Microstructure and oxidation resistance of C-AlPO4–mullite coating prepared by hydrothermal electrophoretic deposition for SiCC/C composites

Oxidation resistant C-AlPO4–mullite coating for SiC pre-coated carbon/carbon composites (SiCC/C) was prepared by a novel hydrothermal electrophoretic deposition process. The phase composition, surface and cross-section microstructure of the as-prepared multi-layer coatings were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The influence of deposition voltage 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 C-AlPO4 and mullite phase can be achieved after the hydrothermal electrophoretic deposition. The thickness, density and anti-oxidation property of the C-AlPO4–mullite coating was improved with the increase of deposition voltage from 160 V to 200 V. The multi-layer coating prepared at a voltage of 200 V exhibit excellent anti-oxidation property, which can effectively protect C/C composites from oxidation in air at 1773 K for 324 h with a weight loss of 1.01%. The failure of the multi-layer coatings is due to the generation of cross-holes in the coating, which cannot be self-cured by the metaphosphate and silicate glass layer after long time oxidation at 1773 K.