Li Ji

Intelligent materials that self-sense and self-adjust are an emerging frontier in sustainable technology. Here we introduce a Cu/C nanocomposite film that acts as a self-adjusting intelligent lubricant. In this film, frictional heating triggers melting and migration of Cu nanoparticles along nanopores to the friction interface, where the Cu catalyzes the in-situ formation of ordered carbon nanostructures. Real-time monitoring of friction coefficient ( μ ), electrical resistance ( R ), and metal release confirms a feedback loop: high friction generates enough heat, melting the metal nanoparticles; the migrating metal then lowers friction by creating low-friction nanostructures, which reduces heat and arrests further migration until friction rises again. This self-limiting feedback enables stable ultra-low friction ( μ ~ 0.04) and an exceptional wear life (>40 km) even in high vacuum. By utilizing friction-derived heat as an intrinsic activation signal, our system establishes a general paradigm for intelligent, self-adjusting materials with applications extending beyond tribology.

Friction is responsible for a substantial fraction of global energy dissipation, limiting the efficiency and longevity of moving machinery. While structural superlubricity, a state of near‐zero friction originating from incommensurability, has been demonstrated at the nanoscale, its extension to engineering‐grade applications remains a significant challenge. This scaling gap is primarily driven by “edge‐pinning” effects, interfacial deformations under high loads that disrupt lattice incommensurability, and the presence of grain boundaries that serve as reactive sites for tribochemical oxidation in humid air. Here, we propose an across‐scale synergistic strategy that bridges macroscale contacts to atomic lattices by patterning random macroscale contacts into controllable amorphous/crystalline meta‐interfaces. By integrating laser‐textured pillars coated with high‐rigidity diamond‐like carbon (DLC) and a reinforced MoS ₂ ‐MXene composite, we establish an interface where the amorphous DLC ensures persistent incommensurability and resists out‐of‐plane deformation. Simultaneously, the high‐strength MXene phase serves as a protective scaffold to maintain MoS ₂ crystal integrity and suppresses oxidation. Our findings demonstrate a robust superlubricity regime with a friction coefficient of 0.008 sustained over 100 000 laps under extreme coupled conditions: millimeter‐scale contact size, 12.7 GPa contact pressure, and 40% relative humidity. This design paradigm extends structural superlubricity from nanoscale model systems to practical technologies for sustainable engineering.

Outstanding oxidation resistance is crucial for widely applying high-entropy carbides (HEC) under high-temperature conditions. However, due to the preferential oxidation, the traditional oxidation resistance strategies depending on generating a dense binary oxide layer present numerous limitations. In this work, we propose a rare earth Y-doping approach to enhance the oxidation resistance of (Ti, Cr, Nb, Al, Y) C HEC and obtain the optimal doping amount of 3.5 at % Y. Leveraging in situ high-temperature XRD, aberration-corrected scanning transmission electron microscopy, and first-principles calculations, we clarify the oxidation products at different oxidation stages and establish the oxidation resistance mechanism. In the initial oxidation stage (below 600 °C), the HEC maintains the original face-centered cubic (FCC) structure and presents no obvious oxidation due to its exceptional thermal stability. As the temperature rises to 600-700 °C of the interim oxidation stage, the FCC lattice collapses to form an amorphous oxide layer, which acts as a great barrier for oxygen diffusion to impede further oxidation. When it comes to the later stages (above 750 °C), as evidenced by the atomic image and the calculated Gibbs formation free energy, the metastable amorphous oxide transforms into a single-phase nanocrystalline high-entropy oxide (HEO) layer. Due to the single homogeneous structure and slow grain growth of the nanocrystalline, the HEO layer can maintain its compactness and provide robust oxidation resistance for the HEC.

