Study on the Effect of Alloying Element Cr on the Corrosion Behavior of Co-Fe-Ni-Mo-W High-Entropy Alloys in Seawater Environments

In marine environments, critical components are susceptible to corrosion failure due to the influence of chloride ions. High-entropy alloys have garnered widespread attention owing to their superior comprehensive properties. This study investigates the corrosion behavior of Co-Fe-Ni-Mo-W high-entropy alloys in seawater and explores the role of chromium (Cr) in modulating their corrosion resistance. Electrochemical methods were employed to compare the corrosion resistance of CoFeNiMo0.1W0.2 and CoFeNiMo0.1W0.2Cr0.7 high-entropy alloys in seawater, while modern physical characterization techniques—including XRD, SEM, and XPS—were utilized to elucidate the underlying corrosion resistance mechanisms. The results demonstrate that during prolonged immersion in seawater, the surface of the Cr-free CoFeNiMo0.1W0.2 alloy fails to develop a stable protective layer, leading to severe surface corrosion, with corrosion products including crystalline Ni(OH)2 among others. In contrast, the Cr-containing CoFeNiMo0.1W0.2Cr0.7 alloy exhibits excellent self-passivation characteristics in seawater: its open-circuit potential remains within a relatively positive range throughout a 49 d immersion period, its charge transfer resistance increases by nearly two orders of magnitude compared to the Cr-free counterpart, and no significant pitting pits or corrosion product accumulation are observed on its surface. The corrosion resistance mechanism can be attributed to the introduction of Cr, which promotes the formation of a dense passive film enriched with Cr2O3 on the alloy surface. This passive film possesses superior physical barrier and charge-shielding properties, thereby significantly inhibiting the adsorption and penetration of aggressive Cl− ions, and thus effectively protecting the substrate.