Oxidation properties of tri-layer ytterbium-disilicate/mullite/silicon-carbide environment barrier coatings for Cf/SiC composites

Mullite (Al6Si2O13) and ytterbium disilicate (Yb2Si2O7) powders were synthesized by the solvent gel (sol-gel) method. To improve the oxidation resistance of Cf/SiC composites at high temperatures, a novel tri-layer Yb2Si2O7/Al6Si2O13/SiC environment barrier coatings (EBCs) was deposited on the surface of Cf/SiC composites by chemical vapor deposition (CVD) and air spray sol-gel methods. Results show that Yb2Si2O7/Al6Si2O13/SiC coating lost its ability to protect Cf/SiC composites in the air environment at 1773 K due to the Yb2Si2O7 particles in Yb2Si2O7 top coating diffused into the Al6Si2O13 middle coating, which eventually form a eutectic interface with the extension of oxidation time. However, Yb2Si2O7/Al6Si2O13/SiC coating can efficiently prevent the oxidation of Cf/SiC composites at 1673 K for 150 h with a weight loss of 2.69 × 10−3 g·cm−2. The growth of grains and the disappearance of micro-holes in Al6Si2O13 and Yb2Si2O7 coatings deposited by air spray sol-gel method led to the excellent oxidation resistance of Yb2Si2O7/Al6Si2O13/SiC coating. •A novel tri-layer Yb2Si2O7/Al6Si2O13/SiC environment barrier coatings (EBCs) is prepared on Cf/SiC composites.•Yb2Si2O7/Al6Si2O13/SiC coating loses the protection ability of Cf/SiC composites at 1773 K.•The Yb-Si-O-Al system began to melt locally at about 1773 K.•Yb2Si2O7/Al6Si2O13/SiC coating has better oxidation resistance for Cf/SiC composites at 1673 K.•The study provides guidance for the design of EBCs.