Tribological behaviour of nano-titanium dioxide filled UHMWPE composites with a variety of micro fillers based on carbon, boron nitride and silicon dioxide under water-lubricated condition

Recent advances in the tribology of polymer composites in water-lubricated conditions have focused on achieving a synergistic effect by incorporating multiple fillers into the polymer matrix. This approach requires a comprehensive understanding of how each filler interacts with the other components, something that remains unknown for hard fillers. This study investigates the tribological performance and tribological mechanisms of a hard filler, nano-titanium dioxide, in a short-carbon-fibre-reinforced, ultra-high-molecular-weight-polyethylene (UHMWPE) composite when combined with microfillers that include graphite, hexagonal boron nitride and silicon dioxide. The results reveal that, while composites with nano-titanium dioxide and microfillers improve the friction by 30–53 % compared to basic fibre-reinforced UHMWPE, the nano-titanium dioxide reduced the friction only with boron nitride and silicon dioxide. In these cases, the nano-titanium dioxide contributes to transferred material onto the steel surface where it embeds in a relatively softer layer of material composed of other components transferred from the composite and thereby reduces the friction. In contrast, all the composites have lower wear rates than the basic carbon-fibre-reinforced composite. We present how the nano-titanium dioxide interacts synergistically with all the microfillers, with each filler contributing in its own way to improving the load-bearing capacity and hindering the fibre pullout. Surprisingly, the combination with the graphite microfiller did not reduce the friction, but had the lowest wear rate in this study of 5–8 × 10⁻ 8 mm³ /Nm. The impact of the contact pressure on the fillers’ interactions and the tribological performance is also highlighted in this study. • Multi-scale polymer composites containing nano-titanium dioxide and microfillers were tested against 316 L steel. • Best-performing compositions exhibited coefficient of friction in the 0.05–0.07 range and wear rate in order of 10 −8 mm 3 /Nm. • Transferred material layer over steel surface was characterized using SEM, AFM, Raman and nano-indentation techniques. • The presence of nano-titanium dioxide in the transferred material layer was noted only for selective compositions. • Contact pressure also influenced the transfer of nano-titanium dioxide onto the steel surface.