Investigating the microstructure of additively manufacture tungsten parts produced by electron beam powder bed fusion process.
Pure tungsten is one of the promising candidate materials for plasma facing components (PFC) of future fusion reactors due to several favourable properties including its high melting point, high thermal conductivity, high strength, high sputtering resistivity and low coefficient of thermal expansion. Increasing geometric complexity and productivity of tungsten plasma facing components is of interest to improve performance and availability for new tokamaks with a view to future steady state plasma operation. Additive manufacturing (AM) by electron beam powder-bed-fusion process (EB-PBF) is identified as potential technology to address these requirements. In this paper we reviewed the literature in EB-PBF of pure tungsten to understand the role that the process parameters have with the microstructure and mechanical properties of manufactured specimens. We present targeted key research in tungsten EB-PBF process development using point melting method, post-AM HIP treatment, destructive and non-destructive evaluation of tungsten parts, microstructure control, in-process monitoring and quality assurance, and possible EB-PBF tungsten geometries for potential use in new PFC architectures. It was found that point melting method reduces cleavage cracking and crack nucleation points while elevated temperature HIP treatment increases work hardening, repeatability and mechanically heals solid-state cracks. It is shown that fusion relevant structures can be achieved by controlling EB-PBF process parameters. That concludes that we can do complex tungsten geometries ranging from intricate thin-wall lattice structures to large solid bulk architectures with relatively high strength (max. room-temperature tensile strength achieved at about 350 MPa) using AM. This demonstrates the potential of EB-PBF process for use in new PFC designs with complex architectures.