• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Survey of previous work
 Experimental methods
 Results
 Discussion
 Conclusions
 Theoris of martensitic transfo...
 Applications of resistance measurements...
 Reference
 Biographical sketch
 Copyright














Title: The influence of heat treatment, neutron irradiation and deformation on the martensitic transformations in metastable B1-brass
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 Material Information
Title: The influence of heat treatment, neutron irradiation and deformation on the martensitic transformations in metastable B1-brass
Alternate Title: Martensitic transformations in metastable B1-brass
Physical Description: xiii, 149 leaves : ill. ; 28 cm.
Language: English
Creator: Koger, John Wayne, 1940-
Publication Date: 1967
 Subjects
Subject: Brass -- Metallography   ( lcsh )
Metallurgical and Materials Engineering thesis Ph. D
Dissertations, Academic -- Metallurgical and Materials Engineering -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis - University of Florida.
Bibliography: Bibliography: leaves 146-148.
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00086032
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000559166
oclc - 13440990
notis - ACY4614

Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
        Page v
    List of Tables
        Page vi
    List of Figures
        Page vii
        Page viii
        Page ix
        Page x
        Page xi
    Abstract
        Page xii
        Page xiii
    Introduction
        Page 1
        Page 2
        Page 3
    Survey of previous work
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
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        Page 18
        Page 19
        Page 20
    Experimental methods
        Page 21
        Page 22
        Page 23
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        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
    Results
        Page 33
        Page 34
        Page 35
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    Discussion
        Page 116
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    Conclusions
        Page 133
        Page 134
    Theoris of martensitic transformations
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
    Applications of resistance measurements for the study of transformations in metals
        Page 142
        Page 143
        Page 144
        Page 145
    Reference
        Page 146
        Page 147
        Page 148
    Biographical sketch
        Page 149
        Page 150
    Copyright
        Copyright
Full Text













THE INFLUENCE OF HEAT TREATMENT,
NEUTRON IRRADIATION AND
DEFORMATION ON THE
MARTENSITIC TRANSFORMATIONS
IN METASTABLE 3 -BRASS






By
JOHN WAYNE KOGER











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









UNIVERSITY OF FLORIDA
December, 1967















ACKNOWLEDGMENTS


The author wishes to express his sincere appreciation to his

committee chairman, Dr. R. E. Hummel, who contributed much valuable

aid and time in fruitful discussions during the course of the research.

Appreciation is also extended to Dr. J. J. Hren for his help in

the interpretation of the electron micrographs and to Drs. F. N. Rhines,

R. G. Blake, and J. B. Conklin, Jr. for serving as members of the au-

thor's committee.

Thanks are given to Mr. E. J. Jenkins for the preparation of elec-

tron microscopy samples and to Mr. V. Pashupathi for help in perform-

ing experiments.

The author would like to thank Dr. J. Stanley of the Oak Ridge

National Laboratory for his assistance in the irradiation procedures.

The author is grateful to the Graduate School of the University

of Florida and the National Aeronautics and Space Administration for

providing his financial support.

The author is indebted to the United States Atomic Energy Com-

mission which supported this investigation under Contract No. AT-(40-1)-

3395.

Last but not least, the author would like to express his everlast-

ing gratitude to his wife, Rosemary, whose love, understanding and sac-

rifices made the completion of this work pos,















TABLE OF CONTENTS


Page

ACKNOWLEDGMENTS. . . . ... .. . ii

LIST OF TABLES . . . . . . vi

LIST OF FIGURES. . . . . . . vii

ABSTRACT . . ... . . . . xii

Chapter

I. INTRODUCTION . . . . . 1

II. SURVEY OF PREVIOUS WORK. . . . . 4

2.1 Historical Information. . . ... .. .. 4

2.2 General Features of Martensite Transformations. ... 5

2.3 The Phases Involved in the Martensitic Trans-
formation of 31-Brass . .... .. .. 6

2.4 The Order-Disorder Transformation . . 8

2.5 The Massive Transformation. . ... .. .. 8

2.6 Martensite Formed by Cooling a1-Brass . .. 10

2.7 The Characteristic Temperatures of the Martensitic
Transformation. . . ... . . 10

2.8 The Kinetics of the Transformation and Growth of
the Martensite Phase. . . . . 11

2.9 The Crystallography of the Martensite Phase Formed
by Cooling. . . . . ... 12

2.10 Deformation . . .... . . 13

2.11 Theoretical Considerations. . . ... 15

2.12 Electron Microscopy . . . ... 16

2.13 Heat Treatment of Quenched 81-Brass . ... 16









Chapter

2.14 Radiation Damage . . . . .

III. EXPERIMENTAL METHODS . . . . .

3.1 Sample Preparation . . . .

3.2 Quantitative Analysis . . . .

3.3 Cryostat and Temperature Control . . .

3.4 Resistance Measurements . . . .

3.5 Metallography . . . . .

3.6 Irradiation and Safety Precautions . .

3.7 X-Ray Diffraction . . . . .

3.8 Electron Microscopy . .. . . .

IV. RESULTS . . . . . .

4.1 The Basic Transformation . . . .

4.2 Thermal Cycling . . . . .

4.3 Effect of a-Phase on the Martensitic Transformation

4.4 Plastic Deformation . . . .

4.5 Electron Microscopy Observations . . .

4.6 Transformations at Elevated Temperatures . .

4.7 Neutron Irradiation . . . .

V. DISCUSSION . . . . . .

5.1 The Temperatures of the Martensitic Transformation.

5.2 Retained Martensite . . . .

5.3 Untransformable Phases . . . .

.5.4 Plastic Deformation . . . .

5.5 Electron Microscopy . . . .

5.6 a,-Brass Martensite Structures. .. . .

5.7 Neutron Irradiation . . . .

iv


Page

17

21

21

23

24

26

26

28

28

29

33

33

38

46

55

73

99

107

116

116

119

122

123

128

129

130










Chapter Page

VI. CONCLUSIONS. . . . . ... ..... 133

Appendix

I. THEORIES OF MARTENSITIC TRANSFORMATIONS. . ... 135

A.1 Crystallography . . . . ... .135

A.2 Thermodynamics.. .. . . . ... 137

A.3 Kinetics and Growth . . . .. .138

II. APPLICATIONS OF RESISTANCE MEASUREMENTS FOR THE
STUDY OF TRANSFORMATIONS IN METALS . . ... 142

REFERENCES . .. . . . ..... 146

BIOGRAPHICAL SKETCH. . . . . ... . 149















LIST OF TABLES

Table Page

1. Summary of neutron irradiation effects on martensitic
transformations .... . . . ... . 20

2. Resistivity of the various phases. . . ... 35

3. Visual observations on B1-brass after various degrees
of rolling at room temperature . . ... 67

4. Percent martensite present at various temperatures (1) 82

5. Percent martensite present at various temperatures (2) 82

6. Influence of fast neutron bombardment on M -temperature. 113
S















LIST OF FIGURES


Figure Page

1. Cu-Zn binary system. . . . . 7

2. Shape of the sample for resistance measurements. ... 22

3. The cryogenic unit . . . .... ... 25

4. Circuit for resistance measurements. . . ... 27

5. Cold unit for the Phillips x-ray diffractometer. ... 30

6. Dimpling unit for preparation of transmission electron
microscopy samples. . . . . .. 31

7. Relative resistivity versus temperature of 01-brass
(38.8 wt. percent zinc). . . . ... 34

8. Transformation curves. . . . . ... 37

9. Relative resistivity versus temperature of 01-brass
(38.8 wt. percent zinc) containing retained martensite 40

10. Optical micrograph of 01-brass (38.8 wt. percent zinc)
after cycling to low temperatures (room temperature,
magnification 250x). . . . . ... 41

11. Transmission electron micrographs of 01-brass martensite
(38.8 wt. percent zinc). . . . ... 43

12. Retained martensite in percent at room temperature
versus M -temperature. . . . . 44
s
13. Relative resistivity versus temperature of 01-brass
(38.8 wt. percent zinc). . . . ... 45

14. Relative resistivity versus temperature of B1-brass
(38.8 wt. percent zinc). . . . ... 48

15. Percent transformation versus temperature. . ... 49

16. Parts of transformation curves with various amounts of
A- and B-phases (calculated) . . ... 51

17. Parts of transformation curves with various amounts of
A- and B-phases (calculated) . . . .. 53

vii









18. H versus percent P1-phase. . . . ... 54

19. Relative resistivity versus temperature for 81-brass
(38.8 wt. percent zinc) at five different degrees of
deformation. . . . . ... ..... 58

20. Shift of Ms(AMs ) versus deformation. . . ... 59

21. Shift of M(AM) versus deformation. . . ... 59

22. 6 and H (percent a1-phase present) versus percent
deformation. . . . . ... ..... 60

23. Optical micrographs of deformed 81-brass (38.8 wt.
percent zinc). . . . . .. ..... 62

24. Optical micrographs of deformed a1-brass (38.8 wt.
percent zinc). . . . . .. ..... 63

25. Optical micrographs of deformed 81-brass (38.8 wt.
percent zinc). . . . . .. ..... 64

26. Optical micrographs of deformed 81-brass (38.8 wt.
percent zinc). . . . . .. ..... 65

27. Optical micrographs of deformed 81-brass (38.8 wt.
percent zinc). . . . . .. ..... 66

28. Transmission electron micrographs of 81-brass (38.8
wt. percent zinc) deformed in tension. . . ... 69

29. Specific resistivity (in p2CM) versus temperature for
a1-brass (38.8 wt. percent zinc) at two different de-
grees of deformation . . . .... .70

30. Percent transformation versus temperature. . ... 71

31. Area of hysteresis loop of percent transformation
curve versus deformation . . . .. .. 72

32. Transmission electron micrographs of 81-brass (38.8 wt.
percent zinc) where martensite formed during thinning. 74

33. Transmission electron micrographs of 81-brass (38.8 wt.
percent zinc) showing striated region which makes up the
martensite formed during thinning. . . ... 75

34. Transmission electron micrograph of $8-brass (38.8 wt.
percent zinc) in cold stage showing growth of martensite
at various temperatures below M -temperature .. 77

