SiC/Si-Al₂O₃-mullite oxidation protective coating for C/C composites prepared by in-situ formation method

A Si-Al₂O₃-mullite oxidation protective coating was prepared on SiC coated carbon-carbon (C/C) composites by in-situ formation using Si and Al₂O₃ as raw materials in an oxidation atmosphere. The effects of the Al₂O₃ content on the phase component, microstructures, and oxidation-resistance property of the Si-Al₂O₃-mullite coating were studied. Results show that the coating is dense and composed of Si, mullite, and Al₂O₃ when the content of Al₂O₃ is 30 wt%-40 wt%. The oxidation test indicates that the SiC/Si-Al₂O₃-mullite coating can protect C/C composites from oxidation in air for 75 h at 1500°C with a weight loss of 4.6%, which shows that the anti-oxidation ability of the SiC/Si-Al₂O₃-mullite coating has obviously been improved as compared with that of single-layer SiC coating. The weight loss of SiC/Si-Al₂O₃-mullite coated C/C composites is primarily due to the formation of holes on the coating surface.