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To improve the oxidation resistance of the SiC-MoSi2 coating prepared by two-step pack cementation, a liquid Si infiltrating method was adopted to modify it. The phase composition and microstructure of the coatings were analyzed by XRD and SEM. The results show that the size and number of the cracks in the modified coating decreased evidently after infiltrating Si. The oxidation test results in air at 1773 K show that the mass loss of the SiC-MoSi2 coating coated carbon/carbon (C/C) composites was up to 1.18% after oxidation for 206 h, while that of the modified coating coated C/C composites was only 0.77% after oxidation for 460 h. The reason is that the cracks formed in the pack cementation process were partly sealed and there were no penetrable cracks in the modified coating. Therefore, there were no direct channels for the oxygen to diffuse into the C/C substrate. [ABSTRACT FROM AUTHOR]

In order to protect carbon/carbon (C/C) composites from oxidation at 1700°C, a MoSi2–SiC–Si/MoSi2 coating was prepared on the surface of these composites by a simple and effective method. The MoSi2–SiC–Si inner layer was obtained by pack cementation, and the MoSi2 outer layer was prepared by slurry coating using silicon-sol as the caking agent. The microstructures of the as-prepared coating were examined by X-ray diffraction and scanning electron microscope. Oxidation test shows that, the as-received coating can protect C/C composites from oxidation for more than 107 h at 1700°C in air. The excellent anti-oxidation ability of this coating is attributed to its dense structure and the formation of the SiO2 film on the coating surface during oxidation. [ABSTRACT FROM AUTHOR]