Tribological properties of ionic liquids for steel/aluminum, steel/copper and steel/Si3N4 ceramic contacts under boundary lubrication

Purpose The purpose of this paper is to study the influence of alkyl chain length and kind of anions of ionic liquids on the tribological properties with different materials as friction pairs (steel-aluminum, steel-copper and steel-Si3N4 ceramic). Design/methodology/approach Tribological properties were evaluated by an optimol-SRV-IV reciprocation friction tester with a ball-on-block configuration at room temperature and high temperature, respectively. Friction-reducing and anti-wear properties of the ionic liquids for steel/aluminum, steel/copper and steel/ceramic contacts were evaluated on the ball-on-block reciprocating UMT-2MT tribometer. The morphologies of the worn surfaces were observed by a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by X-ray photoelectron spectroscopy. Findings Both the alkyl chain length and kind of anion influence the tribological properties of ionic liquids, especially for the length of alkyl chains. With the increase of alkyl chain length, the load carrying capacity of ionic liquids is improved at both room temperature and high temperature, and the friction reducing and antiwear behaviors are also significantly enhanced. Research limitations/implications The paper presents potentially useful and highly efficient lubricants. Practical implications Owing to their good friction-reducing and wear resistance properties, these ionic liquids are promising candidates for versatile applications. Originality/value This work might provide a promising research direction for design and application of ionic liquids as lubricants.