The deformation mechanisms of superplasticity

Abstract

Under various conditions of stress and temperature various deformation mechanisms could be rate-controlling for superplastic deformation. In general at low stresses diffusion creep should be rate-controlling. At temperatures between approximately 40 and 65 pct of the absolute melting point grain boundary diffusion should be the dominant diffusion path while at higher temperatures volume diffusion should dominate. At intermediate stresses, grain boundary sliding should be the major deformation mode, but the sliding rate should be governed by the lesser rate of dislocation creep within the grains. At temperatures between 40 and 65 pct of the melting point, the rate of dislocation creep should be controlled by dislocation pipe diffusion, while at higher temperatures volume diffusion should be ratecontrolling. At high stresses the superplastic effect of unusually large tensile extensibility should diminish due to the greater possibility of work-hardening processes such as dislocation cell, tangle, and pile-up formation.