Oxidation Behavior of Cast Ni3Al Alloys and Microcrystalline Ni3Al+5% Cr Coatings with and without Y Doping

Ni3Al+5% Cr and Ni3Al+5% Cr+∼0.3% Y (wt.%) microcrystalline coatings were produced using a close-field, unbalanced magnetron-sputter deposition (CFUMSD) technique. Isothermal and cyclic-oxidation tests were carried out to assess the oxidation resistance of the coatings. The results showed that Al2O3 formed on the coatings as the main oxidation products, with the formation of θ- and α-Al2O3 scales at 900 and 1200°C, respectively. The spallation resistance of the Al2O3 scales formed on the coatings was superior to the oxide scales formed on cast Ni3Al. After oxidation, interfacial voids were observed on the oxide–metal interface of the cast alloy while no voids were found on the coating surfaces. On the basis of the enhancement of Al diffusion, because of the high density of grain boundaries in the coatings, oxidation mechanisms were proposed.