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 mu m tungsten fibres supplied by OSRAM GmbH have been used. In order to facilitate the better use of textile processes less stiff 16 mu m filaments are being evaluated. The strength of the 16 mu m filament is at 4500 MPa and thus significantly higher than the strength of the 150 mu m fibre (similar to 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 similar to 140 mu m 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.