Interdiffusion between metallic coatings and single crystal superalloys and the strategies to constrain the interdiffusion

The continuing request to improve power-out efficiency and reduce emission of greenhouse gases gives rise to an increasingly higher inlet temperature for advanced gas turbine engines. Bearing such crucial temperatures and suffering from aggressive invasions by oxidation and/or hot corrosion, the key hot-section components of turbines and vanes necessarily utilize single crystal (SX) superalloys with protection of high-temperature metallic coatings. Due to the conspicuous chemical difference, the elemental interdiffusion between coating and substrate has inevitably caused precipitation of needle-like topologically-close-packed (TCP) phases in SX, destroying coherent structure of γ/γ′, and deteriorating mechanical properties (rupture and fatigue lives). This chapter reviews the interdiffusion between protective coating and SX, and more importantly, proposes pathways to constrain this troublesome interdiffusion.