Development of Nanostructure Multilayer Co-Ni Alloy Coatings for Enhanced Corrosion Protection

Nanostructure multilayer alloy coatings (NMAC) of Co-Ni were developed on copper in layered manner using different current pulses. NMAC of Co-Ni was deposited galvaostatically from acid sulphate bath under different combination of cyclic cathode current densities (CCCD’s) and number of layers. Corrosion behaviors of coatings were evaluated in 1 M hydrochloric acid, as representative corrosion medium. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) study revealed that NMAC (Co-Ni) 2.0/4.0/6.0/60/three exhibits~160 times better corrosion resistance than monolayer coating, deposited from same bath for same time. Better corrosion protection was attributed to the increased effect of interface, arising from the exceptional thinness of the layers. As composition of alloys in successive layers were varied, consequent to the deposition current density (c.d.), the change in phase structure of the deposits were observed, confirmed by X-ray diffraction (XRD) study. Layer formation and surface after corrosion tests were examined by scanning electron microscopy (SEM) and optical profilometer, and reasons responsible for better protection were analyzed.