Fabrication and high-temperature strength of 2.5D SiO2f /SiO2 composites prepared by a combined vacuum impregnation and sol-gel method

A combined vacuum impregnation and sol-gel method was used to prepare 2.5D SiO2f/SiO2 ceramic composites with good mechanical properties in both warp and weft direction in this study. Phase change and weight gain during forming process of the ceramic composites were measured to explain the forming process. The mechanical properties of materials along different direction at room temperature and high temperature were systematically analyzed, and the fracture mechanism in different service environments was elucidated. Results indicated that dense SiO2f/SiO2 ceramic composites could be prepared by impregnating the 2.5D woven fabric preforms in silica sol and sintering them at 800 °C for > 5 cycles. Flexural strength of the composite was directly affected by the arrangement density and straightening degree of the fibers in warp/weft direction. The composite prepared in this study showed a higher flexural strength (∼91.21 MPa) in the weft direction. With the increase of temperature, the quartz fibers inside the composites became brittle due to crystallization, resulting in the failure mechanism of the ceramic composite material changing from ductile fracture to brittle fracture.