Abstract: Aiming at the application requirements of hypersonic vehicles for new high-temperature transparent composite materials, Si₃N_4f/BN composite was prepared by using PIP process with three-dimensional woven fabric of Si₃N_4f fiber satin weave as reinforcement and borazine as ceramic precursor. The structure and properties of Si₃N_4f/BN composite were characterized by SEM, XRD, high temperature bending and ablation. The results show that Si₃N_4f/BN composite appears uniform and dense texture and the density reaches 1.82 g/cm³. They have excellent high temperature mechanical properties with a flexural strength of 76.9 MPa at 1 400 ℃ and a strength retention rate exceeding 70%. At 1 400 ℃, the composite still maintains an amorph structure. Si₃N_4f/BN composite also exhibits excellent ablation resistance with a linear ablation rate of 0.026 mm/s for the test that adopted oxygen-acetylene ablation test in accordance with GJB 323A—1996. The surface of ablative area and the area along the direction of heat flow are emerged the ablation center area, the ablation transition area, and the non-ablated matrix area. In the ablation center, the fibers are consumed, leaving only a porous BN matrix and a small amount of oxides. In the ablation transition area, the surface of the fiber is wrapped by molten oxides. The non-ablated area is still a dense Si₃N_4f/BN matrix.

Key words: borazine, boron nitride, ceramic-based composites, high-temperature properties, ablation