Phase-field dislocation dynamics simulations of temperature-dependent glide mechanisms in niobium

Abstract

In this work, we present a three-dimensional ab-initio informed phase-field-dislocation dynamics model combined with Langevin dynamics to investigate glide mechanisms of edge and screw dislocations at finite temperatures in Nb. Over a temperature range of 150 K to 600 K, calculations reveal that the screw dislocation changes its mode of glide at two distinct temperatures. At 200–220 K, the glide mechanism changes from single kink pair motion to multiple kink pair motion. The kink pair enthalpies quantitatively agree with those extracted from experimental tests on Nb single crystals. Between 300 K and 350 K the glide mode transitions to overlapping kink pairs and glide is smooth (non-jerky). The screw to edge mobility ratio is seen to peak at 350 K and plateau thereafter. These two temperatures coincide with temperatures at which yield strengths in Nb are observed to become thermally insensitive and athermal, respectively.