Tribological behavior and lubrication mechanism of polyalphaolefin with added Cu-Ni bimetallic nanoparticles on a TiN coating

[Display omitted] •Cu-Ni NPs can tribologically induced the degradation of PAO6 to form a carbon-based tribofilm.•Macroscale low friciton can achieved by lubricating a steel/TiN sliding interface with PAO6 containing 0.1 wt% Cu-Ni NPs.•The addition of Cu-Ni NPs to PAO6 effectively enhances the lubricating performance of PAO6 in the steel/TiN system. In this study, the tribological behavior of TiN coatings lubricated with a polyalphaolefin (PAO)-based oil containing Cu-Ni bimetallic nanoparticles was investigated under a maximum contact pressure of 0.9 GPa in reciprocating ball-on-disk mode. The addition of 0.1 wt% Cu-Ni nanoparticles to PAO6 reduced the friction coefficient to 0.018 and also decreased the wear rate of TiN coatings to 4.23 × 10-7 mm3/Nm. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed the deposition of Cu-Ni nanoparticles and carbon-based tribofilms on the contact region of the tribopairs. These originated from the tribo-induced degradation of the polyalphaolefin molecule in PAO6 + 0.1 %Cu-Ni nanoparticles, which helped decrease the COF and wear. Moreover, a comparative analysis suggested that the presence of nickel in the Cu-Ni nanoparticles had a catalytic effect during sliding. They facilitated the in situ formation of carbon-based film due to the degradation of polyalphaolefins under the combined effects of frictional heat and contact stress, demonstrating a self-repair capability.