Investigation of ionic liquids with and without graphene as lubricant additive for metal/metal and metal/PEEK contacts over a wide temperature range

The aim of the work is to improve tribological properties of an ATF oil by means of additives. Two ionic liquids (IL) and one IL with 0.1 wt.% graphene were chosen as candidates. The ILs were selected because of their promising surface interactions and proven synergy with anti-wear additives. However, little is known about the addition of ILs to fully formulated lubricants, especially in the low temperature range. Therefore, static and sliding friction as well as wear were measured in an application-relevant temperature range of -30 to 100°C using a rotating ball-on-3-plate test. The best additive for ATF oil for material pairing 100Cr6/polyether ether ketone was 5 wt.% [P66614][TMPP][G] (halogen-free) and for 100Cr6/sintered iron 3 wt.% [P66614][BTA]. The additives lead to a wear reduction of more than 50%. Furthermore, it could be observed that the selected ILs have different effects on the friction behaviour at the temperatures investigated.