Improved grain mapping by laboratory X-ray diffraction contrast tomography

Abstract

Laboratory diffraction contrast tomography (LabDCT) is a novel technique for non-destructive imaging of the grain structure within polycrystalline samples. To further broaden the use of this technique to a wider range of materials, both the spatial resolution and detection limit achieved in the commonly used Laue focusing geometry have to be improved. In this work, the possibility of improving both grain indexing and shape reconstruction was investigated by increasing the sample-to-detector distance to facilitate geometrical magnification of diffraction spots in the LabDCT projections. LabDCT grain reconstructions of a fully recrystallized iron sample, obtained in the conventional Laue focusing geometry and in a magnified geometry, are compared to one characterized by synchrotron X-ray diffraction contrast tomography, with the latter serving as the ground truth. It is shown that grain indexing can be significantly improved in the magnified geometry. It is also found that the magnified geometry improves the spatial resolution and the accuracy of the reconstructed grain shapes. The improvement is shown to be more evident for grains smaller than 40 µm than for larger grains. The underlying reasons are clarified by comparing spot features for different LabDCT datasets using a forward simulation tool.

3D grain mapping by laboratory X-ray diffraction contrast tomography implemented on a conventional tomography setup

“…As a result of unsuccessful reconstruction for small grains, shape reconstruction for already-indexed grains may be affected and may not be accurate due to over-growth. Therefore, increasing the photon flux as well as higher detective quantum efficiency of the detector system are very important to further improve the performance of LabDCT in addition to improvements in spot segmentation and reconstruction algorithm [10,11]. To these aims, we suggest the following measures: 1) allow higher current on the target of the source using thicker material for the anode or improving the heat conduction around the target; 2) use direct photon counting detectors such as the CdTe 'color' detectors, which are expected to produce low background noise, have better detective quantum efficiency at high X-ray energies and offer the capability to define an X-ray energy range for detecting signals.…”

Level-Set modeling of grain growth in 316L stainless steel under different assumptions regarding grain boundary properties

“…The inclination dependency can have an important impact, hence, a complete description of the GB properties is necessary, i.e. µ(M(θ, a), n) and γ(M(θ, a), n), as well as 3D non-desctructive in-situ characterization [45,48,49,89] in order to obtain more realistic values of GB mobility, must be considered as a key perspectives concerning full-field modeling of GG.…”

“…The early measurements of GB properties (mainly GB reduced mobility) were carried out on bicrystals [39,40,41,42,43,44] leading to the well known Sigmoidal model [1]. As experimental and computational technologies are improved, new experimental and computational 3D techniques allow to study GG and recrystallization using, for instance, X-ray [45,46,47,48,49] or molecular dynamics [50,51,52]. Hence, at the mesoscopic scale, few studies have been carried out in 2D using anisotropic GB properties designed by mathematical models [36,37] or by fitting data from molecular dynamics [38].…”

Level-Set Modeling of Grain Growth in 316L Stainless Steel under Different Assumptions Regarding Grain Boundary Properties

“…In [ 33 , 50 , 51 , 52 ], GB properties are defined as heterogeneous and not as anisotropic. The inclination dependency can have an important impact; hence, a complete description of the GB properties is necessary; i.e., and , as well as 3D non-destructive in situ characterization [ 45 , 47 , 48 ] in order to obtain more realistic values of GB mobility, must be considered as a key perspectives concerning the full-field modeling of GG.…”

“…The early measurements of GB properties (mainly GB reduced mobility) were carried out on bicrystals [ 39 , 40 , 41 , 42 , 43 , 44 ] leading to the well-known Sigmoidal model [ 1 ]. As experimental and computational technologies are improved, new experimental and computational 3D techniques allow studying GG and recrystallization using, for instance, X-ray [ 45 , 46 , 47 , 48 ] or molecular dynamics [ 4 , 5 , 49 ]. Hence, at the mesoscopic scale, few studies have been carried out in 2D using anisotropic GB properties designed by mathematical models [ 36 , 37 ] or by fitting data from molecular dynamics [ 38 ].…”