At Karlsruhe Institute of Technology (KIT), Germany, divertor design concepts for future nuclear fusion power plants beyond ITER (International Thermonuclear Experimental Reactor) are being investigated, as well as manufacturing methods for the mass production of such parts. The divertor is one of the most important plasma-facing components of the reactor. The component must remove impurities from the fusion plasma and has to withstand high surface heat loads.
Preferable materials that are able to withstand such extreme conditions are tungsten and tungsten alloys. One of the most promising divertor design concepts developed at KIT for the future nuclear fusion power reactor DEMO (DEMOnstration Power Plant) is based on modular He-cooled finger units. Each 1-finger module consists of many individual parts, for example a tungsten tile and a tungsten alloy thimble. For the whole divertor system more than 250,000 individual parts are needed.
The manufacturing of such tungsten parts by mechanical machining such as milling and turning is extremely cost and time intensive as the material is very hard and brittle. Powder Injection Moulding (PIM) promises to enable the large-scale production of parts with high near-net-shape precision, hence cost-saving when compared to conventional machining. The PIM process was adapted and developed at KIT for one- and two component tungsten PIM and promising results have already been achieved.
The most recent challenge was to apply a suitable joining process to a mass production technology such as PIM. The motivation for this work was therefore the development and investigation of an alternative joining method for two different materials by using 2-Component-Powder Injection Moulding (2C-PIM). Based on the previous results of the tungsten the PIM divertor part, a newly developed fully automatic 2C-PIM tool allows the replication of fusion relevant components such as the tungsten tile and the tungsten alloy thimble in one step without additional brazing. The microstructure of the finished samples, and the quality of the joining zone, were characterised and found to be remarkably fine.
Green parts, finished parts and cut views of the finished mock-ups are shown in Fig. 1. The material connection of the 2C-PIM combination W + W-2La2O3 (Fig. 1, bottom right) are successful. No cracks or gaps in the seam of the joining zone between the W tile and the W-alloy thimble are visible and a solid bond of the material interface was achieved. In comparison, the cut view and the resulting microstructure of the 1C-PIM mock-up consisting of pure tungsten is shown in Fig. 1, bottom left. An interesting detail is the boundary line between the tile and the thimble (marked by the white arrows), which is still visible only for the 2C-PIM parts. Further steps are the investigation of material properties via mechanical characterisation and HHF-tests.
This work, states KIT, has demonstrated that PIM is a powerful and viable process for mass production even when the joining of complex shaped parts is required and is an ideal tool for scientific investigations on prototype materials. For more information please contact Dr. Steffen Antusch, email [email protected]