Advances in X-ray diffraction contrast tomography: flexibility in the setup geometry and application to multiphase materials

Abstract

Diffraction contrast tomography is a near‐field diffraction‐based imaging technique that provides high‐resolution grain maps of polycrystalline materials simultaneously with the orientation and average elastic strain tensor components of the individual grains with an accuracy of a few times 10−4. Recent improvements that have been introduced into the data analysis are described. The ability to process data from arbitrary detector positions allows for optimization of the experimental setup for higher spatial or strain resolution, including high Bragg angles (0 < 2θ < 180°). The geometry refinement, grain indexing and strain analysis are based on Friedel pairs of diffraction spots and can handle thousands of grains in single‐ or multiphase materials. The grain reconstruction is performed with a simultaneous iterative reconstruction technique using three‐dimensional oblique angle projections and GPU acceleration. The improvements are demonstrated with the following experimental examples: (1) uranium oxide mapped at high spatial resolution (300 nm voxel size); (2) combined grain mapping and section topography at high Bragg angles of an Al–Li alloy; (3) ferrite and austenite crystals in a dual‐phase steel; (4) grain mapping and elastic strains of a commercially pure titanium sample containing 1755 grains.

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

“…As proposed by Oddershede et al [26], it is also possible to use near-field and far-field DCT acquisitions of a polycrystalline specimen to determine the average of elastic strain tensors in each grains with a precision close to 10 −4 without having to reconstruct the polycrystalline aggregate. As a second example, Reischig et al based their strain tensor measurements on the reconstructed volume and the Friedel pairs [27,28]. However these grain-resolved strain tensor measurement techniques are restricted to a certain class of materials and has not been tested on Stainless Steel right now.…”

Maximising electro-mechanical response by minimising grain-scale strain heterogeneity in phase-change actuator ceramics

“…41 The exact nature of these local effects is unknown; however, interaction of ferroic domains at grain boundaries and the coupling of extrinsic ferroelectric/ferroelastic strains with the elastic anisotropy of the system are suspected to have an influence. Further development of grain-scale microscopy methods based on 3DXRD, 42,43 diffraction contrast tomography, [44][45][46] darkfield X-rays, 47,48 or transmitted electrons 49 will allow the possibility to establish three-dimensional grain neighbour relations experimentally, quantify intergranular interactions (in particular, stresses and strains, both intrinsic and extrinsic), and build these into predictive models. [50][51][52] Development of these characterisation techniques and predictive modelling covering multiple length scales may be the key tools needed in order to design new reversible phase-change actuator ceramics with improved fatigue properties compared to present generation ceramics.…”

Proceedings of the 13th World Conference on Titanium

“…The standard X-ray DCT analysis methodology has previously been described in detail [18,19] . A series of images (typically 3600-7200) are recorded while the sample is rotated through 360°.…”

“…Any overlapping or unassigned spaces in the 3D map are filled using a morphological dilation. The complete procedure of data processing can be found in [18,19] .…”

“…Examples here are the differential aperture X-ray microscopy (DAXM) [16] and far-field 3D X-ray diffraction (3DXRD) [17]. X-ray DCT [18,19] is a variant of the 3DXRD microscopy technique enabling simultaneous reconstruction of the 3D microstructure (shape and orientation) in suitable polycrystalline materials, along with the absorption map of the specimen. The X-ray DCT methodology provides access to the 3D shape, orientation and elastic strain state of the individual grains from polycrystalline materials fulfilling some conditions in terms of grain size and intra-granular orientation spread.…”