Advanced materials for a damage resilient divertor concept for DEMO: Powder-metallurgical tungsten-fibre reinforced tungsten

Abstract

Material issues pose a significant challenge for future fusion reactors like DEMO. When using materials in a fusion environment a highly integrated approach is required. Damage resilience, power exhaust, as well as oxidation resistance during accidental air ingress are driving issues when deciding for new materials. Neutron induced effects, e.g. transmutation adding to embrittlement is crucial to material performance. Here advanced materials, e.g. Wf/W or W/Cu, Wf/Cu composites allow the step towards a fusion reactor. Recent developments in the area of multi-fibre powder-metallurgical Wf/W mark a possible path towards a component based on standard tungsten production technologies. Field assisted sintering technology is used as production route to achieve 94% dense materials. Initial mechanical tests and micro-structural analyses show potential for pseudo-ductile behavior of materials with a reasonable (30%) fibre fraction. In the as-fabricated condition samples showed step-wise cracking while the material is still able to bear rising load, the typical pseudo-ductile behavior of a composite. Yttria is used as the interface material in order to allow the energy dissipation mechanisms to become active. Wf/W as plasma facing material contributes here to advanced material strength and crack resilience even with a brittle matrix embrittlement, while W/Cu, Wf/Cu composites at the coolant level allow for higher strength at elevated cooling temperatures. In addition to the use of pure tungsten it is demonstrated that tungsten-based self-passivating alloys can also be used in the composite approach.