MgO-ZrO_2焼結体の性質に及ぼす熱処理の影響  [in Japanese] Effects of Annealing on Properties of MgO-ZrO_2 Composite Ceramics  [in Japanese]

MgO-ZrO_2 composites prepared by the pressureless sintering at 1350℃ for 24h were annealed at 1600℃, and the effects of annealing on the properties such asgrain size, phase transformation, bending strength and fracture toughness were investigated. The grain size of ZrO_2 in sintered MgO-ZrO_2 containing more than 20 wt% ZrO_2 was too large for t-ZrO_2 to be stable at room temperature, so that the t-ZrO_2 to m-ZrO_2 phase transformation occurred during cooling from the sintering temperature. Microcracks formed during cooling decreased the bending strength and increased the fracture toughness. When m-ZrO_2 was transformed into c- or t-ZrO_2 by annealing, microcracks in MgO-ZrO_2 composites recombined. Consequently, flaw size in MgO-ZrO_2 composites decreased, resulting in an increase of bending strength. However, fracture toughness decreased due to reduced effect of microcrack toughening mechanism.