Preparation and properties of carbon fiber/Si₃N₄ composites

To investigate the effects of carbon fiber (C_f) adding content on the properties of Si₃N₄, C_f/Si₃N₄ composites with 0, 2 wt% and 5 wt% 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 C_f and Si₃N₄ particles or SiO₂ layer on surface of Si₃N₄ particles during high temperature sintering. The sample with 2 wt% C_f addition achieves a higher value of thermal conductivity (45.8 W/(m·K)), while the thermal conductivity of Si₃N₄ without C_f is only 37.1 W/(m·K). Therefore, the addition of C_f can improve the thermal conductivity of the composites. The fracture toughness of the composites has a slight increase with C_f adding. The measured hardness values for all samples are within a range of 16.6-16.8 GPa.