Tracking polycrystal evolution non-destructively in 3D by laboratory X-ray diffraction contrast tomography

The ability to accurately map crystal grain morphology and grain boundaries in polycrystalline materials, non-destructively and in three-dimensions is required for detailed investigations into many aspects of polycrystalline deformation, as well as many other properties. Previously, the laboratory-based X-ray diffraction contrast tomography technique (LabDCT) has been shown to be capable of reconstructing crystallographic orientations and grain centres in 3D. Here we demonstrate the extension of the method to the reconstruction of the individual 3D grain shapes. Firstly, the grain boundaries are mapped by DCT in a beta‑titanium alloy (Ti-β21S) sample and validated by independent measurements of the grain shapes obtained from phase contrast tomography. The independent validation measurements show that the boundaries can be located with a mean accuracy of 4.4 μm. Secondly, the grain locations and orientations in a copper powder sample sintered at 1050 °C are tracked over time in a time-lapse manner by LabDCT and then the final state compared and validated against destructive serial sectioning EBSD (3D-EBSD) post-mortem. In this case we are able to follow the recrystallisation and competitive grain growth over time, by visualising the migration of selected grain boundaries. In particular the shrinkage and dissolution of grains in the immediate vicinity of a fast-growing grain are observed and quantified in the light of changes in misorientation relationships with the growing grain. More generally, LabDCT can be used to characterise, track or establish realistic 3D image-based models of polycrystalline microstructures across a range of crystal structures.