Synthesis and characterization of Ni–Si$_3$N$_4$ nanocomposite coatings fabricated by pulse electrodeposition

[摘要] Pure Ni and Ni–silicon nitride (Si$_3$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 withX-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 Si$_3$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 Si$_3$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 purenickel due to dispersion-strengthening and matrix grain refining and increased with the enhancement of incorporating Si$_3$N$_4$ particle content. The presence of the Si$_3$N$_4$ particulates slightly decreases the current efficiency. The current efficiency was decreased by increasing current density from 1 to 4 A dm$^{−2}$. Moreover, the corrosion resistance of nanocomposite coatings was significantly higher than the pure Ni deposit. Also, the Ni–Si$_3$N$_4$ coating produced at a density of 4 A dm$^{−2}$ showed thelowest corrosion rate (0.05 mpy).

[学科分类] 材料工程

[关键词] Composite coating;pulse electrodeposition;co-deposition;hardness;corrosion.