Pulse electrodeposition of Ni/nano-TiO2 composites: effect of pulse frequency on deposits properties

Pure and composite nickel deposits containing nano-TiO2 particles (d (m) = 21 nm) were produced under direct-DC and pulse current-PC conditions. The influence of pulse frequency on the codeposition of TiO2 particles, preferred orientation of Ni crystallites and grain size, as well as microhardness of the composites, was investigated systematically. Composites prepared in PC regime displayed higher incorporation percentage than those obtained under DC conditions, and the highest incorporation rates were achieved at pulse frequencies nu > 100 Hz. The application of pulse frequency accompanied by the embedding of TiO2 nanoparticles in the nickel matrix resulted in a strong influence upon the crystalline orientation, the grain size and the corresponding microhardness. All composites exhibited higher microhardness values compared to the pure deposits, independent of the applied current conditions. Overall, when ascribing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms but also preferred crystalline orientation should be taken into consideration.