Friction properties of WS2/MoS2 multilayer films under vacuum environment

We fabricated WS2/MoS2 nanometer-scale multilayer films (superlattice-structured multilayer films) with dry lubricating characteristics using multitarget RF sputtering. Superlattice structures are obtained by layering two or more materials in a regular periodic structure at a thickness of several atoms or several tens of atoms. Superlattice structured film is expected to exhibit good mechanical properties, such as high hardness and high stiffness, resulting in low friction and long endurance life in comparison to those of the individual single-layer materials. In the previous study, this WS2/MoS2 multilayer film showed significantly improved tribological performance in ambient air in comparison to the single-layer MoS2 or WS2 films. To clarify the tribological properties of this multilayer further, sliding friction experiments have been conducted with WS2/MoS2 films formed on silicon substrates in contact with 440 C stainless steel balls under vacuum at room temperature and at a high temperature of 523 K. The results obtained showed clearly that the friction characteristics and friction endurance of these multilayer films were more excellent under a vacuum of 10−5 Pa than under atmospheric conditions.