Flexural Strength Evolution, Microstructure Evolution and Mechanical Strength Failure Mechanisms of the Fused SiO 2 and h-BN Co-modified Quartz Fiber/Benzoxazine Resin Ceramizable Composites

In our research described in this paper, the flexural strength evolution, microstructure evolution and the pyrolysis process of fused SiO2 and h-BN co-modified quartz fiber/benzoxazine resin ceramizable composites with increasing temperature were investigated. It was found that the flexural strength of the ceramizable composites dropped with increasing temperatures. The microstructure observation results depicted that cracks and holes appeared on the surface of the samples and the interfaces were seriously deteriorated after a static ablation test in a muffle furnace at 400–1200 °C for 20 min. Through the characterizations of the quartz fibers, it was revealed that the quartz fibers underwent a crystallization process at 1200 °C, during which micro-cracks were formed in them. As a result of our research the mechanical strength failure mechanism of the ceramizable composites was proposed. It was found that the failure process of the ceramizable composites was the result of matrix pyrolysis, carbon oxidation, interfacial degradation and fiber crystallization.