Tribological performance of an ionic liquid as a lubricant for steel/aluminum contacts

The wear and friction behaviour of an ionic liquid 1 -ethyl-3-hexylimidazolium tetrafluoroborate (L206) was investigated as a lubricant for steel/aluminium contacts using an Optimol SRV^® oscillating friction and wear tester. The elemental composition and chemical nature of the antiwear films generated on the aluminium surface were analysed using a scanning electron microscope with a Kevex energy dispersive X-ray analyser attachment (SEM/EDS) and X-ray photoelectron spectroscopy (XPS). A low friction coefficient (∼0.05) was recorded when lubricating with L206; a small amount of water (5 wt.%) in L206 effectively reduced the wear volume and greatly increased the microhardness of the aluminium alloy, but had little effect on the friction coefficient. The SEM/EDS results showed that severe corrosive wear occurred on the aluminium alloy when lubricating with neat L206, which could be avoided by the addition of water in L206. The XPS results indicated that the species AlF₃, Al₂O₃, AlO(OH), and Al(OH)₃ formed during friction; there was no indication of boron on the worn surfaces.