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 30 vol%. 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 30 vol% ZrO2/BN composite are 183 MPa and 3.80 MPa m1/2, 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.