Sol-enhanced electroplating of nanostructured Ni-TiO₂ composite coatings - The effects of sol concentration on the mechanical and corrosion properties

Novel sol-enhanced Ni-TiO₂ nano-composite coatings were electroplated by adding a transparent TiO₂ sol into the traditional electroplating Ni solution. It was found that the structure, mechanical properties and corrosion resistance of the nano-composite coatings were largely determined by the sol concentration. The higher sol concentration in the plating electrolyte led to a higher content of TiO₂ nano-particles in the coating matrix. The coating prepared at the sol concentration of 12.5 mL/L had the best microhardness, wear resistance and corrosion resistance. Adding excessive sol to the electrolyte changed the surface microstructure, caused cracking on the coating surface and deteriorated the properties. It was demonstrated that the corrosion resistance of the composite coatings is determined by two factors: surface microstructure and incorporation of TiO ₂ nano-particles.