Metallic glasses – Atomic-Scale Flow of the Strongest Metal on Earth
CME Department Seminar
September 26, 2025
11:00 AM - 12:00 PM America/Chicago
Presenter: Robert Maass, PhD, Federal Institute of Materials Research and Testing
Location: ERF Room 1047
Abstract: Glassy solids are ubiquitous in our daily lives, including silicate glasses, amorphous polymers, or glassy oxides. A more modern addition to this class of materials are metallic glasses, representing among the toughest and strongest metals we know. Structurally, metallic glasses distinguish themselves from their crystalline counterparts by a broad distribution of nearest neighbor distances and a lack of long-range order. This has fundamental consequences in terms of both barrier energies for structural transitions and related relaxation times.
In this talk, we will focus on the stress-strain domain prior to macroscopic yielding of metallic glasses and probe transport at the atomic-scale using coherent scattering methods. Specifically, we will first track stress-driven structural dynamics during loading in terms of decorrelation times that give detailed insights into the time scales of microplastic flow (Nature Communications 10 (2019) 5006). These show strong deviations away from the expected time-dependent relaxation dynamics, exhibiting abrupt fluctuations. Finding that such time-scale fluctuations are also present in unstressed metallic glasses (Nature Communications 15 (2024) 6595), we leverage molecular dynamics simulations in the microsecond time domain to understand this phenomenon. The simulations reveal how extend cluster rearrangements can cause abrupt structural dynamics (Acta Materialia 267 (2024) 119730), which manifests itself as intermittency in the time domain. As a final step, we consider the lowest experimentally accessible stress domain to interrogate the true microplastic limit of metallic glasses. It is found that, in contrast to crystalline metals, flow occurs at even the smallest applied stress (Materials Today 82 (2025) 92). This stands in stark contrast to the several GPa-large yield stresses with Weibull moduli as high as for technical Al- or Fe-based alloys. We discuss these findings in the context of an extended glassy microstructure with strong structural partitioning.
Speaker Bio: Robert Maass is head of Materials Engineering and institute director at the Federal Institute of Materials Research and Testing (BAM) in Berlin. He is professor at the Technical University in Munich and holds an adjunct faculty appointment at the University of Illinois at Urbana-Champaign. He received his PhD in 2009 from the Materials Science Department at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. He was a postdoctoral researcher at ETH in Zurich, Caltech, a junior research group leader at the University of Göttingen, and worked as a management consultant for metals at McKinsey & Co. Has published more than 120 international peer-reviewed articles in the area of mechanical metallurgy and given more than 70 invited lectures. His honors include the Emmy Noether award, an Alexander von Humboldt fellowship, the NSF Career award, the Masing memorial medal, and the Brimacombe medal. He is a member of the board of directors at TMS. His research interests revolve around microstructure-property relations, size effects, strain localization and defect structures of amorphous and crystalline metals, defect dynamics, mechanical properties, microplasticity, glass transition phenomena, and test system development.
Date posted
Sep 22, 2025
Date updated
Sep 22, 2025