Zebra stripes of material interfaces
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A grain boundary (GB) patterned state composed of two alternating, distinct GB phases shown in red and blue. The phases are separated by periodically arranged dislocation line defects called GB phase junctions—indicated by yellow circles. At finite temperature, the sizes of the GB islands can fluctuate but the patterned state remains stable due to the elastic interactions between the GB phase junctions, therefore, the same color islands never coalesce. View the full 2 microsecond-long simulation.
Pattern formation and self-assembly are fundamental to many natural and technological phenomena spanning various fields of science—from physics and biology to chemistry and materials science. These processes involve the emergence of organized periodic structures in systems due to interactions at different scales. Oftentimes, very simple interactions can lead to complex and beautiful patterns, whether in materials, microscopic structures, or living organisms. Examples of these ordered systems include quantum dot self-assembly, 2D patterned surface states, helium bubble super-lattice formation within the crystal lattice of materials for magnetic fusion energy, and the stripes on zebras or the spots on leopards.
In a recent study, published in Physical Review Letters, LLNL scientist Timofey Frolov and Ian Winter from Sandia National Laboratory investigate how different structures of material interfaces can self-assemble into stable periodic patterned states with special properties due to simple elastic interactions. The grain boundaries (GB) described in this work are internal interfaces inside a material that exhibit different phases, separated by dislocation line defects called grain boundary phase junctions. The study shows that the long-range elastic interactions between these junctions can have a profound effect on phase transformations and the evolution of grain boundary microstructures.
Frolov’s previous work has shown how these phases arise in important high-temperature materials like the refractory metal tungsten. This new work, funded through Frolov’s Early Career Research Project from Department of Energy’s Office of Fusion Energy Sciences, shows that these phases can self-assemble into stable patterned states. To better understand these states, the researchers created a theoretical model to demonstrate the conditions under which patterned grain boundaries exist. Subsequently, using their theoretical model and LLNL’s Grand Challenge computing resources, they performed atomistic simulations to demonstrate the high-temperature stability of the patterned state in a model copper grain boundary system.
“Our understanding of the dynamic evolution and stability of these GB defect microstructures is only beginning to emerge, and the proposed theoretical frameworks provide guidance on how self-assembly and complex stable microstructures of grain boundaries with special properties can be predicted or tailored,” said Frolov. “For example, the GB patterns studied in this letter effectively introduce a stable, uniformly spaced network of point defect sinks and sources on the GB plane which could have beneficial properties for radiation damage tolerance.”
[I. S. Winter and T. Frolov, Phase Pattern Formation in Grain Boundaries, Physical Review Letters (2024), doi: 10.1103/PhysRevLett.132.186204.]
–Physical and Life Sciences Communications Team
