The use of tungsten yarns in the production for W_f/W

Material issues pose a significant challenge for the design of future fusion reactors. Recently progress has been made towards fully dense multi short-fibre powder metallurgical production of tungsten-fibre reinforced tungsten (W_f/W) as well as optimizing the process understanding for the routes using chemical vapour deposition (CVD). For CVD-W_f/W weaves and textile preforms are being used to facilitate large scale production. Classically 150 μm tungsten fibres supplied by OSRAM GmbH have been used. In order to facilitate the better use of textile processes less stiff 16 μm filaments are being evaluated. The strength of the 16 μm filament is at 4500 MPa and thus significantly higher than the strength of the 150 μm fibre (∼2500 MPa) (in the as-fabricated state). Better weavability allows a more flexible use of fibre preforms Two main yarn production routes have been investigated: Covered yarns where a set of tungsten filaments is held together by a PVA (Polyvinyl alcohol) cover and braided yarns. In order to allow a comparison to the previously used single fibres, yarns with ∼140 μm effective diameter were produced. Braided yarns with tensile strength of 2500 MPa and 6% strain at fracture and twisted yarns with tensile strength of 4500 MPa and 3% strain at fracture. For both yarns single fibre CVD samples have been produced to investigate the infiltration properties of the yarns and thus their applicability for the CVD route. A dense infiltration is observed for all yarns under investigation.