Ch. Linsmeier, F. Koch, Ch. Lenser, M. Balden, M. Rasinski

Self-passivating tungsten-based alloys are currently being investigated with respect to possible application in nuclear fusion technology.
The first wall of a future fusion power plant will be exposed to an extremely high heat flux, highly energetic neutron irradiation and a bombardment of energetic hydrogen isotopes. Therefore, the main candidate material for plasma facing protection is tungsten, due to its high thermal conductivity, high melting point and low erosion by D, T and He ions.
A potential problem with the use of tungsten occurs under accidental conditions with loss of coolant. The temperature of the first wall of the reactor may rise up to 1450 K within 30 days due to the nuclear decay. In combination with ingress of air the tungsten then rapidly oxidises under these conditions to WO3, which above 1250 K has a considerable vapour pressure.
The use of self-passivating tungsten-based alloys as plasma facing material could avoid the release of radioactive WO3. In earlier studies it was demonstrated that ternary alloys of W, Si and Cr develop a protective oxide scale in oxidising atmosphere. The oxidation rate of such alloys was dramatically reduced compared to pure tungsten.
This work investigates the self-passivation potential of the quaternary tungsten alloys W−Si−Cr−Zr and W−Si−Cr−Y with varying stoichiometries. The alloys are tested by thermo-gravimetric analysis with synthetic air at temperatures up to 1373 K. The phases, structure and elemental distribution in the cross-section of the oxide scale is analysed by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. The mechanisms of oxidation and oxide layer formation will be discussed.

Quaternary tungsten-based alloys

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