High-power electron beam powder bed fusion manufacturing of pure tungsten

The exceptional properties of tungsten make it a very attractive material for advanced applications, however, it is challenging to process. Research on electron beam powder bed fusion (PBF-EB) of tungsten is limited but promising. Previous work has mostly focused on low beam powers and scan velocities, which limits the efficiency of the manufacturing process. A higher processing speed is required for economical production of large tungsten components. This paper studies PBF-EB processing of pure tungsten with a power of 5 kW using a Freemelt ONE and scan velocities of several meters per second, making use of the full capabilities of PBF-EB technology. The required energy input for preheating of the powder bed to achieve dense and crack-free bulk samples is investigated in detail. Then, to optimize the heating energy input, a localized heating strategy is introduced where only the sample cross section is heated after general preheating. Hereby, the required energy input for achieving crack-free tungsten was decreased by 50%. Furthermore, the layer time was reduced from initially 44 s to 30 s, since only a short cooling step was required to avoid overheating of the machine. Finally, dense and crack-free tungsten blocks with 80 mm height were successfully fabricated, thus verifying the applicability of high-power PBF-EB for efficiently creating solid tungsten parts. Microstructural and hardness analysis along the build height revealed a columnar grain structure with a slight grain coarsening and corresponding decrease in hardness towards the top of the build, consistent with the evolving thermal history of the process. These findings highlight a path for enhancing the process efficiency and energy utilization in additive manufacturing of tungsten.