Anti-Oxidation Coating Prepared By CVD Technique For Carbon/Carbon Composites

Carbon/Carbon composite (C/C) has been used as the only high-temperature material at above 2000℃, and is considered as the most promising candidate material for high temperature applications such as in aviation, space flight fields. The problem of oxidation at high temperature should been solved if C/C composite would used as the high-temperature structural material. Coatings as the effective oxidation protective technique have been widely studied. Chemical Vapor Deposition (CVD) has been widely used to make anti-oxidation coating for Carbon/Carbon composite. Based on the work of our research group, SiC coating made by chemical vapor deposition with Ar has been investigated; and SiC coating prepared by a two-step technique of pack cementation and CVD for carbon/carbon composites; slurry and CVD have been used to prepare MoSi₂/SiC coating on the surface of packed SiC samples. The prepared coatings are characterized by SEM, XRD, oxidation test. The structures, oxidation properties and failure mechanism of the coatings are also investigated. The main contents and conclusions are as follows:Three kinds of different Ar flux in CVD-SiC processes have been devised. The micrographs of the three kinds of SiC coatings are contrasted. Simple models of temperature filed, flow filed and reactant concentration distribution in the reactor have been provided. The results reveal that the Ar would delay the temperature filed, flow filed and dilute reactant concentration distribution in the reactor. The size of crystal becomes smaller, and the coating is compact.SiC is consistent with C/C at chymic and physical capabilities. It is good to be anti-oxidation coating. But the single SiC coating's anti-oxidation property is limited because of the dismatch of CTE between SiC with C/C. A SiC coating was prepared on C/C by a two-step technique of pack cementation and CVD processes to prevent these composites from oxidation. The weight loss percentage of the coated C/C composites was only 2.01% after oxidation in air at 1500℃ for 60h.Based on the condition of our research group. A MoSi₂/SiC coating was prepared on packed C/C sample by a technique of slurry and CVD processes to prevent these composites from oxidation. And two improved technique was made base on it. The crystal components, micrographs and oxidation properties of three kinds of coatings are studied. The results show that the coating prepared by the second improved technique (packed-slurry-hot treated-CVD) is compact. And it has better anti-oxidation properties...