Oxidation behavior of sputtered Ni-3Cr-20Al nanocrystalline coating

The oxidation behavior of cast Ni-3Cr-20Al (at%) alloy and its sputtered nanocrystalline coating were investigated at 1000°C in air. Owing to the formation of the transient γ-Al2O3, θ-Al2O3 in the initial oxidation period, the mass gains were very rapid. With the transformation of the transition Al2O3 to stable α-Al2O3, the oxidation kinetics became nearly flat. α-Al2O3 and NiAl2O4 were both formed on the sputtered Ni-3Cr-20Al coating after 200-h oxidation. The formation of NiAl2O4 was probably related to the formation of Ni3Al during the oxidation process. The formation mechanism of NiAl2O4 is discussed.