Researchers Develop a New Tool to Study Disordered Atomic Structures

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Researchers in materials science have created a model capable of accounting for irregularities in how atoms organize themselves at the “grain boundaries”, which refer to the interface where two materials meet.

By explaining the packing of atoms at these interfaces, the tool is capable of being used to enable researchers to determine how grain boundaries impact the properties of metal alloys and various other materials.

We’ve known that these grain boundaries influence material characteristics for many decades. But it’s been extremely difficult to understand what those defects look like at the atomic level and, therefore, to understand how these structural irregularities affect a material’s strength, stiffness, ductility and so on.

Srikanth Patala, Assistant Professor of Materials Science and Engineering, NC State University

“Now we have a tool that lets us see and actually understand what these disordered atomic structures really look like – and that’s a big step toward figuring out exactly what’s going on,” Patala says.

Almost all materials have a specific atomic structure that is somewhat regular. For instance, aluminum has a cubic structure, with atoms forming long chains of cubes, whereas titanium develops into what are fundamentally stacks of hexagons. But when two materials meet, like that in a metal alloy, these tidy, organized structures clash with one another, developing the disordered grain boundary.

Patala’s research group developed a model that detects irregular three-dimensional shapes present within the grain boundary. The model then classifies them and identifies patterns of those irregular shapes.

“Advances in microscopy can help us capture images of how atoms are arranged in a grain boundary, but then we don’t really know what we’re looking at – you can connect the dots any way you want,” Patala says. “Our tool helps to discern patterns of geometric features in an atomic landscape that can appear chaotic.

Now that these patterns can be identified, the next step is for computational researchers – like me – to work with experimental researchers to determine how those patterns affect a material’s properties.

Srikanth Patala, Assistant Professor of Materials Science and Engineering, NC State University

After understanding the effect of the patterns, the very same details can then be used to help in identifying the weaknesses and strengths of particular grain boundary types, speeding up the development of alloys or various other materials.

The Polyhedral Unit Model is the tool that helps in modeling grain boundaries for all types of materials in which the attraction between atoms is monitored solely by the distance between atoms, such as ionic solids and metals, including a few ceramics. However, the approach does not work for materials like carbon as these materials produce so-called directional bonds.

We are currently working on making the Polyhedral Unit Model publicly available through open source software. We plan to have it out by the end of the year, and hopefully sooner.

Srikanth Patala, Assistant Professor of Materials Science and Engineering, NC State University

The paper, “A Three-Dimensional Polyhedral Unit Model for Grain Boundary Structure in fcc Metals,” is featured in the Nature journal npj Computational Materials. Arash Banadaki, a postdoctoral researcher at NC State, is the lead author of the paper. The work received support from the National Science Foundation under CAREER award grant DMR-1554270.

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