Some features of the formation and destruction of dislocation barriers in intermetallic compounds: V. Single-valley and multivalley potential relief for dislocations

Abstract

A sufficiently general problem of thermoactivated transitions of dislocations between valleys of the potential relief (single-valley and multivalley) has been considered. The possibility of straightening of dislocations along a preferred direction in the absence of an external stress has been investigated. The controlling factor of this process is a thermoactivated transition (flip) of a dislocation from a shallow valley into a deeper valley of the potential relief. The flip process involves the formation of a double kink and its subsequent reorientation resulting in the formation of an asymmetric kink. The driving force of the flip process has been calculated and shown to be determined by the difference in the depths of the valleys. It has been shown that in the absence of an external stress the flip process is allowed under specific conditions, whereas the escape from a deep valley is hindered with a result that self-blocking of dislocations becomes possible. An analysis of experiments on heating of intermetallic compounds without stress after a preliminary deformation have been analyzed (see parts II-IV of this work), and owing to the experiments, self-blocking of dislocations has been found. The observation or nonobservation of self-blocking in different materials is a tool that enables the character of the potential relief of dislocations to be restored; the self-blocking is possible only in the presence of two types of valleys of different depth. Moreover, the two-valley character of the relief is a prerequisite for the development of an anomalous behavior of the yield strength upon dynamic loading.