Yield drop in high-strain-rate superplastic deformation of ZrO₂-30 vol% MgAl₂O₄spinel composite

The origin of a sudden yield drop in a tetragonal ZrO2 dispersed with 30 vol% MgAl2O4 spinel composite has been examined. The present ZrO2-spinel composite exhibits yield drop in superplastic flow at high strain rates of 0.2s−1 or greater, where the flow behaviour is characterized by a stress exponent of about 3.5 and a grain-size exponent of about 1.0. Experimental examination suggests that a sudden increase in the mobile dislocation density within spinel grains is responsible for the yield drop.