The interaction between Dy, Pt and Mo during the short-time oxidation of (γ’ + β) two-phase Ni[sbnd]Al coating on single crystal superalloy with high Mo content

Mo, as a typical refractory element in Ni-base superalloys, will diffuse outward to the protective coating on the alloy surface during high-temperature oxidation, which will do harm to mechanical properties of the alloy and oxidation resistance of the coating. In this paper, (γ’ + β) two-phase Ni-34Al-0.3Dy coatings with or without Pt were prepared on a single crystal superalloy with high Mo content by electron beam physical vapor deposition (EB-PVD) and Pt electroplating. The short-term oxidation behavior of the coatings was investigated at 1100 °C aiming to explore the role of Dy and Pt on the harmful effect of Mo diffusion and its oxides. The results show that for Pt-free coating, Mo had already diffused to the coating surface after only 1 h. The pre-existing Dy₂O₃ would react with MoO₃ to form Dy₂MoO₆ thus suppressed the volatilization of MoO₃ at the early stage of oxidation. However, as the oxidation proceeded, Dy₂MoO₆ would decompose due to its poor thermal stability. While for Pt-doped coating, no Mo-rich oxides were detected throughout the entire oxidation process due to the suppression of outward Mo diffusion by the Pt layer at coating/substrate interface. The possible mechanisms were discussed in detail.