Abstract
Macroscale superlubricity is a prospective strategy in modern tribology to dramatically reduce friction and wear of mechanical equipment; however, it is mainly studied for point-to-surface contact or special friction pairs in experiments. In this study, a robust macroscale superlubricity for point-to-point contact on a steel interface was achieved for the first time by using hydroxylated modified boron nitride nanosheets with proton-type ionic liquids (ILs) as additives in ethylene glycol aqueous (EGaq). The detailed superlubricity process and mechanism were revealed by theoretical calculations and segmented experiments. The results indicate that hydration originating from hydrated ions can significantly reduce the shear stress of EGaq, which plays an essential role in achieving superlubricity. Moreover, the IL induces a tribochemical reaction to form a friction-protective film. Hydroxylated boron nitride nanosheets (HO-BNNs) function as a polishing and self-repairing agent to disperse the contact stress between friction pairs. Superlubricity involves the change in lubrication state from boundary lubrication to mixed lubrication. This finding can remarkably extend the application of superlubricity for point-to-point contact on steel surfaces for engineering applications.
Highlights
Friction and wear of machinery and equipment are inevitable phenomena that cause a significant loss of energy and equipment damage [1]
The full width at half maxima (FWHM) of Hydroxylated boron nitride nanosheets (HO-BNNs) increased from 13.4 to 30.1 cm–1, which occurred because HO-BNNs have a higher in-plane strain level and lower interlaminar interaction leading to the softening of phonons [39, 40]
The optical images of the newly configured Boron nitride (BN) and HO-BNNs aqueous solution and after 12-h standing are inserted in Fig. 1(f), which revealed that HO-BNNS had better dispersion stability because of the increase in hydroxyl groups
Summary
Friction and wear of machinery and equipment are inevitable phenomena that cause a significant loss of energy and equipment damage [1]. The lubrication behavior of water and polyol systems has been investigated in prior studies [28, 29] They reported that the COF between glass and ceramic or ceramic and ceramic can decrease to 0.004, which arises from hydrated ions generated by acid or a mixture of polyol and acid. On the basis of the superlubricity mechanism of aqueous lubrication, which mainly refers to the hydration effect that reduces the shear strength of the lubricant and the running-in process to decrease the contact pressure, and aqueous ethylene glycol (EGaq) was selected as the base lubricant because of its excellent anticorrosion and sustainability. Hydroxylated boron nitride nanosheets (HO-BNNs) with uniform dispersion were used to accelerate the running-in period [38] The discovery of this lubrication system will greatly promote the application of superlubricity to point-to-point contact at the bearing steel interface
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