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The adoption of metal additive manufacturing (AM) has tremendously increased over the years; however, it is still challenging to explain the fundamental physical phenomena occurring during these stochastic processes. To tackle this problem, we have constructed a custom metal AM system to simulate powder fed directed energy deposition. This instrument is integrated at the Cornell High Energy Synchrotron Source to conduct operando studies of the metal AM process. These operando experiments provide valuable data that can be used for various applications, such as (a) to study the response of the material to non-equilibrium solidification and intrinsic heat treatment and (b) to characterize changes in lattice plane spacing, which helps us calculate the thermo-mechanical history and resulting microstructural features. Such high-fidelity data are made possible by state-of-the-art direct-detection x-ray area detectors, which aid in the observation of solidification pathways of different metallic alloys. Furthermore, we discuss the various possibilities of analyzing the synchrotron dataset with examples across different measurement modes. 

Refractory metals and their carbides possess extraordinary properties when subjected to high temperatures and extreme environments. Consequently, they can act as key material systems for advancing many sectors, including space, energy and defence. However, it has been difficult to process these materials using the conventional routes of manufacturing. Additive manufacturing (AM) has shown a lot of potential to overcome the challenges and develop new material systems with tailored properties. This review provides a fundamental understanding of the challenges in the processing of refractory metals and their carbides, including microcracking, formation of brittle oxide phases and high ductile to brittle transition temperature (DBTT). We also highlight some of the novel approaches that have been taken to improve the processability of these challenging material systems using AM. These include in-situ reactive printing, ultrasonic vibration, laser beam shaping, multi-laser deposition and substrate pre-heating with a focus on microstructural changes to improve the properties of printed parts.