Enhancing the Corrosion Resistance of FeNiCoCrW0.2Al0.1 High-Entropy Alloy in 3.5 wt% NaCl Solution by Bilayer Passivation

Abstract

The strong corrosion resistance and corrosion behavior of the FeNiCoCrW_0.2Al_0.1 high-entropy alloy in 3.5 wt% NaCl solution was investigated. In order to explain the Cl⁻ induced degradation of different metal oxides on the surface of the passivate film, the energy required for the interaction of the corrosion oxidation products NiO, CoO, Fe₂O₃, and Cr₂O₃ surfaces with Cl⁻ is compared and calculated based on the assumptions of the point defect model and the density functional theory by using the electrochemical impedance spectroscopy and the X-ray photoelectron spectroscopy for the analysis of the mono-double-layer structure and elemental compositions of passivate film in the corrosion process. The combined experimental and simulation results showed that the alloy passivates naturally in air, forming a single passivation layer. The compositional layering of the passivation film in 3.5 wt% NaCl solution occurred with the increase of the contact time with NaCl. A double-layer passivation with a two-layered combinatorial structure was formed due to the imbalanced depletion of Co and Fe during corrosion, and that the dense outer structure of this high-entropy alloy, which was made up of NiO and Cr₂O₃, provided the predominantly high corrosion resistance. This paper provided a new perspective to study the strong corrosion resistance of FeNiCoCr-based high-entropy alloys.