35. Transmission electron micrographs of B1-brass (38.8 wt.
percent zinc) in cold stage showing growth of martensite
at various temperatures below M -temperature ...... 78
viii


Page


Figure










Figure Page

36. Volume percent martensite versus AT from the
M -temperature . . . .... ..... 79

37. Transmission electron micrographs of i1-brass (38.8
wt. percent zinc) in cold stage showing growth of
four needles of martensite . . . .... .80

38. Transmission electron micrographs of 81-brass (38.8 wt.
percent zinc) in cold stage showing growth of four
needles of martensite. . . . . ... 81

39. Transmission electron micrographs of a1-brass (38.8 wt.
percent zinc) in cold stage with large martensite
needle still growing . . . .... .83

40. Transmission electron micrographs of B1-brass (38.8 wt.
percent zinc) in cold stage. . . . ... 84

41. Transmission electron micrographs of Bi-brass (38.8 wt.
percent zinc) in cold stage showing the martensite
needle disappearing. . . . . .. 85

42. Transmission electron micrographs of Bl-brass (38.8 wt.
percent zinc) in cold stage showing the martensite
needle almost gone . . . .... 86

43. Transmission electron micrograph of B1-brass (38.8 wt.
percent zinc) in cold stage with martensite needle gone. 87

44. Transmission electron micrograph of 81-brass martensite
(38.8 wt. percent zinc) in cold stage. . . ... 88

45. Transmission electron micrograph of 81-brass martensite
(38.8 wt. percent zinc) in cold stage showing striations
at the center of a plate . . . .... .89

46. Transmission electron micrograph of a1-brass martensite
(38.8 wt. percent zinc) in cold stage with the boundary
between two plates . . . .... 90

47. Transmission electron micrograph of 81-brass martensite
(38.8 wt. percent zinc) in cold stage with plate left of
center much wider at the top than at the bottom. .. .... 91

48. Transmission electron micrograph of 81-brass martensite
(38.8 wt. percent zinc) in cold stage showing inner struc-
ture . . . . . . 92

49. Transmission electron micrograph of Bl-brass martensite
(38.8 wt. percent zinc) in cold stage with a boundary
containing dislocation . . . .... .93












50. Transmission electron micrograph of B1-brass martensite
(38.8 wt. percent zinc) in cold stage. . . ... 94

51. Transmission electron micrograph of a1-brass martensite
plates (38.8 wt. percent zinc) in cold stage ...... 95

52. Transmission electron micrograph of Bl-brass martensite
(38.8 wt. percent zinc) in cold stage. . . ... 96

53. Transmission electron micrograph of B1-brass martensite
(38.8 wt. percent zinc) in cold stage with dislocations
at boundaries. . . . ... ..... 97

54. Transmission electron micrograph of Bl-brass and martensite
(38.8 wt. percent zinc) in cold stage. . ... 98

55. Electron micrograph of replica of B1-brass martensite
(38.8 wt. percent zinc) showing the surface distortion .. 100

56. Transmission electron micrographs of B1-brass (38.8 wt.
percent zinc) showing slip traces with dislocations and
stacking faults. . . . . ... .. 101

57. Transmission electron micrograph of Bl-brass (38.8 wt.
percent zinc) showing tangles of dislocations. . ... 102

58. Transmission electron micrograph of B1-brass (38.8 wt.
percent zinc) showing dislocation line-up. . ... 103

59. Transmission electron micrograph of B1-brass (38.8 wt.
percent zinc) showing pilu-ups of dislocations . .. .104

60. Relative resistivity of B1-brass (38.8 wt. percent
zinc) versus five minute annealing temperatures. ... 105

61. Percent resistance change of Bl-brass (38.8 wt. percent
zinc) versus time in minutes at various temperatures 106

62. Relative resistivity of B1-brass (38.8 wt. percent zinc)
versus temperature before and after heating. . .. .108

63. Relative resistivity of Bl-brass (39.4 wt. percent zinc)
versus temperature before and after irradiation. ... .109

64. AM versus integrated neutron flux . . .. 111

65. AM versus integrated neutron flux (logarithmic scale) 112
66. Transformation curves. .. .. 115
66. Transformation curves. .............. ............ 115


Page


Figure









Figure


Page


67. Superposition of a percent transformation curve with
three different temperature coefficients of resistivity
(a) . . . . . . 118

68. Retained martensite at room temperature in percent
versus shift of M (AM ). . .. .. ..... .... .120
s s
69. Optical micrograph of B1-brass (38.3 wt. percent zinc)
showing BI- (light), martensite, and a- (dark) phase 124

70. Optical micrograph of B1-brass (38.3 wt. percent zinc)
showing 8i- (light), martensite, and a- (dark) phase 125

71. Optical micrograph of B1-brass (38.3 wt. percent zinc)
showing B1- (light), martensite, and a- (dark) phase 126









Abstract of Dissertation Presented to the Graduate Council
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy

THE INFLUENCE OF HEAT TREATMENT, NEUTRON IRRADIATION,
AND DEFORMATION ON THE MARTENSITIC TRANSFORMATIONS
IN METASTABLE 81-BRASS

By

John Wayne Koger

December, 1967

Chairman: Dr. R. E. Hummel
Major Department: Metallurgical and Materials Engineering

A study was made on the martensitic transformations in meta-

stable 81-Cu-Zn (with 38.3 to 39.4 wt. percent zinc) to determine

the effect of repeated thermal cycling, deformation, annealing, bom-

bardment with fast neutrons, and the presence of untransformable

phases on these transformations. The main tool used to monitor the

transformations was the measurement of electrical resistance which

was complemented by optical and electron microscopy and x-ray dif-

fraction analysis.

The principal characteristics of the transformation on cooling,

determined from resistance measurements, were found to be the M -tem-
s
perature, the temperature coefficient of electrical resistivity of

the phases, the area of the hysteresis loop of the (percent) trans-

formation curve, and the rate of transformation.

The M -temperature was found to change according to the treat-
s
ment given the sample. Elastic deformation and the presence of re-

tained martensite would raise the M The M -temperature was lowered
s s
after plastic deformation and neutron irradiation but was not affected

by heat treatments up to 1350C.


xii









Retained martensite formed during the first thermal cycle was

found to be present at room temperature in samples which had an M -
s
temperature above -330C. The amount of retained martensite increased

with increasing M -temperature. The shift of M between two cycles
s S
is a linear function of retained martensite. The retained martensite

was observed to grow above the previously found M -temperature.
S
Untransformable phases, such as a and deformation-martensite,

acted as obstacles to the formation of low-temperature martensite.

As the amount of these phases increased, the area of the hysteresis

loop of the transformation curve increased; the maximum rate of trans-

formation decreased; and the temperature range of transformation was

spread over a wider range, thus increasing the amount of energy needed

to complete the transformation. In samples which were irradiated with

fast neutrons no such increase in the area of the hysteresis loop was

detected, showing that the irradiation induced defects are only small

disturbances.

Using cold-stage electron microscopy it was observed that mar-

tensite formed immediately after a heavy bending movement of the foils.

Differences in the growth mechanism during cooling and heating were

found.


xiii















CHAPTER I


INTRODUCTION


The fact that many alloys and metals undergo a martensitic trans-

formation has been of great interest for a long time. This interest

has stemmed mainly from the shear-like nature of the transformation

and the sometimes enhanced properties of the transformed phase, such

as the increased hardness of the steel martensites.

A relatively new and effective means of influencing a state of

matter that could be used for studying the nature of phase transfor-

mations is neutron irradiation. It is usually of interest as a method

of introducing various kinds of defects and producing certain changes

in the properties of metals and alloys. However, the irradiation may

alter the state of an initial phase and cause some change in its sta-

bility and thus affect the kinetics of subsequent phase transforma-

tions. The strictly regular directed shift of atoms in a martensitic

transformation is extremely sensitive to any disturbance of the lattice

structure in the original parent phase.

Investigations of the effect of irradiation on the martensitic

transformation have been done on alloyed steels which were complex

in both behavior and composition, and the results were not adequate

to give a complete picture of the processes which cause changes in

the transformation. Therefore, it was felt that further irradiation

work was needed on another martensite system which is nonferrous and

would have less variables. The Cu-Zn system was chosen.

1









Quenched Bl-phase Cu-Zn alloys with compositions from 37 to 43 wt.

percent zinc undergo a martensitic transformation when the samples are

cooled to sub-zero temperatures. The occurrence of the transformation

at relatively low temperatures would insure that imperfections introduced

by room-temperature irradiation would not anneal out. Cu-Zn alloys have

a relatively low residual radioactivity after neutron bombardment. (The

only isotope with a long half life is the Zn65 with T/2 = 245 days.)

The previous studies of the martensitic transformation of B1-brass

have concerned the composition dependence of the martensitic-start tem-

perature, the crystal structure of the martensite phase, the observation

of the transformation by optical microscopy, and some effects of deforma-

tion on the transformation.

The purpose of this research was to determine the influence of

heat treatment, neutron irradiation, and deformation on the martensitic

transformations of B1-brass and to investigate whether neutron irradia-

tion causes the same effects as cold-working 81-brass, or produces ef-

fects similar to those found for steels and iron alloys. The trans-

formation was monitored by high precision electrical resistance measure-

ments. Optical and electron microscopy were also used to supplement

the resistivity data.

In the course of the investigation, it was found that very little

was known about the characteristic properties of the transformation and

the parameters which were landmarks of the transformation. Studies there-

fore were made on the effect of repeated thermal cycling. It was neces-

sary to know how the characteristics of the transformation would be af-

fected if the samples were transformed several times so that any effect

due to irradiation would be separated from the cycling effect. The effect









of an added non-transformable phase on the transformation was studied.

Due to the mode of quenching, a-phase could always be present along

with the B1-transformable phase. This study was also helpful in the

interpretation of results gained by deformation. Since it had been

noticed in experiments concerning radiation damage that deformation

caused the same effects as neutron irradiation, the influence of de-

formation on the martensitic transformation was investigated. These

preliminary studies provided a better basis for the interpretation

of property changes which occurred due to neutron bombardment of al-

loys with martensitic transformations.

