Thermal properties and thermal shock resistance of BAS-BN composite ceramics

Barium aluminosilicate (BAS) matrix composite ceramics containing 10, 30 and 50 wt% h-BN and monolithic BAS have been prepared by hot pressing. Results showed that the incorporation of h-BN has a remarkable effect on thermal properties and thermal shock resistance of the composites. The addition of h-BN promoted the thermal conductivity but deceased the average coefficient of thermal expansion. The retained strength rate of sample achieved 42.9% (temperature difference Delta T = 1000 degrees C) when the content of h-BN was 50 wt%. The residual strength of the BAS-BN composites declined rapidly with increasing Delta T from 400 degrees C to 600 degrees C, which is mainly due to the gradual growth of cracks derived from the thermal stress damage. However, the retained strength ratio of the composites rose slightly as Delta T increased from 800 degrees C to 1000 degrees C. This strengthening is ascribed to the formation of the compressive stress layer. These results revealed that the thermal shock resistance of the BAS-BN composites could be enhanced by the introduction of h-BN.