Ultralow Friction Between Steel Surfaces Achieved by Lubricating with Liquid Crystal After a Running-in Process with Acetylacetone

A suitable running-in process is advantageous for reducing friction. The aim of the present work was to study the influence of the running-in with acetylacetone on tribological performance of 4-Cyano-4’-pentylbiphenyl (5CB) liquid crystal. Friction tests were performed between steel surfaces in a ball-on-disk sliding system. After a running-in period of 240 s, the COF of 5CB was measured to be 0.013, which is about a quarter of the value (0.055) without running-in. The reduced contact pressure, caused in running-in process, does not directly lead to a drop in COF. The generation of tris(acetylacetonato) iron(III) induced by the tribochemical reactions between acetylacetone and steel surfaces, and the unique physical properties of liquid crystal are assumed to be reasons for the ultralow COF. Surface analysis was performed to correlate COF with the topography of wear surfaces. An evenly distributed specific grooved structure observed on wear area of the ball may have a beneficial effect on COF as well. We believe our findings can provide an effective and simple solution to reduce COF of liquid crystal between steel surfaces. A better understanding of the tribological behavior is needed for the development of this tribological system and for the possible future applications.