Plastic anisotropy in b.c.c. transition metals

Abstract

The anisotropy of plasticity in b.c.c. metals is decomposed into two parts. The first, a variation of the Peierls stress with slip plane and sense of slip, is intrinsic to the b.c.c. structure and is reflected in the geometry of the screw dislocation core and of the generalized stacking fault energy (γ) surface. The second part, a sensitivity of the Peierls stress to non-glide elements of the applied stress, is shown to be due to small edge fractional dislocation components in the screw dislocation core. These edge components and their change in response to non-glide applied stress can be explained by the characteristics of the γ-surface. These concepts are illustrated by means of atomistic calculations, using Finnis–Sinclair interatomic force laws, for the b.c.c. transition elements of groups VB and VIB of the periodic table. Metals in the two groups are shown to fall into two classes of core structure and behavior; the contrasting properties can be explained in terms of the γ-surfaces, and can be traced further to differences in the elastic constants.