EBC Development for Al2O3/Al2O3 CMC Combustor Liners

Environmental barrier coatings (EBC) are considered mandatory for the application of ceramic matrix composites (CMC) in hot sections turbine engines such as combustors. Low thermal mismatch, good adherence, microstructural stability and resistance against hot corrosion are key material properties. Y2O3-stabilized ZrO2 (YSZ), Yttrium-Aluminum Garnet Y3Al5O12 (YAG) as well as Y2O3 are considered attractive EBC materials for all-oxide CMCs consisting of Al2O3 fibers and matrices. In order to identify the most promising EBC material, Al2O3/Al2O3-CMCs were coated by means of air plasma spraying (APS). EBC-coated CMC coupons were subjected to relevant thermochemical loads such as burner-rig tests and CMAS-type corrosion. It turned out that Y2O3 offers the most favorable combination of corrosion resistance and compatibility to Al2O3/Al2O3 CMC. Two full scale CMC combustor liners were coated with 0.5 and 1 mm thick APS Y2O3 EBC, respectively. An additional array of effusion cooling holes was manufactured by means of Laser-drilling. Tests in a high pressure combustor rig revealed a good coating performance. Specific aspects of laser-drilling of similar CMC components are discussed