Oxidation behavior of cast Ni3Al alloys and microcrystalline Ni3Al+5% Cr coatings with and without Y doping

Ni3Al + 5% Cr and Ni3Al + 5% CI + similar to0.3% Y (wt.%) microcrystalline coatings were produced using a close-field, unbalanced magnetron-sputter de position (CFUMSD) technique, Isothermal and cyclic-oxidation tests were car ried out to assess the oxidation resistance of the coatings. The results sh owed that Al2O3 formed on the coatings as the main oxidation products, with the formation of theta- and alpha -Al2O3 scales at 900 and 1200 degreesC, respectively. The spallation resistance of the Al2O3 scales formed on the c oatings was superior to the oxide scales formed on cast Ni3Al. After oxidat ion, interfacial voids were observed on the oxide-metal interface of the ca st 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 boun daries in the coatings, oxidation mechanisms were proposed.