Work

Potential-dependent evolution and degradation of the protective oxide film on 70Cu-30Ni alloy in marine environment

Year: 2026

Type: article

Abstract: ABSTRACT This work systematically investigates the effect of applied potentials ranging from −100 to −900 mV vs. SCE on the composition, structure, semiconducting properties, and pitting resistance of pre-formed oxide films on 70Cu-30Ni alloy in marine environment. A multi-technique approach combining electrochemical measurements (polarization, EIS, Mott–Schottky), surface and cross-sectional microscopy (OM, SEM, HRTEM-EDS), and XPS compositional analysis was employed. Results reveal a non-monotonic “increase–decrease–increase” trend in pitting depth with decreasing potential, determined by the continuous evolution of the electrochemical driving force, film property and Cl − interaction under the regulation of applied potential. At weak anodic polarization (−100 mV), the film remains compact and highly protective. As cathodic polarization increases, sequential reduction of oxides/hydroxides of Cu/Ni/Fe occurs, accompanied by rising vacancy density, film porosity and pitting depth. At −500 mV vs. SCE, a transient cathodic protection window is identified, wherein annihilation of cation and oxygen vacancies temporarily reduces defect density, repels Cl⁻ penetration, and partially restores film resistance and layered structure. Below −700 mV, extensive reduction of all protective oxides/hydroxides and vigorous hydrogen evolution reaction (HER) induce catastrophic film disintegration, marked by exponential increases in charge carrier density, porous macro-defects and pitting depth. The findings provide a theoretical basis for optimizing cathodic protection strategies for 70Cu-30Ni alloys in marine environment.

Source: Materials Today Communications