Properties of Ni/Nano-TiO Composite Coatings Prepared by Direct and Pulse Current Electroplating.

Pure nickel and nickel matrix composite coatings containing nano-TiO particles were produced under both direct and pulse current conditions from an additive-free nickel Watts' type bath. The surface morphology, crystal size, crystallographic orientation, and microhardness of nickel matrix and the amount of embedded nano-TiO particles in the composite coatings were investigated. The corrosion performance of the coatings was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods. The TiO particles embedded in the nickel matrix exerted strong influence on the texture of the growing nickel layer, changing its texture under both direct and pulse current conditions. The textural perfection of the deposits revealed that the presence of TiO particles led to the deteriorating of [100] preferred orientation. Under direct current conditions, the composite coating exhibited clearly [211] fiber orientation, while pulse current working exhibited a mixed crystal orientation through [100] and [211] axes. It is concluded that in the presence of TiO nanoparticles, the adsorption-desorption phenomena occurring on the metal surface are altered. The experimental results show that composite electrodeposits prepared under pulse plating conditions exhibited higher incorporation percentages than those obtained under direct plating conditions, at particularly 10 Hz and low duty cycles. The results revealed that pulse-plated Ni/TiO nanocomposite coating provided excellent anti-corrosion performance and presented higher microhardness. [ABSTRACT FROM AUTHOR]