Tribological properties of WS2/MoS2-Ag composite films lubricated with ionic liquids under vacuum conditions

- WS2/MoS2-Ag/ionic liquid composite lubricating systems were established.
- They exhibited long wear durability and lower wear rates under vacuum conditions.
- The ionic liquid with short alkyl group produced boundary lubricating film during the sliding.
- The ionic liquid with long alkyl group preferred to adsorb with the crystal basal plane.

In order to improve the tribological performance of MoS2 based films under vacuum conditions, the lubricating properties of WS2/MoS2-Ag film with different ionic liquids (IL1 and IL2) were evaluated. A good synergy effect was present for the composite lubricating systems. They exhibited longer wear durability, lower wear rates than pure solid film. For both the ionic liquids related, IL2 exhibited better tribological performance than IL1, which were due to their different friction mechanisms. IL1 could interact with friction pairs to form tribo-chemical films during the friction process, which ensured effectively the lubricating properties. By contrast, IL2 with longer alkyl chain groups would prefer to adsorb with the basal crystal plane to improve the tribological performance.