Research Overview

In-Situ Diffraction during Mechanical Testing

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Characterizing and optimizing the mechanical properties of engineering components is one of the oldest research domains in materials science, nevertheless still very up-to-date. Mechanical tests followed by microstructural investigations provide engineers with the necessary information to computationally predict the mechanical performance of components. In situ mechanical testing during diffraction is one of the best-known in situ methods during which the microstructure of a device or component is investigated during exposure to stress and/or temperature. Such an experiment allows capturing footprints of the deformation mechanisms responsible for the changing microstructure. The group Materials Science and Simulations has developed several dedicated in-situ testing devices that can be used at various neutron and synchrotron facilities:

Molecular Dynamics Simulations: Nanocrystalline Metals

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Nanocrystalline (nc) metals are by definition polycrystalline structures with a mean grain size below 100 nm and therefore their microstructure contains a significant volume fraction of interfacial regions separated by nearly-perfect crystals. Compared to its coarse-grain counterpart, the mechanical behavior of a fully-dense nc metal is characterized by a significantly enhanced yield stress and a limited tensile elongation. From the early beginning of experimental investigations in the mechanical behavior of nc metals, it has been proposed that the small grain sizes limit the conventional operation of dislocation sources and estimations of strength were made based on simple Frank–Read sources.

With the increase in computational power, one can deform three-dimensional (3D) computational nc samples containing enough grains in order to mimic an nc metal. These simulations have revealed that the deformation behavior is still to a major extent governed by dislocations: however the dislocations are not nucleated via classical Frank–Read sources situated within the grain interior, but are nucleated at GB ledges, with dislocations traveling through the grain and finally being absorbed in opposite GBs. The merit of the atomistic simulations of nc GB networks lies in the revelation of the details of such dislocation mechanisms.Various examples of our contributions to this research field can be found here.