**8. NiCo–Ceramic Composites**

Nanoparticles have been added to the Ni–Co matrix to further improve the properties. Ni–Co nanocomposite coatings exhibit superior hardness and wear resistance to alloy coatings. This can be attributed to inherent hardness of nanoparticles used, coupled with nanoparticle strengthening through Orowan mechanism [30]. According to this mechanism, the adsorbed nanoparticles hinder the formation and propagation of dislocations as the metallic matrix carries the load.

In some instances, the increase in Co concentration in the bath has been reported to improve nanoparticle incorporation thereby improving coating properties such as corrosion resistance [30]. This effect of nanoparticles can be linked to several factors:


Other factors that may be associated with metallic alloy nanocomposite coatings include: reinforcing phase induced hardening, texture evolution, grain refinement of the matrix, and solid solution strengthening depending on selected matrix [129–131]. Wear resistance of Ni–Co alloy coating is greatly improved by incorporation of nanoparticles in the matrix. This increase can be attributed to the dispersion strengthening effect of adsorbed hard nanoparticles coupled with grain-refining tendencies. The uniform dispersion in the matrix and to a small extent particle agglomeration may be linked to improved wear resistance in Ni–Co nanocomposites. Similar conclusions were reached by Shi et al. [60].
