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. (C) 2017 Elsevier B.V. All rights reserved.