SiC coating prepared by a two-step technique of pack cementation and CVD on carbon/carbon composites

A SiC coating was prepared on carbon/carbon (C/C) composites by a two-step technique of pack cementation and CVD processes to prevent these composites from oxidation. SEM, EDS and XRD were applied to analyze the surface and cross-section morphologies, element distribution and phase composition of the coating, respectively. The results show that a transitional layer with gradient distribution of Si and C content is formed between the SiC coating obtained by pack cementation process and C/C substrate, and the compact coating prepared by CVD process effectively fills the pores of the coating by pack cementation. The coating made by the two-step technique exhibits excellent oxidation protective ability. The weight loss percentage of the coated C/C composites is only 2.01% after oxidation in air at 1500°C for 60 h. The weight loss of C/C composites is primarily due to the reaction of C/C and oxygen diffusing through the microcracks in the coating during the thermal cycle between 1500°C and room temperature.