Columnar to Equiaxed Transition in Spot Melt Electron Beam Powder Bed Fusion Scan Strategy and Utilization of Microstructure Informatics

Abstract

Electron beam powder bed fusion (EB-PBF) has significant potential for achieving controlled microstructural development in additively manufactured components while addressing anisotropic mechanical property limitations inherent to conventional powder bed fusion processes. This work evaluated the columnar-to-equiaxed transition behavior and microstructural refinement characteristics of spot melt scanning strategies in EB-PBF processing. IN718 specimens were processed using four distinct scanning patterns and subjected to comprehensive microstructure informatics analysis to examine relationships between processing parameters, thermal management, and resulting grain morphology characteristics. Specimens underwent systematic beam current and dwell time variations to investigate the influence of energy density on microstructural evolution mechanisms. In addition, traditional raster scanning was examined to provide context for comparison with the experimental spot melting approaches. Microstructural characterization was performed using electron backscatter diffraction (EBSD) combined with quantitative informatics methodologies, in which comprehensive statistical analysis of grain dimensions and aspect ratios was conducted to establish processing-structure relationships. Aspect ratio measurements for the spot melting specimens were found to vary by factors of two to four compared with traditional raster scanning results, demonstrating the effectiveness of temporal separation strategies for columnar-to-equiaxed transition control. Scanning pattern configuration did not indicate a significant impact on densification behavior when adequate energy density was maintained. Moreover, equiaxed microstructural development appeared predominantly in specimens with optimized temporal separation between adjacent melt events as confirmed through three-dimensional EBSD reconstruction analysis. The work presented provides systematic assessment of the relationship between spot melting processing conditions, resulting microstructural characteristics, and thermal management strategies, while offering insight into development pathways for improved mechanical isotropy in this technologically important manufacturing process.