New research led by the University of Pittsburgh unveiled the atomic-scale friction of a single tungsten asperity, or rough edge, in real time, showing atomic motion for the first time using electron microscopy.

For machines with mechanical elements, friction is an unavoidable enemy. It is a major source of service failure and can reduce the lifespan of any machinery, from bicycles and cars to airplanes and assembly lines. Friction turns part of the energy going into a machine into heat and the heat requires more energy than the machine’s working load.

The work, completed by two labs in the Swanson School of Engineering, was recently published in the journal Nature Nanotechnology.

Guofeng Wang, CNG Faculty Fellow and professor of mechanical engineering and materials science, whose lab collaborated on this work said, “Until now, no one has been able to actually see the atomically resolved friction process with a clear-cut interface, so the relationship between the friction mechanisms and the interface hasn’t been fully understood. In this study, we were able to actually see the sliding pathway of interface atoms and the dynamic strain and stress evolution on the interface that has only previously been shown by simulations.”

The tungsten substrates with smooth and defective surfaces. (a) The smooth surface. (b) The defected surface with steps. The scale bar is 2 nm. Image Credit: University of Pittsburgh. Click image for the largest view. There are more images in the research paper, however, they are behind a paywall.

Wang’s group collaborated with now-retired John Swanson Endowed Professor Scott X. Mao’s research group in the Swanson School to provide the first visualization of friction at the atomic scale. Using a high-resolution transmission electron microscope, Mao’s group was able to actually view the movement of atoms across the surface when two surfaces made contact and moved. Wang’s group was then able to use their computer simulations to verify what the microscopic visualizations showed and understand more about the forces at play.

Though this study focused on tungsten atoms because of their high resistance to the microscope’s heat, the method can be applied to any material to understand friction and wear.

“What we found is that no matter how smooth and clean the surface is, friction still occurs at the atomic level. It’s completely unavoidable,” said Wang. “However, this knowledge can lead to better lubricants and materials to minimize friction and wear as much as possible, extending the life of mechanical systems.”

The paper, “Atomic-scale friction between single-asperity contacts unveiled through in situ transmission electron microscopy,” was led by recently graduated PhD student Xiang Wang and post-doctoral researcher Zhenyu Liu. It was co-authored by Yang He, Susheng Tan, Guofeng Wang and Scott X. Mao. This work was supported by the National Science Foundation (NSF CMMI 1824816).


Your humble writer has too much experience with friction, lubricants and the heat that friction makes and the excess energy required when friction exceeds engineered allowances. This research and the results that it will make possible in the coming years should save quite a lot of energy due to the reduced power requirements as well as the replacement parts, the energy to make and transport them, as well as cutting downtime and repair costs.

The knowledge might also improve lubricants and their application such that machines are longer lived and lower energy consumption. There seems top be no downside or impediment to this work, it is welcome research indeed!


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