INFLUENCE OF HYDROTHERMAL DEPOSITION VOLTAGE ON THE MICROSTRUCTURES OF CRISTOBALITE ALUMINUM PHOSPHATE COATINGS

Cristobalite aluminum phosphate (C-AlPO4) coatings were deposited on the surface of carbon fiber reinforced carbon (C/C) with SiC coating (C/C–SiC) composite by a hydrothermal electrophoretic deposition process using C-AlPO4 powder, isopropanol and siodine as raw materials, and solvent and charging agent, respectively. The phase compositions and microstructures of the as-prepared multi-coatings were characterized by X-ray diffraction and scanning electron microscopy. The influences of deposition voltage on the microstructures of the C-AlPO4 coatings were investigated. The oxidation resistance property of the C-AlPO4 coatings was tested. The results show that the deposition voltage plays an important role in improving the microstructure of the C-AlPO4 coatings. The C-AlPO4 coating prepared at 220 V is compact, and that prepared at 180–200V is uniform. The deposition amount of the C-AlPO4 coatings and the bonding strength between the C-AlPO4 coatings and C/C–SiC composites increase with the increase of deposition voltage. The deposition mass per unit area of the coatings is linear with the square root of the deposition time. Compared with the SiC coating prepared by the pack cementation method, the C-AlPO4 coatings have better oxidation resistance. The mass loss of as-prepared multi-coatings on C/C–SiC composite is only 0.53% after oxidation at 1 500 ℃ for 37 h in air.