Annihilation of dislocations during tensile and cyclic deformation and limits of dislocation densities

Abstract

Abstract It is proposed that, during dislocation glide at low temperatures, both screw and non-screw dislocations annihilate mutually with dislocations of opposite sign approaching on closely neighbouring glide planes. The experimental evidence is summarized and possible mechanisms are discussed. Phenomenological models of dislocation accumulation during deformation, taking into account the annihilation of dislocations, are formulated. The analysis of selected examples of tensile and cyclic deformation of f.c.c. and b.c.c. metal crystals demonstrates that annihilation of edge and/or screw dislocations occurs during strain hardening and can lead to steady state deformation. It follows that the dislocation densities introduced during deformation cannot exceed well-defined upper limits that are distinctly lower than the hypothetical upper limits estimated for the static case. The observations suggest that the critical spacings of dislocation pairs that annihilate are ∼.50–500 nm for screw and ∼ 1·6 nm for edge dislocations (in copper). The atomic concentration of point defects formed by the annihilation of non-screw dislocations is found to be low in most cases (∼10−3). However, it is concluded that, in the dislocation–rich walls of persistent Blip bands in fatigued copper, a rather high concentration of point defects prevails (∼10−3).