Effect of neutron irradiation on the fracture behaviour of tungsten fibre-reinforced tungsten composites

• Fracture mechanics tests of neutron irradiated W fibre-reinforced W composites • Bulk material produced by chemical vapour deposition (CVD) and powder metallurgy (PM) • Short fibre material produced by PM shows degradation but keeps limited toughness • Long fibre material produced by CVD sustains toughness with very little degradation • W fibres show no sign of reduced ductility after neutron irradiation Tungsten features a unique combination of properties and is therefore the primary candidate for the most highly loaded components in future fusion power plants. However, tungsten suffers from an intrinsic brittleness at low temperature and is susceptible to operational embrittlement, meaning the degradation of material properties due to neutron irradiation will be a huge challenge. Tungsten fibre-reinforced tungsten composites overcome the intrinsic brittleness of tungsten by relying on extrinsic toughening mechanisms. The effect of neutron irradiation on these mechanisms has been an open question up to now. In this context the EUROfusion consortium launched an irradiation campaign at the Belgian reactor BR2 to study the effects of neutron irradiation on the mechanical properties of promising advanced materials including tungsten fibre-reinforced tungsten composites. In this campaign, bulk tungsten long fibre-reinforced tungsten composites produced by chemical vapour deposition and tungsten short fibre-reinforced tungsten composites produced by powder metallurgy have been irradiated for the first time under neutron irradiation. The samples have been irradiated up to 0.7-0.8dpa at 600 ∘ C and 1000 ∘ C. 3-point bending tests on miniaturised notched samples showed that both materials retain toughness after irradiation. While the short fibre-reinforced powder metallurgical material shows a deterioration of properties, the chemically deposited material shows constant toughness after irradiation even at the lowest test temperature of 100 ∘ C. The results reveal that extrinsic toughening in this material is resistant to irradiation embrittlement. Moreover, the reinforcing tungsten fibres show no sign of a reduction in ductility after irradiation. This is in contrast to results obtained for bulk tungsten, which typically suffers from significant irradiation hardening, and opens new design options.