Effect of non-Schmid stresses on 〈a〉-type screw dislocation core structure and mobility in titanium

Abstract

Density functional theory calculations of 〈a〉-type screw dislocation core structures in hcp titanium under a series of applied stresses with zero critical resolved shear stress were performed to investigate the origin of non-Schmid law slip behavior in α-titanium alloys. It was found that compression applied on the [11¯00] direction perpendicular to the Burgers vector leads to more compact pyramidally-oriented cores, while tension applied on the same axis causes an extension of these cores along the prismatic plane. Nudged elastic band calculations of the barrier to slip of the dislocations on the prismatic plane show that extension along this plane leads to reduced slip barriers. This suggests that non-Schmid stresses alter the critical resolved shear stress by inducing changes in the equilibrium core structure.