Creep in metallic materials

Abstract

1. Deformation and Creep. Deformation. Definition of creep. Time dependence of creep strain. Creep Curve. Mechanisms of plastic deformation: A general survey. Mechanical equation of state. Creep test compared with tensile test at constant strain rate and constant loading rate. Creep tests at constant load and constant stress. 2. Motion of Dislocations. Dynamic Recovery. Motion of dislocations. Free, mobile and moving dislocations. Dynamic recovery. 3. Temperature Dependence of Creep Rate. Activation energy of creep. Methods of determination of activation energy of creep. Correction of experimentally determined activation energy of creep for temperature dependence of elastic modulus. Activation energy or creep and activation enthalpy of diffusion. 4. Applied Stress Dependence of Creep Rate. Initial creep rate. Steady-state creep. Transient creep. 5. Influence of Grain Size and Stacking Fault Energy. Grain size. Stacking fault energy. 6. Orowan and Bailey-Orowan Equations. Orowan equation. Bailey-Orowan equation. Relation between Orowan equation and Bailey-Orowan equations. A consequence of the equivalence of Orowan and Bailey-Orowan equations. Experimental verification of Bailey-Orowan equation. Experimental determination of quantities r and h. Incubation period and ``Frictional'' stress. 7. Back Stress. Internal, threshold and frictional stress. Internal and effective stress. Concept of internal and effective stress and the mechanical equation of state. Definitions of experimental parameters. Interpretation of experimental parameters. 8. Dislocation Structure. Development of dislocation structure during creep. Basic quantitative characteristics of dislocation structure. Subgrain structure. Subgrain structure and long-range internal stress. Behaviour of sub-boundaries. Interaction of dislocations with sub-boundaries. Generation of dislocations. Structural steady state. Concept of hard and soft regions and measured internal stress. 9. Dislocation Creep in Pure Metals. Creep controlled by recovery. Creep controlled by dislocation glide. Models based on thermally activated glide and diffusion controlled recovery. Relation between constants A and n in the dorn creep equation and the natural third power law. Harper-Dorn creep. 10. Creep in Solid Solution Alloys. Introduction. Mechanisms of creep strengthening in solid solutions. Creep controlled by viscous dislocation glide. 11. Creep in Precipitation and Dispersion Strengthened Alloys. Models of Ansell and Weertman. Back stress concept. 12. Diffusional Creep. Nabarro-Herring and Coble creep. Subgrain boundaries as sources and sinks for vacancies. Diffusional creep and grain boundary sliding. Reactions on grain boundaries. Diffusional caritational creep. 13. Deformation Mechanism Maps. Equations used for construction of deformation mechanism maps. Examples of deformation mechanism maps. ``Generalized'' deformation mechanism map for pure metals. 14. Grain Boundary Sliding.