Liquid-phase sintering of SiC in presence of CaO

Two SiC samples S1 and S2 containing constant amount of Al2O3, Y2O3 (7 and 2 wt.%, respectively) and different amount of CaO (1 and 3 wt.%) as sintering aids were sintered to >95% of theoretical density (TD) at temperature between 1750 and 1900 °C. The densification occurred by a liquid phase formed among Al2O3, Y2O3 and CaO. A fine elongated and equiaxed grained (average grain size about ≤10 μm) microstructure was obtained. The mechanical properties in terms of hardness (HV), elastic modulus (E) and fracture toughness (KIC) were also measured. Their amounts are also affected by the firing temperature and the obtained microstructure, i.e. by increasing the firing temperature, it is found that, the mechanical properties increase in S1 and S2 after firing up to 1800 °C and then decrease again at 1900 °C. These results confirm the results of densification, i.e. the maximum value of KIC, HV and E were for the samples sintered at 1800 °C. Densification characteristics and microstructural development of the liquid phase-sintered β-SiC are described.