Microstructure and properties of sol-enhanced Ni-Co-TiO2 nano-composite coatings on mild steel

Ni-Co-TiO2 nano-composite coatings were electroplated on mild steel by adding transparent TiO2 sol (0-50 mL/L) into the Ni-Co plating solution. The microstructure, mechanical property and corrosion resistance of the composite coatings were systematically investigated. It was found that after adding an optimum sol concentration into the plating bath, a good dispersion of TiO2 nanoparticles can be achieved in the Ni-Co coating matrix, resulting in a significant improvement in coating mechanical properties. Ni-Co-12.5 mL/L TiO2 coating possessed the best microhardness, wear resistance and corrosion resistance. However, adding excessive quantities of sol (more than 12.5 mL/L) into the electrolyte caused nanoparticle agglomeration and created a porous structure, deteriorating the properties of coatings.