ADVANCED MATERIALS & PROCESSES | JANUARY/FEBRUARY 2025 27 Fig. 3a were found to be in good agreement with those confirmed through wavelength dispersive x-ray spectroscopy (WDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). ATOM PROBE TOMOGRAPHY Atom probe tomography (APT) is a technique used for atomic- scale 3D imaging and chemical composition analysis within a tiny volume of material, typically about 50 × 50 × 100-200 nm³. Results can offer insights into the overall composition of the region studied as well as the size, composition, and number density of individual nanometer-scale solute clusters. Data are usually gathered from within single material grains, though occasionally the analysis may pass through a grain boundary, providing chemical data across grains. Pradeep et al. attempted to study atomic-scale composition variation of a nanocrystalline AlCrCuFeNiZn HEA using APT[7]. Figure 4a displays comprehensive elemental mapping from the material under APT while Fig. 4b presents individual elemental segre- gation across a two-grain zone observed under APT. Cu-Zn rich segregation emerging from the grain boundaries is clearly presented through the APT analysis. Although this technique is highly useful for understanding atomic level precipitation and elemental segregation, it has an inherent drawback. Due to the small material volumes analyzed, concerns exist about whether the data accurately represent the bulk microstructure[6]. X-RAY ABSORPTION SPECTROSCOPY X-ray absorption spectroscopy (XAS) is a technique that measures a material’s x-ray absorption coefficient as a function of energy, providing insights into its local geometric and electronic structure. Unlike XRD, XAS is particu- larly sensitive to local structure, making it an ideal method for studying various amorphous solids, liquid systems, and nanomaterials[8]. Kim et al. explored the possibility of using element-sensitive x-ray absorp- tion spectra to study a FeCoCrMnNi HEA at subnanometric scale. The pixel plots in Fig. 5a-e resemble the elemental distribution maps similar to those Fig. 4 — APT analysis of AlCrCuFeNiZn HEAs: (a) elemental mapping of overall representation of atoms; and (b) reconstruction of atoms Al, Cr, Cu, Fe, Ni, and Zn in 3D form[7]. Fig. 5 — X-ray absorption spectroscopy mapping of five elements across the nanometer scale[9]. (a) (b)
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