Investigate on the dry friction tribological behaviors and mechanism of carbon quantum dot/polyimide composites coating

The comprehensive utilization of biomass resources is to be prepared into functional nanomaterial. This paper prepared carbon quantum dots (CQDs) using citric acid. A new CQDs/polyimide composites (CQDs/PI) coating fabricated on the surface of steel disks, has been widely used in bearing sleeve material or coatings in marine equipment parts and aerospace industries. Tribological properties of coating materials were investigated at different loads and reciprocating speeds of 10 mm/s under dry sliding conditions using a UMT-2 tribometer and compared to those of commercial MoS2 particles in PI composites. Scanning electron microscopy accompanied by energy spectroscopy (SEM/EDS) and 3D laser scanning microscopy were used to characterize the morphologies of the abrasion marks to clarify the tribological mechanisms. Results show that different levels of CQDs can improve composite coatings' anti-wear and friction reduction properties. The tribological mechanisms of CQDs were attributed to the enhancement of the hardness of the polyimide coatings by the CQDs and the formation of a transfer film on the surface of the ceramic balls during the friction process reducing the direct contact at the friction sub-interface.1 •Polyimide coatings including CQDs and MoS2 particles were successfully prepared.•CQDs and MoS2 particles can improve the friction and wear properties of PI.•Tribological behavior of CQDs/PI is better than that of MoS2/PI.•Molybdenum disulfide can cause premature failure of composite materials.•Formation of transfer films resulted in the low friction coefficient and wear rate.