Tribological and corrosion behavior of electrochemically deposited Co/TiO2 micro/nano-composite coatings

Abstract

Co/TiO 2 micro- and nano-composite coatings having different amounts of reinforcing particles were electrochemically deposited on st37 steel sheets, and their characteristics, tribological properties, and corrosion behavior were compared. With a relatively similar hcp structure, the nano-composite coatings had a nodular morphology which was different than the relatively smooth morphology of pure cobalt and micro-composites. The hardest and the most wear-resistant micro/nano-composites were obtained from baths containing 15 g.L −1 TiO 2 particles. Despite their lower hardness, micro-composites generally had smaller volume losses and higher friction coefficients than the nano-composite films. The volume loss of Co/15 g.L −1 micro-TiO 2 was half of Co/15 g.L −1 nano-TiO 2 . With abrasion and oxidation as the main wear mechanisms, the composite coatings possessed smoother worn surfaces and more stable oxide layers on their wear track. According to the corrosion test results, the co-deposition of micro/nano-particles significantly improved the corrosion resistance of pure cobalt film. However, unlike the wear test results, the nano-composite coating had a better corrosion resistance than the micro-composite film. • Nano-composites have a different morphology than pure cobalt and micro-composites. • The optimum concentration of both TiO 2 micro- and nano-particles is 15 g.L −1 . • Nano-composite coatings are harder, but less wear-resistant than micro-composites. • Nano-sized TiO 2 particles effectively improved corrosion resistance.