A CRITICAL-ASSESSMENT OF FLOW AND CAVITY FORMATION IN A SUPERPLASTIC YTTRIA-STABILIZED ZIRCONIA

Tensile tests were performed on specimens of high purity 3Y-TZP (tetragonal ZrO2 stabilized with approximately 3 mol% of Y2O3) at temperatures from 1623 to 1803 K. Superplastic-like flow was achieved with elongations of up to >400%. The experiments show that the stress exponent, n, is approximately 3.0-3.4 and the activation energy for flow, Q, is approximately 602 +/- 20 kJ mol-1. Internal cavities developed in all specimens during flow, and quantitative measurements were taken of the cavity shapes and sizes over a range of experimental conditions. The results demonstrate that there is an increase in the extent of cavitation with (i) decreasing temperature at constant strain rate and (ii) increasing strain rate at constant temperature. The influence of strain rate on cavitation in 3Y-TZP is the opposite of most superplastic metals, and the difference arises because of an inhibition in the diffusion growth process in 3Y-TZP.