Enhanced superlubricity on a-C films by lubrication with 3-hydroxypropionic acid

In this work, the macroscopic superlubricity with an extremely low coefficient of friction (COF) of 0.004 was achieved on the friction pair of the steel/amorphous carbon (a-C) film with the lubrication of 3-hydroxypropionic acid aqueous solution (3HPA((aq))). The excellent lubrication performance was ascribed to the solid-liquid syn-ergistic lubrication effect between the a-C film and the 3HPA. The triboreaction occurred on the friction pair, resulting in the chemisorption of 3HPA molecules on the a-C film and the steel surface. The hydrated water layer was formed on the chemisorption layer through the hydrogen bonding with water, which contributed to the reduction of COF. Moreover, the feasible graphitization of the a-C film also played an important role on the achievement of superlubricity. This work presented a novel approach for achieving superlubricity on the diamond-like carbon (DLC) and provided support on the development of DLC lubrication in industrial applications.