Three ecofriendly protic ionic liquids (PILs), 2-hydroxyethylammonium 2-ethylhexanoate, 2-hydroxymethylammonium 2-ethylhexanoate, and 2-hydroxydimethylammonium 2-ethylhexanoate, with different extents of hydrogen bonding and ionicities, were synthesized and examined as neat lubricants and lubricant additives to a mineral oil (MO) under steel/steel and steel/aluminum contacts. The stability of each PIL-MO blend was observed and correlated to their individual structural features; their physicochemical and tribological properties were investigated and compared to a commercial mineral oil-based lubricant. The addition of any PIL to the mineral oil improved lubricity in steel/steel contact. In aluminum/steel contact, the PILs were studied as neat lubricants and additives showing different effects. The PIL with lower extent of hydrogen bonding but higher ionicity presented poor friction and led to higher wear as neat lubricant. However, as additive, this PIL prevented the intense tribo-corrosion reactions and generated a stable lubrication film that reduced friction; and was capable to form a protective layer on aluminum surface to avoid severe wear.

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Laser micro-texturing treatment has been proved as an efficient way to improve tribological properties of metal alloys. Meanwhile, ionic liquids also show great potential as novel lubricant additives to increase the durability of contacting components and decrease the energy loss during tribological process. This study investigated the influence of the laser micro texturing surfaces on the tribological performance of titanium alloy Ti6Al4V under different lubricant conditions. In this research, two sets of dimple-textured surfaces created by different laser parameters, energy density and area density, were fabricated on Ti6Al4V. Polyalphaolefin (PAO) 40 and 1 wt.% 2-hydroxyethylammonium 2-ethylhexanoate (Eet) used as additive to PAO 40 were designed as lubricants during the sliding tests. First, the geometrical properties of laser micro-textures on the surfaces were characterized. The wetting behaviors of different lubricants on textured surfaces were then examined based on contact angle measurement. All the frictional tests were carried out on the ball-on-flat reciprocating tribometer under the same working conditions. Lastly, the surface morphology of the wear tracks on Ti6Al4V and tungsten carbide balls and their wear mechanisms were evaluated by using the optical microscope, scanning electron microscope, and energy-dispersive X-ray spectroscopy. The results exhibit the laser micro-textures have a positive effect on improving the tribological performance of Ti6Al4V. Meanwhile, the use of Eet as the lubricant additive to PAO 40 can facilitate the formation of the tribo-layer, which enhances the tribological behavior of laser micro-texturing Ti6Al4V surfaces.

Although aluminum alloys are widely used in the automotive and aerospace industries due to their excellent strength-to-weight ratio and good corrosion resistance, the poor tribological performance and low compatibility of these materials with lubricant anti-wear and anti-friction additives in conventional mineral oils are major limitations. In addition, environmental awareness has increased the need for more environmentally friendly lubricants. Ionic Liquids (ILs) have exhibited significant potential as lubricants and lubricant additives. One of the more interesting properties of ILs is that they can form physically-adsorbed or chemically-reacted layers that reduce friction and wear of the surfaces in contact. Among ILs, Protic Ionic Liquids (PILs) have received more attention recently because of their simple and economic synthesis route. Furthermore, the anions and cations of PILs can be selected to be considered environmentally benign. In this article, the tribological behavior of a family of six PILs are studied as additives to a biodegradable oil (BO), under aluminum-steel contact. Al2024 disks slid against AISI52100 steel balls under a normal load of 3 N and a frequency of 5 Hz at room temperature and using a ball-on-flat reciprocating tribometer. PILs used in this study, were synthesized using two strong acids, with short and long hydrocarbon chains, and three weak bases with different propensities to hydrogen bonds. Results show that, although adding just 1 wt.% of any PIL to BO reduced friction and wear, the alkyl chain length influenced the lubricating ability of these ordered fluids. Wear mechanisms and surface interaction are discussed on the basis of 3D profilometry, SEM-EDX and RAMAN spectroscopy.