Unveiling the short-term oxidation behavior of nickel-base superalloy CMSX-4 in high-temperature air

Abstract

Nickel-based superalloys undergo oxidation in high-temperature corrosive environments, however, the oxidation behavior and mechanisms remain unclear. Combining multi-scale characterization techniques, Molecular Dynamics (MD) and density functional theory (DFT), this study investigated the oxidation behavior of the nickel-based superalloy CMSX-4 during the short-term oxidation in air at 1100 °C, with the aim of revealing the oxidation mechanism. The in-situ weight gain experiment demonstrates that the oxidation of the CMSX-4 alloy perfectly follows parabolic kinetics during the short-term oxidation stage. The sequence of oxidation for alloying elements is revealed to be influenced by diffusion, element concentration, and oxygen partial pressure. Specifically, Ni and Co elements preferentially undergo external oxidation, forming NiO and CoO on the surface of the alloy, while other elements experience internal oxidation. Initially, simple oxides form, and subsequently, some of these oxides react to produce complex spinel phases. Ultimately, a complex four-layer oxide scale develops, comprising an outer NiO and CoO layer, followed by a CoCr₂O₄ and TiTaO₄ layer, then a NiAl₂O₄ layer, and finally an innermost Al₂O₃ layer. The presence of a continuous, thick and dense Al₂O₃ layer ensured excellent oxidation resistance for CMSX-4 superalloys.