Fundamentals of Creep in Metals and Alloys

289 Pages·2004·2.12 MB·English

by  Michael Kassner

Fundamentals of Creep in
Metals and Alloys
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Fundamentals of Creep in
Metals and Alloys
Michael E. Kassner
Department of Aerospace and Mechanical Engineering
University of Southern California
Los Angeles, USA
Marı´a-Teresa Pe´ rez-Prado
Department of Physical Metallurgy
Centro Nacional de Investigaciones Metalu´rgicas (CENIM)
Madrid, Spain
2004
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Preface
This book on the fundamentals of creep plasticity is both a review and a critical
analysis of investigations in a variety of areas relevant to creep plasticity. These
areas include five-power-law creep, which is sometimes referred to as dislocation
climb-controlled creep, viscous glide or three-power-law creep in alloys, diffusional
creep, Harper–Dorn creep, superplasticity, second-phase strengthening, and creep
cavitation and fracture. Many quality reviews and books precede this attempt to
write an extensive review of creep fundamentals and improvement was a challenge.
One advantage with this attempt is the ability to describe the substantial work
published subsequent to these earlier reviews. An attempt was made to cover the
basicworkdiscussedintheseearlierreviewsbutespeciallytoemphasizemorerecent
developments.
Theauthorwishes toacknowledgesupport fromtheU.S.DepartmentofEnergy,
Basic Energy Sciences under contract DE-FG03-99ER45768. Comments by
Profs. F.R.N. Nabarro, W. Blum, T.G. Langdon, J. Weertman, S. Spigarelli, J.H.
SchneibelandO.Ruanoareappreciated.Theassistancewiththepreparationofthe
figuresbyT.A.HayesandC.Daraioisgreatlyappreciated.WordprocessingbyMs.
Peggy Blair was vital.
M.E. Kassner
M.T. Pe´rez-Prado
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Contents
Preface v
List of Symbols and Abbreviations xi
1. Introduction 1
1.1. Description of Creep 3
1.2. Objectives 7
2. Five-Power-Law Creep 11
2.1. Macroscopic Relationships 13
2.1.1 Activation Energy and Stress Exponents 13
2.1.2 Influence of the Elastic Modulus 20
2.1.3 Stacking Fault Energy and Summary 24
2.1.4 Natural Three-Power-Law 29
2.1.5 Substitutional Solid Solutions 30
2.2. Microstructural Observations 31
2.2.1 Subgrain Size, Frank Network Dislocation Density,
Subgrain Misorientation Angle, and the Dislocation
Separation within the Subgrain Walls in Steady-State
Structures 31
2.2.2 Constant Structure Equations 39
2.2.3 Primary Creep Microstructures 47
2.2.4 Creep Transient Experiments 51
2.2.5 Internal Stress 55
2.3. Rate-Controlling Mechanisms 60
2.3.1 Introduction 60
2.3.2 Dislocation Microstructure and the Rate-Controlling
Mechanism 67
2.3.3 In situ and Microstructure-Manipulation Experiments 70
2.3.4 Additional Comments on Network Strengthening 71
2.4. Other Effects on Five-Power-Law Creep 77
2.4.1 Large Strain Creep Deformation and Texture Effects 77
2.4.2 Effect of Grain Size 82
2.4.3 Impurity and Small Quantities of Strengthening
Solutes 84
2.4.4 Sigmoidal Creep 87
3. Diffusional-Creep 89
4. Harper–Dorn Creep 97
4.1. The Size Effect 103
viii Fundamentals of Creep in Metals and Alloys
4.2. The Effect of Impurities 106
5. Three-Power-Law Viscous Glide Creep 109
6. Superplasticity 121
6.1. Introduction 123
6.2. Characteristics of Fine Structure Superplasticity 123
6.3. Microstructure of Fine Structure Superplastic Materials 127
6.3.1 Grain Size and Shape 127
6.3.2 Presence of a Second Phase 127
6.3.3 Nature and Properties of Grain Boundaries 127
6.4. Texture Studies in Superplasticity 128
6.5. High Strain-Rate Superplasticity 128
6.5.1 High Strain-Rate Superplasticity in
Metal–Matrix Composites 129
6.5.2 High Strain-Rate Superplasticity in Mechanically
Alloyed Materials 134
6.6. Superplasticity in Nano and Submicrocrystalline Materials 136
7. Recrystallization 141
7.1. Introduction 143
7.2. Discontinuous Dynamic Recrystallization (DRX) 145
7.3. Geometric Dynamic Recrystallization 146
7.4. Particle-Stimulated Nucleation (PSN) 147
7.5. Continuous Reactions 147
8. Creep Behavior of Particle-Strengthened Alloys 149
8.1. Introduction 151
8.2. Small Volume-Fraction Particles that are Coherent and
Incoherent with the Matrix with Small Aspect Ratios 151
8.2.1 Introduction and Theory 151
8.2.2 Local and General Climb of Dislocations over Obstacles 155
8.2.3 Detachment Model 158
8.2.4 Constitutive Relationships 162
8.2.5 Microstructural Effects 166
8.2.6 Coherent Particles 168
9. Creep of Intermetallics 171
9.1. Introduction 173
9.2. Titanium Aluminides 175
9.2.1 Introduction 175
9.2.2 Rate Controlling Creep Mechanisms in FL TiAl
Intermetallics During ‘‘Secondary’’ Creep 178
9.2.3 Primary Creep in FL Microstructures 186
9.2.4 Tertiary Creep in FL Microstructures 188
Contents ix
9.3. Iron Aluminides 188
9.3.1 Introduction 188
9.3.2 Anomalous Yield Point Phenomenon 190
9.3.3 Creep Mechanisms 194
9.3.4 Strengthening Mechanisms 197
9.4. Nickel Aluminides 198
9.4.1 Ni Al 198
3
9.4.2 NiAl 208
10. Creep Fracture 213
10.1. Background 215
10.2. Cavity Nucleation 218
10.2.1 Vacancy Accumulation 218
10.2.2 Grain-Boundary Sliding 221
10.2.3 Dislocation Pile-ups 222
10.2.4 Location 224
10.3. Growth 225
10.3.1 Grain Boundary Diffusion-Controlled Growth 225
10.3.2 Surface Diffusion-Controlled Growth 228
10.3.3 Grain-Boundary Sliding 229
10.3.4 Constrained Diffusional Cavity Growth 229
10.3.5 Plasticity 234
10.3.6 Coupled Diffusion and Plastic Growth 234
10.3.7 Creep Crack Growth 237
10.4. Other Considerations 240
References 243
Index 269