title: Diamond-like carbon coating under oleic acid lubrication: Evidence for graphene oxide formation in superlow friction.
abstract: The achievement of the superlubricity regime, with a friction coefficient below 0.01, is the Holy Grail of many tribological applications, with the potential to have a remarkable impact on economic and environmental issues. Based on a combined high-resolution photoemission and soft X-ray absorption study, we report that superlubricity can be realized for engineering applications in bearing steel coated with ultra-smooth tetrahedral amorphous carbon (ta-C) under oleic acid lubrication. The results show that tribochemical reactions promoted by the oil lubrication generate strong structural changes in the carbon hybridization of the ta-C hydrogen-free carbon, with initially high sp3content. Interestingly, the macroscopic superlow friction regime of moving mechanical assemblies coated with ta-C can be attributed to a few partially oxidized graphene-like sheets, with a thickness of not more than 1 nm, formed at the surface inside the wear scar. The sp2planar carbon and oxygen-derived species are the hallmark of these mesoscopic surface structures created on top of colliding asperities as a result of the tribochemical reactions induced by the oleic acid lubrication. Atomistic simulations elucidate the tribo-formation of such graphene-like structures, providing the link between the overall atomistic mechanism and the macroscopic experimental observations of green superlubricity in the investigated ta-C/oleic acid tribological systems.
authors.affiliation: University of Lyon, Ecole Centrale de Lyon, LTDS, 69380, Ecully, France.
authors.forename: Maria Isabel
authors.initials: MI
authors.lastname: De Barros Bouchet
authors.affiliation: University of Lyon, Ecole Centrale de Lyon, LTDS, 69380, Ecully, France.
authors.forename: Jean Michel
authors.initials: JM
authors.lastname: Martin
authors.affiliation: ANTARES Beamline, Synchrotron SOLEIL Université Paris-Saclay, L'Orme des Merisiers, Saint Aubin-BP 48, 91192 Gif sur Yvette Cedex, France.
authors.forename: José
authors.initials: J
authors.lastname: Avila
authors.affiliation: Kanagawa Industrial Technology Center 705-1 Shimo-Imaizumi, Ebina, Kanagawa, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Kano
authors.affiliation: Kanagawa Industrial Technology Center 705-1 Shimo-Imaizumi, Ebina, Kanagawa, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tsuruda
authors.affiliation: New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
authors.forename: Shandan
authors.initials: S
authors.lastname: Bai
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Higuchi
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Nobuki
authors.initials: N
authors.lastname: Ozawa
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Momoji
authors.initials: M
authors.lastname: Kubo
authors.affiliation: ANTARES Beamline, Synchrotron SOLEIL Université Paris-Saclay, L'Orme des Merisiers, Saint Aubin-BP 48, 91192 Gif sur Yvette Cedex, France.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Asensio