Tribological Characterisation of Graphene Oxide as Lubricant Additive on Hypereutectic Al-25Si/Steel Tribopair

Abstract

The performance of a lubricant greatly depends on the additives it involves. However, recently used additives produce severe pollution when they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) is considered to be environmentally friendly. The scope of this study is to explore the fundamental tribological behavior of graphene, the first existing 2D material, and evaluate its performance as a lubricant additive. The friction and wear behavior of 0.5 wt% concentrations of GO particles in ethanol and SAE20W50 engine oil on a hypereutectic Al-25Si alloy disc against steel ball was studied at 5 N load. GO as an additive reduced the wear coefficient by 60-80% with 30 Hz frequency for 120 m sliding distance. The minimum value of the coefficient of friction (0.057) was found with SAE20W50 C 0.5 wt% GO. A possible explanation for these results is that the graphene layers act as a 2D nanomaterial and form a conformal protective film on the sliding contact interfaces and easily shear off due to weak Van der Waal's forces and drastically reduce the wear. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used for characterization of GO and wear scars.

Lubrication Performance of Graphene as Lubricant Additive in 4-n-pentyl-4′-cyanobiphyl Liquid Crystal (5CB) for Steel/Steel Contacts

“…Graphene, as a sheet-like nano material, is easy to enter the friction region [38]. In addition, graphene sheets with weak van der waals force are easy to slide between each other [39,40]. So we speculate that the addition of graphene reduces the friction coefficient.…”

Formulation, tribological performance, and characterization of base oil with ZnO, graphene, and ZnO/graphene nanoparticles additives

“…The 2D peak is associated with dual phonon scatter suchlike of electron-electron or electron-hole or hole-hole set. Moreover, it indicated as an inference of the D peak, but it does not necessarily represent flaws in the lattice formation [22,30].…”

“…The nanomixture additives associated with the sliding balls produced enriched tribolayer between the mating surfaces of AISI ball. The mixture enriched film played antiwear and friction reduction attributes as demonstrated by energy-dispersive x-ray spectroscopy and elements mapping and Raman spectroscopy [17,30], Figures 11, 12 respectively. The average improvement in specific wear rate was 39.47 % for (0.4 wt.% ZnO + 0.2 wt.% graphene) nanolubricant compared with base lubricant due to the anti-wear mechanism of nano (zinc oxide and graphene) particles [12,31].…”

“…These spectra conform to D, G, and 2D bands consecutively, Figure 12. These three prominent bands D, G, and 2D in the range which is a standard characteristic of graphene [30,39,40]. The G-band appear as stretching waves of sp 2 carbon particles in graphene, the D-band correspond with the breathing form of sp 2 carbon particles in bands having flaws (non-graphitic carbon).…”

Effect of few layer graphene additive on the tribological properties of lithium grease

“…[25][26][27][28][29][30] They are used as additives in certain liquid lubricants to improve the antifriction and anti-wear properties. [31][32][33][34][35][36] Inspired by such established functionality of graphene, researchers have attempted to add it to grease. [37][38][39] Their results showed that graphene not only greatly reduces the friction coefficient but also minimises the wear spot diameter.…”