Temperature-dependent Wear Life of MoS2 Dry Film Lubricants

MoS2 dry film lubricants (DFL) are widely used in space applications because of their resilience to extreme environmental conditions but their behavior has been found to be temperature dependent. In this study, tribometer experiments showed that the wear life of MoS2 DFLs decreased as temperature was lowered to cryogenic conditions. The mechanisms underlying this trend were investigated using reactive molecular dynamics simulations. Simulation results suggested that flake-like particles formed by MoS2 DFLs during sliding may be smaller at lower temperatures due to the increase of MoS2 fracture stress. These smaller flakes were more susceptible to oxidation. A higher coefficient of friction was observed for the smaller flakes, which was made worse by oxidation. Analysis of the flake orientation with respect to the shear direction revealed that smaller flakes were less aligned with shear during sliding. This misorientation along with the accelerated oxidation of the smaller flakes implies faster material removal from the MoS2 DFL resulting in decreased wear life at cryogenic temperatures.