The effect of post-sintering heat treatment on the properties of SiC–LaAlO 3-chromium carbide ceramic material fabricated by a liquid phase sintering: I. Phase relations between LaAlO 3, SiO 2 and SiC in 1300–1600°C

Abstract

La 2O 3 and Al 2O 3 are considered as promising additions to improve SiC fracture toughness by forming LaAlO 3 and promoting SiC liquid phase sintering. Thus, phase relations between LaAlO 3, SiO 2 and SiC in the temperature range 1300–1600°C were studied. It was shown that although LaAlO 3 reacts with SiO 2, forming a La–Al–Si–O glass at 1500°C, addition of SiC to the glass causes devitrification and crystallization of LaAlO 3 above 1550°C. SiC is considered to generate the oxygen-deficient glass. Crystallized LaAlO 3 phase is found to be stable on reheating at temperatures lower than 1400°C and higher than 1500°C. Thus, SiC–LaAlO 3 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.