Dislocation Velocity on the {1̄21̄2}〈12̄13〉 Slip Systems of Zinc

Abstract

Dislocation velocity on the {1̄21̄2}〈12̄13〉 slip systems of zinc monocrystals was deduced from the rate of growth of slip bands. Near 77°K dislocation velocity is directly proportional to stress, and screw dislocations move more rapidly than edge dislocations. The difference between edge and screw dislocation velocity can be interpreted in two ways. The pre-exponential factors in a thermal activation model may differ by a factor 4 while the common activation energy is 0.21 eV, or the pre-exponential factors are the same, but the activation energy for edge dislocations (0.22 eV) exceeds that for screws by 5%. Other experiments will be required to establish the appropriate model. The authors favor the second alternative since extra activation energy might be needed to change the core structure of the edge dislocations (which lie on the basal planes) to make them glissile. Near room temperature, dislocation velocity decreases and cross-glide increases with increasing temperature. It is suggested that dragging dipoles and debris caused by their dissociation are responsible for the decrease in dislocation velocity. Finally, it is shown that the temperature dependence of both the yield strength and the plastic modulus is similar to the temperature dependence of the stress required to produce a constant dislocation velocity.