the most interest for

this dissertation. Figure 4-47 shows the Ni-8Cr-6Al alloy in a 2% SO2 atmosphere, as calculated

by the appended SPIN4 database. As with Figure 4-43, there is again a spike in S2 activity near

the boundary of oxide/alloy stability. The phase fraction diagram in Figure 4-48 shows

stabilization of sulfurous phases--from CrS at low Po2, to Ni3S2 at higher Po2, and finally a gas

consisting mostly of SO2 and Oz. Figure 4-49 shows the activity change for Ni-22Cr-11Al in the

same environment and temperature, and Figure 4-50 shows the phase quantities. The activity






















Ni tl'


Nii


VIIIIIII'III
-45 -40 -35 -30 -25 -20 -15 -10 -5 0
log PO2 (bar)
Figure 4-40. Phase fraction diagram of the Ni-O system showing the change in phase percent
with varying oxygen partial pressure at 800.C in air. Calculated from the SPOT3
database.


profile is similar to that ofNi-8Cr-6Al. In addition, similar phases evolve with the Ni-22Cr-

1 1Al alloy, except with the formation of an co-Cr phase at low Poo. Spinel is now the most

predominant oxide at high Po,, and at intermediate partial pressures of oxygen, the oxide

dominates instead of the alloy.


60


50


S40 -





130

1-











N i
NNi















IGas


60-
5-


50
S3-

--
40


-45 -40 -35 -30 -25 -20 -1~5 -1~0 -5

log PO2 (bar)

Figure 4-41. Phase fraction diagram of the Ni-O-S system showing the change in phase percent
with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2 atmosphere.
Calculated from the SPOT3 database.




1.0 llil
Ar
0.9-

0.8

0.7-

0 .6 -SO2
0.5-

~P0.4

0,3-

0.2--

.1I O
SO;

-45 -40 -35 -30 -25 -20 -15 -10 -5 0
log PO2 (bar)
Figure 4-42. Phase fraction diagram of the Ni-O-S system showing the gas evolution (in partial
pressure [bar]) with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02
SO2 atmosphere. Calculated from the SPOT3 database.













-10-


-20-





-40-


-50-


-60
5 -40 -35 -30 -25 -20 -15 -10 -5 0

log PO, (bar)

Figure 4-43. Phase fraction diagram of the Ni-O-S system showing activity change of each
component with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2
atmosphere. Calculated from the SPOT3 database.





Al




Fd-40

-50

-60

-70

-80
-45 -40 -35 -30 -25 -20 -15 -10 -5 0
log POZ bar)

Figure 4-44. Phase fraction diagram an Ni-8Cr-6Al alloy showing activity change of each
component with varying oxygen partial pressure at 800.C in air. Calculated from the
SPIN4 database.













50--


S40-





1: 0- c






5 -40 -35 -30 -25 -20 -15 -10 -5 0
log PO2 (bar)

Figure 4-45. Phase fraction diagram an Ni-8Cr-6Al alloy showing the change in phase percent
with varying oxygen partial pressure at 800.C in air. Calculated from the SPIN4
database.



-10 -N
Al
-20



ed-40--





-70

-80
5 -40 -35 -30 -25 -20 -15 -10 -5 0
log PO2 (bar)

Figure 4-46. Phase fraction diagram an Ni-8Cr-6Al alloy at 800.C comparing the activity change
calculated for Figure 4-3 8 using the SPIN4 database (black) and the SPOT3 database
(teal).



















-30-



-50-

-60-

-70-

-80
-45 -403 -35 -30 -25 -20 -15 -10 -5 U
log PO2 (bar)
Figure 4-47. Phase fraction diagram of an Ni-8Cr-6Al alloy showing activity change of each
component with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2 atmosphere.
Calculated from the appended SPIN4 database.
60 1 I'l


40








10


-45 -40 -35 -30 -25 -20 -15 -10
log PO2! (bar)


-5 0


Figure 4-48. Phase fraction diagram of an Ni-8Cr-6Al alloy showing the change in phase percent
with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2 atmosphere.
Calculated from the appended SPIN4 database.















-40 -i



a S2
-50-

-60-

-70-

-80 1,
5 -40 -35 -30 -25 -20 -15 -10 -5 0
log PO2 (bar)

Figure 4-49. Phase fraction diagram of an Ni-22Cr-1 1Al alloy showing activity change of each
component with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2
atmosphere. Calculated from the appended SPIN4 database.


~35






)3 15


-40 -35 -30 -25 -20 -15 -10 -5
log PO2 (bar)


Figure 4-50. Phase fraction diagram of an Ni-22Cr-1 1Al alloy showing the change in phase
percent with varying oxygen partial pressure at 800.C in an 0.21 02 + 0.02 SO2
atmosphere. Calculated from the appended SPIN4 database.









CHAPTER 5
EXPERIMENTAL RESULTS

This chapter will discuss the results of the kinetic experiments conducted using the

methodology described in Chapter 3. The results of the kinetic analyses will be shown, and then

the characterization data of the oxidized specimens will be presented.

5.1 TGA Experiments

5.1.1 Oxidation Experiments in Air

The TG experiments were carried out as outlined in Chapter 3. Figure 5-1 shows the

results of a typical oxidation run-a Ni specimen in air at 800.C for 24 hr. Here, the weight

change divided by surface area (in mg/cm2) is plotted against the time in seconds. However, for

the purpose of brevity, further results will be given to best visualize and derive the parabolic rate

constant(s) of each sample run. Figure 5-2 is similar to Figure 5-1 except that the x-axis plots

the square root of time, in s From this figure, one can derive the parabolic rate constant, kP in

mg/cm2S", from the slope of the linear regression which is plotted on the graph. The R2

coefficient of determination is plotted as well to show the global fit of the parabolic rate model.

O.9
R' 0.8-

bD0 0 .6





MO0 0.2-
O.1


O 10000 20000 30000 40000 50000 60000
Time (s)
Figure 5-1. Plot of weight change versus time for Ni specimen at 800.C for 24 hr in air.














O y = 3.13e-3x



RU 02-S9X

0


01 5 0 a



Square Root Time (s1/2)
Figure 5-2. Plot of weight change versus square root time for Ni specimen at 800.C for 24 hr in
air. The formula containing the slope and the coefficient of determination are listed.

Figure 5-3 shows the TG data collected for Ni oxidized at 900oC. This data is noteworthy

because the oxidation growth at the beginning of the test takes on the subparabolic behavior

described by Haugsrud [44]. This is also observed in the Ni specimen oxidized at 1100.C.

However, it is not seen at 1000.C. To compare the growth constants for this study with those of

most every other oxidation study, which plot the weight change squared versus time yielding

units of mg2/CM4S, the kP ValUeS obtain were squared, and then plotted Arrheniusly against the

inverse absolute temperature to determine an activation energy, as shown in Figure 5-4. The

activation energy, QA, can be derived from the slope by:

Q, = m -R (5.1)

where m is the slope of the linear regression obtained from the Arrhenius plot (in K) and R is the

ideal gas constant of 8.3 14 J/mol-K. The oxidation of Ni specimens in this study had an

activation energy of 150.74 kJ/mol.