C/SiC/Si-Mo-Cr multilayer coating for carbon/carbon composites for oxidation protection

To improve the oxidation resistance of carbon/carbon (C/C) composites at high temperature, the C/C composites were first slurry-coated by carbon, then pack cemented by mixtures of Si and graphite powder (60-80∶10-25 wt/wt), followed by heat treatment to form C/C composites coated with a C/SiC layer, and finally a Si-Mo-Cr oxidation protective coating was prepared on the surface of the these composites by pack cementation. Scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy were used to characterize the compositions and microstructure of the coating. The oxidation behavior of the coated C/C composites at 1 873 and 1 973 K in air was investigated. The coating showed excellent oxidation resistance at 1 873 K due to the formation of a glassy layer of SiO₂ and Cr₂O₃ during the oxidation test, which could effectively protect C/C composites from oxidation for 135 h. The coating failed after oxidation for 30 h at 1973 K because the protective glass layer was disrupted.