For a thorough understanding of a material, investigations at the nanoscale are often essential. Analytical techniques like electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) in scanning transmission electron microscopy (STEM) can reveal important chemical information necessary for the development and improvement of high-tech materials. The integrative character of the signal acquired through transmission, however, might hide important morphological details of the material, relevant for its properties. Those details can be revealed through electron tomography, where the data is acquired at different tilt angles and, after alignment, reconstructed to form a full 3D model of the material under investigation. The combination of both techniques, analytical STEM and tomography, gives full insight into structure and composition of a material .
In this study an industrially cast aluminum alloy, containing scandium (Sc) and zirconium (Zr) rich nano-precipitates, was investigated at different stages of ageing. High resolution STEM and analytical EELS and EDX tomographic investigations were carried out. The resulting 3D elemental reconstructions delivered otherwise inaccessible information on the samples’ chemistry and structure (figure 1). Additionally, EDX-spectra of a long aged and electron-beam re-solidified (EBRS) sample were reconstructed channel by channel, resulting in a data cube, in which each voxel (volume pixel) contained an entire spectrum. Via a high angle annular dark field (HAADF) reconstruction and 3D masking, the voxels of the core and the different shell regions of a nano-precipitate were extracted and summed to obtain pure spectra of those volumes, thus overcoming the intrinsic limitations arising from the integrative character of analytical STEM. Comparisons of these results with data from high resolution STEM imaging, HAADF tomography and data from literature have led to the conclusion -opposed to previous believes - that a self-limiting diffusion process takes place within the precipitates stabilizing their core-shell structure (figure 2).
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The authors thank the Austrian Cooperative Research Facility, the European Union (7th Framework Programme: ESTEEM2) and the Austrian Research Promotion Agency FFG (TAKE OFF project 839002) for funding.
To cite this abstract:Angelina Orthacker, Georg Haberfehlner, Johannes Taendl, Maria Cecilia Poletti, Bernhard Sonderegger, Gerald Kothleitner; Analytical electron tomographic investigations revealing self stabilization of core-shell precipitates through opposing diffusion processes. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/analytical-electron-tomographic-investigations-revealing-self-stabilization-of-core-shell-precipitates-through-opposing-diffusion-processes/. Accessed: May 26, 2020
EMC Abstracts - https://emc-proceedings.com/abstract/analytical-electron-tomographic-investigations-revealing-self-stabilization-of-core-shell-precipitates-through-opposing-diffusion-processes/