Cyclic oxidation of palladium modified and nonmodified aluminide coatings deposited on nickel base superalloys

Palladium layer (7 μm thick) was deposited on the surface of the Inconel 713 LC, Inconel 625 and CMSX 4 Ni-base superalloys by the electroplating method. Electroplated samples were annealed at 1050 °C for 2 h in the argon atmosphere. The aluminide coatings were deposited by the CVD method. The nonmodified aluminide coating consists of the NiAl phase. Palladium modification let to formation of the (Ni,Pd)Al phase in coatings. The palladium modified as well as nonmodified coatings were oxidized at 1100 °C in the air atmosphere. For both Inconel 713 LC and CMSX 4 superalloys palladium modified coatings show better oxidation resistance than nonmodified ones. Palladium inhibits the outward diffusion of substrate elements (cobalt and chromium) during oxidation of the aluminide coating. Moreover, it stabilizes the β-NiAl phase, keeps the higher content of aluminum in the β-NiAl phase for a long time and thus increases the lifetime of the coated substrate.