In this work the correlation of the neutron radiation damage and tungsten (W) microstructure is investigated. Further, the modification of the structure as a result of the neutron irradiation is assessed and its effect on the mechanical properties is determined. Forged bar (ITER grade), cold rolled sheet, and single crystalline tungsten materials were neutron irradiated at 600 °C to a damage of 0.12 displacements per atom. Neutron irradiation results in the formation of voids of almost the same size (larger than 1 nm) and dislocations detected by positron annihilation lifetime spectroscopy. All W grades have similar total dislocation densities, in the range of (1.6–2.4)×10 ¹⁴ m ⁻² , as determined by electrical resistivity measurements. After irradiation the hardness of all tungsten grades increases and the largest increase is that of the single crystal (47%), whereas the smallest that of the sheet (13%). Increase in the yield strength, correlated to the increase of the hardness, is also found. The largest increase is observed for the single crystal (25%) and the smallest for the sheet (6%). The different degrees of hardening and strengthening indicate that the microstructure of the different tungsten grades has a significant influence on their neutron radiation damage resistance.

Defect recovery and recrystallization studies of neutron-irradiated tungsten (W) addressing the microstructural evolution in relation to the mechanical properties, provide valuable insight into defect interactions and annihilation processes. Understanding these mechanisms can aid in the development of effective healing processes, potentially extending the lifespan of fusion reactor components. Additionally, this research helps to elucidate how neutron exposure alters the behaviour of materials used in fusion reactor components, contributing to improved design and durability. Within this framework, an ITER grade forged W bar was neutron irradiated to a damage of 0.21 displacements per atom at 600 °C and subsequently isochronally annealed from 700 up to 1550 °C in 50 °C steps. Irradiation causes the formation of dislocation loops and vacancy clusters as well as the formation of Re and Os transmutation products, leading to a 35% increase in hardness and a 23% increase in resistivity. The evolution of the microstructure after isochronal annealing is investigated through positron annihilation lifetime spectroscopy, X-ray diffraction, resistivity, and Vickers hardness measurements. The total dislocation line density as well as the number density and size of voids are determined as a function of annealing temperature. Specifically, the critical resolved stresses of dislocations and voids are correlated with their densities and distinct recovery stages are identified. The kinetics of defect annihilation are discussed in relation to the annealing temperature. Nearly complete dislocation annihilation occurs after annealing at 1300 °C, followed by complete void dissolution and recrystallization at 1450 °C.

During Phase I of WEST operation, one of the lower divertor sectors, known as the test sector, was partially equipped with actively cooled ITER-like plasma-facing units (PFUs) made of 35 monoblocks (MBs). A visual inspection of the test sector after the C4 campaign revealed changes on the surface condition of several MBs located in the outer strike area. In this work, one of the MBs of interest, MB 28 from PFU#13, was extensively investigated focusing on fuel retention, material migration (erosion, transport, redeposition), and surface morphology. The plasma exposed surface of MB 28 exhibited four distinct zones along the toroidal direction. In the first zone, extending up to 4 mm from the leading edge (LE), the surface showed signs of erosion, with periodically spaced cracks oriented perpendicular to the LE. The second zone exhibited the highest material deposition (B, N, Fe and Cu) and fuel (D and He) retention, with the maximum deposit thickness reaching approximately 1.5 μ m. In the third zone, the deposition gradually decreased and accumulated in linear areas. The fourth zone, near the trailing edge, was marked by the maximum hydrogen ( H ) and carbon ( C ) deposition. In this zone, linear deposition areas rich in O and B were detected, running parallel to the edge. A clear correlation was observed between the deposition of B, N, Fe and Cu and the retention of D and He.