High-performance polymer friction materials with tunable tribological behavior to fit varied work conditions remain a challenge of widespread interest for a variety of applications. Shape memory polymer exhibits morphing and modulus changing over temperature changing provides a promising material to adjust the friction process. Herein, we investigated the tribological properties of shape memory cyanate ester (SMCE) under different conditions. The SMCE exhibits the tribological behavior of good friction material with stable high coefficient of friction (COF) and a low wear rate. Besides, the COF increases and wear rate decreases with the temperature increasing show the tunable friction property of the SMCE. We propose a new model of wear-compensation through shape recovery to explain the adjustable friction behavior of thermal-responsive polymer from the aspect of shape recovery and energy conversion. This study provides a high-performance friction material and paves the route for the application of shape memory polymer (SMP) in tribology field with tunable property.

The tribological behaviors of Ti-Ni51.5 at% alloy strengthened by finely dispersed Ni₄Ti₃ particles in reciprocating sliding against GCr15, Al₂O₃, and ZrO₂ at room temperature were studied. Interestingly, the coefficient of friction (COF) suffered a sheer drop (from 0.9 to 0.2) when the aged alloy slid against GCr15 at a frequency of 20 Hz under a 20 N load without lubrication. However, severe-mild wear transition disappeared when a solutionized alloy was used. Moreover, the COF stabilized at a relatively high level when Al₂O₃ and ZrO₂ were used as counterparts, although their wear mechanisms showed signs of oxidation. Scanning electron microscopy (SEM) and X-ray element mappings of the wear scars of the counterparts clearly indicate that the formation of well-distributed tribo-layer and material transfer between the ball and disk are pivotal to the severe-to-mild wear transition in the aged Ti-Ni51.5 at% alloy/GCr15 friction pair. The higher microhardness and superelasticity of the aged alloy significantly accelerate the material transfer from GCr15 to the disk, forming a glazed protective tribo-layer containing Fe-rich oxides.

Polyimide composites have been extensively used as motion components under extreme conditions for their thermal stability and special self-lubricating performance. In the present study, Ag-Mo hybrids as lubricant fillers were incorporated into thermosetting polyimide to prepare a new type of tribo-materials (TPI-1) at high temperature. Comprehensive investigations at different temperatures reveal that the newly developed TPI-1 exhibits a better reduction in friction and wear rate below 100 ^°C, but all of them increase significantly when the bulk temperature exceeds 250 ^°C. The wear mechanisms demonstrated that sandwich-like tribofilms with different layers were established at different temperatures, which was further verified by characterization of scanning electron microscope (SEM), Raman spectroscopy, and transmission electron microscope (TEM). Considering the high-performance TPI coupled with Ag-Mo hybrids, we anticipate that further exploration would provide guidance for designing TPI tribo-materials that would be used at high temperatures.

Two-dimensional (2D) lamellar materials have unique molecular structures and mechanical properties, among which molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) with different interaction forces served as reinforcing phase for polytetrafluoroethylene (PTFE) composites in the present study. Thermal stability, tribological and thermomechanical properties of composites were comprehensively investigated. It was demonstrated that g-C₃N₄ improved elastic deformation resistance and thermal degradation characteristics. The addition of g-C₃N₄ significantly enhanced anti-wear performance under different loads and speeds. The results indicated that PTFE composites reinforced by g-C₃N₄ were provided with better properties because the bonding strength of g-C₃N₄ derived from hydrogen bonds (H-bonds) was stronger than that of MoS₂ with van der Waals force. Consequently, g-C₃N₄ exhibited better thermomechanical and tribological properties. The result of this work is expected to provide a new kind of functional filler for enhancing the tribological properties of polymer composites.