The tribological properties of lubricating oil containing micro/nano-scale WS₂ (90 nm, 2 µm) and ionic liquid [C₇H₁₁F₃N₂O₃S] are evaluated using a four-ball friction tester. Results show that the addition of micro/nano-scale WS₂ can improve the tribological properties of the base oil; moreover, adding the ionic liquid as a solvent may lead to a better mixing of the micro/nano-scale WS₂ and base oil and promote the dispersion of WS₂ in the sample oil. The base oil with 90 nm nano-WS₂ and ionic liquid presents the best anti-friction and anti-wear properties at 1 wt.% content. The surface analysis of wear scars reveals that ploughing is the main cause of wear in the three bottom balls. Furthermore, the wear furrows of nano-WS₂ as lubricating additive are uniform and symmetrical and can homogenously appear on the friction area. This work proves that the micro/nano-scale WS₂ plays an important role in improving the performance of tribological properties of lubricating oil.

In the present work, the relationship curve of the coefficient of friction (COF) with varying loads of different morphology WS₂ lubricating additives in the friction process at various sliding speeds was studied. On this basis, wear marks and elements on the wear surfaces after friction were analyzed, and then the anti-wear and mechanism effects of WS₂ of different forms in the lubrication process were discussed. Meanwhile, the Stribeck curve was used to study the lubrication state of the lubricating oil in the friction process. It was revealed that the COF of lubricating oil containing lamellar WS₂ decreased by 29.35% at optimum condition and the minimum COF was concentrated at around 100 N. The COF of lubricating oil containing spherical WS₂ decreased by 30.24% and the minimum coefficient was concentrated at 120 N. The extreme pressure property of spherical WS₂ was better than that of lamellar WS₂, and the wear resistance of spherical WS₂ was more stable when the load was over 80 N. The different morphology of WS₂ additives can play anti-wear and anti-friction roles within a wide range of sliding speeds.

The microscale/nanoscale lamellar-structure WS₂ particles with sizes of 2 µm and 500 nm were synthesized by solid-phase reaction method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The synergies between microscale/nanoscale WS₂ particles and ZDDP as lubricating oil additives was evaluated by means of UMT-2 tribometer at room temperature. The wear scars were examined with SEM and electron-probe micro-analyzer (EPMA). The results show that the anti-wear properties were improved and the friction coefficient was greatly decreased with the simultaneous addition of WS₂ particles and ZDDP, and the largest reduction of friction coefficient was 47.2% compared with that in base oil. Moreover, the presence of ZDDP additive in the lubricant further enhances the friction-reduction and anti-wear effect of microscale/nanoscale WS₂. This confirms that there is a synergistic effect between WS₂ particles and ZDDP.