1992 Volume 100 Issue 1165 Pages 1113-1116
MgO-ZrO2 composites prepared by the pressureless sintering at 1350°C for 24h were annealed at 1600°C, and the effects of annealing on the properties such asgrain size, phase transformation, bending strength and fracture toughness were investigated. The grain size of ZrO2 in sintered MgO-ZrO2 containing more than 20wt% ZrO2 was too large for t-ZrO2 to be stable at room temperature, so that the t-ZrO2 to m-ZrO2 phase transformation occurred during cooling from the sintering temperature. Microcracks formed during cooling decreased the bending strength and increased the fracture toughness. When m-ZrO2 was transformed into c- or t-ZrO2 by annealing, microcracks in MgO-ZrO2 composites recombined. Consequently, flaw size in MgO-ZrO2 composites decreased, resulting in an increase of bending strength. However, fracture toughness decreased due to reduced effect of microcrack toughening mechanism.
