study of gold-based alloy phase diagrams

282 Pages·2013·12.69 MB·English

STUDY OF GOLD-BASED ALLOY
PHASE DIAGRAMS
Submitted For The Degree Of Doctor Of Philosophy
BY
M. TAQI ZAHID BUTT
Department of Materials Technology,
BruneI, The University of West London, U.K.
July 1990.
ACKNOWLEDGEMENTS
All praIse to Allah, almighty, sustainer of the world, the merciful
and kind who enabled me to complete this work. Blessing and peace
be upon Moses, Jesus and the last prophet Muhammad whom God
sent for guidance to mankind to manifest His extreme mercy.
I should like to express my deep appreciation and gratitude to my
supervisor Prof. C. Bodsworth for his guidance, constructive
criticism and his great patience throughout this project. Also, I
acknowledge the unforgettable guidance and invaluable assistance
of Prof. A. Prince in the course of this work.
I would like to thank Dr. D. Talbot and all office and technical staff
who have helped me in this work over the last few years.
I am thankful to Prof. B. Ralph, Head of the Department of Materials
Technology, for the provision of the laboratory facilities. I, also,
wish to thank Englehard Limited for the loan of Gold.
Finally, I gratefully acknowledge the Ministry of Science and
Technology, Government of Pakistan for the S & T scholarship
award and Punjab University, Lahore for the grant of leave for this
period of research.
DEDICATED TO ALL MY FAMIL Y MEMBERS
ESPECIALL Y MY PARENTS
ABSTRACT
The partial constitutions of the Au-Ge-X and Au-Pb-X ternary alloys have been investigated,
where X is a metallic element, selected from the sub-groups period 1m and rrm of the periodic
table (In, Ga, Zn, or Cd), which forms one or more stable compounds with gold, but which
forms no stable compound with Ge and Pb. The Smith Thermal Analysis Method,
supplemented by metallographic and X-ray techniques, was used to determine the constitutions
of the ternary systems. Eutectiferous, pseudobinary systems were found between Ge and the
stable congruent intermediate compounds, AuIn, Auln2' AuGa, AuGa2' AuZn and AuCd. The
solubility of Ge in the AuX compounds was not determined directly. However, it was 1.3 at.%
Ge for Zn and Cd containing alloys and less than 1.0 at. % Ge for In and Ga containing alloys at
the eutectic temperatures, which is in accordance with the Hume-Rothery rule. Ternary eutectic
points were also determined in the Auln-AuIn2-Ge, Auln2-In-Ge and AuGa-AuGa2-Ge partial
ternary systems. No evidence of liquid immiscibility was found in any of these ternary systems.
The experimental results obtained were in good agreement with computed features of the
diagrams. However, pseudobinary systems were not found between Pb and the stable
congruent melting intermediate compounds, AuG a, AuGa2' AuZn and Aued (the Auln-Pb and
AuIn2-Pb sections had already been investigated). The evidence of an extensive liquid
immiscibility was found in each of these systems. The miscibility in the liquid state was found
to decrease progressively down group IV when the elements of this group react with AuX
compounds, which can be attributed to the progressive increase of the atomic size and decrease
in electronegativities and solubility parameters of the elements, down this group.
Two rules were derived to relate the liquid immiscibility/miscibility of ternary systems. One of
the rules based upon the atomic sizes and melting points of the constituent elements showed a
fair agreement with many systems. However, the other rule based upon the solubility parameter
and electronegativities of the constituent elements showed good agreement with immiscible
systems, but gave a poor predictability for miscible systems.
The lower temperature equilibria of the Au-rich portion of the Au-Sn binary phase diagram are
not well defined. So, long term heat treatment of samples at appropriate temperatures and
compositions was carried out. Optical microscopy and SEMIEDAX techniques were employed
and hence the low temperature equilibria of the Au-Sn binary system have been amended.
