Microstructure evolution and isothermal oxidation properties of c-AlPO4 and SiC whisker co-modified mullite coated SiC-C/SiC composites

Abstract An oxidation protective c-AlPO4 and SiC whisker co-modified mullite coating (c-AlPO4-SiCw-mullite) on SiC coated C/SiC composites were manufactured by hydrothermal electrophoretic deposition accompanied by magnetic stirring. Phase composition of c-AlPO4-SiCw-mullite coatings on SiC coated C/SiC composites with different deposition time was detected by X-ray Diffraction (XRD), element distribution and microstructure were investigated by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Results show that a crack-free, dense and homogeneous coating was prepared by hydrothermal electrophoretic deposition method. The thickness, homogeneity and antioxidant properties of c-AlPO4-SiCw-mullite coating were improved with the extension of deposition time from 10 min to 30 min. The coating manufactured after deposition of 30 min showed smoothest surface and highest density, which can effectively protect C/SiC composites from oxidation for 160 h at 1773 K in air with a weight loss of 10.02 mg cm−2. Microstructural characterization after oxidation indicated that the failure of the c-AlPO4-SiCw-mullite coating was due to the consecutive formation of penetrative micro-cracks and micro-holes.