An investigation of material and tribological properties of Sb2O3/Au-doped MoS2 solid lubricant films under sliding and rolling contact in different environments

• Material does not obey Amontons' law in low humidity due to microstructural changes revealed by TEM.
• Longevity of the coated bearings is directly proportional to the contact stress and the amount of coating material.
• Sliding contact experiments provide no direct correlation to how this material performs in rolling element bearings.

Solid lubricant coatings are commonly employed in mechanical systems operating in environments where oil or grease lubrication is not feasible. In particular, solid lubricant coatings are currently being used in rolling element bearings operating in vacuum environments and/or at high temperatures. Although numerous studies have reported the tribological performance of these materials in sliding contact, few if any studies have reported their performance in rolling contact.Since the functional lifetimes of solid lubricant coatings in rolling element bearings are derived from sliding contact experiments, it is beneficial and important to understand if the actual performance of the coatings in rolling contact bears a relationship to their sliding contact performance. In this work, Sb2O3/Au-doped MoS2 coatings are deposited onto AISI 52100 and M50 specimens by magnetron sputtering. Mechanical properties are studied by scratch tests and nano-indentation techniques; microstructural analysis is undertaken with Raman spectroscopy and transmission electron microscopy. Friction and wear measurements are performed on specimens in both unidirectional and reciprocating sliding, using ball-on-flat tribometers in both vacuum and humid environments. Friction coefficient values as low as ~ 0.04 and as high as ~ 0.14 are measured at different contact stresses, and depend greatly upon the test environment. Functional lifetimes of the coatings are obtained from rolling contact tests performed in a thrust ball bearing tribometer in standard laboratory conditions.