Thermal shock resistance of the porous boron nitride/silicon oxynitride ceramic composites

Abstract The thermal shock resistance of the porous boron nitride/silicon oxynitride ( BN /Si ₂ N ₂ O) ceramic composites were tested by the quenching‐strength method with temperature differences of 600‐1400°C. The residual flexural strength of the composites decreased with increasing temperature difference from 600°C to 900°C. This weakening in flexural strength was attributed to the formation of microcracks in the matrix caused by thermal stress damage. Afterward, as the formation of a dense oxidized layer sealed the surface and hindered further oxidation, the residual flexural strength increased with the further increase of temperature difference from 900°C to 1100°C. Finally, when the temperature differences were above 1100°C, the residual flexural strength gradually decreased with increasing temperature difference, which was attributed to the further oxidation and large thermal stress damage. And the thermal shock resistance of the porous BN /Si ₂ N ₂ O ceramic can be improved by the introduction of high contents of sintering aids and h ‐ BN .