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 1 370 ℃

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 1 370 ℃.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.