Investigation of crystal structure and mechanical properties of Ni-B/SnO2 composite coatings by electrodeposition method

In this study, Ni-B/SnO₂ nanocomposite coatings with different boron contents and SnO₂ additions were successfully fabricated on copper substrates by electrodeposition, and their microstructural, crystallographic, and tribological properties were systematically investigated. SEM analyses revealed a homogeneous and compact surface morphology at low additive contents, whereas agglomeration and irregularities were observed at higher contents. EDS results confirmed that Ni was the primary phase of the coatings and that SnO₂ co-deposited into the matrix within the range of 0.07–0.19 wt.%.XRD analyses showed that the average grain size of pure Ni (21.34 nm) decreased by about 75% in the N3 series, reaching 5.30–7.75 nm. In parallel, the microstrain values increased approximately three- to four-fold (12.3–18.1×10⁻³), while the dislocation density was found to be 8–16 times higher (16.6–35.6×10⁻³ nm⁻²) than that of pure Ni. These structural changes were directly reflected in the tribological performance.The specific wear rate of pure Ni was determined as 0.002084 mm³/N·m, whereas the N3B1S coating exhibited the best performance with an approximately 89% reduction (0.000232 mm³/N·m). Similarly, N6B4S displayed an 84% improvement (0.000343 mm³/N·m), and even the SnO₂-free N6B coating achieved a 79% reduction in wear rate. In contrast, coatings with higher SnO₂ contents showed significantly deteriorated performance; for example, N6B8S (0.001707 mm³/N·m) and N9B1S (0.001775 mm³/N·m) demonstrated nearly threefold higher wear rates than pure Ni. Overall, the results indicated that low to moderate SnO₂ additions (particularly N3B1S, N6B4S, and N9B2S) markedly improved the wear resistance of Ni-B coatings, whereas excessive additions led to agglomeration, microstructural defects, and subsequent deterioration in tribological properties.