Tribological evaluation of PAO 100 oil-based lithium greases with chemically functionalized nanoadditives

The lubricating greases employed in this study were formulated with polyalphaolefin (PAO) 100 as the base oil and 12-lithium hydroxystearate as the thickener. The sol-gel method was used to produce the LaF3 nanoadditives. The oleic acid-treated LaF3 (i.e., OA-LaF3) and carboxylic acid-treated MWCNTs (i.e., COOH-MWCNTs) were blended in the formulated grease samples and used as nanoadditives. The detailed microstructural and chemical properties of chemically treated nanoadditives were investigated using HR-TEM, XRD, FTIR and XPS analyses. Using a four-ball tester, the effect of different concentrations of nanoadditives on the tribo-performance of greases was investigated. Tribo-test results revealed the role of nanoadditives in PAO-based grease lubrication performance. COOH-MWCNTs and OA-LaF3 nanoadditives outperformed PAO grease in terms of physicochemical and tribo-performance for steel-steel tribo-pair. The improved tribo-performance is attributed to the formation of tribo-film on the contact interfaces via nanoadditives. The development of tribo-film was confirmed by XPS analysis of worn surfaces.