Electrochemical passivation and passive-film evolution of laser-cladded AlCrFeNi3 high-entropy alloy in alkaline media

To address the severe challenges posed by extreme high-temperature concentrated alkaline environments in the chlor-alkali industry, an AlCrFeNi 3 high-entropy alloy coating was prepared on a 45 steel substrate by laser cladding. Potentiodynamic polarization, electrochemical impedance spectroscopy, potentiostatic polarization, and Mott–Schottky analyses were conducted in 1 mol/L NaOH solution, and X-ray photoelectron spectroscopy was combined to investigate the electrochemical behavior and passive-film characteristics of the coating, with the aim of exploring its electrochemical passivation behavior and passive-film evolution mechanism in strongly alkaline environments. Meanwhile, immersion tests were performed in 50 wt.% NaOH at 150°C for 7 and 21 days to analyze the long-term corrosion evolution. Electrochemical tests in 1 mol/L NaOH revealed stable passivation of the coating, with the corrosion current density reduced by 80.5% to 6.16×10 −7 A·cm −2 relative to the substrate. During long-term immersion, the coating gradually transitioned from stable passivation to localized passive-film destabilization. After 21 days of immersion, local regions of the coating showed depletion of the amphoteric element Al, accompanied by Ni depletion and a decrease in the O signal, together with the formation of shallow corrosion pits. However, a large area of the coating remained intact, without extensive uniform corrosion. These results provide an interpretation of the corrosion evolution of the AlCrFeNi₃ coating from the perspective of the interplay between multicomponent surface passivation and localized corrosion.