Modeling grain selection for single-crystal thin-wall inconel 718 tubes by laser powder bed fusion

Additive manufacturing using Laser Powder Bed Fusion (LPBF) offers significant potential for fabricating high-performance nickel-based superalloy components; however, achieving single-crystal architectures remains limited by competitive grain growth. This study proposes a geometry-assisted grain selection strategy inspired by directional solidification casting for thin-wall Inconel 718 tubes. A thermo-mechanical simulation framework based on Simufact Additive is employed to evaluate a parametric design space of spiral grain selectors comprising a starter block and a helical section.Seventy geometric configurations are analyzed using macro-scale thermal indicators, including axial thermal gradient (G), temperature rate (|dT/dt|), a solidification-rate proxy (R), the G/R ratio, and residual stress distributions. The predicted thermal gradients and stress levels are consistent with experimentally validated LPBF literature, confirming the reliability of the simulation framework. The results show that four-turn spiral selectors with intermediate take-off angles (15°-20°) and small wire diameters provide optimal thermo-mechanical conditions, characterized by stable thermal gradients, favorable G/R ratios, and moderate residual stresses. In contrast, two-turn configurations fail to achieve sufficient thermal confinement. This study establishes a simulation-driven methodology for identifying geometries that promote single-grain survival in LPBF thin-wall superalloy components.