MICROSTRUCTURAL EXAMINATION OF A SUPERPLASTIC YTTRIA-STABILIZED ZIRCONIA - IMPLICATIONS FOR THE SUPERPLASTICITY MECHANISM

A detailed microstructural examination was conducted on specimens of h igh purity superplastically-deformed 3Y-TZP (tetragonal ZrO2 stabilize d with similar to 3 mol.% Y2O3). Several of the microstructural featur es were similar to conventional superplastic metallic alloys including the retention of an equiaxed grain configuration, evidence for only l imited dislocation activity within the grains and the concurrent devel opment of internal cavitation. There was no detectable amorphous phase at any of the grain boundaries or at the triple junctions but there w as some segregation of yttria to the boundary regions. It is concluded that there are two types of superplastic Y-TZP materials depending up on whether there is an amorphous phase at the grain boundaries. When a n amorphous phase is absent, the behavior is fairly similar to superpl astic metals except that an additional mechanism operates at the lower stress levels to impede grain boundary sliding.