A theory of the formation of slip channels in cold-worked bcc metals

The paper presents a theoretical investigation of microstructural instabilities in bcc metals that are plastically deformed after previous work hardening at low temperatures. Deformation of such materials is, under certain conditions, accompanied by a pronounced localization of plastic strain in narrow slip bands. On the microstructural level, these bands correspond to slip channels in which the dislocations caused by pre-deformation have disappeared almost completely. It is the aim of the present work to formulate the processes which make slip channels emerge from an initially homogeneous dislocation microstructure. To this end, the interplay between collective dislocation motion and strain softening due to dislocation annihilation is treated in terms of a stochastic dislocation dynamics. The development of slip channels is proposed to correspond to a fluctuation-induced phase transition. Critical conditions for this transition are determined, and the results are compared with experimental findings.