Compressive strength and microplasticity in polycrystalline alumina

The compressive strength of polycrystalline alumina at 23° C is found to be strain-rate sensitive, but insensitive to environment. Scanning electron microscopy of specimens loaded to near failure indicates the origin of the strength-strain-rate dependence to be localized plasticity in the form of twinning and, possibly, slip. The interaction of these deformation bands with grain boundaries causes the initiation of microcracks. Higher stresses produce still more twin/slip-nucleated microcracks, which finally coalesce at failure. It is suggested that twinning also may be related to the tensile failure of alumina.