Abstract: In order to protect carbon/carbon (C/C) composites from oxidation at high temperature, a nano SiC_n-MoSi₂  coating was prepared on SiC pre-coated C/C composites by novel hydrothermal electrophoretic deposition. The phase compositions of the as-prepared coatings were analyzed by XRD, the morphologies of the multi-layer coatings were observed by SEM and the high temperature anti-oxidation properties of the multi-coatings were investigated by isothermal oxidation test. The influence of hydrothermal electrophoretic deposition voltage on the phase composition, microstructure and high temperature oxidation resistance of the multilayer coating were particularly investigated. The invalidation behavior of the coated sample during the thermal cycle process was analyzed. Results show that the outer layer coatings are mainly composed of β-SiC and MoSi₂ phases. The thickness, density and anti-oxidation properties of the SiC_n-MoSi₂ coating are improved with the increase of deposition voltage from 100V to 180V. However, cracks are observed at a high deposition voltage (220V) and the decrease in oxidation resistance is detected. The multi-layer coatings deposited at 180V exhibit excellent oxidation resistance ability, which can effectively protect C/C composites from oxidation in air at 1500℃ for 346h with a weight loss of 1.41%. The failure of the coating after 80 thermal cycles between 1500℃ and room temperature is due to the generation of cross-cracks in the coating during the test.

Key words: carbon/carbon composites, multilayer coating, hydrothermal electrophoretic deposition, deposition voltage