A Study on Microstructure, Friction and Rheology of Four Lithium Greases Formulated with Four Different Base Oils

Four lithium greases were prepared with paraffinic oil, naphthenic oil, poly-alpha-olefin (PAO) and polyol ester (PE), respectively. Their physiochemical, tribological and rheological properties were investigated. It was found that naphthenic oil-based grease exhibited the best colloidal stability. SEM analysis revealed that lithium fibers in PE-based grease showed a relatively flat network compared to the three-dimensional entangled structure of the other three greases. Tribological performance of greases differed from their corresponding base oils, which might be attributed to the different microstructure of lithium soap fibers. Three-dimensional entangled structure was more suitable for friction-reducing than flat network structure. Moreover, noise test revealed that naphthenic oil-based grease was suitable for low-noise bearing lubrication. This study provided fundamental guidance for the selection of base oil which is beneficial for the development of high-performance grease products.