Tungsten Foils and Composites for Fusion Applications - Mechanical Testing

Tokamak fusion reactors ultimately should deliver safe, clean, and abundant energy provided that materials and plasma challenges continue to be overcome. Materials that can withstand large heat fluxes and mechanical loads while undergoing intense irradiation are needed for the plasma-facing components of these reactors and are still undergoing development. Tungsten composites are candidates for this purpose; they have low sputtering yields, high melting points, and may be more ductile than pure tungsten. However, the mechanical properties of tungsten composites are not yet well characterized. Tungsten foils produced using severe plastic deformation, e.g. cold rolling, have shown considerable promise for these applications as they may be more ductile than tungsten produced using powder metallurgy alone. Changes to the mechanical properties of tungsten foils have been suggested to be correlated with ultra-fine grained or nanocrystalline microstructures created by severe plastic deformation. Tungsten foils with larger amounts of plastic deformation, i.e. thinner foils, have been shown to have smaller grain sizes and a more pronounced texture in (100) <011>. The grain size and structure of foils with differing degrees of plastic deformation are therefore likely to differ significantly and the foils will likely exhibit very different mechanical properties. To fabricate tungsten foils into a useful structural material for high temperature fusion applications, layered composites are currently being examined. These composites integrate the excellent functional characteristics of tungsten foils with an interlayer such as steel that may improve ductility and toughness. To engineer and optimize layered composites, the mechanical properties of tungsten foils with differing thicknesses and degrees of plastic deformation must be characterized, both pre- and post-irradiation