β-TiNb alloy unlocks load-adaptive macro-superlubricity in WS2 films

Simultaneously achieving macro-superlubricity and self-adaptivity in WS2-based lubrication films remains a significant challenge. Herein, a typical shape memory alloy (SMA), β-TiNb, was incorporated into the WS2 films by co-sputtering deposition method to enhance lubrication properties. The impact of β-TiNb concentrations on the crystallization, structure, mechanical attributes, and lubricating properties of WS2 films was rigorously examined. Impressively, the 1.5 % TiNb additive in WS2 film exhibits an ultra-low coefficient of friction (COF) of 5.6 ± 0.9 × 10−3 prior to sliding for 5.0 × 104 cycles, and a wear rate of 2.27 ± 0.11 × 10−8 mm3 N−1 m−1. Additionally, TiNb1.5-WS2 film demonstrates a tunable COF within the range of 0.0056–0.0104 under loads from 1 to 9 N. The load-adaptive macro-superlubricity of TiNb1.5-WS2 film mainly originates from both of the dispersed β-TiNb SMA nanocrystals within the composite film and the friction-induced well-crystalline WS2 nanocrystals in transfer films. The presence of β-TiNb SMA nanocrystals favor to convert the WS2 plastic deformation into its own elastic deformation during friction. The degeneration of crystallinity in the WS2 transfer film results in the failure of superlubricity. This pioneering strategy for constructing smart factor in lubrication film establishes a foundation for research into intelligent lubrication, thereby laying the groundwork for developing macro-superlubricity materials.