SiC/Yb2SiO5 Multilayer Coatings for Oxidation Protection of Cf/SiC Composites

Ytterbium silicate (Yb2SiO5) is a promising oxidation protective coating material for C fiber-reinforced SiC (C-f/SiC) composites. Firstly, the SiC bond coat was prepared on Cf/SiC composites by pulse CVD. The single-phase Yb2SiO5 powders of 200-300 nm in size were synthesized by sol gel process. Then for the first time, the SiC-Yb2SiO5 intermediate coat was applied on the SiC coated Cf/SiC composites through PCS-SiC-Yb2SiO5 slurry application. The incorporation of PCS could significantly improve the adhesion of the coating because of the great stickiness of PCS and its ability to form SiC ceramic in situ after pyrolysis. The Yb2SiO5 slurry with low viscosity and high solid content was prepared, and the dense Yb2SiO5 top coat with fine crystallites was fabricated by dip-coating and subsequent sintering. The oxidation tests at 1500 degrees C in stationary air indicate that the fabricated SiC/Yb2SiO5 multilayer coatings possess a outstanding oxidation resistance.