Microstructure, hardening and deuterium retention in CVD tungsten irradiated with neutrons at temperatures of defect recovery stages II and III

Samples of ultra-high-purity tungsten prepared using chemical vapour deposition (CVD) technique were irradiated with neutrons at temperatures T irr = 373–483 K (stage II of defect recovery) and T irr = 573–673 K (stage III) up to 0.15 displacements per atom (dpa) in the Belgian reactor (BR2). The study of the microstructure of neutron-damaged samples using transmission electron microscopy (TEM) revealed visible defects with a predominance of dislocation loops. With an increase in the neutron irradiation temperature, the spatial distribution of the loops acquired pronounced inhomogeneity, and their average size moderately increased. Cavities and voids were not observed. Irradiation-induced hardening was found and a linear correlation was obtained between Vickers microhardness and nanohardness for undamaged and neutron-irradiated CVD-W samples. Irradiation of tungsten with neutrons led to a significant increase in the retention of deuterium, which accumulated mainly in vacancy-type traps. Furthermore, the influence of the columnar grain structure in low-dose neutron-irradiated tungsten seemed to be non-trivial upon deuterium retention.