セリア添加ジルコニア多結晶体の還元硬化

概要

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The high temperature Vickers microhardness of 12 mol% ceria-doped tetragonal zirconia polycrystals (12Ce-TZP) was measured in the temperature range of 25℃ to 1000℃ in a vacuum. The measurements were carried out in successive stages of heating and then cooling. The hardness of the 12Ce-TZP abruptly decreased from 8.2 GPa at 25℃ to 4.5 GPa at 400℃, above which it began to gradually decrease, followed by saturation at 1000℃. Upon subsequent cooling from 1000℃ to 25℃, the hardness began to increase back to the original hardness upon heating and it always surpassed the former. The increase in hardness upon cooling was found to be based on the reduction from Ce^>4+> to Ce^>3+> in 12Ce-TZP (CeO_2-ZrO_2) during the high temperature indentation measurements in a vacuum. Also, for the 12Ce-TZP (CeO_>1.5>-ZrO_2) sufficiently reduced by heat-treatment in hydrogen, the reduction-induced hardening did not occur because the Ce cation had been stabilized in a trivalent state during the measurements. Cracking occurred over the entire temperature range measured for the 12Ce-TZP (CeO_>1.5>-ZrO_2). On the contrary, the 12Ce-TZP (CeO_2-ZrO_2) showed pseudo-ductile→brittle transition characteristics; that is, indentation cracks were not observed at all up to 400℃, whereas they were remarkably recognized upon further increasing temperature.
2002-08-01