Beneficial effects of Co²⁺ on co-electrodeposited Ni-SiC nanocomposite coating

Abstract

Ni-SiC nanocomposites were fabricated by co-electrodeposition of nickel with silicon carbide nanoparticles on the pure nickel substrates from a nickel sulfate bath with and without the addition of Co²⁺. The presence of Co²⁺ in the electrolyte modifies the Ni matrix to Ni-Co solid solution matrix. It helps to refine the grain size of the nanocomposite coating and improves the content of SiC dispersed in the matrix, and consequently results in higher microhardness. The cathodic polarization curves and electrochemical impedance spectroscopy (EIS) at cathodic potential were investigated in the electrolyte with and without Co²⁺. A modified cathodic polarization curve with a positive shift in reduction potential and a smaller capacitive loop of EIS are observed. These are attributed to the strong adsorption of Co²⁺ on the SiC nanoparticles. Consequently, it increases the forces of electrostatic attraction between the SiC nanoparticles and the cathode, which promotes the codeposition of SiC nanoparticles in the matrix.