Abstract:

The macroscopic properties of advanced materials emerge from the collective behaviour of grains, subgrains, dislocations, and phase domains across length scales from nanometres to millimeters. Resolving how these structures interact inside bulk matter is central to understanding and controlling material properties and requires a multiscale imaging approach. Non-destructive 3D mapping of complex microstructures with high spatial, angular, and temporal resolution is therefore critical for resolving defect-mediated mechanisms and validating structural and microstructural models under realistic conditions.

Diffraction-based X-ray imaging provides a powerful route to probe internal microstructures in bulk materials. In particular, Dark Field X-ray Microscopy (DFXM) enables full-field, three-dimensional mapping of crystallographic orientation and lattice distortions within individual grains at about 100 nm spatial resolution and with high angular sensitivity. Using hard X-rays, DFXM can probe embedded grains and allow in situ observation of dynamic microstructural processes. Recent developments include pink-beam DFXM, which uses a broader energy bandwidth to increase diffracted intensity by more than an order of magnitude while maintaining spatial resolution. This extends diffraction imaging to weakly diffracting and highly deformed microstructures and is well suited for time-resolved studies on sub-second time scales. Another recent advance is the seamless integration of DFXM with 3D X-ray diffraction (3DXRD), diffraction contrast tomography (DCT), and phase-contrast tomography (PCT) on the same instrument, forming a multiscale microscope. These complementary techniques provide mesoscale information on grain morphology, orientation, boundary networks, and surrounding microstructural context, while enabling non-destructive mapping of thousands of grains in bulk materials and direct zooming into selected grains with dislocation-sensitive contrast, high angular sensitivity, and near-100 nm spatial resolution. This enables rapid and reproducible targeting of selected grains for DFXM imaging without dismounting the sample, allowing seamless navigation across length scales. We present examples illustrating how this multimodal framework reveals the mechanisms governing microstructural evolution. In highly deformed ferritic alloys, pink-beam DFXM resolves dislocation cell structures, intragranular orientation gradients, and spatial variations in stored energy within individual grains, even at plastic strain levels where diffraction peaks are strongly broadened and conventional monochromatic DFXM contrast becomes impractical. During in situ annealing of aluminum alloys, time-resolved DFXM captures grain growth with sub-second time resolution, revealing intermittent boundary migration and strain buildup within recrystallized grains. Together, these results demonstrate how multiscale diffraction imaging, coupled with materials modelling approaches such as CPFEM and phase-field simulations, enables quantitative insight into deformation, recrystallization, and grain growth in bulk, providing a foundation for connecting microstructure, defect dynamics, and macroscopic properties across length and time scales.

Bio:

an Yildirim is a staff scientist at the ID03 Hard X-ray Microscopy beamline at the European Synchrotron Radiation Facility, France. He earned his Ph.D. in condensed matter physics from the University of Liège and Pierre and Marie Curie University in Paris, where he studied glasses using ab initio molecular dynamics. He completed postdoctoral research at ESRF’s ID06-HXM beamline in a project funded by OCAS (ArcelorMittal), followed by a position at CEA-Leti, where he worked on semiconductor defects for infrared detectors. He leads an independent research group supported by an ERC Starting Grant, focusing on thermomechanical behavior in metals and the development of advanced diffraction imaging techniques at synchrotron facilities. His work combines multiple X-ray methods across scales, with a strong emphasis on pioneering Dark Field X-ray Microscopy (DFXM). His research spans structural metals, semiconductors, and energy materials. Dr. Yildirim holds a habilitation (HDR) in physics from Université Grenoble Alpes. He serves on beamtime review panels for the ESRF and European XFEL and contributes to scientific outreach through the organization of conferences, including the 3DMS Specialty Congress of TMS and the MSE Congress in Europe. He has authored over 65 peer-reviewed publications, with an h-index of 19 and an i10-index of 37 as of March 2026.