Powder metallurgical processing of self-passivating tungsten alloys for fusion first wall application

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. (C) 2012 Elsevier B.V. All rights reserved.