Tribological Behavior of Doped DLC Coatings in the Presence of Ionic Liquid Additive under Different Lubrication Regimes

Abstract

Diamond-like carbon (DLC) coatings are widely used in industries that require high durability and wear resistance, and low friction. The unique characteristics of DLC coatings allow for the possibility of creating adsorption sites for lubricant additives through the doping process. In this study, the combined use of europium-doped diamond-like carbon (Eu-DLC), gadolinium-doped diamond-like carbon (Gd-DLC), and pure DLC coatings and an ionic liquid (IL) additive, namely, trihexyltetradecylphosphonium bis (2-ethylhexyl) phosphate [P66614] [DEHP], with a 1 wt.% concentration in polyalphaolefin (PAO) 8 as a base lubricant was investigated. Higher hardness, higher thin-film adhesion, a higher ratio of hardness to elastic modulus, and a higher plastic deformation resistance factor were achieved with the Gd-DLC coating. The CoF of the Gd-DLC coating paired with the IL was superior compared to the other pairs in all lubrication regimes, and the pure DLC coating had a better performance than the Eu-DLC coating. The wear could not be quantified due to the low wear on the surface of the DLC coatings. The friction reduction demonstrates that tribological systems combining Gd-DLC thin films with an IL can be a potential candidate for future research and development efforts to reduce friction and increase the efficiency of moving parts in internal combustion engines, for instance.

Impact of Temperature Variation on Friction Behaviour of Rare Earth-Doped Diamond-like Carbon Coatings with Ionic Liquid Lubricants

“…et.al. shows the similar results found in the optical microscopy images of different lubricant films along with SEM-EDS images, the wear reduction is clearly evident by using ionic liquids as additives and doping of DLC coatings [74].…”

“…A study performed by M Sadeghi. et.al. shows the similar results found in the optical microscopy images of different lubricant films along with SEM-EDS images, the wear reduction is clearly evident by using ionic liquids as additives and doping of DLC coatings [74]. The SEM-EDS technique was used to assess the impact of IL with 2.3% Gd-DLC and 2.4% Eu-DLC.…”

“…The element in the EDS also shows the formation of oxides, which strongly suggest that there is interaction between the coatings and the ionic liquids. The prior research of pure PAO 8 as reference and PAO 8 additivated with {[P 66614 ][DEHP]} by M. Sadeghi has shown the similar results with drastic reduction in wear and CoF [74].…”

“…Research done by Omiya et.al. and Sadeghi et.al has shown that as the concentration of dopants (Eu and Gd) increases in the DLC, their affinity towards the ionic liquid additivated lubricant increases [73,74].…”

Effect of Europium and Gadolinium Alloying Elements on the Tribological Response of Low Hydrogen Content Amorphous Carbon

“…While most published studies focused on doping and/or alloying a-C coatings with metals or metalloids, doping a-C films with rare-earth elements − and rare-earth oxides , has only recently been explored. As one example, Omiya et al, Sadeghi et al, and Shaikh et al evaluated the tribological properties of gadolinium (Gd)- and europium (Eu)-alloyed a-C films deposited by high power impulse magnetron sputtering (HiPIMS) in the presence of synthetic oil containing a class of promising additives for transmission fluids, namely phosphonium phosphate ionic liquids. , The results of tribological experiments and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) measurements indicated that only the introduction of Gd in the a-C matrix favors the formation of a transfer layer on the steel counterbody that enhances the generation and adhesion of a lubricious and antiwear boundary layer (i.e., tribofilm) from the lubricant additives . As another example, Meng et al investigated the effect of the introduction of lanthanum (La) in DLC films grown by magnetron sputtering on the resulting mechanical, tribological, and wetting properties .…”