Using in-situ Dark-Field X-ray Microscopy (DFXM), the team tracked the same dislocation boundaries in a bulk aluminium crystal across successive strain steps with high spatial and angular resolution, the first time such evolution has been followed in bulk material.
Below 5.10% strain, deformation proceeds through a disordered network of incidental dislocation boundaries (IDBs). As strain increases, dislocations accumulate within cell interiors until saturation. Within a narrow strain interval of only 0.05%, this network reorganises abruptly, forming well-defined geometrically necessary boundaries (GNBs) that span tens of micrometres. The transition is marked by dislocation migration and boundary sharpening, reflecting a sudden change in the mechanism of plastic strain accommodation.
Autocorrelation analysis reveals long-range spatial order and crystallographic alignment along specific slip planes, indicating that the boundary formation takes place simultaneously across the field of view. The transition shows how metals can reorganise to relieve internal elastic strain, forming ordered dislocation boundaries out of a disordered network.
The work was carried out by researchers at the Technical University of Denmark and the European Synchrotron Radiation Facility, supported by the European Research Council (PMP), DanScatt, and the ERC Starting Grant “D-REX".
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