Preparation and Properties of Carbon Fiber/Si_3N_4 Composites

To investigate the effects of carbon fiber(Cf) adding content on the properties of Si3N4, Cf/Si3N4 composites with 0, 2wt% and 5wt% of short carbon fibers were prepared by hot-press sintering method, using Y2O3 as sintering additives. With long-time ball milling process, carbon fibers were well dispersed in mixed powders using ethanol as dispersion medium. Carbon fibers distribute uniformly in the composites and Si3N4 grains grow to a certain degree in the vertical direction to the pressure of hot-press. The interfacial by-product silicon carbide(SiC) phase forms due to the reaction between added Cf and Si3N4 particles or SiO2 layer on surface of Si3N4 particles during high temperature sintering. The sample with 2wt% Cf addition achieves a higher value of thermal conductivity(45.8 W/(m K)), while the thermal conductivity of Si3N4 without Cf is only 37.1 W/(m K). Therefore, the addition of Cf can improve the thermal conductivity of the composites. The fracture toughness of the composites has a slight increase with Cf adding. The measured hardness values for all samples are within a range of 16.6–16.8 GPa.