Researchers have made a groundbreaking advancement by capturing atomic-scale observations of grain rotation in polycrystalline materials for the first time. By employing cutting-edge microscopy techniques, the team was able to heat platinum nanocrystalline thin film samples and observe the detailed mechanisms behind grain rotation.
For the first time, scientists at the University of California, Irvine, along with other global institutions, have successfully achieved atomic-scale observations of grain rotation in polycrystalline materials. These materials are integral to various applications such as electronic devices, aerospace technology, automotive industries, and solar energy systems. Their unique properties and structural behavior have been extensively researched over the years.
Utilizing advanced microscopy tools from the UC Irvine Materials Research Institute, the researchers heated platinum nanocrystalline thin film samples to study the mechanisms behind grain rotation with unprecedented clarity. Their findings have been published in a recent paper in Science.
Using sophisticated techniques like four-dimensional scanning transmission electron microscopy and high-angle annular dark-field STEM, the study tackled the challenge of interpreting extensive 4D-STEM datasets by developing a new machine learning algorithm. This innovative tool helped extract essential details from the data, enabling real-time visualization of the atomic interactions, particularly how disconnections at grain boundaries play a critical role.
“For decades, researchers have speculated about the phenomena occurring at crystalline grain boundaries, but now — thanks to the leading-edge instruments available — we’ve moved from hypothesizing to actual observation,” explained Xiaoqing Pan, the lead author and UC Irvine’s Distinguished Professor of materials science and engineering.
Grain boundaries are the interfaces where individual crystal grains meet in polycrystalline materials, often containing defects that can affect conductivity and efficiency. The study revealed that grain rotation is facilitated by the movement of disconnections—defects exhibiting both step and dislocation features—along these grain boundaries. This discovery significantly enhances the understanding of microstructural changes in nanocrystalline materials.
The machine learning-enhanced data analysis also uncovered a statistical relationship between grain rotation and the growth or reduction of grains for the first time. This phenomenon results from shear-coupled migration of grain boundaries prompted by the movement of disconnections, corroborated by STEM observations and atomistic simulations. This pivotal finding not only clarifies the core mechanisms of grain rotation but also provides insights into the dynamics of nanocrystalline materials.
“Our findings deliver clear, quantitative, and predictive evidence of how grains rotate in polycrystals at the atomic level,” Pan stated. He is also a professor in UC Irvine’s Department of Physics & Astronomy, holds a Henry Samueli Endowed Chair in Engineering, and directs the UC Irvine Center for Complex and Active Materials. “Understanding the role of disconnections in grain rotation and boundary migration may unlock strategies to optimize the microstructures of these materials, which is crucial for progress in various industries, including electronics, aerospace, and automotive sectors.”
This research presents new opportunities for enhancing the performance and durability of polycrystalline materials, potentially improving their efficiency across diverse applications.
Collaborators on this project include Yutong Bi, Ying Han, Yuan Tian, and Mingjie Xu from UC Irvine; Xiaoguo Gong and David Srolovitz from the University of Hong Kong; Leonardo Velasco Estrada from Colombia National University; Evgeniy Boltynjuk from Germany’s Karlsruhe Institute of Technology; Horst Hahn from the University of Oklahoma; and Caihao Qiu and Jian Han from City University of Hong Kong. The study received funding from the National Science Foundation’s Materials Research Science and Engineering Centers program, the U.S. Army Research Office, and the Hong Kong Research Grants Council.
