How far does contamination help dry lubrication efficiency?

Space tribology implies lubricating not only in vacuum but also in air and in dry N2 environments. To decipher the influence of environment on dry lubrication, two MoS2-based coatings (MoS2 and MoS2+Ti) with antagonistic behaviours are studied under four different environments (high and moderate vacuum, dry N2, and air 50% HR). By coupling both mechanics and physico-chemistry measurements while conducting experiments on a macroscale level, localization of velocity accommodation is possible. Contrary to general opinion, a dry N2 environment is not neutral. More generally, contaminations and surface complexes help low friction and low wear by delocalizing accommodation from the 3rd body volume to its surface.