Properties of (Y)ZrO 2 –Al 2 O 3 and (Y)ZrO 2 –Al 2 O 3 –(Ti or Si)C Composites

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Abstract
The effect of Al 2 O 3 and (Ti or Si)C additions on various properties of a (Y)TZP (yttria‐stabilized tetragonal zirconia polycrystal)–Al 2 O 3 –(Ti or Si)C ternary composite ceramic were investigated for developing a zirconia‐based ceramic stronger than SiC at high temperatures. Adding Al 2 O 3 to (Y)TZP improved transverse rupture strength and hardness but decreased fracture toughness. This binary composite ceramic revealed a rapid loss of strength with increasing temperature. Adding TiC to the binary ceramic suppressed the decrease in strength at temperatures above 1573 K. The residual tensile stress induced by the differential thermal expansion between ZrO 2 and TiC therefore must have inhibited the t ‐ → m ‐ZrO 2 martensitic transformation. It was concluded that a continuous skeleton of TiC prevented grain‐boundary sliding between ZrO 2 and Al 2 O 3 . In contrast, for the ternary material containing β‐SiC in place of TiC, the strength decreased substantially with increasing temperature because of incomplete formation of the SiC skeleton.

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