Dislocation dynamics and thermally-activated deformation of MgO single crystals

Abstract

Strain rate cycling and stress relaxation experiments were performed to investigate the yielding behaviors and rate-controlling mechanism in nominally pure MgO crystals deformed in cube orientation over the temperature range 77°K to 673°K. Analysis of various activation parameters at different temperatures with respect to strain showed that the deformation dynamics could be rationalized in terms of both the power law approach of Johnston and Oilman (1959) and the thermally-activated rate expression without invoking entropy effects. Up to 673°K, the results showed good agreement with Fleischer's theory for interaction between mobile dislocations and tetragonal strain fields as for impure LiF (Fleischer 1962). The onset of dynamic strain, ageing above about 700°K set the upper limit of the temperature range where useful data could be obtained with a reasonable correlation between the dislocation dynamics and thermally-activated deformation approaches.