Extensive 3D mapping of dislocation structures in bulk aluminum

Abstract

Thermomechanical processing such as annealing is one of the main methods to tailor the mechanical properties of materials, however, much is unknown about the reorganization of dislocation structures deep inside macroscopic crystals that give rise to those changes. Here, we demonstrate the self-organization of dislocation structures upon high-temperature annealing in a mm-sized single crystal of aluminum. We map a large embedded 3D volume ($$100\times 300\times 300$$ 100 × 300 × 300 $$\upmu$$ μ m$$^3$$ 3 ) of dislocation structures using dark field X-ray microscopy (DFXM), a diffraction-based imaging technique. Over the wide field of view, DFXM’s high angular resolution allows us to identify subgrains, separated by dislocation boundaries, which we identify and characterize down to the single-dislocation level using computer-vision methods. We demonstrate how even after long annealing times at high temperatures, the remaining low density of dislocations still pack into well-defined, straight dislocation boundaries (DBs) that lie on specific crystallographic planes. In contrast to conventional grain growth models, our results show that the dihedral angles at the triple junctions are not the predicted 120$$^{\circ }$$ ∘ , suggesting additional complexities in the boundary stabilization mechanisms. Mapping the local misorientation and lattice strain around these boundaries shows that the observed strain is shear, imparting an average misorientation around the DB of $$\approx$$ ≈ 0.003 to 0.006$$^{\circ }$$ ∘ .

Simultaneous bright- and dark-field X-ray microscopy at X-ray free electron lasers

“…A spatial 3D map may therefore be acquired by collecting image stacks while stepping the sample along the axis, though this was beyond the scope of our initial study. We note that the sensitivity of the DFXM microscope requires that the images in such ( x , y , z ) scans are collected with rotational scans of at least one tilt axis for each observation plane to correct for motor drift ( ) or spatial changes to the microstructure over the scan volume 11 . As the reciprocal space resolution function is thinnest in direction , it is natural to perform this additional scan along .…”

“…In this section, we provide an overview of the data analysis approach to evaluate the crystalline domains sampled by different scan modalities. For a detailed overview of the analysis, we encourage the reader to explore more thorough guides of specific analysis tools developed in darfix 43 and elsewhere 11 .…”

“…Lattice defects are comprised of local disruptions in the crystal packing—either a truncated plane (dislocation), or missing/extra atom (vacancy, interstitial), or truncated domain of the crystal (grain boundary). While the cores of defects have Å-nm lengthscales, the long-range distortions from them that span micrometers to millimeters map key interactions that alter the macroscopic properties 5 , 11 , 12 . When these defects interact, the velocity of the property-transforming events can span from ballistic dynamics (ps-ns) through cumulative degradation (months to years), spanning > 15 decades of timescales.…”

darfix – data analysis for dark-field X-ray microscopy

“…Another field for future development is the transformation of a series of 2D scans into a 3D volume model of the sample. At present this is done manually for layer scans (Yildirim et al, 2022), but stacking and registration could be automated. An alternative measurement strategy would be topo-tomo scans (Ludwig et al, 2009), where projections are recorded while the sample is rotated about the scattering vector.…”

Three-dimensional micro-X-ray topography using focused sheet-shaped X-ray beam

“…However, the spatial resolution depends mainly on the sheet height of the X-ray beam and is limited to the sub-mm order. A recently proposed micro-topography technique called dark-eld X-ray microscopy (DFXM) that utilizes a focused sheet-shaped X-ray is reported to obtain a detailed three-dimensional distortion map in a bulk aluminum block 4 . However, the eld of view was limited to 100 µm by the imaging X-ray lens, and observations were made only in the transmission geometry (Laue-case).…”