CONTENTS
Page
CHAPTER NO:- 1 INTRODUCTION 1
(1.1) EQUILIBRIUM PHASE DIAGRAMS 1
(1.1.1) Advantages of Phase Diagrams 2
(1.2) HISTORICAL BACKGROUND 2
(1.2.1) Empirical Determination 2
(1.2.2) Thermodynamical Approach 4
(1.3) RANGE OF INTEREST 6
(1.3.1) Use of Gold and its Alloys 7
(1.3.2) Characteristics of Gold and its Alloys 7
(1.3.3) Characteristics of a solder 8
(1.4) PRESENT WORK 9
(1.4.1) Gold Alloy System 9
(1.4.1.1) Gold ternary alloy system 9
(1.4.1.2) Gold tin binary system 10
(1.4.2) Experimental Techniques Available and
Techniques Used 10
(1.4.3) Thermodynamic Approach and
Computer Calculations 12
CHAPTER NO;- 2 FUNDAMENTALS OF PHASE
EQUILIBRIA 14
(2.1) Symbols And UNITS 14
(2.2) BASIC ASPECTS OF THERMODYNAMICS 1 5
Page
(2.2.1) Equilibrium 15
(2.2.2) Internal Energy and First Law of
Thermodynamics 1 5
(2.2.3) Heat Content or Enthalpy 1 6
(2.2.4) Heat Capacity 17
(2.2.5) Entropy and Second Law of Thermodynamics 1 8
(2.2.6) Gibbs Free Energy 20
(2.2.7) Helmholtz free Energy 21
(2.2.8) Mathematical Manipulation of
Different Equations 21
(2.2.9) The Kinetics of Phase Equilibria 22
(2.3) BINARY PHASE DIAGRAMS 22
(2.3.1) Free Energy of a Binary System 22
(2.3.2) Phase Diagram and Free Energy Curves 23
(2.3.3) Phase Rule 23
(2.3.4) A Simple Phase Diagram 24
(2.3.5) System Exhibiting Miscibility Gap in Solid State 25
(2.3.5.1) Minimum in liquidus 25
(2.3.5.2) Maximum in liquidus 26
(2.3.6) Eutectic System 26
(2.3.7) System Containing Intermediate Phases 2 7
(2.3.8) Other Systems 2 7
(2.3.9) Tie-Lines in Binary System and Lever Rule 2 7
(2.3.5) Rules for the Construction of Binary
Phase Diagrams 28
Page
(2.4) TERNARY PHASE DIAGRAMS 28
(2.4.1) Two Phase Equilibria 29
(2.4.2) Three Phase Equilibria 29
(2.4.3) Four Phase Equilibria 30
(2.4.4) Tie-Lines and Tie-Triangles In Ternary Systems 3 0
(2.4.5) Projected Sections of Ternary Diagrams 3 1
(2.4.5.1) Horizontal (Isothermal) sections 3 1
(2.4.5.2) Vertical sections 3 1
(2.4.6) Rules for the Construction of Ternary
Phase Diagrams 3 2
(2.5) THE LAW OF ADJOINING PHASE REGIONS 3 3
(2.6) QUASIBINARY AND PSEUDOBINARY SYSTEMS 3 4
(2.7) FURTHER READING ON PHASE EQUILIBRIA 34
CHAPTER NO:- 3 THERMODYNAMICS OF PHASE
EOUILIBRIA 35
(3.1) INTRODUCTION 35
(3.2) IMPORTANCE OF CALCULATIONS 36
(3.3) CALCULATION OF PHASE EQUILIBRIA 38
(3.3.1) Calculation of Binary Phase Diagrams 38
(3.3.2) Calculation of Ternary Phase Diagrams 39
(3.3.2.1) Extrapolation of Binary Data into
Ternary (or Multicomponent) System 40
(3.4) MODEL APPROACH TO PHASE EQUILIBRIA 42
