Investigating microstructural anisotropy and productivity in high-power PBF-LB/M of Inconel 718 using dual-spot beam shaping strategy

Laser beam shaping in laser-based powder bed fusion of metals (PBF-LB/M) enables increased volumetric build rates by employing larger and non-Gaussian laser intensity distributions. However, higher productivity is typically accompanied by pronounced microstructural anisotropy due to the formation of wide and shallow melt pools that promote epitaxial columnar grain growth, particularly in high-performance alloys such as Inconel 718. This study investigates how spatially distributed dual-spot laser profiles, enabled by beam shaping technology, influence as-built microstructural anisotropy and improve the productivity of the PBF-LB/M process for Inconel 718. Two Gaussian spots arranged in con-trolled configurations are used to modify melt pool geometry and as-built final part qualities including porosity, top surface roughness, and microstructure. In-situ multispectral imaging is employed as a monitoring tool to analyze melt pool thermal behavior and guide the configuration of dual-spot beam profiles. The experimental results show that a small offset (90 µm) between the two beams leads to the formation of a large, and merged melt pool. In contrast, increasing the offset (up to 130 µm) between two Gaussian beams along the scanning direction prevents melt pool merging, a phenomenon characteristic of this processing condition with closely positioned melt pools. Application of offset between laser beam profiles results in a reduction of infill areal porosity from 2.2% to 0.02%, a decrease in top surface roughness Ra from 41.6 µm to 13.7 µm, a refinement of average grain diameter from 550 µm to 198 µm, and a reduction in texture index from 7.4 to 2.1, indicating a significant decrease in crystallographic anisotropy at comparable porosity levels to state-of-the-art processes. Simultaneously, with the dual-spot beam shaping strategy, the effective volumetric build rate increases from 4.2 m³ /s (Gaussian state-of-the-art) to 16.4 mm³ /s, corresponding to a 390% productivity increase. The findings demonstrate the influence of dual-spot laser intensity distribution on as-built microstructural anisotropy in PBF-LB/M, while the underlying effects on melt pool thermal behavior require further investigation.