Imaging dislocation ensembles during in situ tensile deformation using Dark-Field X-ray Microscopy

Felix Frankus, Technical University of Denmark

Work-hardening in metals is governed by the interactions and self-organisation of dislocations, yet our understanding of these processes remains incomplete, owing to the long-standing difficulty of imaging the evolution of representative dislocation ensembles under bulk conditions.
Dark-field X-ray microscopy (DFXM) enables three-dimensional imaging of dislocation structures within millimetre-sized samples under such bulk conditions. When combined with in-situ tensile loading, DFXM allows the motion of individual dislocations and the evolution of their ensembles to be captured as the material undergoes macroscopic plastic deformation.
In this study, we used DFXM to follow the evolution of individual dislocations within two neighbouring grains, misoriented by 30°, in a polycrystalline AA1050 aluminium tensile specimen. A beam stop was positioned in the microscope’s back-focal plane, acting as a filter in angular space to enhance dislocation contrast. By straining the sample in increments of 0.2% starting from the yield point, we imaged the progressive rearrangement of dislocations, revealing the early stages of dislocation structure formation and its evolution into patterning as deformation proceeds.