Dislocation Velocities in Nickel Single Crystals

The velocities of dislocations moving in nickel single crystals were measured at various temperatures as a function of stress. The data were found to fit an equation obtained from reaction-rate theory. The activated volume varied approximately linearly with temperature and was independent of the applied stress over the rather limited range of stresses investigated. The enthalpy of activation was also independent of stress but changed abruptly with temperature from 1200 cal/mole at approximately 130°K to 2500 cal/mole at higher temperatures. This change is explained by a change in the Peierls stress, which is associated with a sudden increase in dislocation density at higher temperatures. The dislocations were believed to be emitted from sources which are thermally activated.