Phase, microstructure, and oxidation resistance of yttrium silicates coatings prepared by a hydrothermal electrophoretic deposition process for C/C composites

Oxidation-resistant yttrium silicates coatings for SiC precoated carbon/carbon composites were prepared by a novel hydrothermal electrophoretic deposition process. Sonochemical-synthesized yttrium silicates nanocrystallites, isopropanol, and iodine were respectively used as source materials, solvent, and charging agent during the deposition. Phase compositions, surface and cross-section microstructures of the as-prepared multilayer coatings were characterized by an X-ray diffractometer (XRD) and a scanning electron microscopy (SEM). The influence of deposition temperatures on the phase, microstructure, and oxidation resistance of the multilayer coated C/C composites was particularly investigated. Results show that the as-prepared outer coatings are composed of yttrium silicates crystallites with a main phase of Y₂Si₂O₇ and Y₂SiO₅. The thickness and density of the yttrium silicates coatings are improved with the increase of deposition temperature. Compared with SiC coating prepared by pack cementation, the multilayer coatings prepared by pack cementation with a later hydrothermal electrophoretic deposition process exhibit better antioxidation properties. The as-prepared multilayer coatings can effectively protect C/C composites from oxidation at 1773 K in air for 35 h with a weight loss of 0.32 × 10⁻³ g/cm².