Abstract: The corrosion resistance of SiC_f/SiC composites was improved by chemical vapor deposition (CVD) SiC coatings. In this paper, SiC coatings are prepared on reaction sintering SiC matrix with CH₃SiCl₃ (MTS) as the source gas. Surface morphology and corrosion resistance of silicon carbide coatings were related with parameters in CVD such as deposition temperature, furnace pressure and mole ratio of H₂ and MTS. The phase composition and crystallinity of silicon carbide coating under different process conditions were obtained by X-ray diffraction experiment (XRD). The corrosion resistance of the coating was detected by high-temperature water corrosion experiment, and the surface morphology before and after the corrosion was observed by scanning electron microscope (SEM). The results showed that when the deposition time was 8 hours and the deposition temperature was from 1050 ℃ to 1250 ℃, the surface roughness of SiC coating was improved, the deposition thickness increased sharply from 12.97 μm to 71.10 μm, and the grain size of SiC gradually increased and finally presented a pyramid shape. After 60 days of corrosion of silicon carbide coating, the surface presents an acicular structure. The SiC coating deposited at 1250 ℃ had better corrosion resistance. With the increase of deposition furnace pressure, the crystallinity of β-SiC grains decreased sharply and the grain size increased sharply. The crystallinity of β-SiC was the highest (81.08%) and the grain size was smallest (13.7 nm) under 200 Pa. The crystallinity of β-SiC grain decreased sharply with the increase of the molar ratio of H₂ and MTS. When the molar ratio of H₂ and MTS was 6.5, the crystallinity reached its highest point (95.91%).

Key words: SiC_f/SiC, composites, corrosion resistance, SiC coating, chemical vapor deposition, crystallinity