Tungsten-based ceramic composites in extreme fusion reactor environments

Reference Presenter Authors
14-008 Samuel Humphry-Baker Humphry-Baker, S.(Imperial College London); Smith, G.(Tokamak Energy Ltd); Lee, B.(Imperial College London); Vandeperre, L.(Imperial College London); Tungsten carbides and borides are used extensively in wear applications; however, they have recently been identified as promising shielding materials for fusion reactors due to their unrivalled attenuation of high-energy neutrons. In both applications, extreme temperatures, mechanical stresses, and oxidation are problematic, while for fusion reactors, irradiation is an additional difficulty. This paper shows some recent progress in understanding and improving the damage tolerance of these materials under such environments. Our strategy is based on combining the ceramic particles with a metallic binder to improve toughness and manufacturability. We report their stability under: dry isothermal oxidation; creep compression; and helium-ion irradiation. In the case of oxidation resistance, we show encouraging results on some diffusion-impregnated coatings. Surprisingly, the protection of the coated materials is enhanced by the presence of a metallic binder, allowing us to reduce the oxidation rate by 3-4 orders of magnitude at operating temperature. Concerning mechanical deformation, we combine high-temperature indentation and compression creep results, allowing us to develop a deformation map. The irradiation behaviour is complicated due to the high density of grain boundaries and hetero-phase interfaces. However, through systematic TEM investigations we are able to highlight detrimental microstructural features that accumulate radiation damage. Our observations offer engineering limits to use of these materials in extreme environments but more importantly allow us to propose processing routes and materials design strategies for improved damage tolerance.
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