Grain Size Effect on Mechanical Strength of MgO-ZrO2 Composite Ceramics

Cubic- and tetragonal-ZrO2-MgO composite ceramics were prepared by the pressureless sintering at 1650°C for 4h and 1350°C for 24h respectively, and the effect of grain size and ZrO2 phase on bending strength (at room temperature and 1200°C) was investigated. The bending strength at room temperature of ZrO2-MgO composite ceramics increased with increasing ZrO2 content, because the grain size of MgO decreased with ZrO2 addition. But the effect of ZrO2 phase on the bending strength at room temperature was not recognized. In the case of bending test at 1200°C, when grain size of MgO was below 6μm, specimens deformed plastically before breakage, and the yield stress at 1200°C of c-ZrO2-MgO was larger than that of t-ZrO2-MgO, and fracture stress increased with decreasing the grain size of MgO.