Synthesis and characterization of Ni–$\hbox {Si}_{3}\hbox {N}_{4}$ nanocomposite coatings fabricated by pulse electrodeposition

Abstract

Pure Ni and Ni–silicon nitride $(\hbox {Si}_{3}\hbox {N}_{4})$ 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 $\hbox {Si}_{3}\hbox {N}_{4}$ 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 $\hbox {Si}_{3}\hbox {N}_{4}$ 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 $\hbox {Si}_{3}\hbox {N}_{4}$ particle content. The presence of the $\hbox {Si}_{3}\hbox {N}_{4}$ particulates slightly decreases the current efficiency. The current efficiency was decreased by increasing current density from 1 to 4 A $\hbox {dm}^{-2}$. Moreover, the corrosion resistance of nanocomposite coatings was significantly higher than the pure Ni deposit. Also, the Ni–$\hbox {Si}_{3}\hbox {N}_{4}$ coating produced at a density of 4 A $\hbox {dm}^{-2}$ showed the lowest corrosion rate (0.05 mpy).