Environmental barrier coatings on enhanced roughness SiC: Effect of plasma spraying conditions on properties and performance*

Environmental barrier coatings for SiC/SiC composites are limited by the melting temperature of the Si bond coating near 1414 degrees C. Systems without a bond coating may be required for future turbine applications where material temperatures go beyond 1350 degrees C. Enhanced roughness SiC substrates were developed to assess coating adhesion without the bond coating. Two EBCs with different YbMS/YbDS ratios were produced via modified plasma spraying parameters. Coating microstructure, thermal expansion, and modulus were measured for comparison of coating properties. Cyclic steam exposures at 1350 degrees C were performed to assess oxidation resis-tance. The EBC with increased concentration of Yb2SiO5 secondary phase displayed a higher CTE, which is typically expected to decrease adhesion lifetimes due to an increase in stress upon thermal cycling. Yet, the EBC chemistry with increased Yb2SiO5 concentration was able to experience longer cycling times prior to coating delamination, likely due to interface interactions with the substrate and the thermally grown oxide.