Microstructure and oxidation resistance of SiC/W-Al-Si double-layer coatings for carbon-carbon composites

SiC and W-Al-Si oxidation resistant coatings on carbon-carbon(C/C) composites surface were prepared by pack cementation and slurry method. The phases, microstructure of the SiC and W-Al-Si coatings were studied by XRD and SEM. The oxidation resistance of mono-layer SiC and double-layer SiC/W-Al-Si coatings were also tested by isothermal oxidation test at 1773 K in air, respectively. The results show that the mono-layer SiC coatings composed of Si and SiC only can protect C/C composites for several hours from oxidation at 1773 K because of its porous structure. WSi₂ and W(Si, Al)₂ are two main phases of the outer W-Al-Si layer. The anti-oxidation property of the double-layer SiC/W-Al-Si coatings with a approximately 100 μm thickness is superior to that of the mono-layer SiC coatings, and the mass loss of SiC/W-Al-Si coated C/C composites is less than 5% after oxidation at 1773 K in air for 19 h. By optimization of the slurry ratio of W-Al-Si, the oxidation resistance of double-layer SiC/W-Al-Si coatings can be improved to over 19 h at 1773 K due to the elimination of penetrating crack created by dismatch between inner SiC and outer layer W-Al-Si for SiC/W-Al-Si coatings.