Low-temperature deformation of body-centred cubic metals. II. Mechanism of thermally activated flow

Abstract

The experimental results of I indicate that the dislocation velocity is limited by a thermally activated process, and the parameters of the appropriate rate equation are evaluated. At very low temperatures, the stress derivative of the free energy of activation (the 'activation volume') is only a few atomic volumes. It is very difficult to explain the magnitude of the low-temperature stress or that of the activation volume if direct dislocation-impurity interactions are responsible for most of the resistance to motion, and it is concluded that there is probably a significant lattice interaction (a 'Peierls-Nabarro force'). The results are compared with the predictions of recent models for the overcoming of the Peierls barrier by the production of double kinks in straight dislocation lines.