Macroscopic superlubricity achieved by the synergic effect of silver nanoparticles and hexagonal boron nitride nanosheets

Two-dimensional nanomaterials were commonly used as lubrication additives. However, the high demand for the load-bearing capacity limited their industrial applications. This study proposed a new strategy to overcome this limitation by depositing silver (Ag) nanoparticles on hexagonal boron nitride (hBN) nanosheets via dopamine through the reduction reaction of silver ions, and the Ag modified hBN nanosheets (hBN-Ag) were used as additives in aqueous ethylene glycol solution. The results showed that the superlubricity state with a minimum coefficient of friction (COF) of 0.004 at a maximum contact pressure of 1.20 GPa was achieved without the running-in period. The realization of superlubricity was attributed to the synergic effect of Ag nanoparticles and hBN nanosheets, where Ag nanoparticles were attached to the hBN nanosheets by dopamine, enhancing the load-bearing capacity of the hBN nanosheets. Simultaneously, the Ag modified hBN nanosheets were more easily adsorbed and deposited on the friction interface, generating the tribofilm containing hBN-Ag nanosheets through the tribochemical reaction, which reduced the direct contact of the friction pair and provided a low shear strength to generate extremely low friction. The Ag modified hBN nanosheets induced extremely low friction and wear, contributing to the development of lubricants with high load-bearing pressure and low wear rate.