The W-cluster reactive sites interaction model for WDLC coatings with ionic liquids

M. S. Arshad, L. Čoga, T. Geue, J. Kovač, S. M. A. Cruz, M. Kalin

Tribology International 185 (2023) 108550 1-11


This study investigates the use of 1,3-dimethylimidazolium dimethylphosphate ionic liquid (IL) additive in glycerol base oil for improving the lubrication-properties of tungsten-doped diamond-like carbon (WDLC) coatings. Tribological tests were conducted at various applied loads (5 N, 10 N, 20 N) and elevated temperature (100 °C), and the addition of 1 wt% of IL resulted in a significant reduction (∼50%) in friction-coefficient. In-situ neutron-reflectometry analysis revealed a multi-step tribofilm formation mechanism involving IL and W-clusters, resulting in the formation of a 1.24-nm thick tribofilm on the WDLC surface within the first 30-minutes of the friction experiment. The reaction kinetics for tribofilm formation are discussed involving dissociation of dimethylphosphate into dioxo-phosphate, which interacts with W-clusters to form tungsten phosphates and cations adsorbed on their surface.


Keywords: W-doping DLC coatings, ionic-liquid, friction, neutron reflectometry

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