Mechanical Properties of SiC-Matrix Composite Reinforced with Dispersed Graphite Microcrystals

Silicon carbide containing 5-15wt% graphite was fabricated by hot-pressing at 2000°-2300°C using carbon black as a starting carbon material. B4C of 1wt% was doped in SiC as a sintering aid before mixing with carbon black. X-ray diffractometry and SEM revealed that the grain growth of SiC was suppressed by the carbon addition, and that carbon black changed to graphite microcrystals. Carbon addition increased the flexural strength of the composite appreciably. The composite with 10% graphite had the average strength of 820MPa and the maximum value of 1000MPa. The fracture toughness of 4.5MPa √m for the 10% graphite composite was obtained, as compared with 3.3MPa √m for monolithic SiC.