Electrodeposition of nanocrystalline nickel–cobalt binary alloy coatings: a review

The history of Ni–Co alloy deposits is summarised and recent developments are highlighted. Electrodeposition of nanocrystalline Ni–Co binary alloys and, briefly, Co–Ni–P ternary coatings is considered, including chemical composition, phase composition and crystalline nature. Nanostructure, morphology, physical and mechanical properties (including corrosion resistance) vs bath type and composition (including pH and electrolyte additives) and plating conditions, including current density, temperature and agitation are summarised. Applications range from wear and corrosion resistant coatings, particularly as a hard chromium replacement to speciality hydrogen evolution electrodes in water electrolysis. Following this extensive review, future research needs are briefly listed.