Séminaire: Steven Van Petegem, Senior Scientist at the Paul Scherrer Institute

High-power laser–material interaction generates extreme and highly transient conditions, including rapid heating and cooling, steep thermal gradients, and strong fluid flow in the melt pool. These conditions govern microstructure formation in laser-based manufacturing processes but remain difficult to access experimentally due to their short timescales and buried nature.

In this talk, recent advances in operando X-ray diffraction and high-speed X-ray imaging at synchrotron facilities are presented to directly probe these phenomena. Time-resolved diffraction provides access to phase transformations, solidification pathways, and transient strain evolution, while high-speed radiography and tomography reveal melt pool dynamics, keyhole behaviour, and material transport in real time. These experimental observations are complemented by high-fidelity multiphysics simulations, enabling a direct comparison between measured and predicted melt pool dynamics.

The combination of imaging, diffraction, and simulation further enables the correlation of physical events with indirect sensor signals. In particular, synchronized acoustic emission measurements reveal characteristic signatures of regime transitions and defect formation, which can be directly linked to melt pool dynamics observed by X-ray imaging.

These advanced characterisation techniques open up new possibilities to establish quantitative links between processing conditions, microstructure evolution, and resulting material properties, and to guide the design of advanced materials with tailored microstructures.