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

Abstract 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.The project is funded by NPRP Grant # NPRP-4-662-2-249 from the Qatar National Research Fund (a member of Qatar Foundation). It is also supported by a New Zealand Marsden Grant, China Postdoctoral Science Foundation project ( 2013M531849 ) and Auckland UniServices project. The authors would like to thank the technical stuff in the Department of Chemical and Materials Engineering and the Research Centre of Surface and Materials Science for various assistances. We also want to express our gratitude to Mr Glen Slater, Chris Goode and technical stuff in Rigg Electroplating Ltd.Scopu