Cubic- and tetragonal-ZrO
2-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 ZrO
2 phase on bending strength (at room temperature and 1200°C) was investigated. The bending strength at room temperature of ZrO
2-MgO composite ceramics increased with increasing ZrO
2 content, because the grain size of MgO decreased with ZrO
2 addition. But the effect of ZrO
2 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-ZrO
2-MgO was larger than that of t-ZrO
2-MgO, and fracture stress increased with decreasing the grain size of MgO.
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