Tribological Performance of an Automatic Transmission Fluid Additized with a Phosphonium-Based Ionic Liquid Under Electrified Conditions

This study explores the impact of a phosphonium-based IL (trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate, [P6,6,6,14][BEHP])) on the tribological performance of an automatic transmission fluid (ATF) when used as an additive. Tests were carried out under both non-electrified and electrified conditions in a reciprocating ball-on-flat tribometer. After tribological tests, the worn surfaces were subjected to extensive structural and surface analyses to understand the underlying friction and wear mechanisms. The addition of this ionic liquid improved the anti-wear protection of the ATF, although the wear rates were consistently higher than in non-electrified conditions. The tribofilm formed by the IL-containing ATF augmented the electrical resistance at the contact interface, thereby reducing the likelihood of electrification-induced wear. Our results point to the need for further improvements in the chemical formulation of the ionic liquids, like the one used in the present study, to enhance the protection of sliding surfaces against wear in future electric vehicle applications.