Protection of High Temperature Corrosion of Superalloys by the Treatment of Co Cr Al Y Ion Plating

Abstract

U-520 and X-45 coated with CoCrAlY alloy by the ion plating method were investigated on there structure, adhesion and corrosion resistance, etc. The results obtained are summarized as follows: I) The structure of coated layer had no defect. The layer showed excellent adhesion against cyclic thermal shock [1100°C_??_Water (15°C)]. II) Cross sectional element distribution of the coated layers on U-520, X-45 were similar to each other, and Cr concentration was higher in the inner layer than in the outer layer and Al and Co concentrations were higher in the outer layer. This phenomenon seems to be resulted from difference of element's vapor pressure and the oxidation of Al. III) Oxide scale mainly composed of Al₂O₃ was formed on the CoCrAlY coated layer at elevated temperature. Consequently, the layer showed excellent corrosion resistance against V₂O₅-Na₂SO₄, NaCl-Na₂SO₄ synthetic ash corrosion test.