Tribological Properties of Oleylamine-Modified Ultrathin WS2 Nanosheets as the Additive in Polyalpha Olefin Over a Wide Temperature Range

Ultrathin WS2 nanosheets modified by oleylamine (OM) were prepared via a solution-phase method at a relatively high temperature of 300 degrees C. The thermal stability of the as-prepared WS2 nanosheets was evaluated by thermogravimetric analysis. The tribological properties of assynthesized WS2 nanosheets as the additive in polyalpha olefin (PAO6) were evaluated with a four-ball machine and a reciprocating tribometer over a wide temperature range from room temperature to 200 degrees C. The morphology and elemental composition of worn steel surfaces were analyzed with a scanning electron microscope, a three-dimensional optical profiler, an energy dispersive spectrometer and an X-ray photoelectron spectroscope. Results show that OM as the modifier is able to improve the dispersibility of WS2 nanosheets in PAO6 base oil. At a mass fraction of 2.0 % in PAO6 base oil, as-synthesized WS2 nanosheets exhibit excellent antiwear and friction-reducing performance over the selected temperature range. This is because as-synthesized WS2 nanosheets as the additive in PAO6 are able to form adsorbed film with a low shear force and tribochemical reaction film composed of W, Fe and O elements on the worn steel surface.