Microstructure, nanoindentation, and electrochemical properties of the nanocrystalline nickel film electrodeposited from choline chloride–ethylene glycol

A fully dense nanocrystalline (nc) Ni film on the brass substrate was fabricated by a simple electrodeposition from a choline chloride-based ionic liquid (choline chloride–ethylene glycol) at working voltage (between the two electrodes) of 1.0 V and room temperature. It is found that the nc Ni with an average grain size of about 6 nm has a face-centered cubic crystal structure. At the film/substrate interface, the epitaxial growth of some nc Ni grains on brass grains can be evidenced by the high resolution transmission electron microscope. The 6 nm grain sized Ni exhibits a high strain rate sensitivity (m = 0.051) and enhanced hardness values in the range of 7.6–9.7 GPa. The deformation mechanism of the nc Ni under indentation is also discussed with the theoretical model fitting. The potentiodynamic polarization curve shows that the nc Ni film exhibits a much negative corrosion potential, which provides a sacrificial anode protection for the brass substrate.

Research highlights
► Electrodeposition of 6 nm grain sized Ni film from a non-aqueous electrolyte.
► Epitaxial growth of Ni nanocrystallites on the brass substrate.
► Nanocrystalline Ni with high hardness (7.6–9.7 GPa) and obvious passivation.
► No elongated grains on cross-section of electrodeposited nanocrystalline Ni film.