Interaction effects of hexagonal boron nitride, zinc dialkyldithiophosphate and sulfurized isobutylene on tribological performance and stability of lithium grease

Abstract

The development of advanced lubricating materials with tailored functional properties is an important area of research in materials science and nanotechnology. The present study investigates the interactions of nanoparticles and microparticles of hexagonal boron nitride (h-BN), zinc dialkyldithiophosphate (ZDDP) and sulfurized isobutylene (SIB) in lithium grease, focusing on their influence on tribological properties and thermal and mechanical stability. The base grease was formulated from a mineral base oil and lithium 12-hydroxystearate. ZDDP, SIB, and h-BN were used as additives, with h-BN introduced at mass concentrations of 3% and 5%. The dropping point and mechanical stability of greases were determined. Tribological performance was assessed using a four-ball apparatus under a constant load of 300 N and different test durations. The tests were complemented by analysis of wear scar morphology using scanning electron microscopy and chemical composition using energy-dispersive spectroscopy. The most favorable anti-wear performance was obtained for the grease containing ZDDP, SIB, and 5% h-BN, for which the mean wear scar diameter decreased by 27.2–39.8%, the dropping point increased by 9.6%, and mechanical stability improved by 55.2% compared with the base grease. The improved performance is attributed to the formation of a tribochemical layer generated by ZDDP and SIB and the participation of h-BN particles in the formation and stabilization of the lubricating film. The results demonstrate that the synergistic action of conventional additives and nanoparticles and microparticles of h-BN enables the design of lithium greases with enhanced functional performance and improved structural stability.