Amorphous carbon is recognized as an excellent lubricating material; however, its tribological properties are significantly influenced by humidity. To elucidate the mechanism underlying this humidity dependence and to propose a novel enhancement method, we investigated and compared the tribological properties of hydrogenated amorphous carbon (a-C:H) and amorphous carbon/gold (a-C/Au) composite films. First, the friction coefficient of these carbon films under different humidity conditions was tested using a rotational ball-on-disk tribometer. Subsequently, we analyzed the morphology and structure of the sliding interface employing optical microscopy (OM), Raman spectroscopy, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Finally, first-principle calculations were carried out to calculate the adsorption energy of water molecules on different surfaces. The results indicate that the friction coefficient of a-C:H film and the area of transfer film increase with the increase of humidity. This phenomenon can be attributed to the fact that water molecules enhance the interaction between the a-C:H film and steel counterfaces. Notably, in contrast, the friction coefficient of a-C/Au film demonstrates low sensitivity to humidity due to the formation of an Au transfer film that exhibits weak interaction with water molecules. These findings provide a promising strategy for developing environment-adaptive amorphous carbon films and play an important role in promoting the development of intelligent lubricating film.

Friction as a fundamental physical phenomenon dominates nature and human civilization, among which the achievement of molecular rolling lubrication is desired to bring another breakthrough, like the macroscale design of wheel. Herein, an edge self-curling nanodeformation phenomenon of graphite nanosheets (GNSs) at cryogenic temperature is found, which is then used to promote the formation of graphite nanorollers in friction process towards molecular rolling lubrication. The observation of parallel nanorollers at the friction interface give the experimental evidence for the occurrence of molecular rolling lubrication, and the graphite exhibits abnormal lubrication performance in vacuum with ultra-low friction and wear at macroscale. The molecular rolling lubrication mechanism is elucidated from the electronic interaction perspective. Experiments and theoretical simulations indicate that the driving force of the self-curling is the uneven atomic shrinkage induced stress, and then the shear force promotes the intact nanoroller formation, while the constraint of atomic vibration decreases the dissipation of driving stress and favors the nanoroller formation therein. It will open up a new pathway for controlling friction at microscale and nanostructural manipulation.

Superlubricity, a cutting‐edge concept, has the potential to drive the Fourth Industrial Revolution giving its near‐zero energy consumption, but the challenge is how to achieve it in humid air with chemical activity and at macroscale surfaces with unavoidable defects. Here, a novel principle involving the amorphous/crystalline friction pair based on the cognition that tribochemical interaction sites originate from grain boundary defect locations is proposed to achieve macroscale superlubricity in humid air. The absence of grain boundaries in amorphous diamond‐like carbon (DLC) significantly reduces chemical interaction during the sliding process. This is supported by experimental observations of priority oxidation at the grain boundaries. Results indicate DLC versus MoS₂ friction pair has weakened chemical interaction and less humid insensitivity compared to the MoS₂ versus MoS₂ pair, even increasing the contact area. Theoretical simulation suggests that DLC versus MoS₂ pair eliminates the cross‐linking of friction interlayers induced by the enrichment of H₂O molecules at MoS₂ defects. The robust superlubricity is achieved for the typical friction pair of DLC versus MoS₂ in air (RH≤25%) at macroscopic contact pressure (1.1 GPa) with friction coefficient in 10⁻³ magnitude and extra‐long anti‐wear life (more than 2 × 10⁵ cycles), which is of significance for the industrialization of superlubricity.

Friction interfaces in liquid-embedded composite lubrication coatings commonly comprise a combination of discontinuous fluid films and rough solid contact surfaces, which together ensure easy shearing and a prolonged wear life. However, achieving high efficacy in mixed lubrication poses a challenge due to the conflicting nature of enhanced migration freedom for the liquid lubricant and increased mechanical strength of the solid matrix. Recent efforts have focused on incorporating reinforcing fillers to develop multicomponent, multiphase composites that can address this paradox. Here, we describe a modified attapulgite (APT) with strong biphasic wettability via the oil decompressive osmosis treatment on APT nanocontainers grafted with long nonpolar alkyl chains. This modified APT enables control over the size, distribution, and mobility of lubricant droplets by constructing a Pickering emulsion and toughens the solid-phase matrix through dispersion strengthening. Additionally, the introduction of APT induces the formation of a solid tribofilm during friction, which possesses a higher oil adsorption capacity, as verified through first-principles calculations based on density functional theory (DFT). Consequently, the fluid films can be replenished by the fracture of nanocontainers and adsorption from the bulk phase; further comprehensive and effective regulation of the friction interface leads to low friction and wear.