Microstructure evolution and mechanical properties of SiC_f/BN/SiBCN composite after high temperature thermal exposure

The present study investigates the microstructure evolution and subsequent mechanical properties of SiCfiber/BN/SiBCNmatrix composites after high temperature exposure. These composites display a non-brittle failure response under three-point bending retaining 80% of the as-processed strength, even after elevated temperature exposure up to 1350 oC for 10 h. This is due to crack deflection accompanied by extensive fiber pull-out. In addition, both thermodynamic modelling and phase analysis by XRD show higher matrix degradation in vacuum than in N2 atmosphere due to the lower N₂ partial pressure. After thermally exposed at 1500°C, carbothermal reaction in the matrix leads to the formation of a porous composite, and the composites retains a non-brittle failure behaviour. Meanwhile, SiBCN matrix degradation and SiC fiber strength degradation occurs, which results in significant composite strength decrement. Modest increases in the fiber/matrix interfacial shear strength occur upon exposure at temperatures up to 1350°C, and then significantly reduced after expsoure at 1500 oC in N₂.