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

Abstract

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 Dy 2 O 3 would react with MoO 3 to form Dy 2 MoO 6 thus suppressed the volatilization of MoO 3 at the early stage of oxidation. However, as the oxidation proceeded, Dy 2 MoO 6 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. • Pt-free/doped (γ’ + β) NiAlDy coatings are prepared on IC21 with high Mo content. • The role of Dy and Pt on suppressing the formation of harmful MoO 3 is focused on. • Dy delays volatilization of MoO 3 by forming Dy 2 MoO 6 which is not completely stable. • Pt inhibits diffusion of Mo by enhancing Al content in Pt-rich layer at interface. • Weak inter-attraction between Pt and Mo contributes to the Mo diffusion inhibition.