[en] Continuous efforts in the design of plasma-facing components (PFC) for DEMO divertor unravel new challenges to be met by the in-vessel materials. Embrittlement induced by 14 MeV neutrons in tungsten, main candidate for the first wall material, is one of the hottest issues to be addressed in the design of PFCs with a reliable structural integrity. For designing mid heat flux PFCs, chromium (Cr) is currently considered as material for the main body connected to tungsten armour tile and cooling pipe. Cr has the superior toughness property in the low temperature range where the commercial tungsten products are brittle. Cr is an excellent material to reduce the oxidation in case of loss-of-vacuum accident [1], as well as it does not experience such harsh transmutation as W does producing Re and Os yielding to disadvantageous precipitation and embrittlement. The advantages of Cr may help substantiation of water coolant design and usage of ITER experience for licensing of PFC components. However, the mechanical properties of Cr are extremely sensitive to purity. Because of that commercially produced Cr grade (Plansee) in non-irradiated state exhibits rather high ductile to brittle transition temperature (DBTT) ~150-250°C [2].
Here, we employ vacuum arc melting (VAC) equipment for fabrication of Cr and Cr-W alloy suitable for PFCs, which represents new promising alternative route with high upscale potential. VAM fabrication improves Cr quality by avoiding the introduction of interstitial impurities, while the produced grades can be further mechanically treated to design dedicated microstructure and enhance the yield strength. The produced heats of pure Cr and Cr-10W are investigated by means of chemical and microstructural analysis as well as mechanical testing and compared with the Plansee Cr. The VAM-produced pure Cr shows DBTT below room temperature proving the principal advantage of this fabrication route.
Terentyev, Dmitry; Studiecentrum voor Energie = Centre d'Etude de l'Energie Nucléaire - SCK = CEN > Institute of Nuclear Materials Science > Head of NMS research group