Tribological and Vibration Studies on Newly Developed Nanocomposite Greases Under Boundary Lubrication Regime

Greases are widely used in extreme conditions of load, speed, and temperature, altogether with the improvement in the service life of the machinery by reducing the noise and vibration. The present study deals with the development of nanocomposite greases and their tribodynamic evaluation under boundary lubrication (BL), antiwear, extreme pressure (EP), and vibration behavior of nonconformal metallic contacts. The recording of the vibration signals constitutes the indirect approach to evaluate the lubricity of the tribological contacts. The different nano-additives (reduced graphene oxide (rGO) nano-sheets, CaCO3, and alpha-Al2O3 nanoparticles) are dispersed in commercial lithium grease to formulate nanocomposite greases. The microstructural studies of greases are performed on high-resolution transmission electron microscopy (HRTEM). The BL behavior is studied using four ball tester. Further, the functional groups of the greases and the chemistry of the worn surfaces are evaluated through Raman spectroscopy (RS). To explore the involvement of wear mechanism(s), the morphology of worn surfaces is evaluated using scanning electron microscopy (SEM). The results showed that doping of 0.4% rGO and 5% CaCO3 in bare lithium grease can significantly improve the antiwear, EP properties, and vibration behavior, compared to alpha-Al2O3 dispersed composite grease.