The results of this investigation will provide an understanding

of the effect of many controlled variables on the martensitic trans-

formation in $1-brass, will allow an understanding of the basic trans-

formation, and will provide knowledge of the effect of neutron ir-

radiation on martensitic transformations.















CHAPTER II


SURVEY OF PREVIOUS WORK


This chapter will provide a summary of the types of studies made

on 81-brass and its martensitic transformations. The previous investi-

gations concerning the effect of irradiation on martensitic transfor-

mations are also given. Appendix I gives more details about martensitic

transformations and discusses ferrous alloy martensitic transformations

where similar studies were not made on 81-brass.


2.1 Historical Information

Martensite, originally considered just a hard constituent in steel,

was named in honor of A. Martens, a German metallurgist, as proposed by

Osmond in 1895.

In 1946 Troiano and Greninger (1) suggested that the diffusion-

less reactions found in the non-ferrous alloys are similar to the mar-

tensite reaction in steel and that these transformations should be

referred to as martensitic.

Pure metals and alloys found to have a martensitic transformation

are:

Na Cu-Si Fe Re-Mg Li-Mg U-Cr
Li Cu-Zn-Ga Fe-Ni Ti Cr-Mn NH NO3
Zr Ag-Cd Fe-Mn In-Ti Ar BaTiO3
Cu-Zn Ag-Sn Fe-C In-Ta Ar-N2 KNbO3
Cu-Sn Ag-Sb Fe-Ni-Mn In-Cd Ir-Cd V3Si
Cu-Al Au-Zn Fe-Ni-C Ti-Mh Co Au-Cu-Zn
Cu-Mn Au-Cd Fe-Cr-Ni Ti-Ni Co-Ni Cu-Ni-Al
Cu-Ga Au-Mn Fe-Ti TI-Mo Al-bronze

and other ternaries involving the above systems.









The previous list is possibly not complete but does contain most of

the systems where information has been published. Almost all of the

references for the studies of these systems can be found in the sur-

veys given by Christian (2) and Barrett and Massalski (3).


2.2 General Features of Martensite Transformations

Phase transformations in metallic systems are usually considered

to be either nucleation-and-growth transformations or martensitic

transformations. The nucleation-and-growth processes are considered

to be isothermal transformations in that the transformation can take

place at constant temperature with thermal activation and diffusion

playing the important parts.

In general, the characteristics of the martensitic transformations

have been that it is diffusionless (interchange of atoms over a dis-

tance less than the interatomic spacing); it is athermal (transforma-

tion occurring with changing temperature and transformation stops when

temperature change is halted); the transforming region undergoes a

change in shape; there is a definite orientation relationship between

the product and parent phase; and the transformation is aided by cold-

work. Because of exceptions to many of the above characteristics,

"martensitic" now usually refers to diffusionless transformations

having macroscopic shear or a shape distortion.

The following items are also observed in martensitic transforma-

tions. The interchange of atoms takes place through the propagation

of a semi-coherent interface. It is assumed that this interface must

be composed of dislocations whose movement permits the martensitic

product to form rapidly at any temperature. The martensite plates

in many alloys contain a fine structure of slip bands or twins as a









direct result of this transformation mechanism. In alloys which are

ordered, the martensite phase has been found to be ordered. The a-

mount of transformation is characteristic of temperature, provided

other variables such as grain size are held constant. There is no

dependence on cooling rate for the transformation. Martensitic re-

actions are reversible in the sense that an initial atomic configura-

tion can be repeatedly obtained. Thermodynamically, the transforma-

tion is not reversible as seen by the hysteresis loop and the energy

dissipation. It is assumed that the plates which form on cooling

have the same size and shape and appear in the same regions of the

original crystal.


2.3 The Phases Involved in the Martensitic Transformation of 61-Brass

Figure 1 shows a portion of the Cu-Zn phase diagram. The symbols

used to designate the various phases concerned with the martensitic

transformation in 1B-brass have been given by several authors.

B Disordered body centered cubic B-brass

BI Ordered body centered cubic B-brass

8" Martensite formed by cooling (4,5)

a Face centered cubic a-brass

ia Martensite formed on deformation (6)

a Massively transformed brass (3)

The above were those phases involved in this investigation. The fol-

lowing phases are those mentioned in other studies:

a' Quenched martensite-face centered tetragonal (4,5)

a" Quenched martensite with unknown structure (4,5)

a2 Transition phase between B and al (6)

B' Bainite structure (4,5)
















WEIGHT PER CENT ZIC0


6004


X

700


800.



-I A


30 40 80
ATOMIC PER CENT ZINO
---w


Figure 1. Cu-Zn binary system.









Bl Transition lattice between 8' and a'(7)

B"'- Theoretical martensite phase beyond 0"(8)


2.4 The Order-Disorder Transformation

Above 4540C to 4680C, the 8-phase in Cu-Zn is disordered body

centered cubic. Below these temperatures it is ordered body centered

cubic and has the cesium chloride structure. As is well known, the

ordering is found to occur so rapidly that even rapid quenching cannot

suppress the ordering.

The order-disorder transformation is indicated in phase diagrams

by a single line running from 4540C to 4680C in the 8-phase region.

Work has indicated that perhaps 0 and 81 fields are separated by a

normal two-phase field (8+a1) (9).


2.5 The Massive Transformation

In order to obtain the transformable (i.e., metastable) 81-phase,

the alloy must be quenched from the 8-region. The composition of the

alloy before quenching is very important since not all 01-alloys trans-

form to cooling martensite and because of the massive transformation.

Phillips (10) first reported that Cu-Zn, containing between 37.0

and 39.0 wt. percent zinc, when quenched from the 8 region would give

a uniform a structure. As there has been a question on the location

of the boundary between the a and a+a region, Phillips proposed that

the single phase a region lies below 39.0 wt. percent zinc and that

the above mentioned boundary is a straight line at the 39.0 wt. per-

cent zinc composition. This transformation from B to a was seen to

occur with great speed during cooling.

The structures obtained when low zinc content B-brass was quenched

in different manners has been discussed by Schimmel (11). The alloy










was 37.8 wt. percent zinc, rest copper, which is B-phase from 850C to

8950C and a below 550C. On quenching from 8500C, there was a consid-

erable quantity of finely precipitated a disseminated through the 8

crystals with a little massive a along the grain boundaries. On quench-

ing from 890C there were large 8 crystals with a feather-like a along

the grain boundaries. With a more drastic quench, there was a more

general precipitate of a particles with actually more a present than

before. With an extremely rapid quench, the structure became all a.

The explanation of these structures was that with cooling at a moderate

rate, the transformation from 8 to a must take place by diffusion, and

the time will not be long enough for this. If the 8-phase is cooled

rapidly below 550C, no diffusion is required for the transformation,

and it required scarcely any time with only the structure change of

8 a.

The above-mentioned transformation in 81-brass was recognized as

a massive transformation by Hull and Garwood (12).

A study of alloys that exhibit the massive transformation by

Massalski (13) reaffirmed that alloys in the low zinc range of 81-

brass transformed into a face-centered cubic phase on quenching.

This structure obtained by the massive transformation was regarded

as a supersaturated extension of the equilibrium a phase. For a
0
quenched alloy of 37.95 wt. percent zinc, a was found to be 3.700 A.

Recent work on massive transformations (3) showed that the grow-

ing crystals of the massive phase cross the prior grain boundaries of

the parent phase. While the final product of the massive transfor-

mation is usually the equilibrium phase, corresponding to a lower

temperature, the actual reaction may well occur at much higher









temperatures from which slow cooling would produce a two-phase mixture.

The massive transformations require certain critical conditions of

supersaturation and quenching rates. Probably the kinetics of the mas-

sive transformation would be intermediate between that of an equilibrium

reaction and that of a possible martensitic transformation.


2.6 Martensite Formed by Cooling B1-Brass

Martensite is formed when alloys of Bl-brass with 37 to 43 wt. per-

cent zinc are cooled to sub-zero temperatures.

The first mention of this type of transformation in B-brass was

made by Kaminski and Kurdjumov (14) in 1936 but was not recognized as

a martensitic transformation until later. In 1938 Greninger and Moora-

dian (15) also noted this transformation on cooling but did not observe

a critical temperature for the transformation. Bassi and Str6m (4),

Massalski and Barrett (16), and Pops and Massalski (17) found that al-

loys of Bl-brass with more than 43 wt. percent zinc do not transform

to martensite on cooling.


2.7 The Characteristic Temperatures of the Martensitic Transformation

The temperature at which martensitic nuclei start growing (18) has

been designated as Ms. In some iron-nickel alloys a large amount of

martensite will form at one time in a burst. When a burst-type mar-

tensite occurs after the Ms-temperature, a temperature MB is designated

as the martensite burst temperature (19). MF is the temperature at

which the transformation is complete. As is the temperature at which

the parent phase starts re-forming on heating, and A is the tempera-

ture at which the parent phase has completely re-formed.

Titchener and Bever (20) studied the temperature range of the

martensitic transformation as a function of composition in 81-brass.










The compositions of the samples used were from 38.54 to 40.04 wt. per-

cent zinc. It was shown that the M -temperature decreased with decreas-

ing copper content. M -temperature of the samples ranged from about

-200C to -1300C. Electrical resistivity measurements were used,and M

was defined to be that temperature at which the resistivity-temperature

curve on cooling deviated from a straight line. Because of a lack of

accuracy, the temperature of minimum resistivity was taken for M The
s
plot of M -temperature versus zinc content had a somewhat different

slope than the slope of a similar curve given by Kurdjumov (5).

Pops and Massalski (17) proposed that there were two stages in the

transformation. A thermo-elastic phase (appeared and disappeared as

cooled and reheated) formed initially at the M -temperature. On further
s
cooling, an additional martensitic phase formed in rapid bursts at the

lower temperature MB. The M -temperature was considered to be the tem-

perature at which the first evidence of martensite was optically seen.

This temperature could not be observed from their resistivity data.

The M -temperature, as obtained from the optical microscopy, was said

to be equivalent to the minimum temperature of the resistivity-tem-

perature curve. Pops and Massalski also concluded that the M -temper-

atures found by Titchener and Bever were actually MB-temperatures.


2.8 The Kinetics of the Transformation and Growth of the Martensite
Phase

The martensitic transformation of $1-brass is athermal; that is,

the transformation only proceeds with a lowering of the temperature.

