The establishment of superlow friction in moist air is very important for the engineering application of hydrogenated diamond-like carbon (H-DLC) films. Nevertheless, water molecules in the surrounding atmosphere always result in the failure of the near-frictionless state. This work aims to explore the effects of water molecules in the environment and the material of the counterparts on the tribological performance of a composite structure prepared by depositing MoS2 on a H-DLC film. The results indicated that the existence of water molecules in the atmosphere is beneficial for achieving stable superlubricity for the material system because it helps retain the in-situ formed MoS2 transfer film on the counterpart. In the presence of water molecules, the wear interface was replaced by a robust and incommensurate MoS2 tribolayer/H-DLC sliding interface, which was responsible for the superlow friction achieved in this work. The results also revealed that the ZrO2 counterpart was capable of retaining the as-formed MoS2 transfer film and establishing long-lasting superlow friction even in dry air. The mechanisms behind this phenomenon are also discussed in this paper.
