Inelastic recovery in nano and ultrafine grained materials

Abstract

Ultrafine and nano grained metals show plastic strain recovery upon unloading and reverse plastic strain during cyclic loading. It has been suggested that these phenomena are related to the residual stress due to grain size inhomogeneity and to grain boundary deformation mechanisms. Transmission electron microscopy (TEM) experiments indicate that dislocation structures also introduce inhomogeneous stress fields that can drive reverse plastic strain. We present dislocation dynamics simulations that show reverse plastic strain during cyclic loading even in microstructures with homogeneous grain size giving support to these TEM experiments. We also perform dislocation dynamics simulations coupled to a kinetic Monte Carlo algorithm to study thermally activated plastic strain recovery upon unloading. Our simulations show that these two plastic recovery processes are related to the formation of dislocation structures during loading, additionally grain size inhomogeneity increases the amount of plastic strain recovered.