Influence of zirconia on the sintering behaviour and mechanical properties of reaction-sintered mullite-based composite ceramics

High-performance mullite-based composite ceramics were prepared successfully using natural kaolin and alumina as raw materials and ZrO 2 as an additive. The influence of sintering temperature and ZrO 2 content on the sintering behaviour and mechanical properties of zirconia-toughened mullite ceramics was studied systematically. With increasing sintering temperature from 1450°C to 1560°C, the primary phases of as-sintered composite ceramics were mullite and corundum with a small amount of ZrO 2 , and the bulk density of the composite ceramics increased from 2.29 to 2.72 g cm –3 . Furthermore, the ZrO 2 phase transition promoted transgranular fracture, and ZrO 2 grains were pinned at the grain boundaries, thereby enhancing the mechanical strength of the composite ceramics. Moreover, the AZS12 sample, with 12 wt.% ZrO 2 and sintered at 1560°C, had the greatest flexural strength and fracture toughness of 91.6 MPa and 2.47 MPa m –1/2 , respectively. Adding ZrO 2 to the composite ceramics increased their flexural strength by ~37.6%.