(3.4.1) Ideal Solution Model 42
Page
(3.4.2) Regular Solution Model 45
CHAPTER NO:- 4 DETERMINATION OF PHASE
EOUILIBRIA 50
(4.1) INTRODUCTION TO METHODS FOR THE
DETERMINATION OF PHASE EQUILIBRIA 50
(4.1.1) Static Methods 5 1
(4.1.2) Dynamic Method 52
(4.2) THERMAL ANALYSIS 53
(4.2.1) Techniques Dependent on Weight Changes 54
(4.2.2) Techniques Dependent on Dimensional Changes 54
(4.2.3) Techniques Associated with Evolved Volatiles 55
(4.2.4) Techniques Associated with Energy Changes 55
(4.3) PRINCIPLES OF DIFFERENTIAL THERMAL ANALYSIS 58
(4.4) PRINCIPLES OF SMITH THERMAL ANAL YSIS 59
(4.5) COMPARISON OF DTA AND STA 63
(4.6) REASONS OF USING STA FOR PRESENT STUDY 65
(4.7) STA APPARATUS 66
CHAPTER NO:- 5 EXPERIMENTAL METHODS 67
(5.1) MATERIALS 67
(5.2) SAMPLE PREPARATION FOR THERMAL ANALYSIS 68
(5.2.1) Alloys in the AuZn-Pb, AuGa-Pb
and AuGa2-Pb Systems 68
(5.2.2) Alloys in the AuIn-Ge and AuIn2-Ge Systems 68
Page
(5.2.3) Alloys in the AuZn-Ge, AuGa-Ge and
AuGa2 -Ge Systems 69
(5.2.4) Alloys in the AuCd-Ge Systems 69
(5.2.5) Alloys in the AuCd-Pb Systems 70
(5.3) THERMAL ANALYSIS (EXPERIMENTAL PROCEDURE) 71
(5.3.1) Print Out of STA Curve 73
(5.3.2) Calibration of Equipment 74
(5.3.3) Composition 74
(5.4) METALLOGRAPHY (OPTICAL) 75
(5.5) MICROHARDNESS 76
(5.6) SCANNING ELECTRON MICROSCOPY (SEM) 76
(5.7) Au-Sn BINARY SYSTEM 77
(5.7.1) Long Term Annealing 77
(5.7.2) Sample Preparation 77
(5.7.3) Heat Treatment/temperature Control 79
(5.7.4 ) Optical Microscopy 79
(5.7.5) Electron Micro-Probe Analysis 79
CHAPTER NO:- 6 RESULTS 80
(6.1) TERNARY PHASE DIAGRAMS 80
(Thermal Analysis Results)
(6.1.1) Au-Ge-X SYSTEMS 80
(6.1.1.1) Au-Ge-In SYSTEM 82
(6.1.1.2) Au-Ge-Ga SYSTEM 84
(6.1.1.3) Au-Ge-Zn SYSTEM 85
Page
(6.1.1.4) Au-Ge-Cd SYSTEM 86
(6.1.2) Au-Pb-X SYSTEMS 87
(6.1.2.1) Au-Pb-In SYSTEM 88
(6.1.2.2) Au-Pb-Ga SYSTEM 88
(6.1.2.3) Au-Pb-Zn SYSTEM 90
(6.1.1.4) Au-Ge-Cd SYSTEM 90
(6.2) THERMODYNAMIC CALCULATION OF
TERNARY PHASE DIAGRAMS 91
(6.3) Au-Sn BINARY PHASE DIAGRAM 92
(6.4) MICROHARDNESS 93
CHAPTER NO:- 7 DISCUSSION 94
(7.1) LIQUID MISCIBILITY AND IMMISCIBILITY
IN TERNARY SYSTEMS 94
(7.1.1) Direction of Tie-Line 114
(7.1.2) Elements From Group IV of the Periodic Table 115
(7.2) SOLID SOLUBILITY 116
(7.3) VAN'T HOFF EQUATION AT HIGHER
CONCENTRATION OF THE SOLVENT 11 6
(7.4) PossmLE CONSTITUTION OF THE Au-Pb-X SYSTEMS 11 7
(7.5) PROBLEMS ENCOUNTERED, ACCURACY
AND REPRODUCmILITY 11 8
(7.6) COMPARISON OF EXPERIMENTAL AND THERMODYNAMICALLY
COMPUTED SECTIONS AND ISOTHERMS 1 24
(7.7) Au-Sn BINARY PHASE DIAGRAM 126