Electrodeposited Ni-Cu Coatings with Hierarchical Surface Morphology

Abstract

In recent years, Ni-Cu alloy coatings obtained by electrolytic deposition have received increasing interest, because of their good anti-corrosive, mechanical, magnetic, electrical, and decorative properties. Further applications of these coatings for electrode materials and catalysts may be possible by developing hierarchical surface morphology, and thus a combination of high surface roughness, high microhardness, and good corrosion resistance. In the present work, four types of Ni-Cu alloy coatings were deposited in a single-step process from electrolytic baths with Cu2+:Ni2+ concentrations equal to 1:30, 1:20, 1:15, and 1:10 using deposition current densities of 2 A/dm2 and 4 A/dm2. The surface morphology of the coatings was characterized using a scanning electron microscope and an optical profilometer. The coatings exhibited a nodular morphology, which with the change of the Cu2+:Ni2 ratio and the current parameters changed from smooth and compact to rougher with regularly spaced nodular microprotrusions. Thus, a hierarchical surface morphology was obtained. Transmission electron microscopy investigations revealed that the fine-grained microstructure of the coatings consisted of the γ solid solution, as well as the metastable intermetallic L10 NiCu phase. The differences in the Cu concentration at the cross-sections demonstrated by quantitative microanalysis of the chemical composition indicated a dendritic growth of the coatings and a preferential reduction of copper ions over nickel ions. The coatings were also characterized by a microhardness greater than 3.71 GPa and good electrochemical corrosion resistance in chloride media. Coatings with hierarchical morphology and high surface roughness showed a higher corrosion current. The study provides a new method for electrodeposition hierarchical Ni-Cu coatings under specific chemical compositions of the electrolytic bath and current conditions, characterized by a combination of promising properties for electrode and catalytic applications.Graphical