Abstract
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Nickel- aluminium bronze (NAB) is one of the well-known copper-based alloys; it is a well-recognized material in the marine environment thanks to its good corrosion and wear resistance along with its high strength. In this paper, the effect of film-forming potential on the electrochemical behavior of NAB alloy in 0.1 M Na2SO4 solution was evaluated. The study of the stability of passive films formed on NAB alloy was investigated using potentiodynamic and potentiostatic polarizations, Mott–Schottky (MS) and electrochemical impedance spectroscopy (EIS) analysis. The compositions of the passive films were determined by scanning electron microscope (SEM), UV–vis–NIR spectroscopy, and X-ray diffraction (XRD). All electrochemical tests revealed that the anodic potentials had a strong influence on passive films formed on NAB alloy. At intermediate frequencies above 450 mVSCE, the corrosion process is controlled by the adsorption/desorption process along with charge transfer and diffusion processes. Mott–Schottky analysis indicated that the donor density is in the range of 1021 cm−3 and increased with an increase in the film-forming potential. Moreover, the SEM analysis showed that the NAB alloy suffered a severe corrosion attack of the copper-rich α phase leading to the retention of the κ phases of the as-cast NAB in the passive films. The passive films were grown on the NAB alloy and displayed n-type semi-conductor behavior, which is entirely predictable from the main Cu and Al oxide in the film.