Effects of Cr and Mo in substrate on the oxidation behavior of (Ni,Pt)Al coatings at 1200 °C

The (Ni,Pt)Al coatings were applied to four Ni-based superalloys with varying concentrations of Cr and Mo. These coating specimens were subjected to cyclic oxidation at 1200 °C. The coatings on the low-Mo content superalloys exhibited superior oxidation resistance compared to those on the high-Mo content superalloys. The coating on the high-Mo, high-Cr content superalloy showed less alumina scale spallation compared to that on the high-Mo, low-Cr content superalloy. The interaction between molybdenum and O²⁻ in the alumina scales inhibits the formation of columnar alumina grains, leading to higher oxidation rates in coatings applied to high-Mo content superalloys compared to those applied to low-Mo content superalloys. Mo in the substrate accelerates Al depletion in the coating and the formation of volatile oxides, which promote the failure of the alumina scale. And the interaction between Cr and Mo partially mitigates these negative effects.