Influence of transmutation-induced Re/Os content on defect evolution in neutron-irradiated W

The microstructure of neutron irradiated tungsten (0.1 dpa - 0.8dpa at Tirr=1200°C,) was analyzed by transmission electron microscopy applying high-sensitivity energy dispersive X-ray spectroscopy, which enables the visualization of the distribution of transmutation induced Re and Os. The study demonstrates the dose-dependent evolution of radiation-induced defects such as voids and dislocation loops as well as segregation behavior of Re and Os at these defects. Re segregation around voids occurs at the lowest damage dose of 0.1 dpa, while their enrichment on dislocation loops was detected at 0.2 dpa. Further generation of Re and Os leads to the formation of the χ-phase ((Re,Os)3W) precipitates with a needle shape on voids and on dislocation loops. The formation of Os-rich nuclei within Re clouds around loops or voids is crucial for the onset of precipitate formation. It could be shown that the subsequent formation of precipitates on dislocation loops causes the disappearance of the loops. Based on these results, a modification of a well-known defect formation diagram in W has been proposed as a function of the Re/Os content. This would provide a comparison of defect evolution in W irradiated in reactors with different transmutation rates. It would also allow a prediction of the microstructural evolution in W under fusion conditions.