Corrosion protection of XC70 mild steel by a Ni-Co/TiO₂ composite coating in an acidic chloride environment.

In this study, the corrosion behavior of XC70 steel in a 0.5 M HCl acidic medium was investigated using Ni-Co-TiO₂ composite coatings prepared by electrodeposition. The corrosion resistance of bare steel, Ni-Co alloy coating and Ni-Co-TiO2 nanocomposite coatings deposited with various TiO2 concentrations in the bath, was investigated using weight loss measurements and electrochemical techniques. Surface characterization, adhesion tests, and microhardness measurements were also performed. Gravimetric and electrochemical results revealed a significant improvement in corrosion resistance with increasing TiO₂ content up to an optimal concentration of 0.64%. At this concentration, the corrosion current density decreased from 376 µA·cm⁻2 for the Ni-Co alloy to 67 µA·cm⁻2 for the Ni-Co-TiO₂ coating. electrochemical impedance spectroscopy results confirmed this improvement through an increase in charge transfer resistance and a decrease in the constant phase element. Overall, the Ni-Co-TiO₂ (0.64%) nanocomposite exhibited the best corrosion protection, attributed to the uniform incorporation of TiO₂ nanoparticles, leading to coating densification and reduced electrolyte penetration.