Development of a New Coating Compatible with Third-Generation Nickel-Based Superalloys and Thermal Barrier Coatings

Abstract

A new coating has been developed for single-crystal-alloy-coating system (SXS) (single-crystal (SX) superalloy/γ/γ′ bond coat (BC)/thermal barrier coating (TBC)) for aircraft engine turbine blade applications. Design procedure of the new SXS, mechanical, and environment characterizations is presented and compared with other reference systems composed of AM1, CMSX-4 SLS, and CMSX-4 Plus superalloys with β-NiPtAl (BC) and TBCs. Targeted coating compositions were optimized for extending TBC lifetime and avoiding secondary reaction zone (SRZ) formation while maintaining satisfactory level of oxidation resistance. In order to avoid the formation of SRZ, the strategy chosen was to develop new γ/γ′ structural coatings close to the substrate composition. This new SXS exhibits high creep resistance at high temperature compared with the other reference systems while exhibiting high oxidation resistance. Indeed, oxidation resistance of the new SXS with CMSX-4 Plus alloy (CMSX-4 Plus/γ/γ′ coating) at 1100 °C is similar to that of the other reference systems. Otherwise, oxidation resistance of the new SXS with AGAT-3 alloy (AGAT-3/γ/γ′ coating) at 1100 °C is higher than that of the other reference systems. The new coating (γ/γ′) does not generate SRZ even after aging or creep testing at high temperature and ensures high lifetime of thermal barrier coatings (TBCs) (YPSZ-electron beam physical vapor deposition (EB-PVD) and YPSZ-suspension plasma spraying (SPS)). Finally, turbine blades with such a new system were successfully manufactured and will be tested in engine conditions.