**6.5. Ni–W composite coatings**

The behaviour of Ni–W alloy is similar to that of Ni–B. The presence of tungsten in the nickel matrix improves mainly the mechanical properties of the coatings but not their corrosion resistance [64]. Therefore, research to make Ni–W alloy coatings to possess excellent wear and corrosion resistance has intensified to extend the applications of the coatings. The addition of reinforcement particulates and subjecting the coatings to post-plating heat treatment have been used in an effort to enhance their surface properties. Incorporation of SiO2 into Ni–W matrix influences the morphology of the coatings and the resultant microstructure is subject to the content of SiO2 in the coating as shown in Figure 7. The composite coatings are uniform and crack-free. The particles also improved the microhardness and corrosion resistance of the matrix [65]. The lowest particle loading of 2 g/l of SiO2 yielded coatings with best anti-corrosive properties (see Table 6). The optimum particle concentration of 10 g/l in the bath gave the highest microhardness.


**Table 6.** Corrosion parameters of Ni–W alloy and Ni–W–SiO2 nanocomposite coatings

Ref. [25] deposited Ni–W–TiO2 nanocomposite coating using both DC and PC methods. The corrosion resistance for all the deposits increased with the content of TiO2 in the coating. PCplated coatings also had superior corrosion resistance than their DC counterparts. However, ref. [66] obtained different results when they plated the nanocomposites using both methods. DC-electrodeposited Ni–W–TiO2 nanocomposite coatings exhibit inferior corrosion resistance as compared to Ni–W alloy and pulse-plated Ni–W–TiO2 coatings. Therefore, the current regime and other plating process parameters have significant influence on the improvement Tribological and Corrosion Performance of Electrodeposited Nickel Composite Coatings http://dx.doi.org/10.5772/62170 223

**Figure 9.** Surface morphologies of Ni–W alloy and nanocomposite coatings [65]

corrosion resistance of Ni matrix [8]. Sol-enhanced TiO2 nanoparticles yielded similar behav‐ iour with 12.5 ml/l of the particles increasing microhardness of Ni–B from 677 to 1061 HV. The improvement of hardness was also accompanied by reduction in friction coefficient and low volume wear loss [63]. The TiO2 sol leads to dispersion strengthening and fining of grains, hence the improvement in hardness and tribological behaviour. Therefore, the incorporation of second-phase particles in Ni–B alloy matrix has not proved to increase nickel coating

The behaviour of Ni–W alloy is similar to that of Ni–B. The presence of tungsten in the nickel matrix improves mainly the mechanical properties of the coatings but not their corrosion resistance [64]. Therefore, research to make Ni–W alloy coatings to possess excellent wear and corrosion resistance has intensified to extend the applications of the coatings. The addition of reinforcement particulates and subjecting the coatings to post-plating heat treatment have been used in an effort to enhance their surface properties. Incorporation of SiO2 into Ni–W matrix influences the morphology of the coatings and the resultant microstructure is subject to the content of SiO2 in the coating as shown in Figure 7. The composite coatings are uniform and crack-free. The particles also improved the microhardness and corrosion resistance of the matrix [65]. The lowest particle loading of 2 g/l of SiO2 yielded coatings with best anti-corrosive properties (see Table 6). The optimum particle concentration of 10 g/l in the bath gave the

Samples SiO2 addition (g/l) *E*corr/*V i*corr/μA cm–2

A 0 –0.588 13.95 B 2 –0.562 8.76 C 5 –0.580 16.75 D 10 –0.603 24.64 E 15 –0.630 37.43 F 20 –0.672 44.14

**Table 6.** Corrosion parameters of Ni–W alloy and Ni–W–SiO2 nanocomposite coatings

Ref. [25] deposited Ni–W–TiO2 nanocomposite coating using both DC and PC methods. The corrosion resistance for all the deposits increased with the content of TiO2 in the coating. PCplated coatings also had superior corrosion resistance than their DC counterparts. However, ref. [66] obtained different results when they plated the nanocomposites using both methods. DC-electrodeposited Ni–W–TiO2 nanocomposite coatings exhibit inferior corrosion resistance as compared to Ni–W alloy and pulse-plated Ni–W–TiO2 coatings. Therefore, the current regime and other plating process parameters have significant influence on the improvement

corrosion resistance, but its mechanical and tribological properties.

**6.5. Ni–W composite coatings**

222 Electrodeposition of Composite Materials

highest microhardness.

of functional properties. PTFE (polytetrafluoroethylene) particles co-deposited with Ni–W alloy using pulse current electrodeposition showed improvement in morphology, hardness, corrosion resistance, and tribological properties of the deposits [67]. The increase in particle content in the coatings from 0 to 20 g/l had positive influence on the mentioned properties. PTFE particles are chemically inert and possess low coefficient of friction when compared to other polymers. SiC nanoparticles showed similar behaviour when they were incorporated into Ni–W alloy [68]. Boron nitride particles possess excellent self-lubrication properties and reduce the surface roughness of Ni–W alloy, thus decreasing friction of the coatings and improving their wear resistance [69]. The inclusion of the particles also significantly affects the corrosion resistance of the coatings (30 mV potential shift). Ref. [70] reported MoS2 particles to lower friction the coefficient of Ni–W matrix and enhance its tribological properties.
