Fabrication and Properties of SiO2-BN-Si3N4 Composites

SiO2-BN-Si3N4 composites were prepared by in-situ liquid pressureless sintering process using Y2O3 and Al2O3 powders as sintering additives. The green body was fabricated by gel-casting process, and then sintered at 1780 degrees C for 2 h. The sintered body was mainly composed of the plate-like Si2N2O and rod-like alpha-Si3N4 grains. BN was dispersed in the grains. The Si2N2O phase was obtained by in-situ reaction of SiO2+Si3N4 -> 2Si(2)N(2)O. Si2N2O possesses the excellent oxidation resistance, Si3N4 has high strength, and the addition of BN can improve the machining property. The excellent properties of all phases are combined into the materials. The results show that the materials have good thermal shock resistance. When the temperature of the thermal shock is 800 degrees C, the residual strength is improved slightly and when the temperature was 1200 degrees C, the residual strength is unchangeable.