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℃for 60h.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℃and room temperature.