Abstract
Room temperature ionic liquids (RTILs) have several properties that make them interesting candidates as base fluids for extreme conditions. However, a lack of compatibility with tribo-improving additives combined with an often overly aggressive nature is limiting their use as base fluids. To overcome these drawbacks, hydrocarbon-imitating RTIL base fluids have recently been developed. In this study, the effects of several common additives in the novel RTIL (P-SiSO) were examined by laboratory tribotesting. A reciprocating steel-steel ball-on-flat setup in an air atmosphere was used, where the lubricant performance was evaluated over a range of loads and temperatures. Surface analyses after testing were carried out using optical profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Neat P-SiSO displayed high performance in the tribotests. At an elevated load and temperature, a shift in lubrication mode was observed with an accompanying increase in friction and wear. Surface analysis revealed a boundary film rich in Si and O in the primary lubrication mode, while P was detected after a shift to the secondary lubrication mode. An amine additive was effective in reducing wear and friction under harsh conditions. The amine was determined to increase formation of the protective Si–O film, presumably by enhancing the anion activity.
Highlights
Lubricants enable the efficient and reliable operation of moving mechanical assemblies by reducing friction and wear
The GL-5 gear oil is seen to follow the typical behavior expected for traditional lubricants containing extreme pressure (EP) and AW additives
Based on the work reported in this paper, the following conclusions can be drawn
Summary
Lubricants enable the efficient and reliable operation of moving mechanical assemblies by reducing friction and wear. To avoid excessive wear in these regimes, wear and friction reducing additives are required. The past century has seen the development of an extensive set of lubricant additives that can significantly improve the tribological performance of hydrocarbon oils in combination with steel surfaces [1,2]. The additive performance is well known to be dependent on the entire tribosystem, meaning that the effect of base fluids, surface materials, and operating conditions all must be considered [3]. Our understanding of tribo-improving additives is still evolving, and significant clues on the mechanisms of these are still being uncovered [4,5]
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