Advances in 6d diffraction contrast tomography

Abstract

The ability to measure 3D orientation fields and to determine grain boundary character plays a key role in understanding many material science processes, including: crack formation and propagation, grain coarsening, and corrosion processes. X-ray diffraction imaging techniques offer the ability to retrieve such information in a non-destructive manner. Among them, Diffraction Contrast Tomography (DCT) is a monochromatic beam, near-field technique, that uses an extended beam and offers fast mapping of 3D sample volumes. It was previously shown that the six-dimensional extension of DCT can be applied to moderately deformed samples (⩽ 5% total strain), made from materials that exhibit low levels of elastic deformation of the unit cell (⩽ 1%). In this article, we improved over the previously proposed 6D-DCT reconstruction method, through the introduction of both a more advanced forward model and reconstruction algorithm. The results obtained with the proposed improvements are compared against the reconstructions previously published in [1], using Electron Backscatter Diffraction (EBSD) measurements as a reference. The result was a noticeably higher quality reconstruction of the grain boundary positions and local orientation fields. The achieved reconstruction quality, together with the low acquisition times, render DCT a valuable tool for the stop-motion study of polycrystalline microstructures, evolving as a function of applied strain or thermal annealing treatments, for selected materials.

Three-dimensional reconstruction of intragranular strain and orientation in polycrystals by near-field X-ray diffraction

“…21 for an overview of data representation). "6D" stands for the combined representation of three real space and three orientation space dimensions, and it has been demonstrated to provide accurate grain maps with micrometre resolution when the mosaicity of the crystal lattice is moderate (Poulsen, 2003;Nicola Viganò et al, 2014;Nicola Viganò, Tanguy, et al, 2016;N. Viganò & Ludwig, 2018) [51,52,53,54,55].…”

“…When overlaps are more prominent, indexing may not be feasible using spot centroids, and a preliminary orientation map may be obtained by the 6D approach [53,55] or scanning orientation space for each voxel [48]. Such a map may then be refined by the presented methods to infer deformation.…”

X-ray orientation microscopy using topo-tomography and multi-mode diffraction contrast tomography

“…The reconstructions were performed at 0.05 degrees orientationspace resolution, using the 6D Chambolle-Pock isotropic TV-min implementation from [38], already used in [39], with weight = × 1 10 4 , and 100 iterations.…”