Environmentally Adaptive Lubrication of MoS₂-WS₂ Films through Composition-Controlled Crystal Orientation

Significant efforts have been dedicated to improving the tribological performance of thin films in both atmospheric and vacuum environments. However, property differences between individual components in films often lead to microstructural defects and interfacial mismatches, thereby limiting the tribological performance. In this work, MoS₂-WS₂ films are precisely deposited via a multimagnetron cosputtering system. A crystal orientation design approach, implemented through fine-tuning of the WS₂/MoS₂ ratio during deposition, is employed to construct two-dimensional (2D) transition-metal dichalcogenide (TMD) films. The effects of the WS₂/MoS₂ ratio on the morphology, structural characteristics, and tribological properties of the as-prepared films are systematically investigated. It is demonstrated that a narrow optimal WS₂/MoS₂ range is critically required to achieve the observed environmentally adaptive lubrication, which is characterized by a stable friction coefficient below 0.08 and a wear rate under 3.0 × 10^-16 m³·N^-1·m^-1 over 30,000 cycles in both humid air and vacuum environments. This composition-controlled process creates a ternary alloy that can promote the favorable alignment of the (002) basal plane parallel to the substrate. Systematic investigation reveals that excellent environmentally adaptive lubrication in MoS₂-WS₂ films occurs only within a narrow, optimal range of WS₂/MoS₂ ratios. The distinctive lubrication behavior of the composite films stems from their capacity to maintain a pristine layered structure in vacuum while generating mildly oxidized tribo-films in air. This finding establishes a novel surface engineering strategy offering a feasible and generalizable design concept for long-life, adaptive lubrication films.