A platinum-enriched γ + γ′ two-phase bond coat on Ni-based superalloys

A Pt-enriched γ + γ′ two-phase coating was applied to directionally-solidified Ni-based superalloy René 142 substrates with three different Hf levels (0.02, 0.76, and 1.37 wt.%). The coating was prepared by electroplating a thin layer of Pt on the superalloy followed by a diffusion treatment. The as-deposited coating exhibited a γ + γ′ two-phase microstructure with a major composition of Ni–16Al–18Pt–7Cr–9Co (in at.%) along with some incorporation of refractory elements from the substrates. Cyclic oxidation testing at 1100 °C in air indicated improved oxidation resistance of the René 142 alloys with the Pt-enriched γ + γ′ coatings. In addition, the oxidation resistance of both uncoated and coated alloys was proportional to the Hf content in the substrate. Compared with the single-phase β-(Ni,Pt)Al coating, slightly higher mass gains and localized spallation were observed on the γ + γ′ two-phase coating, which might be due to the segregation of refractory elements and high sulfur levels in these superalloy substrates.