Physicochemical and tribological characterizations of WDLC coatings and ionic-liquid lubricant additives : potential candidates for low friction under boundary-lubrication conditions

M. S. Arshad, J. Kovač, S. Cruz, M. Kalin

Tribology International 151 (2020) 106482 1-10


An interaction between tungsten-doped diamond-like-carbon (WDLC) coatings and ionic-liquid (IL) additives under boundary-lubrication conditions is investigated. Three phosphate-based IL additives were employed: two had dimethylphosphate anion however, third one hydrolytic trifluorophosphate anion. In tribological tests, low friction (0.024) was achieved at 10 N and 100 °C with both dimethylphosphate containing IL additives. In contrast, IL with the trifluorophosphate anion had the poorest performance of all the ILs. Surface analyses revealed the thermal dissociation of dimethylphosphate into phosphate radicals which interacted with the WDLC surface to form phosphate-based tribofilm, which provides an easy shear thus reduces the friction. However, trifluorophosphate anions are thermally stable in given conditions and don't form a tribofilm on the WDLC surface hence show poor tribological performance.


Keywords: WDLC coatings, ionic liquids, glycerol, close-to-ultra-low friction, wear-resistant coatings, XPS, ToF-SIMS, tribofilm, green tribology

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