Effect of ZrO₂ content on microstructure, mechanical properties and thermal shock resistance of (ZrB₂+3Y-ZrO₂)/BN composites

(ZrB₂+3Y-ZrO₂)/BN composites were fabricated by hot-pressing with different contents of 3Y-ZrO₂ ranging from 0 to 30vol%. The mechanical properties and thermal shock resistance of composites were systematically investigated. The mechanical properties of the composites exhibit a gradual degradation while the thermal shock resistance is improved with the increasing ZrO₂ content. The flexural strength and fracture toughness of 30vol% ZrO₂/BN composite are 183MPa and 3.80MPam^1/2, respectively. The residual strength ratio claims a slight decline to the lowest value of 86.8% after thermal shock, which is improved mainly due to the lower elastic modulus and higher ratio of fracture toughness to flexural strength with increasing ZrO₂ content. Furthermore, when temperature difference ranges from 1100 up to 1400°C, the residual flexural strength of the composites increases, which is attributed to the self-healing of cracks and the thermal-barrier effect of the oxide layer.