Development of Nanocomposite Grease: Microstructure, Flow, and Tribological Studies

Abstract

Greases are widely used for variety of applications at extreme pressures, temperatures, and speeds with obligation of high bearing and shaft life with low noise. The present study deals with the development of nanocomposite greases and records their flow and frictional characteristics. The commercial grease is modified, by dispersing nanoparticles, to get the nanocomposite greases. Reduced graphene oxide (rGO), calcium carbonate (CaCO3), and alpha-alumina (α-Al2O3) are used as nano-additives. The microstructure of newly developed greases is examined using high-resolution transmission electron microscopy (HRTEM), and the presence of different chemical functional groups is explored using Fourier transform infrared spectroscopy (FTIR). Further, the new greases are investigated for rheological, consistency, and tribological behavior using Visco Tester, penetrometer, and elastohydrodynamic (EHD) rig, respectively. The flow properties reveal the shear-thinning, yielding, and thixotropic nature of lubricating greases. The study shows that there is an optimality in concentration of different nano-additives above which grease's flow and tribological performance degrades. Up to 35%, 27%, and 10% reduction in coefficient of friction is recorded for optimum concentration of rGO nanosheets, CaCO3, and α-Al2O3 nanoparticles, respectively. The difference in the performance of nanocomposite greases can be attributed to the appearance of different friction mechanisms for different nano-additives.