Effect of Heat Treatment of Carbon Fibers on Mechanical Properties of Carbon Fiber/SiC Composites

抄録

CF/SiC composites were prepared using polycarbosilane impregnation/pyrolysis technique and PAN-based carbon fibers heat-treated at 1400°C, 1500°C, 1600°C, 1800°C and 2000°C for 1 hour, respectively. The effect of heat treatment temperature (HTT) on the mechanical properties of the carbon fibers and the CF/SiC composites was investigated. With the increase of HTT, the crystallinity and elastic modulus of the carbon fibers were slightly improved, while the tensile strength of the carbon fibers reached highest values at the HTTs between 1400°C and 1600°C. However, the ultimate tensile loads (UTL) of the CF/SiC composites appear no direct relation with the strength of the carbon fibers. The CF/SiC composites with carbon fibers heat-treated at 1400°C exhibited a low tensile strength and completely brittle fracture. The composites with carbon fibers heat-treated at 1500°C and 2000°C exhibited a moderate UTL and short fiber pullout (lower than 5μm). The composites with carbon fibers heat-treated at 1600°C and 1800°C exhibited the highest UTL and longer fiber pullout (20-30μm). The difference was attributed to the change in the interface characteristics. With the graphitization degree of the carbon fibers being improved by the heat treatment, the surfaces of the carbon fibers became less active, and the fibers tended to bond weakly with the matrix. However, for the carbon fibers heat-treated at 2000°C, it was considered that the surface roughening might make the interface strong, resulting in lower strength and short fiber pullout. The above results suggest that the properties of CF/SiC composites can be controlled through heat treatment of the carbon fibers.