Effect of magnesium aluminum silicate glass on the thermal shock resistance of BN matrix composite ceramics

The effects of magnesium aluminum silicate (MAS) glass on the thermal shock resistance and the oxidation behavior of h-BN matrix composites were systematically investigated at temperature differences from 600°C up to 1400°C. The retained strength rate of the composites rose with the increasing content of MAS showing a maximum value at the 60 wt% MAS. Compared with the original strength, the retained strength of the specimen after thermal shock increased to 77% (ΔT=1000°C). The strengthening effect of MAS and the surface microstructural evolution of composites are responsible for the improved thermal shock resistance. Surface oxidation of the composites during the thermal shock process plays a positive role in enhancing the retained strength by self-healing cracks and the appearance of the compressive stress. The oxide layer also acted as a thermal barrier to decelerate the actual thermal stress. Furthermore, this dense layer also improved the oxidation resistance of h-BN matrix composites by prevent diffusion of oxygen. These results indicated that short-term surface oxidation during thermal shock process is favorable to the enhancement of the thermal shock resistance of BN-MAS composite ceramics.