Multi-response Optimization of Tribological Characteristics for Graphene-Gear Oil Nanolubricants Using Grey-Taguchi Methodology Followed by Scrutinization of Lubrication Mechanisms

This study investigates the tribological performance and explores the lubrication mechanisms exhibited by graphene nanoparticles (GnPs) as nano-additives in gear oil (SAE EP-90) for heavy-duty applications. Nanolubricant (NL) samples were prepared with predefined volume fraction of the nanoparticles. Tribological properties of the NL were obtained using a pin-on-disc tribometer. The tribological experiments were carried out by grey-Taguchi orthogonal array. NL showed appreciable dispersion stability and oxidation stability. Prepared NL samples yielded a maximum reduction of 54.12% in pin wear, 18.46% in frictional force and 31.76% in wear scar diameter compared to plain gear oil. An optimized set was obtained from confirmatory test for best tribological efficacy. From surface morphology and roughness study of the worn pin samples, it was inferred that ball bearing and mending mechanisms occur. Further, from film thickness investigation, the lubrication was observed as mixed elastohydrodynamic (EHL) lubrication.