Effect of Sc/Y Co-Doping on Initial Alumina Growth of Electron Beam Physical Vapor Deposited FeCoNiCrAl High-Entropy Coating

FeCoNiCrAl and FeCoNiCrAlScY high-entropy coatings were fabricated via electron beam physical vapor deposition. The microstructure and short-term isothermal oxidation behavior of the coatings were compared. Sc and Y inhibited coating element diffusion to the superalloy substrate and formed co-precipitated phases during coating manufacturing. The Sc/Y co-doped coating exhibited accelerated phase transformation from θ- to α-Al2O3 as compared to the undoped one. The effect mechanism associated with the nucleation of α-Al2O3 was discussed. The preferential formation of Sc/Y-rich oxides promoted the nucleation of α-Al2O3 beneath them, and the θ-α phase evolution process was directly skipped, which suppressed the rapid growth of θ-Al2O3 and the initial formation of cracks in the alumina film and provided the FeCoNiCrAl high-entropy coating with an improved oxidation property in the early oxidation stage.