The influence of electrolyte composition on the properties of Ni-Co alloy coatings reinforced by SiC nano-particles

Ni-Co alloy coatings reinforced by SiC nano-particles (Ni-Co/SiC nanocomposite coatings) were deposited in a modified Watts bath with different electrolyte compositions by sediment codeposition (SCD) technique. Chemical composition, phase structure, surface morphology, microhardness, and corrosion resistance of the coatings were studied. It was observed that the cobalt content in the coatings was increased by increasing the cobalt concentration in the bath. Moreover, particle incorporation was enhanced significantly from 2.0 vol.% to 8.1 vol.% as a function of the cobalt concentration. The studied surface morphologies were changed from pyramidal to spherical by increasing the cobalt content and the amount of SiC nano-particles. X-ray diffraction (XRD) patterns revealed that peak positions of the nanocomposite coatings were not changed appreciably whereas the phase structure, and peak intensities were significantly varied by adding cobalt in the electrolyte. The phase structure of the deposits was changed from fcc to fcc + hcp. The chemical composition of matrix and the amount of the incorporated particles had considerable influences on the microhardness and corrosion properties of the Ni-Co/SiC nanocomposite coatings. Ni-55Co/SiC nanocomposite coatings containing 55 wt.% Co and 8.1 vol.% SiC nano-particles exhibited the highest microhardness and the best corrosion resistance.