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

Abstract

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 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 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 pure nickel 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 the lowest corrosion rate (0.05 mpy).

Improvement in comprehensive properties of nanocomposite coatings electro-codeposited with nitride and ceria

“…The i corr value of Ni-15Si 3 N 4 -3CeO 2 coating is approximately two orders of magnitude lower than that of pure nickel deposit, indicating the remarkable protective properties, as shown in Table 3. In addition, The i corr value of Ni–15Si 3 N 4 –3CeO 2 coating is lower than that of the Ni–Si 3 N 4 [26] and Zn–CeO 2 [34].

Figure 9 The polarisation curves of the composite coatings tested in 3.5 wt-% NaCl solution.

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“…Thirdly, the dispersed ceramic nanoparticles in the nickel-matrix can alter the texture and change the columnar microstructure to an equiaxed grain, thus cutting off the shortcut for the corrosion path to the substrate [42]. Fourthly, the nanoparticles typically locate in the grain boundary, which can inhibit the propagation of corrosion paths and increase corrosion resistance [8,26]. In the present study, the Ni–15Si 3 N 4 –3CeO 2 composite coating has a small grain size of 39.4 nm with the strongest (111) texture, and shows a very smooth and uniform surface structure, which results from the codeposition of Si 3 N 4 and CeO 2 nanoparticles in the bath solution, as shown in Figure 3(b).…”

“…Li et al [25] fabricated Ni-W/Si 3 N 4 nanocomposite coatings and reported that the mechanical properties of the coatings could be obviously enhanced by increasing the content of Si 3 N 4 in an aqueous bath. Some other studies have shown that the coatings incorporated with Si 3 N 4 particles have improved mechanical and anti-corrosion properties [26,27].…”