The effect of post-sintering heat treatment on the properties of SiC–LaAlO3-chromium carbide ceramic material fabricated by a liquid phase sintering: I. Phase relations between LaAlO3, SiO2 and SiC in 1300–1600°C

La2O3 and Al2O3 are considered as promising additions to improve SiC fracture toughness by forming LaAlO3 and promoting SiC liquid phase sintering. Thus, phase relations between LaAlO3, SiO2 and SiC in the temperature range 1300–1600°C were studied. It was shown that although LaAlO3 reacts with SiO2, forming a La–Al–Si–O glass at 1500°C, addition of SiC to the glass causes devitrification and crystallization of LaAlO3 above 1550°C. SiC is considered to generate the oxygen-deficient glass. Crystallized LaAlO3 phase is found to be stable on reheating at temperatures lower than 1400°C and higher than 1500°C. Thus, SiC–LaAlO3 ceramic materials obtained by liquid phase sintering are expected to show the deterioration of high temperature mechanical properties in the temperature range 1400–1500°C.