BN纤维束增强氮化物复合材料的制备与性能

BN _f /BN, BN _f /SiBN and BN _f /Si ₃ N ₄ mini-composites were fabricated by low pressure chemical vapor deposition/infiltration (LPCVD/CVI) process. The microstructure, tensile property and dielectric property of BN fiber bundle and these three mini-composites were investigated. Results indicate that BN fiber is composed of h-BN with low crystallinity, whose phase structure is unchanged after heat treatment at 650℃ and 800℃. A large amount of micro pores with size of 50~500 nm exist on the surface of BN fiber. Mean tensile strength of BN fiber bundle heat treated at 800℃ is 94 MPa. Average tensile strengths of BN _f /BN, BN _f /SiBN and BN _f /Si ₃ N ₄ mini-composites decrease in turn, which are 68.8, 30.6 and 26.2 MPa, respectively. Three mini-composites all exhibit brittle fracture behavior, owing to the modulus mismatch between fiber and matrix and strong interphase bond strength. Cracks cannot be effectively deflected and fibers cannot bear the load effectively. Real part of dielectric constant and dielectric loss are lower than 3 and 0.04, respectively, leading to good electromagnetic wave transmitting property. BN _f /BN possesses the best comprehensive performance.