Electrodeposition of nanocrystalline Ni/Ni–Al₂O₃ nanocomposite modulated multilayer coatings

Highlights: • Electrocrystallization of multilayer coatings with alternative nanocrystalline Ni/Ni–Al2O3 nanocomposite layers is possible. • Electrodeposition of alternative hard and soft layers can improve tribological properties of the coatings. • Multilayer coatings of nanocomposite layers and nanocrystalline layers can have better performance than single layer nanocomposite coatings. In this research, nanocrystalline Ni/Ni–Al₂O₃ nanocomposite modulated multilayer coatings were fabricated by direct current electrodeposition using dual bath technique. A Watts-type bath was used as the main solution of the baths. Saccharin was added to the first bath for producing nanocrystalline nickel layers and γ-alumina nanoparticles were added to the second bath to produce nanocomposite layers. The effect of coating's configuration like number of layers and their order was evaluated. The microstructures of the coatings, including relative texture coefficient and grain size, were studied by X-ray diffraction analysis. Energy dispersive spectroscopy and scanning electron microscopy were used to investigate the chemical composition and morphology of the coatings. Their tribological properties were investigated. The results exhibited that variation of order and configuration of layers had a significant effect not only on the adsorption of nanoparticles in the nanocomposite layers, but also on their growth texture in each multilayer coatings. In general, the results of tribological studies revealed that the optimum number of layers is 6 and all Ni–Al₂O₃/Ni CMM coatings, consisting soft layers (nanocomposite) and approximately hard layers (nanocrystalline), had better tribological properties than single layer nanocomposite coating and also worse performance than nanocrystalline one with the same total thickness.