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This paper presents a unique tribological system that is able to produce no measurable wear of material combination and that reduces friction markedly in the ultralow regime under boundary lubrication. Ultralow friction (0.03) was obtained by sliding hydrogen-free Diamond-Like-Carbon ta-C against ta-C lubricated with Poly-alpha Olefin base oil containing Glycerol Mono-Oleate (GMO) additive. The origin of ultralow friction in these conditions has been investigated by surface analysis techniques. Results are in agreement with the formation of a OH-terminated carbon surface. This new surface chemistry might be formed by the tribochemical reaction of alcohol function groups with the friction-activated ta-C atoms. The origin of low friction could be due to the very low-energy interaction between OH-terminated surfaces.

Tested in boundary lubrication, inorganic fullerene-like WS 2 nanoparticles used as additives in oil present interesting friction reducing and anti-wear properties. A dispersion with only 1 wt% of particles leads, from a contact pressure of 0.83 GPa, to a drastic decrease of the friction coefficient below 0.04 and to very low wear. High resolution transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and video imaging were used to explain the lubrication mechanisms. A structural modification of fullerene-like nanoparticles into sheets during the friction test was evidenced to be the main effect at the origin of these properties.

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