Effect of cobalt content on electrodeposition and properties of Co–Ni alloy thin films

Co–Ni thin films alloys were deposited on ruthenium substrates by the electrochemical method from chloride bath at pH 3.8. The effect of cobalt content on the composition, morphology, electrochemical and microstructural properties of the electrodeposited thin films was investigated. Effectively, the conditions of electrodeposition of Ni–Co deposits were determined using the cyclic voltammetry at three ions concentration ratios Co/Ni (5:1, 1:1 and 1:5). Combined results from the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) study, show an excellent corrosion resistance for the deposits obtained when the cobalt concentration is low. The morphology of the electrodeposited Co–Ni alloys thin films is intimately associated with the Co content in the bath. Atomic force microscopy (AFM) observations of the deposits show a granular structure of the electrodeposited thin films and when the amount of Co was decreased in the solution bath; a strong decrease in the grain size was observed. X-ray diffraction measurements (XRD) indicate a small crystallite size with the presence of a mixture of hexagonal close-packed (hcp) and face-centered cubic (fcc) Co–Ni structures. The phase structure gradually changed from fcc to hcp with the increase of cobalt content.