Double-layer oxidation protective SiC/Cr-Al-Si coating for carbon-carbon composites

Double-layer oxidation resistant SiC/Cr-Al-Si coating for carbon-carbon composites was prepared by a two-step method of pack cementation and slurry. The phase composition, micro-structure and oxidation resistance of mono-layer SiC coating and double-layer SiC/Cr-Al-Si coating were studied by XRD, SEM, and isothermal oxidation test at 1773 K in air, respectively. Mono-layer SiC coating consists of SiC and Si, which can protect carbon-carbon composites for several hours depending on its thin thickness and porous structure. After adding outer Cr-Al-Si alloy coating, the as-prepared double-layer SiC/Cr-Al-Si coating with a dense surface and about 150 μm thickness showed improved oxidation resistance, which can protect carbon-carbon composites for 197 h with only 0.079 wt.% mass gain. The failure of the double-layer SiC/Cr-Al-Si coating is thought to occur due to the excessive depletion of the outer Cr-Al-Si alloy coating and the appearance of defects in the SiO₂ glass layer.