Current-carrying friction and wear behavior of the amorphous carbon film lubricated by ionic liquid

The work aims to investigate the current-carrying friction and wear behaviors of the amorphous carbon (a-C) film in both dry friction and ionic liquid (IL) lubricated conditions. The friction tests were carried by grinding stainless steel, steel coated with IL, a-C film and a-C film coated with IL (a-C-IL) with stainless steel balls under direct current of 0.2 A to compare the friction behaviors of various samples. The wear traces and wear scars of the samples were characterized by scanning electron microscopy, surface 3D profiler and Raman spectrum, and the wear mechanisms of the friction pairs were discussed. Both the a-C film and IL could effectively decrease the current-carrying friction coefficient of the steel-steel friction pair, and reduce the steady friction coefficient values to ~0.15 and ~0.20 from ~0.8, respectively. The composite lubrication of the a-C and IL further decreased the current-carrying friction coefficient (~0.1), but the wear resistance decreased accordingly. The friction coefficient of the steel-steel friction pair is high and the wear is severe. The mechanism is severe abrasive wear with slight adhesion wear. The IL lubrication can obviously reduce the friction coefficient and wear rate of steel-steel friction pair, and the wear mechanism is acceptable abrasive wear. The a-C film can provide good lubrication and wear resistance for the electrical contact material in dry friction. In the current-carrying friction process, the formed transfer film by the a-C wear debris is graphitization and the mechanism of the a-C films is slight abrasive wear. The friction coefficient of the a-C-IL solid-liquid composite lubrication coating is lower than that of a-C film, but the wear resistance is weaker. In friction process, the surface structure of the a-C is broken, and the generated wear debris mixed with the IL can form a solid-liquid composite lubrication coating, which can reduce the friction force, but is easily extruded out of the friction contact zone. Therefore, a steady solid-liquid composite lubrication coating needs to be reconstructed with more wear debris worn off from the a-C film to increase the wear rate. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.