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IIT Kharagpur
i CONTENTS
Title Page i
Certificate of Approval iii
Certificate v
Acknowledgements vii
Declaration ix
List of Symbols xi
List of Abbreviations xiii
Abstract xv
Contents xvii
List of Tables xxiii
List of Figures xxvii
PART I
CHAPTER DESCRIPTION PAGE NO.
CHAPTER 1 INTRODUCTION 1
1.1 General background 1
1.2 Objective and scope of Part I of the thesis 2
1.3 Layout of Part I of the thesis 2
CHAPTER 2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Effect of processing on microstructure of WHAs 6
2.3 Effect of chemistry on microstructure of WHAs 9
2.4 Effect of microstructure on mechanical properties of WHAs
14
2.5 Deformation behaviour of WHAs 18
2.6 Adiabatic shear band formation in WHAs 20
2.7 Scope of present investigation on WHAs 23
CHAPTER 3 EXPERIMENTAL PROCEDURE 25
3.1 Introduction 25
3.2 Alloy preparation 25
3.3 3.3.1 3.3.2 3.3.3 3.3.4 3.3.5 3.3.6 3.3.7
Characterisation techniques Chemical analysis
Density measurement
Specimen preparation for optical metallography, SEM and EPMA studies
Specimen preparation for TEM
Optical metallography and SEM study TEM study
XRD study
26 27 27 27 27 28 28 28
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3.4 Mechanical testing 28
3.4.1 Compression tests 28
3.4.2 Tensile tests 29
3.4.3 Hardness tests 29
CHAPTER 4 TENSILE PROPERTIES AND
FRACTOGRAPHY OF SOME TUNGSTEN HEAVY ALLOYS
31
4.1 Introduction 31
4.2 Results 31
4.2.1 Characterisation of precursor powders 31
4.2.2 Optical microscopy 33
4.2.3 Density of alloys A to J 38
4.2.4 Room temperature mechanical properties 39
4.2.4.1 Hardness 39
4.2.4.2 Tensile properties 41
4.2.5 Fractography 44
4.2.6 Elevated temperature tensile properties of alloys G and I
48 4.2.7 Fractography of alloys G and I 49
4.3 Discussion 52
4.4 Conclusions 57
CHAPTER 5 COMPRESSIVE FLOW BEHAVIOUR OF
ALLOY-I
59
5.1 Introduction 59
5.2 Results 59
5.3 Discussion 76
5.4 Conclusions 80
CHAPTER 6 TENSILE FLOW BEHAVIOUR OF ALLOY-I 83
6.1 Introduction 83
6.2 Results 83
6.3 Discussion 90
6.4 Conclusions 100
CHAPTER 7 THERMO-MECHANICAL PROCESSING,
MICROSTRUCTURE AND TENSILE PROPERTIES OF ALLOY-I
103
7.1 Introduction 103
7.2 Results 103
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7.2.1 Microstructure 104
7.2.2 Hardness 107
7.2.3 X-ray diffraction study 109
7.2.4 Tensile properties and failure modes 110
7.3 Discussion 116
7.4 Conclusions 122
CHAPTER 8 SUMMARY OF CONCLUSIONS 123
References 125
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iv PART II
CHAPTER DESCRIPTION PAGE NO.
CHAPTER 1 INTRODUCTION 135
1.1 General background 135
1.2 Objective and scope of Part II of the thesis 136
1.3 Layout of Part II of the thesis 137
CHAPTER 2 LITERATURE REVIEW 139
2.1 Introduction 139
2.2 2.3
Literature review
Scope of present investigation on W-Nb alloy
139 141 CHAPTER 3
3.1
EXPERIMENTAL PROCEDURE Introduction
143 143
3.2 Details of as-received powder 144
3.3 3.4
Preparation of alloys
Characterisation techniques
144 145 3.4.1
3.4.2 3.4.3 3.4.4 3.4.5 3.4.6 3.4.7
3.4.8 Chemical analysis
BET surface area measurement Density measurement
Specimen preparation for optical metallography, SEM and EPMA studies
Specimen preparation for TEM studies Optical metallography and SEM study TEM study
XRD study
145 145 145 146 147 147 147 147
3.4.8.1 Rietveld refinement 147
3.4.8.2 3.4.8.3
Determination of extent of alloying
Determination of crystallite size and lattice strain
148 149 3.5
3.5.1 3.5.2 3.6
Mechanical testing Compression tests Hardness tests Oxidation study
151 151 151 151
3.6.1 Isothermal oxidation study 151
3.6.2 Pseudo-isothermal oxidation study 151
CHAPTER 4 RESULTS 153
4.1 Introduction 153
4.2 Results 153
4.2.1 Characterisation of as-received powders 153 4.2.2 Characterisation of mechanically alloyed powders 154 4.2.3 Characterisation of sintered alloys 158 4.2.3.1 Sintered alloys prepared from 5 h milled powders 158
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4.2.3.2 Sintered alloys prepared from 15 h milled powders
159 4.2.3.3 Hot isostatically pressed (HIPed) compacts 163
4.2.4 Mechanical properties 163
4.2.5 Isothermal and pseudo-isothermal oxidation test 165
4.2.6 Characterisation of oxide scale 168
CHAPTER 5 DISCUSSION 177
5.1 Mechanical alloying 177
5.2 Sintering 179
5.3 Oxidation 180
CHAPTER 6 CONCLUSIONS 187
Directions for the Further Research
189
References List of Publications About the Author
191 195
197
