Strengthening contribution arising from residual stresses in Al2O3/ZrO2 composites : a piezo-spectroscopy investigation

Piezo-spectroscopy measurements were performed in order to obtain information about the internal stresses in a series of (2 mol% Y2O3-stabilised) ZrO2 ceramics with added fine Al2O3 dispersoids. These composites were previously reported to fracture at remarkably high strength levels. Residual stresses arising from the thermal mismatch between the ZrO2 matrix and the Al2O3 dispersoids were found to be of the order of several hundreds MPa, in agreement with the predictions of an elastic stochastic stress analysis. Taking into consideration the results of the present piezo-spectroscopic analysis, a micromechanism of microcrack shielding by residual microstresses is proposed, which overlaps with the effect of phase transformation on strength. A theoretical assessment is given which enables the presence of a maximum of strength at 0.2-0.4 volume fraction of Al2O3 dispersoid to be explained. 28 refs.