Influences of Superalloy Composition and Pt Content on the Oxidation Behavior of Gamma-Gamma Prime NiPtAl Bond Coatings.

The effects of superalloy composition and Pt content on the high-temperature oxidation behavior of γ-γ' NiPtAl diffusion coatings were investigated over the temperature range of 1050-1150 °C. Simple NiPtAl diffusion coatings with 7 or 12 µm electroplated Pt thickness were evaluated in 1-h cycles in dry O for up to 2500 cycles on four superalloys: directionally solidified (DS) alloy 142, 1st generation single-crystal (SX) alloy 1483, and 2nd generation SX alloys X4 and N5. Coatings on high-Hf alloy 142 experienced severe internal oxidation of Hf at all temperatures. Coatings on ~5 at. % Ti alloy 1483 were protective at 1050 °C, but exhibited severe scale spallation at 1100 °C, with extensive formation of Ti- and Ni-rich oxides at the gas interface. Coatings with 7-µm Pt on X4 were extremely protective at 1100 °C, but failed rapidly at 1150 °C, which also was associated with the formation of Ti-rich oxides. Increasing the coating Pt content on X4 improved the 1150 °C oxidation behavior. Coatings on Ti-free N5 showed the best performance at 1150 °C, especially with 12-µm Pt. Although γ-γ' coatings can exhibit outstanding cyclic oxidation resistance with minimal Al depletion, they appear to be sensitive to substrate composition, as well as eventual Pt depletion due to interdiffusion. [ABSTRACT FROM AUTHOR]