Dresden 2017 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 4: Topical session: Dynamics, relaxation and deformation in deeply supercooled metallic liquids and glasses I - Structural Transitions

MM 4.2: Vortrag

Montag, 20. März 2017, 10:45–11:00, IFW A

Identifying structural changes in the medium range order of metallic glasses by Fluctuation Electron Microscopy (FEM) — •Dominik Tönnies, Lin Tian, and Cynthia A. Volkert — Institute of Materials Physics, University of Göttingen, Germany

The structural heterogeneity of a metallic glass (MG) is known to have tremendous impact on many important properties of the system, such as the mechanical performance and the formation of shear bands. While it is commonly understood how to qualitatively alter the structure by thermal and mechanical treatments, it is still extremely difficult to precisely quantify the subtle changes in the real-space order induced by structural alterations. For the characterization of medium range order (MRO) of an amorphous system, the method of Fluctuation Electron Microscopy (FEM) has been found useful in the past. In this method, very small volumes of the MG structure are probed by an electron beam in the Transmission Electron Microscope (TEM). Information about changes in the MRO is subsequently inferred from pixel variances of diffraction patterns taken at many different sample sites. We have used this technique to characterize the structure of a Pd_77.5Cu₆Si_16.5 MG at different structural states induced by thermal annealing, cooling to cryogenic temperatures, and mechanical rejuvenation. The results will be compared with nanoindentation pop-in studies to understand the influence of structure on the onset of mechanical deformation.