Tribological behaviors of novel crown‐type phosphate ionic liquids as lubricants for steel/aluminum contacts

Abstract

Purpose

The purpose of this paper is to synthesize a novel kind of crown‐type phosphate ionic liquids with better tribological properties for steel/Al system. The anions of crown‐type phosphate ionic liquids contain no F element, which are non‐corrosive to metal.

Design/methodology/approach

To improve the tribological properties of ionic liquid lubricants for the extremely difficult system of the steel‐against‐aluminum metal couple, novel crown‐type phosphate ionic liquids were prepared. The tribological properties of the crown‐type phosphate ionic liquids were evaluated at different loads and frequencies on an Optical SRV oscillating friction and wear tester. The morphology and chemical compounds of the wear scars were investigated by scanning electron microscope (SEM) and X‐ray photoelectron spectroscopy (XPS).

Findings

Compared with conventional ionic liquids, the novel crown‐type phosphate ionic liquids prepared in the present work exhibit a more excellent anti‐wear ability for steel/Al2024 contact at different loads and frequencies. By the morphological analysis with SEM, less debris was observed in the worn surface lubricated with crown‐type phosphate ionic liquids, though more debris was observed when lubricated with LB106 and LP106. By the XPS analysis, boundary lubrication film composed of aluminum (III) oxide, organometallic compounds, and silicon aluminum phosphate were found in the worn surface. Namely, the tribological behaviors of the crown‐type phosphate ionic liquids could be attributed to their stronger adsorption and tribochemical interactions with the Al alloys.

Research limitations/implications

Because of the higher mean friction coefficients of crown‐type phosphate ionic liquids in the research, researchers are encouraged to modify their structure for better tribological properties.

Practical implications

The crown‐type phosphate ionic liquid exhibited better anti‐wear performance for steel/aluminum contact than the conventional ionic liquids containing F element. This will expand the application of high strength aluminum alloys.

Originality/value

The phosphate ionic liquid is a non‐corrosive liquid and would not cause metal corrosion. Also, the tribological properties of crown‐type phosphate ionic liquid with steel/aluminum contact are better than that of conventional ionic liquids. By the designing of molecular structure, new phosphate ionic liquids will exhibit excellent tribological properties: lower wear volume and lower friction coefficient.

Citation

Jiang, D., Hu, L. and Feng, D. (2013), "Tribological behaviors of novel crown‐type phosphate ionic liquids as lubricants for steel/aluminum contacts", Industrial Lubrication and Tribology, Vol. 65 No. 4, pp. 219-225. https://doi.org/10.1108/00368791311331194