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

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. I...

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Bibliographic Details
Published in:Tribology international 2020-11, Vol.151, p.106482, Article 106482
Main Authors: Arshad, Muhammad Shahid, Kovač, Janez, Cruz, Sandra, Kalin, Mitjan
Format: Article
Language:English
Subjects:
Additives
Anions
Close-to-ultra-low friction
Coatings
Diamond-like carbon
Diamonds
Friction
Friction reduction
Glycerol
Green tribology
Ionic liquids
Lubricants
Lubricants & lubrication
Lubrication
Thermal dissociation
Thermal stability
ToF-SIMS
Tribofilm
Tribology
Tungsten
WDLC coatings
Wear-resistant coatings
XPS
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Summary: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. Tribofilm formation on the surface of the WDLC coatings with dimethylphosphate anions. [Display omitted] •Ionic liquid additives interact with WDLC coatings.•Phosphate-based tribofilm form on the WDLC surface by dimethylphosphate anion dissociation and reaction with tungsten atoms.•Tribofilm provide an easy shear thus significantly reduce the friction.
ISSN:0301-679X
1879-2464
DOI:10.1016/j.triboint.2020.106482