Nature and thermal stability of radiation defects in single-crystal tungsten

Conclusions

• 1. The irradiation of single-crystal tungsten of the electron-beam zone-melted type with an integrated neutron flux of 1.4·10²² neutrons/cm² (4·10²¹ neutrons/cm² with an energy of E>1 MeV) at 450–500°C raises the electrical resistivity by 18% at 298°K, 140% at 77°K, and almost 1000 times at 4.2°K, and also causes rhenium to accumulate to the extent of 0.2 at.%.

• 2. We observed three annealing stages of the radiation defects, identified as follows: at 500–800°C (“stage IV”), small hydrogen aggregates; at 950–1200°C (“stage V”), single vacancies and small vacancy aggregates; at 1200–1900°C (“stage VI”), dislocation loops and pores. The activation energies for these three stages are 0.70±0.03, 3.2±0.3, and 6.4±0.5 eV respectively, and the annealing-rate maxima occur at 0.24, 0.35, and 0.45 T_m.

• 3. The change in the resistivity of single-crystal tungsten on irradiation is associated with the formation of small aggegates of hydrogen atoms (20.2%), single vacancies (16.5%), complex defects (43.3%), and rhenium (20%).

• 4. A high integrated neutron flux, a high irradiation temperature, e.g., (0.20–0.21) T_m, and the absence of grain boundaries as sinks for defects lead to the predominant accumulation of complex defects in single-crystal tungsten; these are stable up to 1900°C and their chief effect is that of a change in electrical resistance.