Study of the Microstructure, Morphology, Micro- and Nanoindentation Hardness, and Corrosion Behavior of Ni-SiO2 Composites Electrodeposited from a Deep Eutectic Solvent

Composite coatings containing Ni and small amounts of SiO2 nanoparticles (NPs) were electrodeposited from an environmentally friendly deep eutectic solvent (DES) containing 0, 15, and 30 g/L of SiO2. The effects of the presence of SiO2 in the Ni coatings were investigated in relation to their microstructure, as well as their mechanical and corrosion properties. The average crystallite size of Ni decreased by approximately 9% with the incorporation of 30 g/L SiO₂. At this SiO2 concentration, the Si content reached 0.56 wt.% in the bulk and 4.1 wt.% at the surface of the coating based on the results obtained by EDX and XPS, respectively. Microstructure studies of all coatings identified a granular growth with a broad Ni cluster size distribution. With the addition of 30 g/L of SiO2, the surface roughness decreased, and the normality of the surface texture improved. Maximum micro- and nanoindentation hardness values of 4.9 GPa0.0981 N (500 Hv0.0981 N) and 6.7 GPa20 mN, respectively, were achieved with the addition of 30 g/L of silica nanopowder, representing increases of 18% and 8% compared to pure Ni. Electrochemical results showed that the incorporation of 15 and 30 g/L SiO₂, along with reduced surface defects, significantly improved polarization behavior. This enhancement is attributed to improved passive film formation and the role of SiO₂ as a corrosion barrier. Corrosion current density decreased by factors of 11 and 7, respectively, compared to unreinforced Ni.