Study on high-temperature flexural properties and damage mechanisms of 3D five-directional braided structured Al₂O₃/mullite CMCs

This study investigates the high-temperature flexural properties and damage mechanisms of three-dimensional five-directional (3D5d) braided Al₂O₃/mullite ceramic matrix composites(CMCs). The flexural tests were carried out at room temperature and at 900 °C, 1000 °C, 1100 °C, and 1200 °C. The results show that the load-displacement curve of the 3D5d material evolves with temperature in a two-stage manner: they continuously improves from room temperature to 1000 °C, and reaches its peak at 1000 °C; while in the high-temperature range from 1000°C to 1200 °C, its curve rapidly declines, and the curve becomes relatively flat at 1200 °C. At 1000 °C, the 3D5d composite achieved a flexural strength of 135 MPa and a modulus of 12.2 GPa. Microstructural characterization revealed that the damage mechanism evolves with temperature. As the temperature rises, the failure mechanism of the material undergoes a significant transformation: at room temperature, the failure mode mainly consists of matrix cracking, interface debonding and fiber bridging; at high temperature, it gradually transitions to mode controlled by matrix cracks, interface degradation and fiber strength attenuation. Among them, the failure within the temperature range of 900°C–1100 °C is mainly dominated by interface weaking; while when the temperature reaches 1200 °C, the matrix undergoes significant softening, becoming the key factor leading to a drastic decline in performance.