Investigating the microstructure of additively manufactured tungsten parts produced by electron beam powder bed fusion process

• Additive manufacturing (AM) of unalloyed tungsten parts by electron beam powder-bed-fusion process (EB-PBF) via spot melting methods. • EB-PBF process parameters developed for increased productivity and reduced cracking. • Hot Isostatic Pressing (HIP) of EB-PBF tungsten parts. • Effect of varying HIP temperature in the mechanical properties and microstructure of EB-PBF tungsten specimens. • Effect of wire electrical discharge machining (wire-EDM) on EB-PBF tungsten material. • AM process monitoring by Backscatter Electron (BSE) imaging of EB-PBF tungsten parts. 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 PFC is of interest to improve thermal performance and availability for new tokamaks with a view to future steady state plasma operation. Additive manufacturing (AM) by the electron beam powder-bed-fusion process (EB-PBF) is identified as a potential technology to address these requirements. In this paper we reviewed the literature in EB-PBF of unalloyed tungsten to understand the role that the manufacturing parameters have in the microstructure and mechanical performance of as-printed specimens. We present targeted key research in tungsten EB-PBF process development using a modulated point melting method, post-AM hot isostatic pressing (HIP) treatment, destructive and non-destructive evaluation, microstructure control, and in-process monitoring. It was found that the modulated point melting method reduces cleavage cracking and crack nucleation points while elevated temperature HIP treatment improves the repeatability of the tensile behaviour, while mechanically healing process induced defects like solid-state cracks and nanopores.