Electrodeposition of Hydrophobic Ni-Co-TiO2 nanocomposite coatings on XC70 mild steels for improving corrosion resistance
Résumé
The electrodeposition of Ni-Co-TiO2 composite coatings on XC70 mild steel was investigated using the chronoamperometry method. This technique allowed the co-electrodeposition of titanium dioxide (TiO2) nanoparticles with the Ni-Co alloy, from stirred solutions containing very low TiO2 concentrations. To determine the range of deposition potential, linear sweep voltammetry and chronopotentiometry experiments were carried out. The effect of TiO2 nanoparticles on the surface properties was evaluated from the point of view of their morphology, composition, structure, wettability, and corrosion resistance. The deposited coatings were analyzed using Focused Ion Beam (FIB) coupled with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscope (AFM), contact angle measurements, and microhardness tests. The corrosion behavior of the pure Ni-Co alloy and Ni-Co-TiO2 nanocomposites was assessed by weight loss method, potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The corrosion performance of the composite coatings improved with increasing TiO₂ concentration, reaching a maximum at 0.64%. Ni-Co-TiO2 coatings exhibited more positive Ecorr values and lower icorr than the pure Ni-Co alloy. The addition of 0.64% TiO₂ increased the microhardness of the pure Ni-Co deposit by 170 HV0.05 and raised the surface roughness from 170 nm to 428 nm. Furthermore, the contact angle increased from 80° to 125°, corresponding to a more hydrophobic surface and hence a better durability in corrosive environments.