Friction and Wear Life of Doped and Undoped MoS2 Dry Film Lubricants

Molybdenum Disulfide (MoS ₂ ) is the leading dry film lubricant (DFL) for space applications due to its superior tribological performance in space conditions. However, MoS ₂ DFLs are sensitive to the operating environment. In this study, we characterized commercially available sputter deposited MoS ₂ -based DFLs, either undoped or with Ni, Ti, or Sb ₂ O ₃  + Au dopants. The DFLs were tribotested at room temperature in dry nitrogen and ambient air conditions, as well as at 0°C in dry nitrogen. Unidirectional sliding tests run until coating failure were carried out to measure friction coefficient and wear life. All four DFLs performed much better in dry nitrogen than air and some performed slightly better at room temperature than at 0°C. Undoped and Ni-doped MoS ₂ exhibited similar friction and wear life in all testing conditions. In terms of friction, the Ti-doped coating performed best in air but worst in nitrogen at either temperature. For wear life, the Sb ₂ O ₃  + Au-doped DFLs exhibited the best performance in all three testing conditions. Finally, results were analyzed using subsequent short duration tests to enable scanning electron microscopy of wear tracks during the run-in process and identify potential mechanisms.