Lubrication of DLC Coatings with Two Tris(pentafluoroethyl)trifluorophosphate Anion-Based Ionic Liquids

Abstract

The lubrication of a Cr-DLC coating with ethyl-dimethyl-2-methoxyethylammonium tris(pentafluoroethyl)trifluoropho-sphate [(NEMM)MOE][FAP] and 1-butyl-1-methylpyrro-lidinium tris(pentafluoroethyl)trifluorophosphate [BMP] [FAP] ionic liquids (ILs) as 1 wt% additives to a polyalphaolefin (PAO 6) was studied. Zinc dialkyldithiophosphate (ZDDP) was also used as reference in order to evaluate the effectiveness of the ILs. Reciprocating ball-on-plate tribological tests at loads of 20 and 40 N were performed. The results showed that both ILs exhibited a friction reduction, especially at the lowest load tested. Antiwear properties were also improved; the PAO 6 + 1% [BMP][FAP] mixture was slightly better, close to the values for PAO 6 + 1% ZDDP. Scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) analysis indicated that the additive–surface interaction was responsible for the tribological improvement.

KEY WORDS:

• DLC
• Ionic Liquid
• Lubrication
• Additive

ACKNOWLEDGEMENTS

The authors are grateful to the FICYT (the Foundation for the promotion in Asturias of the Applied Scientific Research and Technology) and the Ministry of Science and Innovation, Spain, for supporting this work within the framework of the research projects IB09–047 and DPI2010–18166, respectively. In addition, we would like to thank the Unit for Molecular Spectroscopy and XPS from the Scientific-Technical Services of the University of Oviedo.