Salinas Ruiz, V.R.V.R.Salinas RuizKuwahara, TakuyaTakuyaKuwaharaGalipaud, J.J.GalipaudMasenelli-Varlot, K.K.Masenelli-VarlotBen Hassine, M.M.Ben HassineHéau, C.C.HéauStoll, MelissaMelissaStollMayrhofer, LeonhardLeonhardMayrhoferMoras, GianpietroGianpietroMorasMartin, J.M.J.M.MartinMoseler, MichaelMichaelMoselerBarros Bouchet, M.-I. deM.-I. deBarros Bouchet2022-06-242022-06-242021https://publica.fraunhofer.de/handle/publica/26837810.1038/s41467-021-24766-6Friction and wear reduction by diamond-like carbon (DLC) in automotive applications can be affected by zinc-dialkyldithiophosphate (ZDDP), which is widely used in engine oils. Our experiments show that DLCs tribological behaviour in ZDDP-additivated oils can be optimized by tailoring its stiffness, surface nano-topography and hydrogen content. An optimal combination of ultralow friction and negligible wear is achieved using hydrogen-free tetrahedral amorphous carbon (ta-C) with moderate hardness. Softer coatings exhibit similarly low wear and thin ZDDP-derived patchy tribofilms but higher friction. Conversely, harder ta-Cs undergo severe wear and sub-surface sulphur contamination. Contact-mechanics and quantum-chemical simulations reveal that shear combined with the high local contact pressure caused by the contact stiffness and average surface slope of hard ta-Cs favour ZDDP fragmentation and sulphur release. In absence of hydrogen, this is followed by local surface cold welding and sub-surface mechanical mixing of sulphur resulting in a decrease of yield stress and wear.enatomistic modelChemical Physicsmechanical engineeringweardiamond-like carbonlubricationcontact mechanicsquantum chemistrymechanochemistry620journal article