Study of oxidation mechanisms of Ni-Al alloys with different phase structures at 1200 °C

Abstract

In this study, Ni-Al alloys with different phase structures were prepared by varying Al content using vacuum arc melting technique, and suitable doping of reactive elements (Hf, Y) was carried out to improve the oxidation resistance at 1200 °C. It was found that the isothermal oxidation performance of β-NiAlHf alloy was much better than that of γ'-NiAlY alloy. The growth mechanism of TGO on Ni-Al alloys with different phase structures is significantly different. On the surface of β-phase alloys, TGO was transformed from unstable θ-Al2O3 to stable α-Al2O3 at the early stage and maintained for long-term. By contrast, on the surface of γ' phase alloys, NiO and NiAl2O4 were firstly generated, then Al2O3 was generated at the bottom layer accompanied by the disappearance of NiO, and finally the constitute of the TGO was consisted of NiAl2O4 and Al2O3. The growth mechanism of the TGO and the regulatory role of reactive elements are discussed for alloys with different phase structures.