Corrosion in NaCl of Ni-B based coatings produced by electrodeposition method

Keywords: Electrodeposition Coatings, Ni-B Based Coatings, CorrosionIn this study, Ni-B based coatings were produced by electrochemical deposition method. The optimum producing conditions and corrosion behavior in 3.5% NaCl solution for these coatings were investigated.Coating process was carried out within a standard cell with three electrode system using graphite as auxiliary and saturated calomel as reference electrodes onto AISI 1020 steel substrate. Ni-B based coatings were prepared using Watt?s nickel bath modified with the addition of dimethylamine borane. The obtained coatings were analysed by optical microscope, scanning electron microscopy (SEM) and x-ray diffraction (XRD). The microstructural characterization was detailed with energy dispersive spectroscopy (EDS) and elemental maps. The surface morphology of coatings was examined with atomic force microscopy (AFM) and hardness of coatings was measured by using Vickers microhardness tester.Then, the produced coatings under various conditions were corroded in 3.5% NaCl solution prepared with distilled water under ambient atmosphere at room temperature. The corrosion behaviour of coatings was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).After characterization, the presence of Ni and Ni3B phases at coatings was determined. The results showed that the proportion of these phases was affected with applied current, pH of solution and dimethylamine borane content, but coating time has no effect. Coating hardness changed after and before heat treatment of the coatings. The coatings were homogeneous in thickness and their surface roughness was quite low. The corrosion studies showed that corrosion resistance of the coatings was increased with increasing of Ni-phase.