The dislocation distribution, flow stress, and stored energy in cold-worked polycrystalline silver

Abstract

Distribution and densities of dislocations, determined by electron transmission microscopy, flow stress and stored energy measurements (by microcalorimetry) on cold-worked polycrystalline silver are correlated with each other, The dislocations are arranged in dense networks forming the boundaries of an otherwise relatively dislocation-free cell structure. The flow stress is explained quantitatively in terms of the forest intersection mechanism at the boundaries. The stored energy after recovery is of the same order as the total self-energy of the dislocation arrangement, so that the long-range stresses must be largely relaxed. The considerable energy release during the recovery stage produces no observable change in dislocation distribution. This recovery stage is thought to be due to the relief of long-range stresses or to the removal of point defects. While the values of flow stress and stored energy can be accounted for in terms of the observed non-uniform distribution of dislocations (cell structure), they are not compatible with each other on a model based on a uniform distribution of pile-ups; nor are pile-ups observed on the electron micrographs.