Compression creep tests were performed on a 3-phase alumina–zirconia–mullite composite at 1673 to 1773K. The data revealed a steady-state deformation behavior at a high strain rate. Logarithmic plots of strain-rate versus applied stress had a sigmoidal shape. That is, there was an increase in stress exponent with decrease in applied stress. It was shown that such an increase in the stress exponent with increasing stress could be related to the existence of a threshold stress which decreased with increasing temperature. Transmission electron microscopic studies revealed dislocation activity, in some grains of the deformed material, which was not present in as-sintered materials. This indicated that dislocations were generated during deformation. These results, which were similar to those reported for superplastic metallic alloys, led to the conclusion that dislocation motion played a role in accommodating grain-boundary sliding in this material.

Threshold Stress Superplastic Behavior and Dislocation Activity in a Three-Phase Alumina–Zirconia–Mullite Composite. T.Chen, F.A.Mohamed, M.L.Mecartney: Acta Materialia, 2006, 54[17], 4415-26