| Copper-nickel alloys have been used in many applications in marine environments, because of excellent corrosion and biofouling resistance. In this study, the effect of alloying elements (including iron, aluminum, chromium, cobalt, titanium, molybdenum, indium, and vanadium) on the corrosion behaviour of 90 w% copper-10 w% nickel alloys in sea water are investigated. Experiments were performed at 298 K on a commercial copper-nickel alloy C70600 to serve as a reference point for the synthetic alloys. New copper-nickel alloys were prepared in an induction furnace, in an argon/7% vol. hydrogen atmosphere in cylindrical boron nitride crucibles. They were then homogenized at 950°C for 10 hours in the same protective atmosphere. The electrochemical behaviour was investigated by linear sweep voltammetry (LSV), cyclic polarization (CP), cyclic voltammetry (CV), Tafel extrapolation (TE) and electrochemical impedance spectroscopy (EIS). The corrosion product that formed on the surface was characterized using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA), and wavelength dispersive spectroscopy (WDS).;The electrochemical behaviour of commercial alloy C70600 depends on the amount of sulphate in the solution. Increasing the amount of sulphate to more than 400 ppm in the electrolyte limits the ability of the passive film to protect the alloy. The behaviour of the commercial alloy in sea water was similar to that in a 2260 ppm sulphate artificial saline solution but was not exactly the same. The passive film formed on the surface was uniform in thickness and consisted of more than one layer. The passive film consisted mainly of chlorides in solutions with no sulphate. The presence of sulphate in the corrosive solutions produces a passive layer containing mainly chlorides with some sulphides (FeS, NiS, and CuS).;The electrochemical behaviour of the synthetic Cu-Ni-Fe alloys depends on maintaining iron in a single phase in the solid solution (the maximum amount of iron can be used was 1.5 w%). Quenching improves the electrochemical behaviour of synthetic Cu-Ni-Fe alloys containing relatively high iron content. The outer layer of the passive film is porous in the absence of iron, but when iron is added, the pores disappear and cracks appear. When no sulphate is present in the solution, the passive film formed on synthetic Cu-Ni-Fe alloys consists entirely of chlorides, and Fe2O3. In the presence of sulphate FeS and NiS where detected in the corrosion film.;Cu-Ni-2.0 w% Co is the most protective alloy in both the 2260 ppm sulphate artificial saline solution and N.S. sea water, and it can replace the Cu-Ni-2.0 w% Fe [quenched] alloy in marine applications. The Cu-Ni-2 w% Al alloy is recommended to be used only in clean sea water (without sulphate content). It is not recommended to use Cu-Ni-2 w% Mo, Cu-Ni-2 w% In, Cu-Ni-2 w% V, or Cu-Ni-2 w% Ti alloys in all three environments. The behaviour of Cu-Ni-2 w% Cr alloy indicates that this alloy could be used to some extent. Addition of alloying elements to the copper-nickel alloys resulted in the presence of these elements in the passive film as oxides, and sometimes chlorides. |
