Microstructural, surface and electrochemical properties of a novel Ni–B/Ni–W–BN duplex composite coating by co-electrodeposition

Abstract

In this study, a novel Ni–B/Ni–W–BN duplex nanocomposite coating was successfully developed by co-electrodeposition. Their microstructural, surface and electrochemical properties were evaluated and compared to that of monolayer Ni–B, Ni–W, and Ni–W–BN coating by SEM, AFM, EDS, XRD and XPS. The electrochemical behaviors of the coatings were investigated by EIS in 3.5 wt% NaCl aqueous solution. The effects of graphite-like BN nanoparticles on the properties of the duplex coating were discussed. The mechanism of electrochemical co-deposition was proposed. Results show that all the coatings are uniform, compact and crack-free. The crystal size of the Ni-B/Ni-W-BN duplex composite coating is smaller compared to monolayer Ni–W–BN coating. The inclusion of BN nanoparticles in Ni-W matrix affect the content of nickel and tungsten of the deposits, increase the hardness and reduce the wear weight loss of the duplex composite coating. As a newly deposited layer with more active sites, the underlayer Ni–B much affects the morphologies of the top layer Ni–W–BN of the duplex coating. The incorporation of graphite-like BN nanoparticles into spherical-like Ni–W matrix increased the surface roughness and decreased the porosity. The Ni–B/Ni–W–BN duplex composite coating exhibited higher corrosion resistance than Ni–W and Ni–W–BN coating. The corrosion resistance was firstly increased and then decreased with the increase of BN. The optimum corrosion resistance could be obtained at 5 g L−1 BN nanoparticles in bath. However, a higher concentration of BN nanoparticles is detrimental to the properties of the duplex coating.