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Interplay of mechanics and chemistry governs wear of diamond-like carbon coatings interacting with ZDDP-additivated lubricants

: Salinas Ruiz, V.R.; Kuwahara, T.; Galipaud, J.; Masenelli-Varlot, K.; Ben Hassine, M.; Héau, C.; Stoll, M.; Mayrhofer, L.; Moras, G.; Martin, J.M.; Moseler, M.; Barros Bouchet, M.-I. de

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Nature Communications 12 (2021), Art. 4550, 15 S.
ISSN: 2041-1723
Bundesministerium fur Wirtschaft und Energie BMWi (Deutschland)
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IWM ()
atomistic model; Chemical Physics; mechanical engineering; wear; diamond-like carbon; lubrication; contact mechanics; quantum chemistry; mechanochemistry

Friction 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.