Direct observation of voids decorated with transmuted rhenium atoms in neutron-irradiated tungsten by correlative use of TEM and APT

The microstructure of tungsten (W) irradiated by neutrons up to 1.54 displacements per atom at 750 degrees C in the fast-neutron experimental reactor Joyo, where the thermal neutron ratio is low, was characterized by observing same needle specimen by both transmission electron microscopy (TEM) and atom probe tomography (APT). TEM showed nanoscale voids with a high number density in the matrix, while APT showed nanoscale rhenium (Re)enriched clusters with a similar number density in the matrix. By comparing the TEM image and APT map in the same area of the same needle specimen, a one-to-one correspondence was clearly obtained between the voids observed by TEM and the Re-enriched clusters observed by APT. Furthermore, the size distributions for the voids and Re-enriched clusters were almost the same. Thus, it was found that all voids were decorated with transmuted Re atoms in the (initially pure) W neutron-irradiated in Joyo where the thermal neutron ratio is low.