Extensive 3D mapping of dislocation structures in bulk aluminum

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 x 300 x 300 mu m(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 computervision 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 degrees, 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 approximate to 0.003 to 0.006 degrees.

Automated summary

Thermomechanical processing, such as annealing, is a primary method for modifying the mechanical properties of materials. However, there is still much unknown about the reorganization of dislocation structures during annealing. In this study, we used dark field X-ray microscopy to map the dislocation structures in a large single crystal of aluminum. We observed that even after long annealing times at high temperatures, the remaining dislocations formed well-defined boundaries on specific crystallographic planes.