Sun Taotao, Gao Enlai, Jia Xiangzheng, Bian Jinbo, Wang Zhou, Ma Ming, Zheng Quanshui, Xu Zhiping
Center for Nano and Micro Mechanics, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing, China.
Railway Engineering Research Institute, China Academy of Railway Sciences Corporation Limited, Beijing, China.
Nat Commun. 2024 Jul 15;15(1):5952. doi: 10.1038/s41467-024-49914-6.
Structural superlubricity (SSL) is a state of contact with no wear and ultralow friction. SSL has been characterized at contact with van der Waals (vdW) layered materials, while its stability under extreme loading conditions has not been assessed. By designing both self-mated and non-self-mated vdW contacts with materials chosen for their high strengths, we report outstanding robustness of SSL under very high pressures in experiments. The incommensurate self-mated vdW contact between graphite interfaces can maintain the state of SSL under a pressure no lower than 9.45 GPa, and the non-self-mated vdW contact between a tungsten tip and graphite substrate remains stable up to 3.74 GPa. Beyond this critical pressure, wear is activated, signaling the breakdown of vdW contacts and SSL. This unexpectedly strong pressure-resistance and wear-free feature of SSL breaks down the picture of progressive wear. Atomistic simulations show that lattice destruction at the vdW contact by pressure-assisted bonding triggers wear through shear-induced tearing of the single-atomic layers. The correlation between the breakdown pressure and material properties shows that the bulk modulus and the first ionization energy are the most relevant factors, indicating the combined structural and electronic effects. Impressively, the breakdown pressures defined by the SSL interface could even exceed the strength of materials in contact, demonstrating the robustness of SSL. These findings offer a fundamental understanding of wear at the vdW contacts and guide the design of SSL-enabled applications.
结构超润滑（SSL）是一种无磨损且摩擦超低的接触状态。SSL已在与范德华（vdW）层状材料的接触中得到表征，但其在极端负载条件下的稳定性尚未得到评估。通过设计由高强度材料构成的自匹配和非自匹配vdW接触，我们在实验中报告了SSL在非常高的压力下具有出色的稳健性。石墨界面之间的非 commensurate 自匹配vdW接触在不低于9.45 GPa的压力下可保持SSL状态，而钨尖与石墨基底之间的非自匹配vdW接触在高达3.74 GPa时仍保持稳定。超过此临界压力，磨损被激活，表明vdW接触和SSL的破坏。SSL这种出乎意料的强大耐压性和无磨损特性打破了渐进磨损的图景。原子模拟表明，压力辅助键合在vdW接触处导致的晶格破坏通过单原子层的剪切诱导撕裂引发磨损。破坏压力与材料性能之间的相关性表明，体积模量和第一电离能是最相关的因素，表明了结构和电子的综合效应。令人印象深刻的是，由SSL界面定义的破坏压力甚至可能超过接触材料的强度，证明了SSL的稳健性。这些发现为vdW接触处的磨损提供了基本理解，并指导了基于SSL的应用设计。
