Effects of Direct and Pulse Plating on the Co-Deposition of Sn-Ni/TiO₂ Composite Coatings

Sn-Ni alloy matrix coatings co-deposited with TiO₂ nanoparticles (Evonik P25) were produced utilizing direct (DC) and pulse electrodeposition (PC) from a tin-nickel chloride-fluoride electrolyte with a loading of TiO₂ nanoparticles equal to 20 g/L. The structural and morphological characteristics of the resultant composite coatings were correlated with the compositional modifications that occurred within the alloy matrix and expressed via a) TiO₂ co-deposition rate and b) composition of the matrix; this was due to the application of different current types (DC or PC electrodeposition), and different current density values. The results demonstrated that under DC electrodeposition, the current density exhibited a more significant impact on the composition of the alloy matrix than on the incorporation rate of the TiO₂ nanoparticles. Additionally, PC electrodeposition favored the incorporation rate of TiO₂ nanoparticles only when applying a low peak current density (J_p = 1 Adm^-2). All of the composite coatings exhibited the characteristic cauliflower-like structure, and were characterized as nano-crystalline. The composites' surface roughness demonstrated a significant influence from the TiO₂ incorporation rate. However, in terms of microhardness, higher co-deposition rates of embedded TiO₂ nanoparticles within the alloy matrix were associated with decreased microhardness values. The best wear performance was achieved for the composite produced utilizing DC electrodeposition at J = 1 Adm^-2, which also demonstrated the best photocatalytic behavior under UV irradiation. The corrosion study of the composite coatings revealed that they exhibit passivation, even at elevated anodic potentials.