Self-passivating tungsten based alloys are expected to provide a major safety advantage compared to pure tungsten when used as first wall armour of future fusion reactors, due to the formation of a protective oxide scale, preventing the formation of volatile and radioactive WO3 in case of a loss of coolant accident with simultaneous air ingress. In this work results of isothermal oxidations tests at 800 and 1000 degrees C on bulk alloy WCr12Ti2.5 performed by thermogravimetric analysis (TGA) and by exposure to flowing air in a furnace are presented. In both cases a thin, dense Cr2O3 layer is found at the outer surface, below which a Cr2WO6 scale and Ti2CrO5 layers alternating with WO3 are formed. The Cr2O3, Cr2WO6 and Ti2CrO5 scales act as protective barriers against fast inward O2- diffusion. The oxidation kinetics seems to be linear for the furnace exposure tests while for the TGA tests at 800 degrees C the kinetics is first parabolic, transforming into linear after an initial phase. The linear oxidation rates are 2-3 orders of magnitude lower than for pure W.

The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on "Materials Science and Modeling." This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modeling, and validation experiments.

Self-passivating tungsten based alloys are expected to provide a major safety advantage compared to pure tungsten, presently the main candidate material for first wall armour of future fusion reactors. In case of a loss of coolant accident with simultaneous air ingress, a protective oxide scale will be formed on the surface of W avoiding the formation of volatile and radioactive WO3. Bulk WCr12Ti2.5 alloys were manufactured by mechanical alloying (MA) and hot isostatic pressing (HIP), and their properties compared to bulk WCr10Si10 alloys from previous work. The MA parameters were adjusted to obtain the best balance between lowest possible amount of contaminants and effective alloying of the elemental powders. After HIP, a density >99% is achieved for the WCr12Ti2.5 alloy and a very fine and homogeneous microstructure with grains in the submicron range is obtained. Unlike the WCr10Si10 material, no intergranular ODS phase inhibiting grain growth was detected. The thermal and mechanical properties of the WCr10Si10 material are dominated by the silicide (W,Cr)(5)Si-3; it shows a sharp ductile-to brittle transition in the range 1273-1323 K. The thermal conductivity of the WCr12Ti2.5 alloy is close to 50 W/mK in the temperature range of operation; it exhibits significantly higher strength and lower DBTT - around 1170 K - than the WCr10Si10 material.

Self-passivating tungsten-based alloys may provide a major safety advantage in comparison with pure tungsten, which is presently the main candidate material for the plasma-facing protection of future fusion power reactors. WCrSi alloys were manufactured by mechanical alloying (MA) and HIP at 1300 degrees C and 200 MPa for 1 h. Different MA conditions were investigated to obtain powders with lowest possible amount of contaminants and small and homogeneous particle and crystallite size. Milling in WC vials under Ar without process control agent provided best results. After HIP densities close to 100% were obtained. First oxidation tests on preliminary alloys showed self-passivating behavior with rates comparable to WCrSi thin films at 800 degrees C but worse performance at 1000 degrees C. In all cases a Cr(2)WO(6) protective layer is formed at the surface.

Self-passivating tungsten-based alloys are expected to provide a major safety advantage compared to pure tungsten, which is at present the main candidate material for the first wall armour of future fusion reactors. WC10Si10 alloys were manufactured by mechanical alloying (MA) in a Planetary mill and subsequent hot isostatic pressing (HIP), achieving densities above 95%. Different MA conditions were studied. After MA under optimized conditions, a core with heterogeneous microstructure was found in larger powder particles, resulting in the presence of some large W grains after HIP. Nevertheless, the obtained microstructure is significantly refined compared to previous work. First MA trials were also performed on the Si-free system WCr12Ti2.5. In this case a very homogeneous structure inside the powder particles was obtained, and a majority ternary metastable bcc phase was found, indicating that almost complete alloying occurred. Therefore, a very fine and homogeneous microstructure can be expected after HIP in future work.