The time at a certain temperature or during cooling has no effect on

the fraction transformed.

Hull and Garwood (12) and Pops and Massalski (17) observed the

growth of the martensite in detail using cold-stage optical microscopy.









First seen were thin "needles" which grew in the lengthwise direction

and then thickened slowly. The plates did not reach their final size

at once but did definitely grow when the temperature was lowered.


2.9 The Crystallography of the Martensite Phase Formed by Cooling

Kaminski and Kurdjumov (14) and Greninger and Mooradian (15) de-

termined in early work that the structure of the martensite was near

that of a face centered tetragonal lattice.

Using B1-brass containing approximately 39.0 wt. percent zinc,

Garwood and Hull (21) employed a Laue x-ray method to determine the

lattice orientation relationship between the martensite and the parent

phase. The values obtained were seen to be the same as exist in the

martensite transformation in the Cu-Al system. When the measured

shear was applied to a theoretical unit cell of the 8 lattice, a body-

centered triclinic lattice was produced, which did not agree with ex-

perimental results. Garwood and Hull assumed that the lattice of the

martensite phase would be close-packed because of the identification

of a prominent basal plane in each martensite plate. They felt that

in view of the diffusionless nature of the transformation at sub-zero

temperatures that the ordered structure which is not suppressed by

quenching would be retained in the martensite product. In other alloy

systems there are faults in the stacking sequence of the martensite

phase after the transformation (22). These faults may also be present

in this system. Distortions of these types are mainly responsible for

the complexity of the x-ray spectra reported for the low-temperature

martensite.

Jolley and Hull (23) determined from x-ray and electron diffrac-

tion data that the martensite obtained on cooling a 81-brass sample









containing approximately 39.0 wt. percent zinc had an orthorhombic

crystal structure. Using these and other data, they applied the

Wechsler, Lieberman, and Read theory. The calculated habit plane

compared favorably to the experimentally determined habit plane.

In a very detailed crystallographic study with x-ray measurements

at low temperatures, Kunze (7) showed a monoclinic (also called body-

centered pseudorhombic) transition lattice (8') between parent and mar-

tensitic phase (W"). The superlattice cell of the martensite phase B"

was said to be triclinic face-centered on one face (pseudomonoclinic).

About 25 percent of this transition lattice was always present with

the martensite at liquid nitrogen temperature.


2.10 Deformation

Greninger and Mooradian (15) noticed "markings" in deformed B1-

brass containing 39.22 wt. percent zinc and determined the crystal-

lographic directions to which these markings were parallel. X-ray

work on hammered powder samples showed some lines corresponding to

a face-centered tetragonal structure.

Reynolds and Bever (24) elastically compressed a B1-brass sample

containing approximately 39.98 wt. percent zinc and therefore induced

plates of deformation martensite. After the stress was released, the

plates disappeared. When samples were stressed and unstressed in suc-

cessive cycles, the plates appeared in the same locations. They also

cooled a specimen which had residual strain-induced martensite plates.

As thh specimen was cooled below room temperature, some of the plates

increased in size, and others were formed. The thermally induced and

strain-induced plates had a similar metallographic appearance. It was

concluded that strain-induced martensite was mechanically reversible

with considerably hysteresis and that elastic stresses were operative









in this reversal. Suoninen, Genevray, and Bever (25) investigated the

effect of elastic stress on the transformation. It was shown that the

M -temperature increased with increasing stress. Also, an alloy con-
s
training approximately 39.5 wt. percent zinc was partially transformed

by cooling it under stress. The stress was released, and the marten-

site disappeared. After further cooling, the martensite started form-

ing as usual. This was considered to be consistent with the concept

of "thermo-elastic" martensite first considered by Kurdjumov (5) and

confirmed by Kurdjumov and Khandras (26).

Massalski and Barrett (16) studied the effect of cold work on the

transformation in B1-brass alloys with compositions from 39.73 to 51.80

wt. percent zinc. Alloys which would not transform on cooling; i.e.,

above 43 wt. percent zinc, were seen to transform on cold work. All

the alloys did transform on cold work even though in some cases low

temperatures were required. A temperature, MD, has been defined by

McReynolds (27), as was previously done in an Fe-Ni alloy, as being

the temperature above which no martensite will be formed on deforma-

tion. The M- temperatures were determined for some of the high zinc

content alloys, and a plot was made of MD-temperature versus zinc con-

tent. The structure of the deformation martensite was found to be

face-centered cubic with stacking faults for the lower percent zinc

alloys and hexagonal close packed for the higher percent zinc alloys.

The face-centered cubic structure had parameters that could be extra-

polated from the a-phase region assuming line shifts from the stacking

faults. For alloys with compositions above 45.59 wt. percent zinc,

the transformation product reverted to the parent phase after a few

weeks. Thus, B1-brass with 37.0 to 42.0 wt. percent zinc is metastable









with regard to cooling and deformation and B1-brass with above 42.0

wt. percent zinc is metastable with regard to deformation. Massalski

and Barrett assumed that in the latter case only the disordered 8-

phase was metastable. Therefore, the cold work disordered the alloy

and the low temperatures caused the transformation.

Hornbogen, SegmUller, and Wassermann (6) studied the transforma-

tion during deformation using elastic and plastic tensile stresses.

It was seen with the use of x-ray measurements that after 10-15 per-

cent deformation the Bl-brass (composition between 39.5 and 39.8 wt.

percent zinc) would transform to a tetragonal phase a,. This phase

was described as an ordered a-brass of the Cu-Au type. A transition

phase a2 was seen between the a1- and al-phases. At higher degrees of

deformation the al-phase would transform into a disordered supersat-

urated a-brass.

Investigations from the Southern Research Institute (28) also

found martensite in Muntz metal (59.98 wt. percent copper and 38.71

wt. percent zinc) which had been rolled to 53 percent reduction at

240C and to 28 percent reduction at -1960C. The studies were made

using optical photomicrographs and were performed to improve the

strength.


2.11 Theoretical Considerations

Kunze (8) considered the theory of elasticity and the contribu-

tion of the Fermi energy to the transformation. The Fermi energy,

which'controls the stability of the 81-lattice at room temperature,

was also said to carry the principal weight in controlling the steps

of the low temperature transformations. This kas shown from the









calculations of the Brillouin zones of the low temperature phases.

It was predicted from these electron theoretical considerations that

the martensite may possibly undergo a further transformation at low

temperatures. This transformation from 6" ~ "'would be a close

packing of (110) atomic planes. He assumed that the first step

(shearing), 81 + 1', of the low temperature transformation corresponded

to the first step in the martensitic transformation by plastic deforma-

tion (1 -* ac) and quenching (,1 a') and that the unknown structure

a2 between Bl and al is identical to that of the transition lattice

8'. The martensitic transformation by deformation proceeds by other

mechanisms than the low temperature transformation after the first

transformation step.


2.12 Electron Microscopy

Hull (29) observed in thin foils of S1-brass, containing approxi-

mately 39.0 wt. percent zinc, martensite which apparently occurred

during the preparation of the foils in thin regions at the edges of

the specimens. Orientation relationships were determined, and it was

seen that the interface between the martensitic phase and parent phase

did not follow any particular habit plane. This has been seen in other

alloy systems which undergo a martensitic transformation.


2.13 Heat Treatment of Quenched B1-Brass

In 1924 Homerberg and Shaw (30) determined strength characteristics

of 81-brass at various temperatures during reheating after quenching.

Later, Hansen (31) determined that heating the quenched 81-brass above

1500C caused a rise in resistivity of about 10 percent. Changes in

resistivity and hardness were correlated with composition, temperature,

and time changes.










Garwood (32) studied the isothermal decomposition of 81-brass

samples containing 41.3 wt. percent zinc at temperatures from 170C

to 4700C. A bainitic transformation was assumed to occur at temper-

atures between 1700C and 2250C. The structure of this phase was not

determined. Above 225C thea-and 8-phases (evidenced by x-ray dif-

fraction) occurred as expected.

Bassi and Strom (4) heat-treated a 81-brass sample of 40.5 wt.

percent zinc for 73 hours at 150C and also detected a new phase but

could not determine its structure.

Hornbogen (33) aged quenched 81-brass containing about 40 wt.

percent zinc between 2000C ad 3000C. Precipitation occurred which was

connected with an increase in hardness. The final transformation to

a-brass was accompanied by a decrease in hardness. Two tetragonal

intermediate phases were found before the transformation was complete.

Hornbogen and Warlimont (34), using the electron microscope,

studied the mechanism of the isothermal transformation of quenched

8-brass and proposed a generalized definition of the bainite trans-

formation. The bainite transformation is between the martensitic

and nucleation-and-growth transformations. Lattice defects in great

density are created which allow a segregation of the atoms, and they

act as nucleation sites. The transformation, itself, occurs like

martensite by a shear process.


2.14 Radiation Damage

Little work has been done on the effect of radiation on the mat-

tensitic transformation. Zakharov and Maksimova (35) studied the ef-

fect of neutron irradiation on the martensitic transformation of










hi-carbon alloy steels and Fe-Ni-Mn alloys. The samples were irra-

diated at ambient reactor temperature (4 = 5 x 1016 and 1017n/cm2)

and the course of the transformation was followed with magnetic meas-

urements. In the steels which contained carbon, the irradiation

raised the transformation start temperature 150C. This was considered

an activating effect. (Porter and Dienes assumed that this was due to

precipitation of austenite.) The "activating effect" was decreased

after larger irradiation times and was removed after aging the speci-

mens at temperatures below 1000C. Also, more martensite was formed

at a given temperature than before. In the Fe-Ni-Mn alloys, which

contained hardly any carbon, the reverse effect was obtained. The

stability of the austenite was increased, the martensitic start tem-

perature was lowered, and the amount of transformation was decreased.

It was concluded from these results that during irradiation there is

a simultaneous development of structural changes which affect the

austenite stability in opposite directions. Therefore, the obser-

vation of opposing effects depends on the total neutron flux and the

properties of the alloy. In the early stages of damage, transforma-

tion is favored. Later, there are structural changes which have the

opposite effect.

