Evaluation of Additives to PFPEs in Boundary Lubrication

A report describes experiments on the wear-reducing performances of six additives to perfluoropolyether (PFPE)-based fluids in the boundary-lubrication regime. The additives were a phosphate, a thiophosphate, a β-diketone, a benzothiazole, an amide/thiol, and a sulfite. Each additive was dissolved, at a concentration of 1 weight percent, in a PFPE based on hexafluoropropene oxide. The resulting formulation was exposed to the boundary-lubrication regime in a four-ball vacuum tribometer at a temperature ≈ 23 °C, an initial Hertzian stress of 3.5 GPa, and a sliding speed of 28.8 m/s. The wear rate for each formulation was determined from the slope of wear volume as a function of sliding distance.