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Abstract Dynamic solidification behavior during metal additive manufacturing directly influences the as-built microstructure, defects, and mechanical properties of printed parts. How the formation of these features is driven by temperature variation (e.g., thermal gradient magnitude and solidification front velocity) has been studied extensively in metal additive manufacturing, with synchrotron x-ray imaging becoming a critical tool to monitor these processes. Here, we extend these efforts to monitoring full thermomechanical deformation during solidification through the use of operando x-ray diffraction during laser melting. With operando diffraction, we analyze thermomechanical deformation modes such as torsion, bending, fragmentation, assimilation, oscillation, and interdendritic growth. Understanding such phenomena can aid the optimization of printing strategies to obtain specific microstructural features, including localized misorientations, dislocation substructure, and grain boundary character. The interpretation of operando diffraction results is supported by post-mortem electron backscatter diffraction analyses. 

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.