Porter and Dienes (36) investigated the effect of neutron irra-

diation on the martensitic transformation in Fe-Ni alloys. They

found that the M was lowered for doses above 2.5 x 1017 nvt at 1000C.
S
They observed no change in the kinetics. This effect was thought to

be associated with an increase in the critical shear stress of the

matrix material. For samples which were partially transformed to

martensite, neutron irradiation lowered the M point and partially
s









recovered the plastic deformation produced by the prior transformation.

This strain recovery was thought to be due to the annealing of shallowly

trapped damage by enhanced diffusion and by the mutual annihilation of

point defects.

Weiss-Hollerwager (37) studied the effect of neutron irradiation

on the martensitic transformation of a chrome steel which contained

1.26 percent carbon. For doses of 1017 and 5 x 1017n/cm2, 5 percent

more martensite than before was found at the end of the transformation.

During irradiation with doses of 1018n/cm2, 25 percent martensite was

found. Cooling created only about 10 percent more martensite.

A summary of the past work that concerns irradiation effects on

the martensitic transformation is given in Table 1.






TABLE 1. Summary of neutron irradiation effects on martensitic transformations.


Ms IRRADIATION EFFECTS
AUTHOR and YEAR MATERIAL
UNIRRADIATED (INT. FLUX IN NEUTRJCM2)


AILZAKHAROV 8 0.48% C 0=5.1016: Ms+50C ------ -60
%M
O.P MAKSIMOVA 7.7 % Mn IO1C 10% more end-mortensite s.o16 '

(1957) 2.2 % Cu u -20t
Balance Fe 0
-22q (TOO -100 0

B.WEISS- I. 26% C 0=10. and 5.10: ..
-50
HOLLERWOGER 0.36% Mn 5-- 5C Ms=+10*C and ca.+ 35 C unirr.

(1960) 0.42%Si 5% more end- mortensite iO8
5.40 %Cr = 101:22% martensite at "
Balance Fe room temp. and 20% less .10

end-martensite T*C -150 -too -50 0

A.I. ZAKHAROV 8 0.02 % C ~1017: Ms=-60*C 20
O.P.MAKSIMOVA 22.4%Ni -39C 3 % less end-martensite o 7-1 10
(1957) 3.48 %Mn
Balance Fe (T C)-100 00

L.F. PORTER 8 26.37% Ni +2.60C ,* 1.6.1018 Ms=-12"C 7t 10
G.J. DIENES 0.018 %C (Variation between T
'*e*o'-7 IR e
(1959) 0.197% Mn +11.2 and +2.6*C) I
.4
0.045 %Si

Balance Fe TC -32-20 -10 0















CHAPTER III


EXPERIMENTAL METHODS


3.1 Sample Preparation

81-brass samples containing between 38.3 and 39.4 wt percent zinc

were prepared. These compositions were selected in order that the

temperatures of the transformation would be in a range practical for

the experimental apparatus.

The purity of the samples was very important. Unstable impurities

which might precipitate or dissolve during the various temperature

changes could affect the characteristics of the martensitic transforma-

tion, and some impurities when irradiated could give unwanted products

with long radiation half-lives.

The alloys were made from 99.999 percent copper rods obtained from

A. D. Mackay, Inc. and 99.9999 percent zinc pellets supplied by United

Mineral and Chemical Corporation. The copper and zinc were melted in

an evacuated vycor tube using an induction furnace. The melted alloy

was shaken manually and quenched in water to eliminate segregation.

The outside layer was removed on a lathe after which the alloys were

worked, re-incapsulated,and homogenized for 300 hours at 800C. Then

the alloys were rolled into long strips of about O.lmm thickness. Al-

loys'containing the higher percentages of zinc had to have an inter-

mediate heat-treat before being rolled to the final size. The samples

were cut into the shape shown in Figure 2 and heat-treated in a quartz





















< 70mm




10mm
_______________________________________: --- -i


Shape of the sample for resistance measurements.


Figure 2.









tube. The tube was first repeatedly evacuated and flushed with argon

with the samples at the cold end of the tube. With the argon atmos-

phere present, the samples were moved into the hot end of the tube,

heated at 8700C for five minutes, and quenched into previously boiled

water of 20C. The quench yielded the metastable ordered Bl-phase.

Scraps of brass around the samples were used to prevent de-zincing.

About 15 samples in a pack were heat treated together. The com-

position of some samples was such that the "massive transformation"

to the supersaturated a-phase occurred. Because the samples had to

fall about two feet before being quenched, some were cooled slightly.

This lowered the quenching temperature of these samples into the a+B

region where some a precipitated out. Because of these procedures,

various amounts of a-phase were present along with the 81-phase.


3.2 Quantitative Analysis

The amount of a and B1-phase present in the samples was obtained

after the final quench using x-ray diffraction, resistivity measure-

ments, and optical microscopy. In the x-ray method, the amounts were

determined by comparing the integrated intensities of two of the main

peaks of each of the phases. This method was non-destructive and very

convenient for this work. Since the electrical resistivity of a two-

phase material is a linear function of the volume fractions of the

two phases present, the amount of each phase could also be determined

by knowing the resistivity of the sample and the individual resistivi-

ties of the two phases. The third method of determining the amounts

of the phases present was by quantitative metallography. All three

methods yielded, within the error limit, the same ratio of a and









B1-phase. Chemical analysis was provided by V. Horrigan of the Ana-

conda American Brass Company. The zinc content of the samples varied

less than 0.06 percent.


3.3 Cryostat and Temperature Control

Two units could be used for the temperature bath. In the tem-

perature range between +10C and -160C, which covers almost every

M -temperature in these experiments, isopentane was employed as the

cooling medium. Isopentane could not be used much above +10C be-

cause of its high vapor pressure and below -1600C because of high

viscosity. The isopentane, which was held in a one-gallon metal Dewar

flask, was cooled by liquid nitrogen pumped under pressure (provided

by an argon tank and regulator) through a 15-foot copper tubing coil

immersed in the flask. The flow was regulated by a Linde temperature

controller using two thermistors in the cooling bath. The tempera-

ture was found to be constant within 20C. The bath was continuously

circulated by means of a magnetic stirrer. An electric immersion heat-

ing coil was built into the Dewar flask for use when heating was needed.

For alloys with an M -temperature near 00C, the samples were ini-
s
tially placed in a water bath whose temperature could be maintained

between +20C and +980C. As cooling was desired, the water was allowed

to circulate through an ice bath. The amount of cooling was regulated

by a heating device which worked at the temperature specified by a

controller.

The temperature of the samples was taken during each resistivity

measurement with a copper-constantan thermocouple and a Leeds and

Northrup potentiometer with temperature calibration.

A schematic of the cryogenic unit is given in Figure 3.














Controller --- -
_________________ .


Compressed
Gas .--=


Liquid N2


Thermostat


Dewar


N2


Specimen


Immersion
Heater


Magnetic Stirrer


Figure 3. The cryogenic unit.









3.4 Resistance Measurements

The resistance measurements were obtained using a Leeds and

Northrup K-3 potentiometer to measure the voltage drop across the

potential leads of the sample. A one-amp direct current was made

to flow through the sample. The current was regulated by a vari-

able resistor of 12 ohms and monitored across the potential leads

of a 0.001 ohm standard resistor by an auxilliary input of the K-3

potentiometer. Three 12-volt batteries in parallel were used as a

current source, thus affording a more nearly constant current than

only one battery. The resistance measurements were found to be re-

producible at a given temperature within 0.03 percent. The circuit

diagram is shown in Figure 4.

Three sample holders of micarta were used so up to three samples

could be measured at one time. Tests were made on the reproducibility

of the resistance of samples removed from the sample holders, turned

over, and replaced in the sample holders. The change in resistance

was again within 0.03 percent.

A Starrett micrometer was used to measure the dimensions of

the samples in order to obtain resistivity data from resistance meas-

urements.


3.5 Metallography

For metallography work, the specimens were polished by standard

techniques through Linde B and diamond paste. The specimens were

etched for a few seconds in a solution of 25 mL of ammonium hydroxide,

35 ml.of water, and 1 ml. of hydrogen peroxide. a-phase, B1-phase,

and martensite could be differentiated as they all gave different






12V-


Figure 4. Circuit for resistance measurements.









appearances after etching. A Bausch and Lomb metallograph was used

for the optical microscopy.

For a quick examination of samples to determine if the Bl-phase

was present, a macroetch of equal parts HNO3 and water was used. The

81-phase appeared as small crystallites which were very distinguish-

able from the larger unetched grains of a-phase.


3.6 Irradiation and Safety Precautions

The samples were irradiated in the Oak Ridge National Laboratory's

Bulk Shielding Reactor with integrated fluxes between 5 x 1016 and

5 x 1018n/cm2, E > 1 mev. The samples were under helium atmosphere

with a pressure of one atmosphere and the temperature was 510C.

The irradiated samples, when not being used, were kept in an

enclosed lead container with a wall thickness of 1 inch. With all the

irradiated samples in this lead container, a Geiger counter at a dis-

tance of 12 inches showed a radiation level not beyond the cosmic

radiation level. A wall of 2-inch lead brick and a bottom plate of

1-inch steelwere placed around the cryostat during measurements. A

Geiger counter showed no increased radiation level outside this wall.


3.7 X-Ray Diffraction

A Norelco diffractometer with a high-intensity copper tube was

used for the x-ray work. Modifications were made to the radiation

shield so the samples for these experiments could be handled without

bending and so cold-stage work could be done.

Dry nitrogen from a tank forced liquid nitrogen into the elongated

radiation shield, whose window was closed from the atmosphere by mylar.

After cooling started, any areas which could let air in became frosted









and were sealed. Thus, no icing took place on the sample as a nitro-

gen atmosphere was formed. Figure 5 shows this unit.


3.8 Electron Microscopy

The same material which was used in the resistance studies served

as stock material for the transmission electron microscopy.

The first sample preparation step was the "dimpling" of small

disks. The dimpling technique consisted of allowing a thin stream

(jet) of liquid electrolyte (50 percent orthophosphoric acid) to im-

pinge on the disk and produce a concave surface. Initially, a disk

would be thinned until a hole appeared. Then a smaller amount of elec-

trolyte would be used to produce the dimple in the other samples. The

jet producer and container for the electrolyte were made of glass and

contained a platinum wire which constituted the cathode. The speci-

men was the anode (Figure 6).

