Investigation of the Tribological Effects of Nano-Sized Transition Metal Oxides on a Base Oil Containing Pour Point Depressant and Viscosity Modifier

This study investigates the tribological effects of nano-sized metal oxides (ZrO2, CuO, Y2O3 and TiO2) in Group III type base oil containing 0.3% pour point depressant (PPD) and 5% viscosity modifier (VM) to enhance friction and wear performance. The homogenized lubricant samples with varying concentrations of oxide nanoparticles (0.1–0.5 wt%) on a linear oscillating tribometer performed static and dynamic frictional tests. Optical and confocal microscopy surface analysis evaluated the wear of the specimen, and SEM and EDX analyses characterized the wear tracks, nanoparticle distributions, and quantification. The cooperation between PPD and nanoparticles significantly improved friction and wear values; however, the worn surface suffered extensively from fatigue wear. The collaboration between VM and nanoparticles resulted in a nanoparticle-rich tribofilm on the contact surface, providing excellent wear resistance that protects the component while also favorably impacting friction reduction. This study found CuO reduced wear volume by 85% with PPD and 43% with VM at 0.5 wt%, while ZrO2 achieved 80% and 63% reductions, respectively. Y2O3 reduced wear volume by 82% with PPD, and TiO2 reduced friction by 20% with VM. These nanoparticles enhanced tribological performance at optimal concentrations, but high concentrations caused tribofilm instability, highlighting the need for precise optimization.