Structure and corrosion property of pulse electrodeposited nanocrystalline nickel-tungsten-copper alloy coating

Nanocrystalline Ni-W-Cu alloy coatings, synthesized by pulse electrodeposition technique from aqueous sulphate-citrate solution, have been investigated to study the evolved phases, crystallite size, micro-strain, and morphology. The effect of alloying with Cu and its concentration on the corrosion behavior of the Ni-W-Cu coatings in sodium chloride medium was examined through potentiodynamic polarization technique and electrochemical impedance spectroscopy. The increase in the Cu content of the electrodeposited coating improves the crystallinity, leads to grain coarsening, and reduces micro-strain of the Ni-W-Cu alloy coatings. The corrosion resistance is observed to improve because of the formation of Cu2O-rich barrier film on the Ni-W-Cu alloy surface, which was confirmed through X-ray photoelectron spectroscopy. The addition of Cu is considered as responsible for strengthening the passivation phenomenon and enhancing the oxidation resistance of the Ni-W phase in the coating.