The effect of yttrium addition on oxidation of a sputtered nanocrystalline coating with moderate amount of tantalum in composition

Graphical abstract: - Highlights: • Effect of Y addition on oxidation of nanocrystalline coating is studied. • Y addition delays transformation of q-Al₂O₃ to a-Al₂O₃ during oxidation. • Y addition prevents scale rumpling. • Y segregates at grain boundaries of the nanocrystalline coating. • Y retards the transportation of Ta thus reduces its oxidation. - Abstract: The effect of yttrium addition on isothermal oxidation at 1050 °C of a sputtered nanocrystalline coating with moderate amount of tantalum in composition was investigated. Results indicate that yttrium addition delays transformation of metastable θ-Al₂O₃ to equilibrium α-Al₂O₃ grown on the nanocrystalline coatings. It prevents scale rumpling and promotes the formation of oxide pegs at interface between the oxide scale and the underlying coating. Besides, yttrium prefers to segregate at grain boundaries of the nanocrystalline coating and retards the outward transportation of tantalum from coating to oxide scale, thus reducing the excessive oxidation of tantalum.