Effect of displacement damage level on the ion-irradiation affected zone evolution in W single crystals

Pure tungsten (W) single crystals of (001) and (011) surface orientations, denoted as W{001} and W{011}, respectively, were irradiated with 6.4 MeV Fe3+ ions up to the displacement damages of 0.1 and 2 dpa at 573 K. Nanoindentation (NI) hardness measurements showed that the hardness profiles of both the W single crystals were independent of the damage level and kept the same trend of the orientation dependence that the hardening profile of NI hardness was deeper in W{001} than W{011}. In contrast, TEM examinations revealed that the ion-irradiation affected zone evolution was remarkably influenced by the damage level showing 1.5 times deeper extended ion-irradiation affected zone in W{001} than in W{011} after irradiation to 2 dpa, while no such an orientation dependence was observed after irradiation to 0.1 dpa. In W{011}, the ion-irradiation affected zone sizes almost matched the target depth results of SRIM code calculation irrespective of damage level. At the displacement damage of 1 and 2 dpa, a double black band structure with a number of ordered networks of dislocation loop rafts was observed in both the W{001} and W{011}, while in the case of 0.1dpa, the major defect type in W{001} was isolated dislocation loops and those in W{011} was dislocation loop rafts. The TEM microstructural evolution affected by damage level and crystal orientation was interpreted in terms of 1D motion of dislocation loops.