The Continuous Plating of Ni-Cr Composite Coatings and TiO₂ Nano-Modify

Abstract

Ni-Cr films were electrodeposited from a nickel sulfate, chromium chloride and chromium sulfate bath. To avoid the poor adhesion and bad surface morphology of the secondary-co-deposition of Ni-Cr alloy films, H 2 O and DMF (volume ratio as 1:1) is used as solvent. Along with the alloy films growing thick, their surface apertures become larger correspondingly, which causes the hardness and corrosion resistance of the films becoming poor. For comparison, nanocrystalline Ni-Cr films with TiO 2 nanoparticles were obtained on the same condition. TiO 2 nanoparticles have an average size of 40 nm. The corrosion resistance of the Ni-Cr composite coatings were comparatively evaluated by salt spray test. It is found that the incorporation of TiO 2 particles enhances the microhardness and corrosion resistance of the coatings. The reason is that the nano-TiO 2 particles in the deposit effectively reduce the size of Ni and Cr crystals through grain refinement-strengthening and dispersion-strengthening effect. The observation results of scanning electron microscopy (SEM) indicated that the Ni-Cr films without dispersions of TiO 2 nanoparticles exhibited numerous large and deep crackles, however, the crackles of nano-TiO 2 Ni-Cr film distinctly became less.