Significantly enhanced thermal shock resistance of α-Si3N4/O′-Sialon composite coating toughened by two-dimensional h-BN nanosheets on porous Si3N4 ceramics

Abstract

To enhance the ability of α-Si3N4/O′-Sialon coating on porous Si3N4 ceramics for resisting the damage caused by aerodynamic loading and heating, h-BN nanosheets (BNNSs) were used as reinforcement phase to improve mechanical and thermal properties of the coating. The results show that the prepared coating exhibited good softening and toughening effects due to the mechanisms of the BNNSs including bridging, kinking, slipping and crack deflection, thereby improving the damage tolerance and toughness of the coating. At the same time, the thermal diffusivity and conductivity of the coating were significantly improved due to the ultra-high thermal conductivity of BNNSs, which can quickly disperse heat during thermal cycling and greatly reduce thermal stress. Therefore, as-prepared coating showed a good thermal shock resistance. After thermal cycling for 15 times at ΔT=1100 °C, the water absorption of coated samples only increased to 14.4%, and the residual strength ratio reached to 73%. The results will be a solid foundation for the practical application of the coating in the long-term extreme environment of aerospace engineering.