By Patricia DeLacey
Researchers from the University of Michigan (UMich), in collaboration with beamline scientist Xianghui Xiao, have made significant advancements in understanding the solidification mechanism of an aluminum-nickel alloy. Utilizing a state-of-the-art transmission X-ray microscope at the Full Field X-ray Imaging (FXI) beamline at the National Synchrotron Light Source II, they combined real-time radiographic imaging with high-resolution tomographic imaging. This innovative approach allowed them to study the formation of different microstructures during eutectic solidification.
Xiao hosted this project with sponsorship from the Department of Energy’s Science Graduate Student Research program. The research aims to tune material properties such as strength and flexibility for various applications. For more information on Brookhaven's role, contact Denise Yazak at dyazak@bnl.gov or 631-344-6371.
The study, recently published in Acta Materialia, captured real-time solidification of an aluminum-nickel eutectic alloy (Al-Al3Ni) at nanometer resolution. It revealed that increasing the solidification velocity shifts microstructure from irregular and faceted to regular and rounded. This new understanding is expected to help design materials used in high-temperature components like turbines or reactors.
“I have always been captivated by patterns in nature—like snowflakes, where no two are ever identical,” said Ashwin Shahani, an associate professor of materials science and engineering and chemical engineering at UMich and senior author of the study. “In materials science, the same kind of wonder applies: how do small changes in conditions lead to dramatically different microstructures?”
To explore eutectic microstructure formation, the team designed a new in-situ furnace for directional solidification at the synchrotron beamline. This apparatus allowed precise control over solidification processes, enabling detailed studies of pattern formation.
Combining optical microscopy with synchrotron transmission X-ray microscopy provided both large-scale and nanoscale insights into solidification processes. These techniques were conducted at Brookhaven National Laboratory’s National Synchrotron Light Source II.
The researchers observed interactions between liquid aluminum (Al) and nickel aluminide (Al3Ni) crystals under varying conditions. The growth rate comparison between Al3Ni and Al determined the shape of resulting microstructures. Lower velocities led to irregular growth, while higher velocities resulted in regular growth patterns.
Paul Chao, a doctoral graduate from UMich who spent a year as a resident researcher at the synchrotron beamline, emphasized the importance of these experiments: “Our first-of-its-kind experiments and real-time observations help explain the diversity of patterns produced by eutectics containing stiff intermetallic phases.”
The findings have broad implications for various eutectic systems including metallic, semi-metallic, and organic ones. “Manipulating these patterns is more than just a technical pursuit—it is a way to unravel fundamental principles and apply them meaningfully,” said Shahani.
This research was supported by grants from the National Science Foundation CAREER program (1847855), Air Force Office of Scientific Research United States (FA9550-21-1-0260), and the Department of Energy (DE-SC0012704; 2021 Office of Science Graduate Student Research Award).