Superplasticity in fine-grained 20% Al 2O 3/YTZ composite

Abstract

The microstructure and superplastic deformation of fine-grained, 20% Al 2O 3-reinforced, yttria-stabilized, tetragonal zirconia (Al 2O 3/YTZ) has been investigated. Hot identation and tensile tests were carried out at temperatures between 1000° and 1650°C. The material exhibited extensive plasticity at temperatures higher than 1200°C, and a maximum tensile elongation of over 625% was recorded. The microstructure of the Al 2O 3/YTZ was thermally unstable, and concurrent grain growth, and in particular dynamic grain growth, was observed at temperatures higher than 1450°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 Al 2O 3/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 studies using transmission electron microscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. No glassy phase was detected at grain boundaries.