Lubrication of Inconel 600 with ionic liquids at high temperature

The friction and wear behavior of Inconel 600 against AISI 52100 steel have been studied in the presence of three ionic liquid (IL) lubricants, two imidazolium derivatives, 1-methyl-3-octylimidazolium tetrafluoroborate (L108) and 1-methyl-3-hexylimidazolium hexafluorophosphate (L-P106), and the quaternary ammonium chloride AMMOENG™101 (AM-101), and compared with a mineral base oil at room temperature. The IL lubricants have been studied at high temperature. While the ammonium derivative has been used at 100 and 200 °C, the higher thermal stability of the imidazolium derivatives allows them to be used up to 300 °C. The results show that the imidazolium derivatives are the best lubricants at all temperatures. A temperature increase from 100 to 200 °C reduces wear rates for all ILs due to a transition form abrasive to adhesive wear and formation of a tribolayer on the Inconel wear track. At 300 °C, the hexafluorophosphate derivative produces tribocorrosion attack on the steel ball and severe wear of Inconel 600 due to decomposition of the IL. The wear mechanisms and surface interactions are discussed in terms of IL-metal surface interactions from SEM, EDX and XPS data.