Temperature and strain rate dependent flow criterion for bcc transition metals based on atomistic analysis of dislocation glide

Abstract

Abstract 1/2111 screw dislocations that possess non-planar cores and thus a high lattice friction (Peierls) stress control the plastic deformation of pure bcc metals. In this paper we formulate an analytical flow criterion based on the recognition that at finite temperatures the screw dislocations glide via formation and subsequent propagation of pairs of kinks. This development employs first an atomistically calculated dependence of the Peierls stress on the applied loading to construct the Peierls potential that depends on the applied stress tensor. This Peierls potential is then used to evaluate the activation enthalpy for the kink-pair formation employing mesoscopic dislocation models and its dependence on the applied stress tensor is then approximated by a relatively simple analytical form. Using the standard transition state theory to ascertain the dislocation velocity and related strain rate allows us to formulate the temperature and strain rate dependent flow criterion. Implications of this criterion are then compared with available experimental data demonstrating its excellent predictive value.