High-temperature performance of (Ni,Pt)Al coatings on second-generation Ni-base single-crystal superalloy at 1100 °C: Effect of excess S impurities

Acidic and basic single-phase beta-(Ni,Pt)Al coatings were prepared by Pt electroplating (employing acidic and alkaline Pt-plating baths, respectively) and gaseous phase aluminizing. In both isothermal and cyclic oxidation tests at 1100 degrees C, the acidic (Ni,Pt)Al coating showed inferior oxidation resistance compared to the basic coating. The poorer oxidation performance and higher scale spallation tendency of the acidic (Ni,Pt)Al coating was attributed to the presence of excess S, which deteriorated oxide scale adherence by promoting the formation of pores and cracks under Al2O3 scale. The void formation mechanism and detrimental role of excess S in state-of-the-art Pt-modified aluminide coatings are discussed.