Formation of dislocation structures during cyclic deformation of F.C.C. crystals—I. Formation of PSBs in crystals oriented for single-slip

Abstract

The formation of persistent slip bands (PSBs) in cyclicly deformed copper crystals oriented for single slip has been investigated. Both macroscopic data, the stress-strain responses, the change of the shape of hysteresis loops and the nucleation stresses for PSB formation, and the direct TEM observations of dislocation structures at structural transition and saturation stages suggest that the formation of dislocation walls of PSBs takes place either through breach of dislocation veins in their centers along (111) planes or through a gradual development of walls alongside veins. While the former mechanism is dominant for low plastic strain amplitude cases, where the dislocation veins are well developed before structural transition; the latter is more important for high plastic strain amplitude cases, where the dislocation veins are incomplete at transition stage. The pre-existing dislocation structure is supposed to be an important factor affecting the structural transition. Various observations reported in the literature have also been discussed.