Corrosion of nanocrystalline and coarse-grained nickel-iron (Ni-Fe) alloys in neutral and alkaline sulfate environments

•Similar overall polarization behaviour for conventional poly- and electrodeposited nanocrystalline Ni-Fe alloys.•Differences in anodic polarization behaviour in neutral environment attributed to sulfur impurities more so than grain size.•Negligible difference in corrosion behaviour in alkaline environment irrespective of grain size and composition. Potentiodynamic polarization behaviour of electrodeposited nanocrystalline and conventional polycrystalline Ni-Fe alloys of similar compositions was investigated in neutral (pH 7) and alkaline (pH 10) 0.5 M Na2SO4 environments. In neutral solution, elevated current densities and delayed passivation were observed for all nanocrystalline materials, independent of composition. This behaviour was attributed to sulfur, present in the nanocrystalline materials as an impurity, more so than an effect of grain refinement. In alkaline solution, the effect of sulfur was exceeded by oxide film formation, and no significant difference in corrosion behaviour was observed as a function of grain size i.e. intercrystalline volume fraction.