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 (I and 3 wt.%) as sintering aids were sintered to >95% of theoretical density (TD) at temperature between 1750 and 1900degreesC. The densification occurred by a liquid phase formed among Al2O3, Y2O3 and CaO. A fine elongated and equiaxed grained (average grain size about less than or equal to 10 mum) microstructure was obtained. The mechanical properties in terms of hardness (HV), elastic modulus (E) and fracture toughness (K-IC) 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 1800degreesC and then decrease again at 1900degreesC. These results confirm the results of densification, i.e. the maximum value of K-IC, HV and E were for the samples sintered at 1800degreesC. Densification characteristics and microstructural development of the liquid phase-sintered beta-SiC are described. (C) 2004 Elsevier Ltd and Techna Group S.r.l. All fights reserved.