PBF-EB process development of chemically reduced tungsten via a dual-gradient parameter approach utilizing the backscatter signal

Abstract This study introduces an innovative approach for optimizing process development in electron beam powder bed fusion (PBF-EB) of non-flowing chemically reduced tungsten powder. Both line- and spot melting strategies were employed, with gradient-based variations of key processing parameters—beam current and scanning speed (line melting)/dwell time (spot melting)—applied across the XZ and XY planes on prismatic specimens. This method allowed mapping the transition from porous to swelling material within a single specimen and exposed the effects of changing gradient directions. Scripts were developed to analyze swelling and porosity from stacked backscattered electron data, providing valuable insights into material density and defect distribution. Optimal parameters for line melting (1400 W, 115 mm/s) and spot melting (1400 W, 4.5 ms dwell time) were identified, resulting in high-density samples. Solid samples were achieved with Archimedes densities of 99.8% and 99.9% respectively. Microscopical analysis verified parameter windows with dense, swelling-free material, selected for further builds and detailed characterization. Microstructural and compositional analysis was conducted using SEM and EBSD, while local micromechanical properties were assessed through micro hardness. Scaling up line melting was deemed infeasible due to warping, while spot melting was scaled to a melting area of 50 mm × 50 mm.