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

Abstract

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 (Jp = 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.