Microstructural Evolution in High Strain, High Strain-Rate Deformation

摘要

Under high strain rates, plastic deformation can be assumed to be adiabatic, anda significant temperature increase can occur at large strains. In this study, shock-hardened polycrystalline copper was subjected to high strains at high strain rates using a stepped specimen in a Hopkinson bar. Microstructural analysis by transmission electron microscopy revealed that the highly deformed shear-band region consisted of a gradual decrease in grain size with increasing strain. The center of the shear band is characterized by very small grains with a relatively low dislocation density. An analysis is developed, based on dynamic recrystallization (enabled by the adiabatic temperatures rise associated with plastic deformation), that predicts a transient grain size during plastic deformation in which grain size varies inversely with strain and strain rate. This analysis has been used to predict that nanocrystalline grain sizes are achievable. This dramatic microstructural refinement enables a thermomechanical response that may lead to extensive, stable plastic deformation tension. (MM).