Dislocation mechanisms and steady states in the cyclic deformation of facecentred cubic crystals

Abstract

Abstract A model is presented which describes cyclic saturation in a structure consisting of a hard (wall) phase and a soft (channel) phase. The processes leading to a saturation of the density of screw dislocations in channels are investigated in detail; emphasis is put on multiplication processes which have not, up to now, been incorporated in such models. It is shown that all the quantities which characterize a state of dynamic equilibrium (the mean free paths of screw dislocations, multiplication or annihilation rates, irreversibility of slip) can be estimated in terms of a few parameters accessible to experiment: the density of screw dislocations at saturation, the plastic shear strain amplitude, the critical annihilation distance and the geometry of a dislocation loop expanding from one wall to an opposite wall. Numerical estimates are presented, for copper single crystals, and the model is applied to the transition between static and dynamic equilibria, to the matrix structure and to the persistent slip band structure for which simple expressions are established. Similarities and differences with respect to previous models presented by Essmann and Mughrabi (1979) and Essmann (1982, 1984) are discussed.