Effects of AlN Content on the Thermal Properties and Thermal Shock Resistance of BN Matrix Composite Ceramic

Using BN, SiO2, AlN as the raw materials, BN matrix composites ceramics were fabricated by hot-press sintering. Effects of AlN content on the thermal properties and thermal shock resistance of the composites were studied. It was found that thermal expansion coefficient of the composites decreased at first and then increased with the increase of AlN addition. When 5vol% AlN was used as the raw materials, the produced composite exhibited the minimum coefficient of thermal expansion, which was 2.22x10(-6)/K. Thermal conductivity of the composites increased at first and then decreased, and reached the highest value when 10vol% AlN was used as raw materials. The residual strength after thermal shock of the composites without AlN increased with the increase of thermal shock temperature difference. Residual strength of composite ceramic after thermal shock showed downward trend with the introduction of AlN. For composite ceramic adding with 5vol% AlN, the residual strength was 219.7 MPa and the residual strength was 88.9% after thermal shock from 1100 degrees C to ice water, showing a good thermal shock resistance.