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    Elasto-hydrodynamic friction changes on steel surfaces arising from the modified surface energy of the steel due to additive boundary films

    Year: 2021

    Journal: Tribol. Int., Volume 164, DEC

    Authors: Polajnar, Marko; Thiebaut, Benoit; Jarnias, Frederic; Kalin, Mitjan

    Organizations: company TotalEnergies; Centre deRecherche de Solaize (France); Slovenian Research Agency [Z2-1868, P2-0231]

    Keywords: Elastohydrodynamic; Lubricant additive; Traction; Wetting

    The effect of three different film-forming additives mixed in PAO oil on the elasto-hydrodynamic (EHD) friction was investigated and compared to cases with the base oil only. When the boundary films were formed on the surfaces, the organic friction modifier (OFM) decreased the EHL friction by up to 8.7%, the ionic liquid (IL) decreased it by up to 6.4%, while the polymeric organic friction modifier (pOFM) increased it by up to 4.2%. In contrast, if the boundary films were not formed, the EHL friction remained the same as with the base oils only. The oils' surface tension and viscosity were analysed at 25 degrees C and 100 degrees C as potential influencing effects, and the most important parameter for friction changes was found to be the surface energy. The mechanism behind this EHL friction reduction is, therefore, the effect of the boundary films on the poor oil-surface wetting and the consequent boundary slip. This study confirms the poor wetting arising from additive boundary-film formation as a relevant EHL friction-reduction mechanism. This observation is similar to that observed previously for surface coatings, thus suggesting that the boundary films of the surface-energy-reducing additives is a parameter with the potential to reduce the EHL friction.
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