Microstructure and anti-oxidation property of mullite oxidation protective coating prepared by hydrothermal electrophoretic deposition for SiC–C/C composites

Oxidation resistant mullite outer coating for SiC pre-coated carbon/carbon composites (SiC–C/C) was prepared by a novel hydrothermal electrophoretic deposition process using mullite powders, isopropanol and iodine as the start materials, solvent and charging agent, respectively. The phase composition, surface and cross-section microstructure of the as-prepared multilayer coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The influence of hydrothermal deposition temperature on phase composition, microstructure and oxidation resistance of the as-prepared coatings was particularly investigated. Results show that the outer layer coating mainly composed of mullite phase can be achieved by hydrothermal electrophoretic deposition. The thickness, density and anti-oxidation property of the mullite coating were improved with the increase of deposition temperature from 353 K to 393 K. The mullite coating prepared at 393 K exhibits excellent anti-oxidation property, which can effectively protect C/C composites from oxidation in air at 1773 K for 172 h with a weight loss of 1.65%. The failure of the multilayer coatings is considered to be caused by the volatilization of the SiO2 glass and the formation of microholes and microcracks on the coating surface.