After dimpling, the sample was electro-polished until the very

first small hole appeared. For this, the sample was held with plat-

inum-tipped tweezers between two point electrodes. There was a po-

tential difference between the tweezers and the electrodes. The elec-

trolyte was again 50 percent orthophosphoric acid which was cooled

below room temperature with acetone and dry ice to slow down the re-

action. During this final polish the sample was periodically removed,

washed with alcohol, and examined for a small hole with the aid of a

light placed behind the specimen. The area around the first hole was

usually thin enough for transmission work. If the sample was polished

very long after the first hole appeared, all the thin area was de-

stroyed. The yield of useable samples was very small. If a satis-

factory sample was obtained, care had to be taken to wash the sample


well with alcohol to prevent contamination.











Radiation Shielding


-Sample
I--Barrel


e

Exhaust


Counter
Liquid
N2


Dry
N2


Figure 5. Cold unit for the Phillips x-ray diffractometer.
























glass
container


+


"dimpled" sample


Figure 6.


Dimpling unit for preparation of
transmission electron microscopy samples.





32


A cold stage built for the Phillips 200 Electron Microscope by

Ladd Research was used in this work. The unit consisted of a sample

holder, dewar, and thermocouple. After insertion of the sample in the

microscope, liquid nitrogen was added to the dewar and the cooling

would begin. The temperature was monitored by a built-in copper-con-

stantan thermocouple. The speed of cooling could be adjusted by the

amount of liquid notrogen added and by a built-in heating unit.















CHAPTER IV


RESULTS


4.1 The Basic Transformation

The main features of the martensite transformation curve of BI-

brass, as monitored by electrical resistance measurements at changing

temperatures, are discussed in order to determine the characteristics

of the transformation.

Figure 7 shows relative resistance or relative resistivity (set

equal to 1 at 0C) vs. temperature. (This will be referred to as the

resistivity-temperature curve in the future.) The relative resistance

decreases with constant slope as the temperature is lowered. At a

certain temperature, the curve deviates from a straight line. This is

the starting point of the transformation (Ms). Since the slope changes

very gradually at this inflection point, the M -temperature can only

be determined to within an accuracy of 1fC. At a lower temperature,

the resistivity-temperature curve shows a resistivity minimum which

is designated as M. At the temperature MF, the transformation is

finished, after which the resistivity-temperature curve again becomes

a straight line. On heating the sample, the curve again deviates from

a straight line. This is the A -temperature, lower than the M -tem-
s s
perature, where the parent phase starts forming. The transformation

is completed at a temperature AF after which the resistivity-temper-

ature curve is a straight line.





34















1.05
_ Mr




I.0





.95


M. t


.90 M

S -10 -20 -30 -40 -50 -60 -70 -80 -90 T (0)
I I I I I i i I i I I I


Figure 7. Relative resistivity versus temperature of B1-brass (38.8 wt.
percent zinc).









To find the amount of martensite formed at a given temperature

and the degree of hysteresis after cooling and heating, a plot of

percent transformation vs. temperature was made from the resistance

data (Figure 8a). This curve was constructed by taking the ratio

of the difference in resistivity between the straight line or extra-

polated straight line portion of the curves for the parent phase and

the martensite phase at a given temperature to the difference in

resistivity between the curve and the straight line or extrapolated

straight line of the curve for the parent phase at the same tempera-

ture;
p-p
percent martensite = (100) (see Appendix II).
M 81

The rate of transformation-temperature curve, which is equivalent to

the amount of martensite formed per degree, was constructed from the

derivative of the data of the percent transformation-temperature curve.

The martensite phase formed by cooling had a higher specific

resistivity (p) and a greater temperature coefficient (6) than the a1-

phase. Table 2 gives the resistivities and temperature coefficients

of all the phases studied in this work.


TABLE 2. Resistivity of the various phases.


Phase p at 0OC (p-ohm-cm) e(1/deg)


81 5.3 .0128

8" (cooling martensite) 6.9 .0179

a 6.8 .0116

al (deformation martensite) 7.4 .0133






























Figure 8. Transformation curves.

a. Percent transformation versus temperature.

b. Percent transformation per degree versus
temperature. (Calculated from Figure 7.)










z

S5-
0



LL.


10 -



wM
o
0

t00



90-


80


w
S70-


Li 60 -
o/
0
U-
Z 50
c-


-20 -30 -40 -50 -60


0 -10


-70 -80 --90









The reason for using the resistance measurements to monitor the

martensitic transformation of Bl-brass was that the resistivity of

the martensite in 81-brass is much higher than the resistivity of

the parent phase and resistance can accurately and easily be measured.

Thus, very small amounts of transformation could be detected. (More

details are given in Appendix II.)

All factors such as long-range order, short-range order, anti-

phase boundaries, and lattice defects which cause changes in resis-

tivity were not changed during cooling.

Local stresses set up by the formation of martensite plates might

be expected to increase the resistance of both the martensite and the

surrounding parent phase and thus influence the resistivity-temperature

curve. The amount of the increase in resistance should not be greater

than would be caused by extensive cold work. This increase is usually

not more than one percent for most alloys. Experiments were made that

showed that the samples of 81-brass had to be bent enough to create

a permanent crease in the metal to cause a 0.5 percent change in re-

sistance. It is assumed that the transformation strains would never

be this great. Therefore, the stresses accompanying the transforma-

tion introduce no serious error.


4.2 Thermal Cycling

The M -temperature and other characteristics of the martensitic
s
transformation were found not to be reproducible when samples of a

certain composition were repeatedly cooled to the temperature of com-

plete martensite formation and heated to room temperature.

These effects were attributed to retained'martensite which was

substantiated from the following observations:









1. After one full cycle, the resistivity curve obtained from

heating the sample (later referred to as heating curve) does

not meet the resistivity curve obtained from cooling the

sample (later referred to as cooling curve) in the linear

region around 0OC; i.e., the specific resistivity (p) of the

sample is higher after cycling (Figure 9). Since the martensite

phase has a higher specific resistivity, the increase of p at

0C is thought to mean that some martensite is retained at

that temperature.

2. The slope of the linear portion of the resistivity vs. tem-

perature curve (the temperature coefficient 8) at temperatures

below MF is larger than e at temperatures above Ms. This is

indicated in Figure 9, where a line parallel to the linear

portion at temperatures below MF is drawn on the cooling curve

near OOC. This line is labeled martensitee." Figure 9 also

shows that 8 from the heating curve at temperatures above AF

is larger than 0 from the cooling curve in the same temperature

range. Since a larger 6 implies the presence of martensite, it

is deduced that the observed larger 6 at temperatures above A ,

obtained after cooling and heating, implies retained martensite.

3. Metallographic evidence of martensite plates was found at

room temperature after a full cycle and was interpreted to

mean that some martensite was retained (Figure 10). The needles

could not be detected in all sections examined and this was

attributed to the fact that the amount of retained martensite

is small and to the possibility that the martensite plates

which were retained have a size below that of the resolution

of the optical microscope.


















































-20 -30 -40 -50 -60
I I 1 I 1 I I I I I


-80 -90 -100
I I I I I


TEMPERATURE (C)




Figure 9. Relative resistivity versus temperature of B1-brass (38.8
wt. percent zinc) containing retained martensite.


- 1IO






-1.05


- .96


- .90


-10
I




























































Figure 10. Optical micrograph of B$-brass (38.8 wt. percent zinc)
after cycling to low temperatures (room temperature,
magnification 250 x) .










4. Retained martensite was also observed in transmission-electron

micrographs made from a sample which had been cooled below M"

and heated back to room temperature in a cold stage (Figure 11).

No attempt was made to compare the amounts of retained mar-

tensite observed by optical and electron microscopy because of

the difference in behavior of thin films and bulk samples.

5. A third cycle reproduced the second cycle almost perfectly.

This means that after the second cycle no additional retained

martensite is left at temperatures above AF.

The amount of retained martensite at 0OC was computed by taking

the ratio of the difference between the resistivity curves before and

after cooling to the difference between the parent phase resistivity

curve and the extrapolated straight line portion of the martensite

phase resistivity curve. The amount of retained martensite calculated

by this method was found to be dependent upon the Ms-temperature. At

M -temperatures lower than about -330C no martensite is retained at O0C.
s
With increasing M -temperature, the amount of retained martensite in-

creases. Figure 12 shows that up to 5 percent of the total amount of

martensite can be retained at 0OC.

When the same sample is cooled a second time, Ms is shifted to a

higher temperature (Figure 13). No change is noted in Ms on the third

cycle.

In summary, some martensite, formed when B1-brass is cooled to

sub-zero temperatures, is retained at room temperature. This marten-

site is stable and only occurs in samples with high Ms-temperatures.

After the first cycle the samples which contained martensite had in-

creased M -temperatures.
s









































*


w.


Figure 11.


Transmission electron micrographs of 81-brass martensite
(38.8 wt. percent zinc). Magnification 14000x.


a. During cooling.


b. Retained.


r

d



rt
C1






44














z
S4-











-o1 -20 -30 -40 M8 [C]


























Figure 12. Retained martensite in percent at room temperature
versus M -temperature.
s


I


























































TEMPERATURE (C)


Figure 13.


Relative resistivity versus temperature of 81-brass
(38.8 wt. percent zinc).









4.3 Effect of a-Phase on the Martensitic Transformation

In the course of this investigation it was found that the resis-

tivity-temperature curves of a group of samples which had the same

composition and heat treatment were not the same (Figure 14). Optical

microscopy, x-ray diffraction, and resistivity measurements showed the

presence of varying quantities of a-phase, which was first observed

by Phillips (10).

From the quantitative analysis it was seen that the sample of

Figure 14a was about 100 percent B1-phase, and the sample of Figure 14b

contained about 54 percent 01-phase. Five main differences of these

curves were observed.

1. The difference between M and M was greater in Figure 14b than
s
in Figure 14a.

2. There is a considerable variation in M between the curves in
s
Figure 14a and Figure 14b.

3. At OC the resistivity difference between the parent phase and

the martensite phase (pM-p ) is about twice as large in Figure
M PI
14a as in Figure 14b (pM at O0C was obtained by extrapolation).

pM-P 1 is called H and may also be taken as the amount of 81-

phase present.

