Influence of the Gas Atmosphere on the In-Situ Formation of Low-Friction Molybdenum and Tungsten Diselenides

Abstract This study investigates the influence of the gas atmosphere on friction and wear characteristics of transition metal dichalcogenides synthesized via an in-operando method. MoSe 2 and WSe 2 layers are formed through tribochemical reactions between molybdenum or tungsten coatings and nanosized selenium powder. Their tribological behavior is evaluated under nitrogen and ambient air conditions using a ball-on-disc tribometer within a custom-built inert gas chamber. The results indicate that both MoSe 2 and WSe 2 layers exhibit consistently low friction coefficients (below 0.1) across different atmospheric conditions, with slightly lower friction coefficient observed in air compared to nitrogen. However, the durability of the transition metal dichalcogenide layers is significantly extended under nitrogen, particularly for MoSe 2 , which demonstrates superior durability compared to WSe 2 in nitrogen. This disparity becomes less pronounced under ambient air conditions. The enhanced wear resistance of MoSe 2 in nitrogen may be attributed to easier in-operando formation, as confirmed by transmission electron microscopy analysis, which reveals a thicker and more well-defined layered tribofilm. These findings suggest that in-operando synthesized MoSe 2 and WSe 2 layers serve as effective solid lubricants, offering promising potential for a broader range of solid lubrication applications. Graphical Abstract