High strength retention and improved oxidation resistance of C/C composites by utilizing a layered SiC ceramic coating

Silicon carbide (SiC) ceramic coating prepared by pack cementation (PC) can provide effective oxidation protection for carbon/carbon (C/C) composites at high temperatures. However, the reaction between free silicon and C/C substrates would cause the serious damage to mechanical properties of C/C composites. In current work, a carbon transition coating (C_TC) was pre-prepared on C/C composites by slurry-carbonization before the preparation of SiC coating to eliminate the negative effect of siliconization. For comparison, SiC coating on C/C composites without C_TC was also prepared. Due to the retardation effect of C_TC on siliconization erosion, the flexural strength of SiC coated C/C composites with C_TC maintained ~76.35 % compared with the raw C/C substrates, whereas the strength retention rate of SiC coated specimens without C_TC was only ~36.92 %. Furthermore, the existence of C_TC can densify the microstructure of as-prepared SiC coating by sufficiently reacting with free silicon during PC. Therefore, the SiC coated C/C composites with C_TC possessed better oxidation resistances both under thermal cycling condition (between room temperature and 1500 °C) and in a water-vapor environment at 1500 °C.