SiCn/SiC Multilayer Oxidation Protective Coatings for C/C Composites Prepared by a Hydrothermal Electrophoretic Deposition Process

Nano-SIC coatings (SiCn) were deposited on SiC-C/C composites surface by a hydrothermal electrophoretic deposition. Phase compositions, surface and cross-section morphologies of the as-prepared multilayer coatings were characterized by XRD and SEM. The influences of hydrothermal deposition temperatures on the microstructures and high temperature oxidation resistance of the SIC, coatings were particularly investigated. And the invalidation behaviors of the as-prepared multilayer coatings coated samples at 1600 degrees C were analyzed. Results show that the as-prepared nano-SiC outer layers are composed of beta-SiC. The thickness and density of the nano-SIC coatings improve with the increase of hydrothermal temperature. With the increase of hydrothermal temperature, the anti-oxidation properties of the coating samples increase. The prepared coating samples deposited at 120 degrees C can effectively protect C/C composites from oxidation at 1500 degrees C in air for 202h with weight loss only about 2.16 x 10(-3) g/cm(2). While the weight loss of coated C/C composites after 64 h oxidation at 1600 degrees C in air is 3.7 x 10(-3) g/cm(2). The failure of the coatings is due to the long time volatilization of SiO2 thin film at high temperature, which makes the coating defects fall to be self-cured by SiO2 glass layer and form the penetrative microholes in the SiC bonding layer.