Karl Franzens University Graz
Graz University of Technology
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Karl Franzens University Graz | Graz University of Technology | |
Electron Microscopy and Spectroscopy of L12 Complex Nanostructures This presentation will illustrate the importance of understanding the fundamental features that underlie the behavior of nanoscale phases embedded in a solids and their role in the evolution of microstructure in materials. Because of the scale and nature of such microstructures, atomic resolution electron microscopy and spectroscopy in tandem with first-principles calculations are essential tools in their characterization. Al-Li-Sc alloys are of great interest for aerospace and cryogenic applications due to their low density and high strength-to-weight ratio. These alloys were found to contain a fine distribution of remarkably monodisperse core/shell precipitates consisting of an Al3ScLi core surrounded by a shell of pure Al3Li. These core/shell particles can be created via a two-stage heat treatment. The atomic structure of these precipitates has been studied by a range of advanced microscopy and spectroscopy techniques in tandem with first-principles calculations of interaction between Sc and Li confined in the ordered structure. Conventional high-resolution phase contrast imaging reveals the fully ordered L12 structure of the shell. Atom-probe tomography reveals that Sc is present in the core while Li is present in both, the core and the shell. The phase of the exit wave distinguished clearly Al columns from Li columns in the Li rich L12 shell. A detailed analysis of these precipitates has provided important insights into their atomic structure and composition. |