Synthesis and characterization of Ni-Si3N4 nanocomposite coatings fabricated by pulse electrodeposition

摘要

Pure Ni and Ni-silicon nitride (Si3N4) nanocomposite coatings have been successfully fabricated on copper substrates by a pulse electrodeposition method employing the Watts bath. The obtained coatings were characterized with X-ray diffractometry and scanning electron microscopy. Also, surface hardness and the corrosion behaviour of the coatings were analysed by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. It was found that incorporation of Si3N4 particulates has reduced the crystallite size and also changed the growth orientation of the crystallite from (111) to (220) and (200) crystal planes. The co-deposition of Si3N4 in the Ni matrix led to better properties of these coatings. Accordingly, the hardness value of nanocomposite coatings was about 80-140 Hv higher than that of pure nickel due to dispersion-strengthening and matrix grain refining and increased with the enhancement of incorporating Si3N4 particle content. The presence of the Si3N4 particulates slightly decreases the current efficiency. The current efficiency was decreased by increasing current density from 1 to 4A dm(-2). Moreover, the corrosion resistance of nanocomposite coatings was significantly higher than the pure Ni deposit. Also, the Ni-Si3N4 coating produced at a density of 4A dm(-2) showed the lowest corrosion rate (0.05 mpy).