Electrodeposition and characterization of Ni-Cu alloys

Nickel-copper alloys are electrodeposited with approximately the same metal content in the film. Alkaline electrolytes are used in molar ratio of Cu+ 2/Ni+ 2 as 1:2, 1:4, 1:6 and 1:8, respectively. The composition and structure of the obtained coatings are examined by X-ray fluorescence, energy dispersion X-ray (EDX) and X-ray diffraction (XRD). Different contents of nickel, depending on the current density, concentration of nickel ions in the electrolyte and natural convection (providing difference up to 10 wt.% nickel along the coating surface) are detected. The composition of Ni-Cu alloy deposits is calculated by Vegard's law from XRD data lattice constants, which shows a good correlation with those obtained from the EDX analysis. The morphology of deposited layers is investigated by scanning electron microscopy (SEM). The increase of the nickel ion concentration in the electrolyte leads to a smooth surface at low current density. The roughness increases with the rising of the current density resulting in a typical dendritic growth at a low concentration of the nickel ions. The dendritic morphology is changed in a cauliflower-like structure with the augmentation of the nickel ion concentration at a higher current density. The results also show that the copper deposits mainly on the convexity, while the nickel is distributed in the concavity.