Effect of Adding TiO2 Nanoparticles to a Lubricant Containing MoDTC on the Tribological Behavior of Steel/Steel Contacts under Boundary Lubrication Conditions

The tribological performance of lubricants containing TiO2 nanoparticles and Molybdenum DiThioCarbamate (MoDTC) was investigated using a reciprocating ball-on-flat tribometer in steel–steel contacts. Lubricants containing only MoDTC were used for comparison. The influences of the additive concentration (0.1 wt% and 0.5 wt%) and of the roughness of the counterparts (Ra from 10 to 200 nm) on the performance of the lubricant were studied. Improved friction modification and anti-wear properties were found when TiO2 nanoparticles were blended with MoDTC compared to MoDTC alone, even at low concentration and with rough surfaces. XPS characterizations and FIB-TEM analyses of tribofilms were performed and suggested that the formation of MoS2 from MoDTC is favored in the presence of TiO2 nanoparticles. The results are discussed, taking into account the tribocatalytic properties of TiO2 nanoparticles.