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By uncoupling the manufacturability from the design process, additive manufacturing of the baseline material EUROFER97 can open significant design freedom for divertor and breeding blankets in fusion technology. As additive manufactured components are known to possess unique microstructures compared to EUROFER97 from standard technologies, the aim of this paper is to investigate additive manufactured EUROFER97 components and the influence of post processing steps on their microstructure and mechanical properties from a materials science point of view. This paper covers the technological fabrication process of EUROFER97 by selective laser melting (SLM), including the production of pre-alloyed EUROFER97 powder, an SLM-parameter study and the design and production of custom-build thin walled test components by SLM. In the initial state after fabrication, SLM-EUROFER97 components exhibit a bimodal, anisotropic microstructure with large ferritic grains. The fraction of ferritic grains increases with decreasing wall thickness. A heat treatment including austenitization, quenching and tempering, allows to achieve a fully martensitic, uniform microstructure for all wall thicknesses. Therefore, there is no influence of wall thickness on mechanical properties of EUROFER97 produced by SLM to be expected, as long as the SLM-part is submitted to an appropriate heat treatment. Further, the comparison of the initial state after fabrication and after post processing reveals the necessity of both hot isostatic pressing and heat treatment to improve the performance. While all material conditions lead to sufficient tensile properties, the Charpy impact properties of SLM-EUROFER97 are inferior in comparison to conventionally produced EUROFER97. A heat treatment alone only improves the ductile-to-brittle transition temperature, whereas hot isostatic pressing reduced the residual porosity of the SLM parts and a subsequent heat treatment improved the ductile-to-brittle transition temperature as well as the upper shelf energy.

For high-temperature environments, as in future fusion reactors, the use of tungsten materials has been sincerely discussed in the last decade. Although severe cold-rolling of tungsten leads to significant improvements in mechanical properties, the fine-grained microstructure of such tungsten material has to be stabilized. For that, the use of potassium-doping (K-doping) in tungsten sheets is investigated in our ongoing study. In this work, we compare mechanical properties of warm- and cold-rolled sheets of pure tungsten and K-doped tungsten (for five different degree of deformation respectively) by means of fracture toughness tests and tensile tests.Fracture toughness and brittle-to-ductile transition temperatures (TBDT) are assessed, showing a slightly lower transition temperature for the cold-rolled K-doped sheets (lower than −100 °C for the 50 µm thick foil). The better performance of the K-doped sheet is related to its finer grain size. The thickest K-doped sheet shows a much higher TBDT than its pure tungsten counterpart. This is presumably caused by the presence of several tens of micrometre thick bands, containing only low angle boundaries, in the microstructure of the K-doped sheet.Tensile tests reveal an outstanding yield strength of 2860 MPa and an ultimate tensile strength of 2970 MPa for the thinnest K-doped sheet with similar, but slightly lower values for the pure tungsten counterpart. Both thinnest sheets show a drastic increase in ultimate tensile strength in correlation to their mean grain size, much higher than expected by a Hall-Petch relation. This deviation has been observed for the microhardness as well and is assumed to be caused by an extraordinary increase in the density of dislocations.Our results indicate that no disadvantages in tensile strength and brittle-to-ductile transition are to be expected compared to pure tungsten, when K-doped tungsten is used to inhibit recrystallization in high-temperature environments.