Abstract
Under alkaline conditions, copper-nickel alloys are covered by passive oxide films containing Cu and Ni oxides. In chloride ion containing environments, they are therefore susceptible to localized corrosion. In this paper, the susceptibility of selected Cu-Ni alloys (UNS C70600, UNS C71500 and UNS N04400) to localized corrosion was investigated by measuring the crevice stabilization and repassivation potentials (Ecrev and Ercrev, respectively) in alkaline sodium chloride solutions. Correlations between environmental variables, such as chloride ion concentration, pH and temperature and Ecrev, as well as Ercrev were established. It was found that: (i) Ecrev and Ercrev decrease with increasing chloride ion concentration; (ii) there is a linear relationship between Ecrev and Ercrev and the logarithm of chloride ion concentration; (iii) Ercrev does not depend on the solution pH; (iv) there is a complex relationship between Ecrev and Ercrev and the alloy composition as well as the temperature. The electrochemical properties of the selected alloys were also investigated in synthetic seawater with and without the presence of free chlorine. It was found that the pitting and repassivation potentials in synthetic seawater are strongly dependent on the alloy composition. The presence of free chlorine did not significantly affect the cathodic reaction kinetics. It, however, increased the corrosion potential and changed the corrosion morphology.
