A research team led by Professors Weitao Zheng and Kan Zhang from the College of Materials Science and Engineering at Jilin University, in collaboration with Professor Changfeng Chen from the University of Nevada, Las Vegas, has published a research article in Acta Materialia entitled “Macroscale Ultradurable Superlubricity on Passivated Transition-Metal Diborides.” This work reports the design of a solid–liquid hybrid system based on transition-metal diborides (TMB₂), a classic class of hard materials, wherein friction-induced catalytic formation of an organic self-assembled passivation layer at the contact interface enables superlubricity and exceptional wear resistance over kilometer-scale sliding distances.
TMB₂ + NPGD hybrid system: achieving kilometer-scale superlubricity and wear resistance
In mechanical systems, friction and wear between moving components are inevitable and often lead to significant energy losses, equipment failure, and even catastrophic mechanical accidents. Superlubricity—defined as a near-zero friction state with coefficients as low as 0.001 or less—offers a promising solution to these problems. Initially observed in incommensurate atomic interfaces, superlubricity has been extended to weak-shear materials such as 2D layered systems (e.g., MoS₂, graphite, DLC) and various liquid lubricants (e.g., oil-based fluids, hydrated ions, polymer brushes).
However, maintaining superlubricity is extremely challenging due to wear-induced alterations of the contact interface. Mechanical delamination and chemical degradation often compromise the superlubricant state. Hard and superhard ceramic materials possess excellent mechanical strength and high wear resistance, making them ideal candidates for long-term lubrication applications. Yet, their inherently high shear strength makes them incompatible with traditional lubrication mechanisms, creating a fundamental trade-off between low friction and wear resistance.
To overcome this bottleneck, the team shifted their focus from conventional weak-shear lubricants to robust ceramic systems. They developed a solid–liquid hybrid lubrication strategy using TMB₂ thin films and unsaturated vegetable oil as the lubrication environment. The combination leverages the high compressive resistance imparted by the high electron density of transition metals and the exceptional deformation resistance from boron’s strong covalent bonding network.
Under frictional loading, catalytic reactions occur between the TMB₂ surface and the unsaturated oil, leading to the in-situ formation of an organic self-assembled passivation layer at the interface. This passivation layer, stabilized by a combination of boundary and elastohydrodynamic lubrication mechanisms, enables macroscale superlubricity with a friction coefficient as low as 0.002 and an ultra-low wear rate of ~10⁻¹⁹ m³/N·m, persisting over kilometer-scale sliding distances.
Bridging hardness and lubricity: a new pathway to robust superlubricity
This study introduces a new strategy for realizing long-lasting macroscale superlubricity by combining surface passivation with robust ceramic materials. By integrating high-strength TMB₂ films with in-situ lubricating reactions, this work unlocks the potential for durable, low-friction systems under demanding operating conditions, with promising implications for industrial-scale applications.
Jingjie Pan, a Ph.D. candidate from Jilin University, is the first author of this paper. Professor Kan Zhang, Professor Mao Wen, and Dr. Chang Liu are the corresponding authors. This work was supported by the National Science Fund for Excellent Young Scholars, the China Postdoctoral Science Foundation, and the Natural Science Foundation of Jilin Province.
Related article:
"Macroscale Ultradurable Superlubricity on Passivated Transition-Metal Diborides",
Acta Materialia, Vol. 262, 119439 (2024).
https://doi.org/10.1016/j.actamat.2023.119439