Effect of Al content in an Al/Si layer on the oxidation behavior of the Mo/Si-Al/Si double-layer coated C/C composites at 1370℃

A Mo/Si slurry was coated onto the surface of Al/Si-coated carbon fiber reinforced carbon (C/C) composites and vacuum-sintered to form a fused double-layered coating. The effect of the Al content (6 and 10 mass%) in the Al/Si layer on the oxidation resistance of the composites was investigated. Results indicate that the presence of Al effectively prevents liquid Si infiltration into the composites. The composite with the 10 mass% Al has a much lower oxidation resistance than that with the 6 mass% Al. It is revealed that when the Al content is 10 mass% an Al phase dispersed around MoSi₂ grains is found in the Mo/Si layer, which decreases the oxidation resistance of the composite at 1370℃. This can be ascribed to voids generated within the Mo/Si layer due to the outward diffusion of Al and pores in Al₂O₃ formed during oxidation, which provide paths for oxygen diffusion.