Investigation of the multi-coating for high temperature and long life oxidation protection of C/C composites

A SiC-WSi₂/MoSi₂ multilayer oxidation protective coating for carbon/carbon (C/C) composites was prepared by pack cementation. Effects of the total content of W and Mo on the microstruc-ture and high temperature anti-oxidation property of the multi-coating were studied by XRD, SEM, EDS and isothermal oxidation test. The results show that with the total content of W and Mo increasing in the pack powders, the as-received multi-coating thickness first increases and then decreases. The multi-coating with 10.0at% (W and Mo) has a thicker, denser structure and higher content of WSi₂ and MoSi₂ than those with 0at%, 8.4at% and 13.1at% (W and Mo). A stable and dense glassy SiO₂ film can be formed on the coating surface with 10.0at% (W and Mo) during the oxidation test. The coated specimen with 10.0at% (W and Mo) has no weight loss after oxidation in air for 315h at 1500°C and no cracks after thermal cycling between 1500°C and room temperature for 18 times, which implies that the multi-coating has excellent oxidation protective ability and thermal shock resistance.