Effect of Ni content on the corrosion behavior of Cu–Ni alloys in neutral chloride solutions

The effect of systematic increase of Ni content on the electrochemical behavior of the Cu–Ni alloys in neutral chloride solutions was investigated. The pitting corrosion behavior of Cu–Ni alloys with different Ni contents, namely, 5, 10, 30 and 65 mass% Ni, in a stagnant 0.6 mol dm−3 NaCl solution of pH 7.0 was studied. The effect of chloride ion concentration on the electrochemical behavior of these alloys was also investigated. The results show that the increase in nickel content decreases the corrosion rate of the alloys in the neutral chloride solution. The increase of chloride concentration up to 0.3 mol dm−3 increases the corrosion rate. At higher concentrations ([Cl−] > 0.3 mol dm−3) the corrosion rate decreases due to the hydrolysis of Cu(I) chloride to form the passive Cu(I) oxide film. The breakdown potential depends on the chloride ion concentration and the nickel content of the alloy. For these investigations conventional electrochemical techniques and electrochemical impedance spectroscopy (EIS) were used. The impedance measurements have shown that the increase of the Ni content and the immersion time of the alloys in the chloride solution increase the corrosion resistance of the alloys. The experimental impedance data were fitted to theoretical values according to a proposed equivalent circuit model.