Stress breaks universal aging behaviour in a bulk metallic glass
Department of Materials Science and Engineering
University of Illinois at Urbana-Champaign
Subjecting a metallic glass to increasing temperature leads to thermally-activated relaxation dynamics that is well described with monotonously decreasing relaxation times. Similarly, relaxation times are known to increase as a function of waiting time (aging) at a given temperature. Here we use x-ray photon correlation spectroscopy (XPCS) to reveal how the structural dynamics of a prototypical Zr-based metallic glass changes due to internal residual stresses or applied stresses.
Our findings are discussed in the context of pre-yield structural excitations, structural relaxation and rejuvenation, as-well as mesoscopic effects of shear banding during plastic flow.
Robert Maass received a triple diploma in Materials Science and Engineering from the Institut National Polytechnique de Lorraine (INPL-EEIGM, France), Luleå Technical University (Sweden) and Saarland University (Germany) in 2005. In 2009, he obtained his PhD from the Materials Science Department at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. During his doctoral work, Robert designed and built an in-situ micro-compression set-up that he used to study small-scale plasticity with time-resolved Laue diffraction at the Swiss Light Source. From 2009-2011 he worked as a postdoctoral researcher at the Swiss Federal Institute of Technology (ETH Zurich) on plasticity of metallic glasses. Subsequently, he joined the California Institute of Technology as an Alexander von Humboldt postdoctoral scholar to continue his research on plasticity of metals. After working as a specialist management consultant for metals at McKinsey & Co., he transferred to the University of Göttingen as a junior research group leader. He joined the faculty of the University of Illinois at Urbana-Champaign as Assistant Professor of Materials Science and Engineering in 2015. His research interests include 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. His honors include the Young Scientist Award from the German Materials Society, an Alexander von Humboldt Fellowship, the prestigious Emmy Noether award from the German Research Foundation, the NSF Career Award, the TMS Young Leaders Award, the TMS Emerging Leaders Alliance Award, the American Society for Nondestructive Testing Award, and the Masing Memorial Medal from the German Materials Society.