查看更多>>摘要：Focused ion beam (FIB) tomography with combined electron backscatter diffraction (EBSD) and energy dispersive x-ray spectroscopy (EDS) is a technique capable of statistically characterizing the microstructure and spatial compositional variation of nuclear fuel in three-dimensions (3D). The 3D visualization from FIB tomography provides a comprehensive picture of the interconnected microstructural and compositional features that can impact fuel performance. While these features are often characterized with surface examination, the complexity and relationship of fission products and grain boundary networks may not fully be captured by these 2D methods. This work presents a practical guide to FIB tomography that is tailored to nuclear fuel characterization. The steps used to collect and process the data are provided along with the scripts used to process the data. Additionally, suggestions for future characterization efforts utilizing this approach are given.
查看更多>>摘要：Herein, CoCrxCuFeMnNi (x = 0, 0.5, 1.0, 1.5, and 2.0, in molar ratio) high-entropy alloys (HEAs) are fabricated by vacuum hot-pressing sintering (VHPS). The effect of Cr content on the microstructure and oxidation behavior are studied. When x <= 1.5 mol, the phases of the four alloys were all composed of FCC2 major phase and FCC1 secondary phase, while Cr-2.0 alloy consisted of a small amount of FCC1 phase and rho phase in addition to FCC2 main phase. The elemental segregation increased with the increase of Cr content. Cr2.0 alloy exhibited the lowest oxidation rate constants in the oxidation stage and the slow oxidation stage, which were 2.29 x 10(-11) and 3.46 x 10( 12) g(2) cm(-4) s(-1), respectively, showing the best oxidation resistance. The oxidation products of CoCrxCu-FeMnNi HEA system were mainly Mn4O3, Mn3O2, Cr2O3 and (M,Cr)(3)O-4-type spinel oxides. The oxidation mechanism is mainly selective oxidation, that is, the outward diffusion of metal cations and the inward diffusion of oxygen ions. The oxidation resistance of the Cr-rich FCC1 and rho phases is better than that of the copper-rich FCC2 phase.
查看更多>>摘要：X-ray micro-computed tomography (mu CT) was applied upon selected ophiolitic rock samples from various localities of the Vardar ophiolite outcrops in North Greece. Effectiveness of the mu CT application was evaluated through this case study by comparing results with other state-of-the-art techniques (e.g., optical microscopy, mineral chemistry microanalyses, XRD and QEMSCAN) to provide suggestive methodologies for optimum characterization, geological modeling, and visualization of ophiolitic rocks. The research outcomes provide an innovative approach for accurate modal composition calculations, crystal structure and mineral distribution in a 3D perspective, by combining mu CT results with mineral chemical analyses. The information obtained is critical for investigating ophiolitic rocks to resolve complex petrogenetic and post-magmatic phenomena, to identify fabrics related to deformation, and furthermore results can also be used for applied research purposes. The obtained mu CT results suggest that distributions of mineral's grayscale values strongly rely on three key factors: (i) participation of mineral phases with distinct attenuation coefficient and/or density properties, (ii) coexistence of different mafic minerals or mafic with non-mafic phases, (iii) variability in their mineral chemistry. The ability to analyze and visualize the internal mineral constituents of ophiolitic rocks samples, through the combination of mu CT and Energy-Dispersive X-ray spectroscopy (EDS), can lead to advanced 3D stereological rock fabric analyses, which is advantageous compared to 2D methodologies. The mu CT allowed to perform rock fabric calculations (best-fit ellipsoids and with volume) upon specified grain size distributions to identify and characterize the 3D morphological properties of the participating crystals and their preferable orientation.
NSTL
Elsevier