Comparison of electrodeposition aspects and characteristics of Ni-W and Co-W alloy nanocrystalline coatings

Ni-W and Co-W alloy nanocrystalline coatings were electrodeposited on copper substrate at different current densities. Electrochemical impedance spectroscopy results showed that the co deposition mechanism of tungsten in Ni-W deposition is the reduction of tungsten oxide which changed to the reduction of tungsten-containing ion complexes at higher current densities. In Co-W electrodeposition, the tungsten co deposition takes place via reduction of tungsten oxide, although, the role of tungsten-containing complexes at higher current densities cannot be ruled out. The surface morphology of Ni-W coatings was crack-free and was strongly dependent on deposition current density. In addition, higher grain size and lower tungsten content were obtained by increasing the current density. In Co-W coatings, no obvious variation in surface morphology was observed except for the fine cracks appeared at higher current densities. In this system the grain size remained almost constant with increasing current density. The microhardness values of Ni-W and Co-W coatings decreased due to the increase in the grain size and/or decrease in tungsten content.