Abstract:
The ideal material for highly loaded areas in a future fusion device needs to combine properties such as low sputter yield, high melting point, high thermal conductivity and moderate activation. Tungsten, as a promising candidate for such structures, has in addition also a high strength and creep resistance at elevated temperatures. However, the inherent brittleness below the ductile-to-brittle transition temperature and the embrittlement during operation, e.g. by overheating and/or neutron irradiation are the main drawbacks for the use of pure tungsten. To overcome this limitation, tungsten fibre-reinforced tungsten composites (Wf/W) were developed which utilizes extrinsic mechanisms to improve the toughness similar to ceramic fibre-reinforced ceramics [1]. As an integral part of this novel composite system drawn tungsten wire used as reinforcing fibre has been part of intensive research work [2-8].
In this presentation we give an overview on this new composite material and its intended use in a fusion reactor. The focus will be on the review of conducted work on tungsten wire with a focus on microstructure and mechanical properties as well as textile processing. Tungsten wire shows a very high strength [2] and in contrast to conventional bulk tungsten large ductility [3] even at room temperature. The elongated grain structure was identified as the key parameter for the ductility [4]. Used in a composite the ductile deformation significantly contributes to the toughening [1,5]. By using potassium as doping material, the microstructure and properties of the wire exhibit excellent thermal stability [6]. To utilize these wires for the use in composites different textile techniques have been established i.a. weaving [1] and braiding [7] and investigations on the production of tungsten based yarns is ongoing [8]. In a powder metallurgical manufacturing approach wire pieces are used as random orientated short fibre reinforcements [9].