FUNDAMENTALS OF CREEP IN METALS AND ALLOYS

By Y. MIMAT

CONTENTS 1 INTRODUCTION 1 1 DESCRIPTION OF CREEP 1 2 OBJECTIVES 2 FIVE-POWER-LAW CREEP 2 1 MACROSCOPIC RELATIONSHIPS ACTIVATION ENERGY AND STRESS EXPONENTS INFLUENCE OF THE ELASTIC MODULUS STACKING FAULT ENERGY AND SUMMARY NATURAL THREE-POWER-LAW SUBSTITUTIONAL SOLID SOLUTIONS 2 2 MICROSTRUCTURAL OBSERVATIONS SUBGRAIN SIZE, FRANK NETWORK DISLOCATION DENSITY, SUBGRAIN MISORIENTATION ANGLE, AND THE DISLOCATION SEPARATION WITHIN THE SUBGRAIN WALLS IN STEADY-STATE STRUCTURES CONSTANT STRUCTURE EQUATIONS PRIMARY CREEP MICROSTRUCTURES CREEP TRANSIENT EXPERIMENTS INTERNAL STRESS 2 3 RATE-CONTROLLING MECHANISMS INTRODUCTION DISLOCATION MICROSTRUCTURE AND THE RATE-CONTROLLING MECHANISM IN SITU AND MICROSTRUCTURE-MANIPULATION EXPERIMENTS ADDITIONAL COMMENTS ON NETWORK STRENGTHENING 2 4 OTHER EFFECTS ON FIVE-POWER-LAW CREEP LARGE STRAIN CREEP DEFORMATION AND TEXTURE EFFECTS EFFECT OF GRAIN SIZE IMPURITY AND SMALL QUANTITIES OF STRENGTHENING SOLUTES SIGMOIDAL CREEP 3 DIFFUSIONAL-CREEP 4 HARPER–DORN CREEP 4 1 THE SIZE EFFECT 4 2 THE EFFECT OF IMPURITIES 5 THREE-POWER-LAW VISCOUS GLIDE CREEP 6 SUPERPLASTICITY 6 1 INTRODUCTION 6 2 CHARACTERISTICS OF FINE STRUCTURE SUPERPLASTICITY 6 3 MICROSTRUCTURE OF FINE STRUCTURE SUPERPLASTIC MATERIALS GRAIN SIZE AND SHAPE PRESENCE OF A SECOND PHASE NATURE AND PROPERTIES OF GRAIN BOUNDARIES 6 4 TEXTURE STUDIES IN SUPERPLASTICITY 6 5 HIGH STRAIN-RATE SUPERPLASTICITY HIGH STRAIN-RATE SUPERPLASTICITY IN METAL–MATRIX COMPOSITES HIGH STRAIN-RATE SUPERPLASTICITY IN MECHANICALLY ALLOYED MATERIALS 6 6 SUPERPLASTICITY IN NANO AND SUBMICROCRYSTALLINE MATERIALS 7 RECRYSTALLIZATION 7 1 INTRODUCTION 7 2 DISCONTINUOUS DYNAMIC RECRYSTALLIZATION (DRX) 7 3 GEOMETRIC DYNAMIC RECRYSTALLIZATION 7 4 PARTICLE-STIMULATED NUCLEATION (PSN) 7 5 CONTINUOUS REACTIONS 8 CREEP BEHAVIOR OF PARTICLE-STRENGTHENED ALLOYS 8 1 INTRODUCTION 8 2 SMALL VOLUME-FRACTION PARTICLES THAT ARE COHERENT AND INCOHERENT WITH THE MATRIX WITH SMALL ASPECT RATIOS INTRODUCTION AND THEORY LOCAL AND GENERAL CLIMB OF DISLOCATIONS OVER OBSTACLES DETACHMENT MODEL CONSTITUTIVE RELATIONSHIPS MICROSTRUCTURAL EFFECTS COHERENT PARTICLES 9 CREEP OF INTERMETALLICS 9 1 INTRODUCTION 9 2 TITANIUM ALUMINIDES RATE CONTROLLING CREEP MECHANISMS IN FL TIAL INTERMETALLICS DURING ‘‘SECONDARY’’ CREEP PRIMARY CREEP IN FL MICROSTRUCTURES TERTIARY CREEP IN FL MICROSTRUCTURES 9 3 IRON ALUMINIDES ANOMALOUS YIELD POINT PHENOMENON CREEP MECHANISMS STRENGTHENING MECHANISMS 9 4 NICKEL ALUMINIDES NI3AL NIAL 10 CREEP FRACTURE 10 1 BACKGROUND 10 2 CAVITY NUCLEATION VACANCY ACCUMULATION GRAIN-BOUNDARY SLIDING DISLOCATION PILE-UPS LOCATION 10 3 GROWTH GRAIN BOUNDARY DIFFUSION-CONTROLLED GROWTH SURFACE DIFFUSION-CONTROLLED GROWTH CONSTRAINED DIFFUSIONAL CAVITY GROWTH PLASTICITY COUPLED DIFFUSION AND PLASTIC GROWTH CREEP CRACK GROWTH 10 4 OTHER CONSIDERATIONS REFERENCES