Additive manufacturing technologies for EUROFER97 components

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

Computational Fluid Dynamic Investigations on a Small-Scale Liquid Sodium Loop

Liquid metal heat transfer systems are a technically attractive option to increase the efficiency of CSP plants. Sodium as heat transfer medium is promising especially due to high heat transfer rates. In this paper, basic considerations are made to match the requirements of a small-scale loop with sodium as heat transfer medium. The setup of the test facility KArlsruhe ReceIver test FAcility (KARIFA) to heat up this loop with a 20 kW IR laser is described. The loop is planned as an integrated design using an additive manufacturing process. Different technologies like selective laser melting (SLM) are established processes to realize an integrated design and to bring together components in one part. Some variations must be implemented to adapt these processes to liquid metal loops. The high heat fluxes also demand a flow simulation to ensure an efficient and safe operation. A Reynolds-averaged Navier-Stokes (RANS) steady state simulation was performed to show the surface and duct temperatures as well as dimensionless values to analyse the characteristics of the sodium flow

Cold Spray metal powder deposition with 9 %Cr-steel applied for the HCPB First Wall fabrication: Proof of concept and options for ODS steel processing

At the KIT a hybrid manufacturing concept for nuclear fusion First Walls is developed combining aspects of conventional and Additive Manufacturing (AM) technologies. The state of the art for ITER does not cover all specifications of a DEMO relevant First Wall. Thus, additional R&D-work has been initiated in terms of manufacturing. The AM technology basis used in the presented process combination is Cold Spray metal powder deposition applied in alternation with machining including the feature of filling grooves temporarily with a water-soluble granulate for creation of closed channels and cavities. Thus, the technology provides the option to manufacture shells with a thin gas tight membrane on top of previously machined structures. This membrane is used as pressure seal and makes the joining of shells by Hot Isostatic Pressing (HIP) into one monolithic body possible. This paper describes the manufacturing process and recalls differences and common aspects with regard to conventional concepts of First Wall manufacturing. The achievement of Technology Readiness Level TRL 3 by mechanical qualification and comparison of the results to other HIP joint experiments is also demonstrated. Finally, an outlook is given concerning integration options of the technology into manufacturing of shells with cooling channel structures using Oxide Dispersion Strengthened (ODS) materials