4 research outputs found
Registration between DCT and EBSD datasets for multiphase microstructures
The ability to characterise the three-dimensional microstructure of
multiphase materials is essential for understanding the interaction between
phases and associated materials properties. Here, laboratory-based
diffraction-contrast tomography (DCT), a recently-established materials
characterization technique that can determine grain phases, morphologies,
positions and orientations in a voxel-based reconstruction method, was used to
map part of a dual-phase steel alloy sample. To assess the resulting
microstructures that were produced by the DCT technique, an EBSD map was
collected within the same sample volume. To identify the 2D slice of the 3D DCT
reconstruction that best corresponded to the EBSD map, a novel registration
technique based solely on grain-averaged orientations was developed -- this
registration technique requires very little a priori knowledge of dataset
alignment and can be extended to other techniques that only recover
grain-averaged orientation data such as far-field 3D X-ray diffraction
microscopy. Once the corresponding 2D slice was identified in the DCT dataset,
comparisons of phase balance, grain size, shape and texture were performed
between DCT and EBSD techniques. More complicated aspects of the
microstructural morphology such as grain boundary shape and grains less than a
critical size were poorly reproduced by the DCT reconstruction, primarily due
to the difference in resolutions of the technique compared with EBSD. However,
lab-based DCT is shown to accurately determine the centre-of-mass position,
orientation, and size of the large grains for each phase present, austenite and
martensitic ferrite. The results reveals a complex ferrite grain network of
similar crystal orientations that are absent from the EBSD dataset. Such detail
demonstrates that lab-based DCT, as a technique, shows great promise in the
field of multi-phase material characterization.Comment: 15 pages, 11 figures. Preprint submitted to Materials
Characterizatio
Registration between DCT and EBSD datasets for multiphase microstructures
The ability to characterise the three-dimensional microstructure of multiphase materials is essential for understanding the interaction between phases and their associated materials properties. Here, laboratory-based diffraction-contrast tomography (lab-based DCT), a recently-established materials characterization technique that can determine grain phases, morphologies, positions and orientations in a voxel-based reconstruction method, was used to map part of a dual-phase steel alloy sample. To assess the resulting microstructures produced by the lab-based DCT technique, an electron backscatter diffraction (EBSD) map was collected within the same sample volume. To identify the two-dimensional (2D) slice of the three-dimensional (3D) lab-based DCT reconstruction that best corresponded to the 2D EBSD map, a novel registration technique based solely on grain-averaged orientations was developed – this registration technique requires very little a priori knowledge of dataset alignment and can be extended to other techniques that only recover grain-averaged orientation data such as far-field 3D X-ray diffraction microscopy. Once the corresponding 2D slice was identified in the lab-based DCT dataset, comparisons of phase balance, grain size, shape and texture were performed between lab-based DCT and EBSD techniques. More complicated aspects of the microstructural morphology such as grain boundary shape and grains less than a critical size were poorly reproduced by the lab-based DCT reconstruction, primarily due to the difference in resolutions of the technique compared with EBSD. However, lab-based DCT is shown to accurately determine the centre-of-mass position, orientation, and size of the large grains for each phase present, austenite and martensitic ferrite. The results reveals a complex ferrite grain network of similar crystal orientations that are absent from the EBSD dataset. Such detail demonstrates that lab-based DCT, as a technique, shows great promise in the field of multi-phase material characterization
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Grain-level effects on in-situ deformation-induced phase transformations in a complex-phase steel using 3DXRD and EBSD
A novel complex-phase steel alloy is conceived with a deliberately unstable austenite, γ, phase that enables the deformation-induced martensitic transformations (DIMT) to be explored at low levels of plastic strain. The DIMT was thus explored, in-situ and non-destructively, using both far-field Three-Dimensional X-Ray Diffraction (3DXRD) and Electron Back-Scatter Diffraction (EBSD). Substantial α′ martensite formation was observed under 10 % applied strain with EBSD, and many ε grain formation events were captured with 3DXRD, indicative of the indirect transformation of martensite via the reaction γ → ε → α′. Using ε grain formation as a direct measurement of γ grain stability, the influence of several microstructural properties, such as grain size, orientation and neighbourhood configuration, on γ stability have been identified. Larger γ grains were found to be less stable than smaller grains. Any γ grains oriented with {1 0 0} parallel to the loading direction preferentially transformed with lower stresses. Parent ε-forming γ grains possessed a neighbourhood with increased ferritic/martensitic volume fraction. This finding shows, unambiguously, that the nearby presence of α and α′ promotes ε formation in neighbouring grains. The minimum strain work criterion model for ε variant prediction was also evaluated, which worked well for most grains. However, ε-forming grains with a lower stress were less well predicted by the model, indicating crystal-level behaviour must be considered for accurate ε formation. The findings from this work are considered key for the future design of alloys where the deformation response can be controlled by tailoring microstructure and local or macroscopic crystal orientations