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Lubricants 2018, 6(3), 59; https://doi.org/10.3390/lubricants6030059

Ultra-Low Friction on Tetrahedral Amorphous Diamond-Like Carbon (ta-C) Lubricated with Ethylene Glycol

1
Physics of Surfaces, Institute of Materials Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 16, D-64287 Darmstadt, Germany
2
Center of Smart Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, D-64287 Darmstadt, Germany
3
BMW Group, D-80788 Munich, Germany
4
Institute for Surface and Thin Film Analysis (IFOS), Trippstadter Straße 120, D-67663 Kaiserslautern, Germany
*
Author to whom correspondence should be addressed.
Received: 23 May 2018 / Revised: 25 June 2018 / Accepted: 3 July 2018 / Published: 7 July 2018
(This article belongs to the Special Issue Applied Nanotribology)
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Abstract

Lubricated tetrahedral amorphous carbon coatings can show a very complex tribological behavior. In particular, friction regimes with extremely low friction have been observed. In tribological experiments with a ta-C/steel friction pair that was lubricated with ethylene glycol, we observed a sudden and very strong decrease in the effective friction coefficient from 0.45 to 0.01 after running-in. By varying different components of the tribological system after this abrupt decrease we investigated the role of the counter-body, the lubricant and the coating. To investigate the surface chemistry, static time-of-flight secondary ion mass spectrometry (ToF-SIMS), dynamic secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS) measurements were performed. Using deuterated lubricants, ToF-SIMS measurements allowed us to distinguish adsorption of hydrogen and hydroxyl-groups from the lubricant from the adsorption from the environment. Deuterated hydroxyl-groups from the lubricant adsorbed to the surface during the experiment. In particular, more adsorbed deuterated hydroxyl-groups were detected prior to the sudden decrease in the friction coefficient. Thus, the sudden decrease in the coefficient of friction was most likely caused by an interplay between the lubricant, the ta-C coating and the counter-body which lead to the formation of transfer and adsorption layers. View Full-Text
Keywords: diamond-like carbon; ToF-SIMS; XPS; coefficient of friction; ethane-1,2-diol; ta-C diamond-like carbon; ToF-SIMS; XPS; coefficient of friction; ethane-1,2-diol; ta-C
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Bachmann, S.; Schulze, M.; Krell, L.; Merz, R.; Wahl, M.; Stark, R.W. Ultra-Low Friction on Tetrahedral Amorphous Diamond-Like Carbon (ta-C) Lubricated with Ethylene Glycol. Lubricants 2018, 6, 59.

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