Effect of Deposition Current Density on Superhydrophobicity Characteristic and Corrosion Resistance of Nickel Electrodeposited Coating

The purpose of this work is to investigate the effect of deposition current density on superhydrophobicity characteristic and corrosion resistance of nickel electrodeposited coating. Nickel coating with hierarchical structure was fabricated on copper substrate by electrodeposition process at current density of (10 and 20) mA/cm2. The surface morphology of electrodeposited nickel coatings was examined by scanning electron microscope which showed that the coating structure consisted of micro and nano shaped cones and the size of micro cones decreased by increasing the current density. The relative texture of the coatings was also determined by X-ray diffraction pattern. The results showed that the relative texture direction changed from (220) to (311) by increasing the current density from 10 to 20 mA/cm2. The surface topography studies by atomic force microscope showed decrease in surface roughness by increasing the current density. The wet angle measurement results showed that the wettability of nickel coatings varied from super- hydrophilicity to super- hydrophobicity by exposing the coating in air at room temperature. The reason of this behavior is the formation of NiO on the surface of rough nickel film which decreased the surface energy. The corrosion behavior of the coatings was evaluated in 3.5wt% NaCl solution by electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results revealed the positive effect of hydrophobicity on increase in corrosion resistance of coatings and it was shown that the coating formed at 20 mA/cm2 had higher polarization resistance compared to other coating.