Researchers at the University of California, Irvine and other international institutions have made a significant breakthrough by achieving atomic-scale observations of grain rotation in polycrystalline materials. These materials, commonly used in electronic devices, aerospace technologies, automotive applications, and solar energy systems, have been studied for their unique properties and structural dynamics. Using advanced microscopy tools at the UC Irvine Materials Research Institute, scientists were able to heat samples of platinum nanocrystalline thin films and observe the mechanism driving grain rotation in unprecedented detail, as outlined in a recent publication in Science.
The study utilized cutting-edge techniques, such as four-dimensional scanning transmission electron microscopy and high-angle annular dark-field STEM, to capture real-time views of the atomic processes involved in grain rotation. To tackle the challenge of interpreting large 4D-STEM datasets, the researchers developed a novel machine learning-based algorithm that could extract essential information from the data. These powerful imaging and analysis tools revealed the crucial role of disconnections at grain boundaries, shedding light on phenomena that have been theorized for decades but were now observable through the use of advanced instruments.
Grain boundaries, which are interfaces between individual crystal grains in polycrystalline materials, are known to contain imperfections that can affect conductivity and efficiency. The researchers found that grain rotation in these materials occurs through the propagation of disconnections along the grain boundaries. This discovery significantly advances the understanding of microstructural evolution in nanocrystalline materials. Furthermore, the study revealed a statistical correlation between grain rotation and grain growth or shrinkage for the first time, highlighting the role of shear-coupled grain boundary migration driven by disconnection motion.
According to lead author Xiaoqing Pan, this research provides quantitative and predictive evidence of the mechanism by which grains rotate in polycrystals on an atomic scale. Understanding how disconnections control grain rotation and grain boundary migration processes can lead to new strategies for optimizing the microstructures of these materials, ultimately enhancing their performance and reliability for various applications. The findings offer new prospects for improving the efficiency and durability of polycrystalline materials in industries such as electronics, aerospace, and automotive sectors.
The research team, comprised of collaborators from various institutions including UC Irvine, the University of Hong Kong, Colombia National University, Karlsruhe Institute of Technology in Germany, the University of Oklahoma, and City University of Hong Kong, was supported by 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. This study not only advances our understanding of grain rotation in polycrystalline materials but also paves the way for further innovations and improvements in the field, benefiting a wide range of industries and applications.