Zn-Ni/nano-TiO2 composite electrodeposits: surface modifications and protective properties

Zn-Ni composite coatings were obtained by electrochemical co-deposition of TiO2 nano-particles (mean diameter 21 nm). Zn-Ni alloy coating was also produced under the same experimental conditions for comparison. The surface morphology, crystallographic structure, and the grain size of the deposits were investigated, along with the percentage of the embedded nano-particles in Zn-Ni matrix, as a function of concentration of TiO2 nano-particles in the bath. As the titania incorporation percentage is increased, a grain refinement in the nanometer region was revealed followed enhanced microhardness values and an improvement of the content of the nickel in the alloy. Annealing of all coatings at 200 A degrees C revealed the crystallization of the matrix accompanied by a decrease of microhardness followed by stability for 24 h. The corrosion behavior of Zn-Ni/nano-TiO2 composite coatings with various amount of particle content was mainly studied by electrochemical impedance spectroscopy in 3 % NaCl. It was seen that Zn-Ni/nano-TiO2 composite coatings exhibited higher corrosion resistances comparing to Zn-Ni alloy coating and corrosion protection improved with increasing nano-TiO2 in coatings.