Temperature dependence of yielding and work-hardening rates in magnesium oxide single crystals

The mechanical properties of MgO single crystals have been analysed for their yielding and work-hardening behaviour as a function of purity and deformation temperature. The Fleischer theory accounts for the observed temperature dependence of the critical resolved shear stress well. Depending on temperature and impurity content, the MgO single crystals are shown to exhibit two-stage work-hardening behaviour, with the hardening shown to be athermal in nature. At and below room temperature, a temperature-dependent contribution results from dislocation-point defect interactions, while the primary athermal contribution arises out of dislocation-dislocation dipole interactions. The CRSS and work-hardening behaviour of MgO single crystals indicates a close relationship to the deformation characteristics of NaCl-structure alkali halides.