BN纤维束增强氮化物复合材料的制备与性能

Preparation and Properties of BN Fiber Reinforced Nitride Mini-composites

采用低压化学气相沉积/渗透法(LPCVD/CVI)制备了BN_f/BN、BN_f/SiBN和BNf/Si_3N_4纤维束复合材料,研究了BN纤维束及3种纤维束复合材料的微结构、拉伸性能和介电性能。结果显示,BN纤维是由晶化程度较低的h-BN组成,其相结构在制备温度下(650~800℃)未发生变化。纤维的表面存在大量50～500 nm的微孔缺陷。800℃处理后纤维束的平均抗拉伸强度为94 MPa。BNf/BN、BNf/SiBN以及BNf/Si3N4抗拉伸强度依次降低,平均值分别为68.8,30.6,26.2 MPa,断裂模式均为脆性断裂。原因在于:纤维损伤随制备温度升高而加剧;纤维/基体模量失配,纤维不能有效承载;界面结合强度过高,裂纹不能有效偏转。3种纤维束复合材料的介电常数实部ε′<3.0,介电损耗tanδ<0.04,电磁透波性能良好,其中BNf/BN复合材料具有最佳的综合性能。

BNf/BN,BNf/Si BN and BNf/Si3N4 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 BNf/BN,BNf/Si BN and BNf/Si3 N4 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.BNf/BN possesses the best comprehensive performance.