Preparation and Properties of Carbon Fiber/Si$lt;inf$gt;3$lt;/inf$gt;N$lt;inf$gt;4$lt;/inf$gt; Composites

To investigate the effects of carbon fiber (C f ) adding content on the properties of Si 3 N 4 , C f /Si 3 N 4 composites with 0, 2wt% and 5wt% of short carbon fibers were prepared by hot-press sintering method, using Y 2 O 3 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 Si 3 N 4 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 Si 3 N 4 particles or SiO 2 layer on surface of Si 3 N 4 particles during high temperature sintering. The sample with 2wt% C f addition achieves a higher value of thermal conductivity (45.8 W/(m K)), while the thermal conductivity of Si 3 N 4 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.