<italic>In situ</italic> characterization for additive manufacturing： applications of synchrotron-based ultrafast X-ray imaging and diffraction techniques

Synchrotron radiation technology serves as a “super microscope” for unveiling multi-scale physical metallurgy behaviors during additive manufacturing （AM）， providing groundbreaking research tools to decode the “black box” challenges inherent in AM processes. This paper review systematically summarizes recent advances in synchrotron radiation applications for AM：in imaging， ultrafast X-ray imaging with high spatiotemporal resolution enables in situ observation of melt pool dynamics， defect formation mechanisms， and solidification behavior， revealing key phenomena such as keyhole fluctuation-induced porosity and Marangoni force-driven defect suppression； in diffraction， ultrafast X-ray diffraction quantitatively resolves phase transformation kinetics and residual stress evolution during rapid solidification. Furthermore， this work explores emerging trends in integrating synchrotron technology with deep learning and multiphysics simulations， while envisioning its potential for AM process optimization， intelligent defect detection， and novel material development. It is pointed out that such technology establishes a theoretical foundation and technical pathway for transitioning AM from empirical trial-and-error to mechanism-driven methodologies.