Hyperthermal atomic oxygen interaction with MoS2 lubricants and relevance to space environmental effects in low earth orbit – effects on friction coefficient and wear-life

Abstract

Wear-life of the MoS 2 film was evaluated by in situ tribological testing under 5 eV atomic oxygen exposures which simulated atomic oxygen environment in low Earth orbit. A combination of a laser-detonation atomic oxygen source and a conventional pinon-disk friction tester was used to perform tribological tests. It was confirmed that the friction coefficient was not affected by atomic oxygen exposure when atomic oxygen fluence was low; however, the friction coefficient increased with increasing atomic oxygen fluence and it reached as high as 0.05 at the atomic oxygen fluence of 3.4 · 10 16 atoms/cm 2 /cycle (nine times larger than the normal value). Effect of atomic oxygen on the wear-life of the film has much more drastic. With atomic oxygen fluence of 1.7 · 10 16 atoms/ cm 2 /cycle, wear-life of the film was reduced less than one-tenth of that during ex situ testing result of the same film. It was also observed that the wear-life of the film was inversely proportional to the atomic oxygen fluence between sliding passes.

Space environmental effects on MoS2 and diamond-like carbon lubricating films: Atomic oxygen-induced erosion and its effect on tribological properties

“…This was confirmed by AES analysis of the wear track (Fig. 5) [17]. Relationship between atomic oxygen flux and wear-life is represented in Fig.…”

Comparison of Macro and Microtribological Property of Molybdenum Disulfide Film Exposed to LEO Space Environment

“…Formation of molybdenum oxide and carboxyl group at the sample surface caused increase in surface oxygen. The overall changes in surface composition observed in this study basically agree with that reported previously [12].…”

Carbon-based solid-liquid lubricating coatings for space applications-A review

“…High-energy particulate radiation is predominantly trapped radiation like EL (up to several MeV) and Pr (up to several hundred MeV). The primary effects of these particulate radiations on materials are ionization, phonon excitations and atomic displacement, resulting in crosslinking, chain scission or polymerization [29]. The major atmospheric constituent in LEO is atomic oxygen (AO) from photo-induced dissociation of O 2 in the upper atmosphere.…”