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 C-f/SiC composites at high temperatures, a novel tri-layer Yb2Si2O7/Al6Si2O13/SiC environment barrier coatings (EBCs) was deposited on the surface of C-f/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 C-f/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 C-f/SiC composites at 1673 K for 150 h with a weight loss of 2.69 x 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.