Episode 7: Nanotomography enables insight into the microstructure of a material

In this podcast episode, MRS Bulletin’s Laura Leay interviews Ashwin Shahini and Alan Taub from the University of Michigan about their group’s simulations and experimental work detailing the formation mechanisms, morphologies, and microstructures of an in situ Al/TiC metal matrix nanocomposites processed via salt flux reaction. Using these insights, the microstructure of a material can be tuned in order to optimize the materials properties. While the three-dimensional imaging is critical to gaining insight into the structure, computational models can facilitate this optimization. This work was published in a recent issue of Acta Materialia. 

Transcript

LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on hot topics in materials research. My name is Laura Leay. Increasingly, we see research moving forwards when diverse expertise comes together. One such collaboration has achieved the first multiscale analysis of a hierarchical material where characterization has been achieved down to atomic level, providing unique insight into the mechanism of nanoparticle formation and redistribution. Synchrotron-based x-ray nanotomography was instrumental in gaining this new insight where an in situ aluminum titanium carbide metal matrix nanocomposite processed via salt flux reaction was characterized. The analysis was complemented by scanning and transmission electron microscopy, with simulations providing a vital understanding of the mechanism of formation.

ASHWIN SHAHINI: I did not realize how complex these microstructures can be. I think it has opened a realm of opportunities to explore further the mechanisms of microstructure selection and control.

LAURA LEAY: That was Professor Ashwin Shahini from the University of Michigan. A surprising variety of titanium aluminide morphologies were seen, including an orthogonal plate structure. The simulations showed that this growth form originates from the intermetallic nucleating epitaxially on a titanium carbide particle as long as this particle is larger than a critical size at a given undercooling. Titanium carbide particles that are too small to nucleate titanium aluminide also influence the growth of the intermetallic, by splitting the intermetallic plates during solidification. While the simulations were carried out by Professor Katsuyo Thornton’s group at the University of Michigan, many of the materials were produced by other collaborators. Professor Alan Taub who is also at the University of Michigan explains.

ALAN TAUB: Some of our material was done in collaboration with our colleagues at UCLA and Ohio State University, you know to get the right material in the right form, as well as David Weiss who was at Eck Industries. You can’t underemphasize; making the specimens is not easy under these controlled conditions.

LAURA LEAY: Even performing the characterization was not straightforward. The nanotomography required samples of specific dimensions while the electron microscopy took time.

ASHWIN SHAHINI: These are typically micropillar samples which means that they’re 50 micrometers or less in diameter and so machining a sample that small that is still going to be representative of the bulk is non-trivial. And then also in terms of the electron microscopy, you know catching the point of nucleation, it’s like finding a needle in a haystack. We spent a long time linking length scales, so going from the results at the synchrotron at the nanometer scale to the atomic scale.

LAURA LEAY: Students in the research group were challenged to work on all aspects of the experimental work which means they had to prepare samples, collect the data, process it, then provide interpretation. The nanotomography was key to this research; trying to obtain the same information using only electron microscopy of thin sections would have required significantly more effort.

ALAN TAUB: It’s really professor Shahani introducing the ability to do nanoscale three-dimensional imaging. Without that we could not – without laborious, you know, hundreds of sections – have known that we really had orthogonal plates, that those orthogonal plates had these critical sized nuclei inside. It’s the enabler of 3D visualization.

LAURA LEAY: The research was supported by grant funding from the US National Science Foundation under their GOALI program and is part of a wider program of work. Using these insights, the microstructure of a material can be tuned in order to optimize the materials properties. While the 3D imaging is critical to gaining insight into the structure, computational models can facilitate this optimization. This work was published in a recent issue of Acta Materialia. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on X, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.