Synergistic anti-wear performance of TiO2 nanoparticles and ZDDP: Influence of dispersion methods

Zinc dialkyldithiophosphate (ZDDP) remains a cornerstone anti-wear additive in lubricants, particularly in applications demanding extreme boundary lubrication performance. However, emerging challenges in electric vehicle (EV) transmissions, such as higher available torque at standstill and lower lubricant viscosity, necessitate advanced formulations. Metal oxide nanoparticles, particularly anatase TiO₂, have demonstrated potential to enhance wear protection through the formation of protective tribofilms. This study investigates the benefits of combining TiO₂ nanoparticles with ZDDP in mitigating wear under boundary conditions. We evaluate the impact of dispersion methods, including oleic acid-based physical dispersion and chemical functionalization, on the tribological performance of these hybrid formulations. Using a combination of ball-on-disc tribological testing, profilometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) analyses, we demonstrate a synergistic effect between ZDDP and TiO₂ nanoparticles, delivering superior wear protection and friction reduction compared to individual components, regardless of dispersion method. However, chemically functionalized TiO₂ outperforms physically dispersed nanoparticles by forming a thicker and more uniform anti-wear tribofilm. These findings highlight the potential for hybrid lubricant formulations to meet the demands of advanced automotive applications.