CalPhaD Coffee Lecture – Synchrotron X-ray Hierarchical Imaging of Laser Additive Manufacturing

Laser Additive Manufacturing (LAM), has the potential to revolutionize manufacturing processes. However, its wider industrialisation is currently inhibited by solidification cracking, residual stress and distortion, anisotropic microstructures and most importantly a large distribution of entrained defects. It is critical to establish a scientific understanding of how to control defect formation and thus optimise mechanical performance in LAM. At the European Synchrotron (ESRF), taking advantage of the recent Extremely Brilliant Source upgrade and the most advanced synchrotron material characterisation techniques, in-situ and ex-situ investigation have been used to establish a well-rounded picture of the LAM process. The outstanding photon flux density at ESRF can reach ultra-high temporal resolution at hard X-ray energies in combination with coherence levels which allow for imaging with high sensitivity. Combining fast synchrotron radiography (> 40 kHz) with an in-situ LAM rig, fast X-ray imaging enables the observation, in both real and reciprocal space, of the laser-matter interaction, defects formation, material phase transformations and microstructural features evolution. High angular resolution Dark Field X-ray Microscopy (DFXM) is used to quantify the resulting LAM microstructure including spatially resolved 3D grain maps, 3D distribution of strains, lattice misorientation and Geometrically Necessary Dislocations (GNDs). Microstructure development is explored via solidification sequence modelling, which is calibrated by in-situ synchrotron imaging of the manufacturing process. The results presented here provide new insights into the LAM process with relevance to microstructure and defects control in AM fabricated components. They provide information that can contribute directly to industrial practice while producing quantitative data to inform and validate physical models in support of digital twins.