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

• A single crystal of a precipitation-hardened Ni-based alloy was fabricated. • The laser powder-bed fusion method with μ-helix scanning was used. • The fabricated part had a single crystal at the center and polycrystalline edges. • Solute segregation occurred in the microstructure of the single-crystal region. • Heat treatment reduces crystal orientation and solute distribution inhomogeneities. The application of additive manufacturing (AM) to Ni-based superalloys has attracted considerable attention because it enables the production of high-temperature parts that are lighter, integrally formed, and less expensive. However, single-crystal fabrication of precipitation-hardened Ni-based superalloys using AM remains challenging. 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.