Slip geometry and plastic anisotropy of body-centered cubic metals

The plastic anisotropy of bcc metals comprises the absence of well-defined slip planes, an orientation dependence of the uniaxial flow stress which seems to be in disagreement with Schmid's law of resolved shear stress, and an asymmetry between tension and compression. Recent theoretical and experimental work has shown that these phenomena are closely correlated to elementary slip on {211} planes in an intermediate temperature range. After a discussion of crystallographic peculiarities of <111> {211} slip, a kinematic model for microscopic cross-slip on triplets of slip planes is proposed which, in combination with the well-established model of thermally activated kink-pair formation, allows quantitative calculations of the plastic anisotropy.