4. The degree of hysteresis (defined as the temperature difference

between the means of maximum and minimum resistance of cooling

and heating (15)) is about 50 percent larger in the curve of

Figure 14b than in the curve of Figure 14a.

5. The slope of the straight-line portion of the curve above the

M -temperature is larger in Figure 14a than in Figure 14b.

Percent transformation-temperature curves (Figure 15) and rate of

transformation-temperature curves were constructed as described earlier.





























Figure 14. Relative resistivity versus temperature of 81-brass
(38.8 wt. percent zinc).

a. 100 percent Bl-phase in sample.

b. 54 percent 81-phase in sample.





48


















(A)






t




(B)








I I I I I I I
-10 -20 -30 -40 -50 -60 -70 -80 -90
TEMPERATURE (C)



















































--- TEMPERATURE (C)

100% 0, PHASE


D)


0 -20 -40 -60 -80-100-120-140
C-- TEMPERATURE (C)

54% 0, PHASE


Percent transformation versus temperature.
a. 100 percent B1-phase.
b. 54 percent Sl-phase.
Percent transformation per degree versus t
c. 100 percent a1-phase.
d. 54 percent 81-phase.
(Calculated from Figure 14)


temperature.


Figure 15.









The area of the hysteresis loop increased, the maximum rate of trans-

formation per degree decreased, and the temperature range of transforma-

tion (Ms-M_) increased as the amount of a-phase in the samples increased.

Theoretical resistivity-temperature curves were made to determine

the effect of the presence of the a-phase.

The resistivity-temperature curve of a-brass was found to be a

straight line with a slope less than that of the linear part of the

01-brass transformation curve at temperatures above M These measure-
s
ments were made to assure that no transformation of any type occurred

in the a-brass at temperatures in the range used in these experiments.

Using the actual resistivity-temperature curves of a sample of

100 percent a-phase and a sample of 100 percent $1-phase, curves with

different amounts of 81 and a were constructed. The proportion of the

resistivity of each of the two phases was taken at a given temperature

(using the assumed amounts of each phase), added together, and plotted

(Figure 16).

The following features were noted from the theoretical curves:

1. The M -temperature was not influenced by the mathematical

addition of a-phase to 81-phase.

2. Additions of a-phase to BS-phase increased the temperature

difference between M and M.
s
3. With increased additions of a-phase the resistivity difference

H at O0C decreased.

4. At a critical amount of a-phase (around 15 percent) no minimum

resistivity was observed.

5. The slope of the straight line portion of the curves above the

M -temperature approached the slope of the curve of the a-phase
as the amount of a-phase in the samples was increased.
as the amount of a-phase in the samples was increased.



















I
I
I


-LO5


L .95




S.90



.90


50% B








25 % B


9%B
5 %B
W


S 10 -00 -30 -40 -50 -60 -70
I I I l I I I I I I I I T ( C)


Figure 16.


Parts of transformation curves with various amounts of A- and
B-phases (calculated). 6 of A smaller than 0 of B.


-0-I


tAI


---


m









No changes are noted in the percent transformation-temperature

curves or rate of transformation-temperature curves since all the

theoretical curves were mathematically constructed from the 100 per-

cent B1-phase transformation curve.

To describe, in general, the behavior of an added non-transform-

able phase, another curve was constructed assuming that the non-trans-

formable phase had a greater slope than the linear portion of the 100

percent B1-brass transformation curve above the M -temperature (Figure

17). The same features as listed above were noted.

The resistivity difference (H), taken from the theoretical curves,

plotted versus percent B1-phase present (Figure 18) was used to de-

termine the amount of B1-phase present from experimental resistivity-

temperature curves.

Any changes seen in both the theoretical and experimental resis-

tivity curves are geometrical effects due to the added a-phase. The

increased difference in M and M with increasing amounts of a-phase
s
and the very similar shapes of the curves including the changes in H

and the slope are examples.

The M -temperature of samples originally the same composition which

contain equal amounts of a-phase after heat treatment may not be the

same because of one or all of the ways the a-phase can be formed.

1. If a sample has a composition in the range where the massive

transformation occurs, the quenched samples will contain dif-

ferent amounts of a-phase due to the quenching speed. The

M -temperature of these samples will probably be a function

of the amount of a-phase present.

2. When several samples are quenched together, some may lose more

zinc than others. The loss of zinc will change the composition





































































Figure 17.


Parts of transformation curves with various amounts of
A- and -B-phases (calculated). 6 of A larger than 6
of B.
















100

90

80

70-


L B 6o

a-
. 40



20
Io
10-


0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30


H


Figure 18. H versus percent 81-phase.









and thus change the M -temperature.

3. The a-phase may also be formed if the sample is cooled into

the a+B region and quenched. Samples treated in this manner

will contain different compositions of the 81-phase and dif-

ferent amounts of the a-phase, both of which will change the

M s-temperature.

Thus, with one or a combination of the three occurrences, the true

effect of the a-phase on the M s-temperature is "masked."

Therefore, the changes due to the actual physical presence of

the a-phase are seen in the experimental percent transformation-tem-

perature curves of samples containing different amounts of a-phase.

The area of the hysteresis loop increased, the maximum rate of trans-

formation per degree decreased,and the temperature range of transforma-

tioned widened as the amount of a-phase in the samples increased.


4.4 Plastic Deformation

Bl-brass samples were deformed to learn more about transformation

caused by deformation and how plastic deformation influences the char-

acteristic points when the sample undergoes the martensitic transforma-

tion on cooling. These experiments were also done in view of the fact

that very often neutron irradiation and plastic deformation cause simi-

lar effects to metals.

After a pre-deformation run, i.e., a measurement of resistance from

room temperature to a temperature of complete transformation and back to

room temperature, the samples were deformed a small amount and run again.

The samples would then be deformed many times, with runs made in between

each deformation. The deformation was by rolling and was measured by










the percent reduction in thickness. From the resistance-temperature

curves the changes in the characteristics of the curves could be noted.

Figure 19 presents five different resistivity-temperature curves

corresponding to the transformation from the 81 to B" phase after dif-

ferent degrees of reduction in thickness on the same sample. The fol-

lowing observations were made from these curves.

1. With increasing degree of deformation the M -temperatures are

shifted to lower temperatures. This shift amounts to some 350,

compared to the undeformed state. This is also indicated in

Figure 20 where AM (the shift of M compared to the undeformed
s s
state) is plotted versus the degree of deformation. AM in-
s
creases rapidly to about 16 percent reduction. For higher

deformations the further increase of AM was about negligible.
s
2. With increasing degree of deformation the temperature of mini-

mum resistivity (M) is also shifted to lower temperatures.

This shift is about 60*C, compared to the undeformed state.

In Figure 21, AM is plotted as a function of deformation. It

is seen that AM increases rapidly until about 16 percent de-

formation then it levels off.

3. The temperature coefficient of resistivity, e, i.e., the slope

of the straight-line portions of the resistivity-temperature

curves at temperatures above Ms,is seen to be a function of

deformation as it decreases with increasing amount of deforma-

tion. Three different slopes, corresponding to three degrees

of deformation are drawn in Figure 19 on the curve of 15.3 per-

cent deformation. In Figure 22 e is plotted as a function of

deformation. A rapid change in e is observed up to deformations
































Figure 19. Relative resistivity versus temperature for $1-brass
(38.8 wt. percent zinc) at five different degrees of
deformation.










































































0 -20 -40 ,-60 -80 -100 -120

-- TEMPERATURE (C0)


C,,




LiL
U

C,)






















40

230

20

10

0
0
Co


Figure 20.


Shift of M (AM ) versus deformation.
s s


0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

% DEFORMATION

Figure 21. Shift of M(AM) versus deformation.


2 4 6 8 10 12 14 16 18 20 22 24 26 28

% DEFORMATION


I 1 a I I a a a


M


.e


















23

22




20

PI9

0,8


0 2 4 6 8


10 12 14 16

% DEFORMATION


18 20 22 24 26


Figure 22. 6 and H (percent B1-phase present) versus percent deforma-
tion.


-. No



+\+
+

. I I I I a a I a


100

90

80

70

60

50

40










of 12 or 13 percent. With higher degrees of deformation 6 is

almost constant.

4. A further characteristic property of the transformation curve

is the resistivity difference between the cooling curve and

the extrapolated linear portion of the heating curve at 00C.

This quantity was denoted previously as H and was taken as a

measure of the amount of the 01-phase present (Figure 18). H

(the percent B1-phase present after deformation) is seen to

decrease with increasing amounts of deformation (Figure 22).

At small deformations, H decreases rapidly up to 12 to 16

percent deformation after which it decreases only gradually.

5. With increasing degree of deformation, A is shifted to lower
s

temperatures. AA plotted versus deformation would be similar

to the AM vs. deformation curve. The A -temperature, after
s s
deformation, is shifted 330C, compared to the undeformed state.

The five above mentioned properties all point to a common behavior.

At the beginning of deformation they change rapidly, but after a criti-

cal degree of deformation (12 to 16 percent) they almost become constant.

It had been mentioned by other investigators (24) that when de-

formed, B1-brass would transform to martensite. In this research, this

martensite is called deformation-martensite. The proof of the presence

of deformation-martensite in this work is given by optical micrographs,

electron microscopy, resistivity measurements, and x-ray diffraction.

A series of a1-brass samples with 38.8 weight percent zinc which

were plastically deformed by cold-rolling and investigated with optical

microscopy are shown in Figures 23-27 and the results are listed in

Table 3. At deformations of 3 percent and larger, the martensite needles can



























































Figure 23. Optical micrographs of deformed 81-brass (Q8.8 wt. percent
zinc). Magnification 560x.

a. 1 percent deformation.

b. 2 percent deformation (needles are deformation-martensite
from cutting).


























































Figure 24. Optical micrographs of deformed 81-brass (8.8 wt. percent
zinc). Magnification 560x.

a. 3 percent deformation.

b. 6.5 percent deformation.


























































Figure 25.


