Anomalous grain growth as a pathway toward fully single-crystallization in IN738LC Ni-based superalloy fabricated by laser powder bed fusion

Masayuki Okugawa; Kazufumi Nose; Sei Hirooka; Sukeharu Nomoto; Yuheng Liu; Makoto Watanabe; Yuichiro Koizumi; Takayoshi Nakano

doi:10.1016/j.matdes.2026.116222

Journal article Anomalous grain growth as a pathway toward fully single-crystallization in IN738LC Ni-based superalloy fabricated by laser powder bed fusion

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Masayuki Okugawa, Kazufumi Nose, Sei Hirooka, Sukeharu Nomoto, Yuheng Liu, Makoto Watanabe, Yuichiro Koizumi, Takayoshi Nakano. Anomalous grain growth as a pathway toward fully single-crystallization in IN738LC Ni-based superalloy fabricated by laser powder bed fusion. Materials & Design. 2026, 266 (), 116222. https://doi.org/10.1016/j.matdes.2026.116222

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This study demonstrates that a single crystal (SX) of the IN738LC Ni-based superalloy can be fabricated via laser powder bed fusion (PBF-LB) and the quality of the built SX part can be improved via optimal thermal annealing. The as-fabricated part exhibits inhomogeneities in crystal orientation: the central area is a single crystal, whereas the edges are polycrystalline. The crystal orientation of the single-crystal region is largely affected by gas flow during the build, which could be detected by the in-process melt pool monitoring system. Additionally, significant solute-element segregation is observed in the microstructure of the single-crystal region, consistent with the distribution predicted by the multi-phase-field simulation. Notably, we found that anomalous grain growth, induced by optimal annealing at 1200 ◦C, selectively expands the SX region while eliminating solute-element segregation, thereby improving the overall quality of the single-crystal part. These findings provide insight into the development of single-crystal fabrication via the PBF-LB process for aerospace and energy applications.

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