Electrodeposition of Ni-B/Al2O3–TiO2 nanocomposite coatings with variable ceramic particle content and investigation of their properties

In this study, Ni-B/Al2O3–TiO2 nanocomposite coatings were produced on copper substrates by DC electrodeposition from a TMAB-containing Watts-type bath, and the effect of the Al2O3/TiO2 ratio on the structural and tribological properties was investigated at a fixed total ceramic content of 20 g/L. XRD results revealed that the FCC-Ni matrix was preserved in all samples, while the incorporation of ceramic reinforcements reduced the crystallite size into the nanometric range and, in contrast, increased the microstrain and defect density. SEM–EDS analyses showed that Al2O3 and TiO2 particles were embedded in the Ni-B matrix and, depending on the composition, formed a more homogeneous and fine distribution in the equi-ratio hybrid coating, whereas the TiO2-rich composition exhibited locally continuous reinforcement regions.Ball-on-disk wear tests under a normal load of 2 N indicated that the equi-ratio hybrid coating yielded the lowest average coefficient of friction (µ ≈ 0.38), while the TiO2-rich sample, despite its higher µ, exhibited the minimum wear track depth (≈ 3.62 µm). Overall, the findings demonstrate that the tribological performance is governed not only by the mere presence of the ceramic phase, but also by the load-bearing mode defined by the phase type–ratio and the spatial distribution of the particles within the matrix. In this context, hybrid Al2O3–TiO2-reinforced architectures appear more suitable for low/medium load conditions, whereas Al2O3-dominated designs are considered to be more promising at higher load levels.