Thermal Shock Resistance of Si₃N₄/h-BN Composites Prepared via Catalytic Reaction-Bonding Route

Si₃N₄/h-BN ceramic matrix composites were prepared via a catalytic reaction-bonding route by using ZrO₂ as nitridation catalyst, and the water quenching (fast cooling) and molten aluminum quenching tests (fast heating) were carried out to evaluate the thermal shock resistance of the composites. The results showed that the thermal shock resistance was improved obviously with the increase in h-BN content, and the critical thermal shock temperature difference (ΔT_c) reaches as high as 780 °C when the h-BN content was 30 wt.%. The improvement of thermal shock resistance of the composites was mainly due to the crack tending to quasi static propagating at weak bonding interface between Si₃N₄ and h-BN with the increase in h-BN content. For the molten aluminum quenching test, the residual strength showed no obvious decrease compared with water quenching test, which could be caused by the mild stress condition on the surface. In addition, a calculated parameter, volumetric crack density (N_f), was presented to quantitative evaluating the thermal shock resistance of the composites in contrast to the conventional R parameter.