Recently, the research team led by Professors Zheng Weitao and Zhang Kan from the College of Materials Science and Engineering, Jilin University published an article titled Macroscale Ultradurable Superlubricity on Passivated Transition-Metal Diborides in Acta Materialia. Taking classic hard coating materials—transition-metal diboride thin films—as the research object, this work constructs a solid-liquid composite lubricating system. Tribocatalysis at the contact interface induces the in-situ formation of a self-assembled organic passivation layer, achieving kilometer-scale superlubricity and extraordinary wear resistance.
Caption: Kilometer-level superlubricity and wear resistance realized by TMB₂ coupled with NPGD.
Friction and wear are inevitable between moving components in all mechanical systems. Severe frictional loss leads to massive energy waste, economic losses, and even catastrophic mechanical failures. As a vital solution to mitigate friction and wear, superlubricity technology has attracted extensive research attention. Theoretically, superlubricity refers to a lubrication regime where friction force between two contacting surfaces approaches zero. In practical testing, a lubrication state with a friction coefficient as low as 0.001 or below is generally defined as superlubricity. Superlubricity was first discovered on incommensurate atomic contact planes and later extended to materials with weak shear characteristics, including two-dimensional layered materials (molybdenum disulfide, graphite, diamond-like carbon, etc.) and liquid lubricants (oil-based lubrication, hydrated ionic lubrication, polymer molecular brushes, and so forth).
Superlubricity imposes stringent requirements on contact surfaces; any interfacial variation caused by material abrasion will break the superlubric state. Therefore, minimizing solid material loss induced by mechanical delamination and chemical consumption is essential to establish and sustain superlubricity. Superhard/hard ceramic materials possess outstanding mechanical properties and fully satisfy the high wear-resistance demands of lubricating systems. Nevertheless, their intrinsically high shear strength endows them with negligible inherent lubricating capacity, restricting their tribological applications. Integrating lubricating performance with high hardness and breaking the trade-off between low friction (weak shear) and high wear resistance (high mechanical strength) constitutes the core challenge for realizing stable long-duration, long-distance superlubricity.
To address this bottleneck, the research team shifted focus from conventional weakly-shearable lubricants to superhard, wear-resistant ceramics and developed a solid-liquid composite lubricating system matched to practical service environments. Transition-metal diborides (TMB₂) serve as classic superhard thin films with exceptional mechanical
strength: transition metals deliver high electron density and superior compressive resistance, while boron forms robust covalent networks that resist plastic deformation—these combined merits guarantee outstanding wear resistance. To further achieve superlubricity, unsaturated vegetable oil was introduced into the service environment of TMB₂ films. Driven by frictional load, tribocatalytic reactions occur between diborides and unsaturated vegetable oil, stimulating the growth of a self-assembled organic passivation film at contact interfaces. Combined with boundary lubrication and elastohydrodynamic lubrication effects, kilometer-scale superlubricity (friction coefficient down to 0.002) and exceptional wear resistance (wear rate as low as 10⁻¹⁹ m³/N·m) are successfully realized. This study expands the superlubricity library with a brand-new TMB₂ material system and achieves long-lasting macroscale superlubricity leveraging its high strength and hardness. The proposed strategy exhibits promising prospects for demanding large-scale and even industrial operating conditions.
Pan Jingjie, a doctoral candidate from the College of Materials Science and Engineering, Jilin University, is the first author of this paper. Corresponding authors are Professor Zhang Kan, Professor Wen Mao (College of Materials Science and Engineering, Jilin University), and Dr. Liu Chang, postdoctoral researcher at the University of Nevada, Las Vegas, USA. Professors Zheng Weitao and Chen Changfeng (University of Nevada, Las Vegas) provided substantial support for this research. This work was funded by the National Science Fund for Excellent Young Scholars of China, the China Postdoctoral Science Foundation, and the Natural Science Foundation of Jilin Province.
