High-Temperature Flexural Properties and Failure Mechanisms of MoSi₂–B₄C Modified Quartz Fabric/Boron-Phenolic Ceramizable Composites

The incorporation of inorganic fillers has demonstrated remarkable potential in enhancing ablation resistance and mechanical performance of polymer composites. However, the evolution of fracture properties of ceramizable composites with temperature remains insufficiently understood, which is significant to the safety and application in thermal protection systems. In this study, the thermal stability, high-temperature flexural properties, and failure mechanisms of MoSi₂–B₄C particles modified quartz fabric/boron-phenolic ceramizable composites were investigated. Through three-point bending tests conducted from 25°C to 1100°C, we found that flexural strength generally declines with the rising temperature and decreases as the holding time increases from 10 to 15 min. The high-temperature failure mechanisms of the ceramizable composites were analyzed through macro and micro analysis. It is found that the matrix thermal degradation, accompanied by interface deterioration and multiscale structural damage, is the primary mechanism for the significant reduction in high-temperature flexural strength. However, the ceramization reactions of MoSi₂ and B₄C contribute to enhanced high-temperature mechanical properties, resulting in an unprecedented improvement in flexural strength observed at 900°C. Moreover, a high-temperature strength model for these ceramizable composites was developed. These findings provide valuable insights for evaluating the performance and potential applications of ceramizable composites in thermal protection systems.