Optical micrographs of deformed S1-brass (38.8 wt. percent
zinc). Magnification 560x.

a. 13.4 percent deformation.

b. 17.0 percent deformation.





























































Figure 26.


Optical micrographs of deformed B1-brass (38.8 wt. percent
zinc). Magnification 560x.

a. 23.2 percent deformation.

b. 35.5 percent deformation.




























































Figure 27.


Optical micrographs of deformed 81-brass (48.8 wt. percent
zinc). Magnification 560x. 43.8 percent reformation.






67


TABLE 3. Visual observations on 81-brass after various
degrees of rolling at room temperature.



Degree of deformation in percent Observations
.. Observations
(reduction in thickness)


1 Only 81-phase and a little a-
phase.

2 Only 81-phase and a little a-
phase. Needles shown are those
of deformation-martensite formed
when the sample was cut.

3 Isolated needles of martensite.

6.5 Martensite needles seen in almost
all areas, some untransformed
left. Grain boundaries are still
visible.

13.4 Thick needles in all areas.

17 Deformed thick needles.

23.2
35.5 } No individual needles are seen
43.8 anymore.









be seen. For deformations above 13.4 percent, the martensite needles

begin to be deformed.

Figure 28 shows electron micrographs of B -brass that had been

pulled in tension and then prepared for the electron microscope. The

plates seen are those of deformation-martensite.

In Figure 29 the absolute resistivity-temperature curves of the

transformation of a sample, undeformed and 13 percent deformed, are

given. The resistivity change after deformation is shown. This sample

contained 21 percent a-phase (calculated as mentioned earlier) and 79

percent transformable 1B-phase. The 13 percent deformation transformed

a portion of the 81-phase to deformation-martensite so that after de-

formation, the sample contained 41 percent deformation-martensite, 38

percent $1-phase, and 21 percent a-phase. It can be seen also from

this plot that the temperature coefficient of resistivity of the de-

formation martensite is lower than that of both the cooling martensite

and the parent $1-phase.

The percent transformation versus temperature curves were constructed

for the deformed samples as described in section 4.1 (Figure 30). These

curves, drawn for cooling and heating, form a hysteresis loop. The first

derivative of the above data for the cooling curve was taken to obtain

the rate of transformation per degree and was plotted versus the temper-

ature.

The area of the hysteresis loop was seen to increase as the amount

of deformation increased (Figure 31). Also, the maximum rate of trans-

formation per degree on cooling decreased and the temp rature range of

transformation was spread as the amount of deformation increased.

The investigations described in this section showed that five char-

acteristic properties of the transformation curve changed rapidly up to



























































Figure 28. Transmission electron micrographs of 81-brass (38.8 wt.
percent zinc) deformed in tension. Magnification 8200<.













































TEMPERATURE (*C)


Figure 29.


Specific resistivity (in pQCM) versus temperature for s1-brass (38.8
wt. percent zinc) at two different degrees of deformation.















60
o 60
o 40
30
30
p,


20 0 -20 -40 -60 -80 -100 -120
TEMPERATURE
0% DEFORMATION


Figure 30.
a,
b.

C.
d.


2.0 [


20 0 -20 -40 -60 -86 -100 -120 -140
TEMPERATURE
15.3% DEFORMATION


Percent transformation versus temperature.
0 percent deformation.
15.3 percent deformation.
Percent transformation per degree versus temperature.
0 percent deformation.
15.3 percent deformation.
(Calculated from Figure 19)


> 0 -20 -40 -60 -80 -100 -120 -140


d)


_j __ i


i


50
40













w 20-


15-



t
< 10 -


< 5 -



O 2 4 6 8 10 12 14
/o Plastic Deformation


Figure 31. Area of hysteresis loop of percent transformation curve versus
deformation.


16










about 15 percent deformation and remained constant at higher deforma-

tions. The hysteresis loop was widened, the maximum speed of transforma-

tion decreased, and the temperature range of transformation was spread

over a greater range when the samples were deformed. These property

changes were due to the formation of deformation-martensite which was

seen in optical and electron micrographs.


4.5 Electron Microscopy Observations

Although some of the observations of the martensitic transforma-

tion which were made by using the electron microscope have been mentioned

earlier, it is believed that a separate section would be beneficial.

It was seen in these investigations and in studies by Hull (29)

that after preparation of some B1-brass samples for transmission elec-

tron microscopy, martensite needles appeared near the edge of the

foils at the very thin regions (Figures 32 and 33). This martensite

was interpreted to be deformation-martensite as the structure was face-

centered cubic (as determined from electron diffraction) which is the

same as that of highly deformed Bl-brass. This phenomenon did not

occur in each sample but in enough to make their appearance signifi-

cant. This martensite (deformation-martensite) did not grow when the

foil was cooled and transformed in the electron microscope. The most

distinctive features of the martensite are the striations within the

needles.

In evaluating the absolute temperatures obtained with a thermo-

couple, it must be noted that the electron beam will heat up a portion

of the sample and it is not really known if the temperature recorded










-i

(4


*1 ,


Figure 32.


Transmission electron micrographs of $1-brass (38.8 wt.
percent zinc) where martensite formed during thinning.


a. Magnification 12600x.
b. Magnification 17000x.


V


5:


























































Figure 33. Transmission electron micrographs of B1-brass (38.8 wt..
percent zinc) showing striated region which makes, up the
martensite formed during thinning.

a. Magnification 25200x.


b. Magnification 58900x.









is that of the part of the foil being examined. However, the tempera-

ture differences should be accurate.

As the prepared foils were cooled in the electron microscope and

just before any of the cooling martensite was seen, there was a great

movement of the contours of the foil, somewhat of an undulating motion

believed to be due to a bending of the foil. Immediately after this

the first martensite was seen. If the cooling was fast, the martensite

plates "exploded" into view and grew until stopped by a barrier. With

slow controlled cooling, the plates were seen as thin lines growing

first in length then in thickness when further cooled.

Figure 34a shows the first evidence of a martensite plate at sub-

zero temperatures. A thin line was first seen. (This foil was very

dirty because of problems with the vacuum system of the electron micro-

scope.) The black dot is an impurity used as a landmark. As the tem-

perature was lowered, the amount of martensite increased. Figures 34

and 35 show the plates at various stages of the transformation. A

second needle and the thickening and joining of the two needles is

easily seen. The percent of martensite seen in the same section of

each picture is measured by the area of the martensite compared to the

area of the section and is givenin Table 4 and Figure 36.

Figures 37 and 38 show the growth of martensite in another area.

Table 5 gives the temperature difference and amount of martensite seen

in a common area of each of the pictures. These pictures were made at

the temperatures of the greatest martensite growth. The inner striated

structure can be seen in these needles. The inner structure, in most

cases, was seen to form after the needle was formed.
I

























'3d


'I


Figure 34.


c d


Transmission electron micrographs of 81-brass
percent zinc) in cold stage showing growth of
at various temperatures below M -temperature.
tion 8200x.


(38.8 wt.
martensite
Magnifica-


a. M -temperature AT = 0.
s


b. AT = 50C

c. AT = 70C

d. AT = 80C


2.9 vol. percent martensite.

9.6 vol. percent martensite.

16.7 vol. percent martensite.









t---


Figure 35.


c d


Transmission electron micrographs of 81-brass
percent zinc) in cold stage showing growth of
at various temperatures below M -temperature.
tion 8200x. s


(38.8 wt.
martensite
Magnifica-


a. AT = 10C

b. AT = 120C

c. AT = 150C

d. AT = 180C


39.5 vol. percent martensJte.

64.0 vol. percent martensite.








































(CT--)


Figure 36.


Volume percent martensite versus AT from
the M -temperature.
s




-L-


80




























a

























b

Figure 37. Transmission electron micrographs of B1-brass (38.8 wt.
percent zinc) in cold stage showing growth of four needles
of martensite. Magnification 8200x.

a. AT = 0 37.5 vol. percent martensite.


b. AT = 3"C 59.4 vol. percent martensite.

























































b


Figure 38. Transmission electron micrographs of $1-brass
percent zinc) in cold stage showing growthlof
of martensite. Magnification 8200x.


a. AT = 5C

b. AT = 60C


(38.8 wt.
four needles


77.1 vol. percent martensite

85.0 vol. percent martensite.









TABLE 4. Percent martensite present at various temperatures (1).



Figure AT(OC) Vol. percent martensite


34 5 2.9
7 9.6
8 16.7
35 10 39.5
12 64.0
15
18






TABLE 5. Percent martensite present at various temperatures (2).



Figure AT(OC) Vol. percent martensite


37 0 37.5
3 59.4
38 5 77.1
6 85.0



When the foils were heated from temperatures of complete marten-

site formation, the martensite disappeared. The striated bands across

the needles first disappeared, starting at one end of the needle and

going to the other. There was no change in the width (Figures 39-43).

Thus, there were differences in the way the needles grew and disap-

peared.

Figures 44-54 show foils at various temperatures during the mar-

tensite formation. These pictures and the ones above of 81-brass mar-

tensite formed in the electron microscope using a cold stage were

probably the first of their kind. Many different areas of the foils

are shown. The inner structure of the needles and their boundaries

are particularly interesting.






























































Figure 39. Transmission electron micrographs of 81-brass (38.8 wt.
percent zinc) in cold stage with large martensite needle
still growing. Magnification 8200x.

a. T.


b. T 60C.




























































Figure 40.


Transmission electron
percent zinc) in cold
unification 8200x.


micrographs of B1-br ss (38.8 wt.
stage. Heating the ample. Mag-


a. T + 460C.

b. T + 580C.





























































Figure 41. Transmission
percent zinc)
disappearing.


electron micrographs of 81-b ass (38.8 wt.
in cold stage showing the ma tensite needle
Magnification 8200x.


a. T + 47C.

b. T + 810C.





























































Figure 42.


Transmission electron micrographs of a1-bi
percent zinc) in cold stage showing the mu
almost gone. Magnification 8200x.


a. T + 890C.

b. T + 1020C.


ass (38.8 wt.
.rtensite needle





























































Figure 43.


Transmission electron micrograph of 81-brass (38.8 wt.
percent zinc) in cold stage with martensite needle gone.
Magnification 8200x. T + 108C.




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