Temperature-Adaptive Ultralubricity of a WS₂/a-C Nanocomposite Coating: Performance from Room Temperature up to 500...

This study reports on the ultralubricity of a high-temperature resilient nanocomposite WS₂/a-C tribocoating. The coefficient of friction of this coating remains at around 0.02 independently of a thermal treatment up to ∼500 °C, as confirmed by high-temperature tribotests. Moreover, the coating annealed at 450 °C keeps exhibiting a similar ultralubricity when cooled back down to room temperature and tested there, implying a tribological self-adaptation over a broad temperature range. High-resolution TEM observations of the tribofilms on the wear track unveil that WS₂ nanoplatelets form dynamically via atomic rearrangement and extend via unfaulting geometrical defects (bound by partial climb dislocations). The (002) basal planes of the WS₂ nanoplatelets, reoriented parallel to the tribo-sliding direction, contribute to a sustainable ultralubricity. The declining triboperformance beyond 500 °C is associated with sulfur loss rather than the transformation of WS₂ into inferior WO₃ via oxidation as suggested earlier. This self-adaptive WS₂/a-C tribocoating holds promise for a constant ultralubrication with excellent thermal performance.