Abstract
Solidification in fusion-based metal additive manufacturing (AM) occurs under non-equilibrium conditions, often producing microstructures that deviate from classical theories, such as refined grains with high twin density arising from abnormal columnar-to-equiaxed transition (CET). While such feature has been linked to liquid atomic orderings, direct mechanistic evidence has been lacking. Here, we perform operando synchrotron X-ray total scattering measurement with rapid pair distribution function (PDF) analysis to probe atomic structures in AM melt pools. We resolve the evolution of short- and medium-range orderings and connect their selective consumption to distinct solidification pathways in Inconel 718 and other alloys. Our findings not only confirm the importance of icosahedral clusters in controlling solidification behavior, but also suggest a distinct nucleation and growth pathway responsible for abnormal CET. This insight offers opportunities for alloy design and microstructure control in metal AM.
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Acknowledgements
We thank Peter Kenesei at the Advanced Photon Source and Jiayun Shao and Zhiyuan Li at Northwestern University for their assistance with synchrotron experiments. We also thank Leonid Zhigilei, Yuan Xu, and Chaobo Chen at the University of Virginia for fruitful discussions. L.G. thanks Refak Mohamed Makeen at the University of Alabama for partial assistance with sample preparation and characterization during the manuscript revision. This research was performed on APS beam time award(s) (https://doi.org/10.46936/APS-188951/60013446) from the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Funding
T.S., X.L., and K.M. discloses support for the research of this work from National Science Foundation [DMR-2427686]. Z.R. discloses support for his partial effort for this work from the 18-ID (FXI) beamline of the National Synchrotron Light Source II (NSLS-II), a U.S. Department of Energy Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory [DE-SC0012704].
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Gao, L., Mumm, K., Ren, Z. et al. Operando X-ray scattering reveals ordering-mediated solidification in additive manufacturing. Nat Commun (2026). https://doi.org/10.1038/s41467-026-73647-3
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DOI: https://doi.org/10.1038/s41467-026-73647-3
