Tribological behavior and action mechanism of several fluorinated diones as lubricants of a steel-on-steel system

The friction-reducing and antiwear behaviors of several fluorinated diones as lubricants of a steel-on-steel frictional pair were comparatively evaluated with that of 2,4-pentanedione on an Optimol SRV oscillating friction and wear tester in a ball-on-disc configuration. The action mechanism of the lubricants was explored based on the observation and analysis of the morphologies and elemental distributions of the worn steel surfaces with a scanning electron microscope equipped with an energy dispersive spectrometer attachment and the analysis of the chemical states of the worn surfaces on an X-ray photoelectron spectroscope. The correlation between the chemical structure and the friction-reducing and antiwear behaviors of the fluorinated diones as lubricants was discussed, while the load dependence of the friction-reducing and antiwear behavior of the fluorinated diones as lubricants was examined as well. The results showed that fluorinated alkaryl dione had better antiwear ability than fluorinated alkyl dione. The tribochemical reaction was involved in the sliding of steel-against-steel lubricated by the fluorinated diones, with the generation of a surface-protective layer composed of inorganic fluoride FeF₂, which together with the adsorbed film of the lubricant contributed to improve the friction-reducing and antiwear behaviors of the fluorinated diones as lubricants. However, the corrosiveness of the fluorinated diones was ineligible. In other words, the fluorinated diones of excessive corrosiveness was harmful to the friction-reducing and antiwear ability owing to the increased corrosion to the sliding surfaces of the steel-on-steel frictional pair.