Ablation characteristics of carbon fiber reinforced carbon (CFRC) composites in the presence of silicon carbide (SiC) coating

Carbon fiber reinforced carbon (CFRC) composites were employed in carbothermal reduction of silica to form silicon carbide (SiC) coatings on the composites. The conditions of carbothermal reduction process were changed to evaluate the effects of coating conditions on ablation resistance of the composites. The coating thickness increased as reaction temperature and time increased, but the thickness did decrease at 1800 °C, assuming that carbon substrates were oxidized as well as converted into SiC. The oxidation inhibition behavior of the composites seems to be related with coating thickness; oxidation inhibition increased as reaction temperature and time increased, but the effect again decreased at 1800 °C. The ablation resistance behaviors of the composites were intriguing; the ablation rate decreased as temperature increased, even at 1800 °C unlike oxidation inhibition. It was found that SiC coating structure and orientation are responsible for this behavior. The size of coating particle became greater as reaction temperature increased; the higher the reaction temperature, the greater the size of the coating particle. It is concluded that the microstructure of protective coatings should be well controlled to improve not only oxidation inhibition but also ablation resistance.