Nanostructured Tungsten Alloys for Nuclear Fusion

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Nuclear fusion offers the prospect of large-scale low carbon energy with no long-lived radioactive waste. Over 50 years of worldwide research to overcome the significant technological challenges is culminating in the ITER experiment, currently under construction in Cadarache, France to be completed by 2025. In this, 50 MW of input heating is anticipated to output 500 MW of fusion power from a 150 million degrees C plasma sustained for up to 1,000 seconds, which will demonstrate the commercial potential of fusion power. The materials used to construct such reactors are exposed to extreme conditions in terms of temperature, heat flow and plasma ablation as well as neutron irradiation. This is despite the highly sophisticated magnetic confinement of the fusion plasma used to shield the reactor's physical components and materials. The leading plasma facing material to withstand such temperatures is tungsten, the highest melting point metal. However, tungsten exhibits a brittle to ductile transition temperature (DBTT), and also suffers from irradiation embrittlement.In this project new tungsten alloys with increased performance will be developed following two microstructural design concepts. Firstly, utilising two-phase microstructure to enable nano-scale grain refinement to improve ductility and fracture toughness. Secondly, utilising nano-scale grain boundaries and semi-coherent interfaces to act as sinks for irradiation damage. Such microstructures have been demonstrated within recently developed Ti 'bcc superalloys' using beta-beta' TiFe, which are suggested to be possible for W within the W-Ti-Fe ternary system. An alternative route is to use a two-phase miscibility gap as in W-Cr or even within refractory metal 'high entropy alloys' (HEAs) such as TaNbHfZr. This project would produce new two-phase tungsten 'bcc superalloys', characterise their microstructures and evaluate their mechanical properties as well as underlying deformation mechanisms and irradiation damage performance.