SUPERPLASTICITY IN FINE-GRAINED 20-PERCENT A12O3/YTZ COMPOSITE

The microstructure and superplastic deformation of fine-grained, 20% Al2O3-reinforced, yttria-stabilized, tetragonal zirconia (Al2O3/YTZ) has been investigated. Hot indentation and tensile tests were carried out at temperatures between 1000-degrees and 1650-degrees-C. The material exhibited extensive plasticity at temperatures higher than 1200-degrees-C, and a maximum tensile elongation of over 625% was recorded. The microstructure of the Al2O3/YTZ was thermally unstable, and concurrent grain growth, and in particular dynamic grain growth, was observed at temperatures higher than 1450-degrees-C. Although the apparent strain rate sensitivity exponent was determined to be approximately 0.5, the true strain rate sensitivity, after compensation for grain growth, is about 0.67. The activation energy for superplasticity in Al2O3/YTZ was determined to be 257 kJ/mol which is much lower than the activation energy for superplastic Y-TZP. Of particular interest were the grain-boundary structures and the chemical compositions of the grain boundaries. Microstructures were studied using transmission electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. No glassy phase was detected at grain boundaries.