Annealing of radiation-induced damage in tungsten under and after irradiation with 20 MeV self-ions

Abstract

Accumulation and recovery of radiation defects under/after self-ion irradiation in tungsten (W) have been investigated via decoration with deuterium (D) and scanning transmission electron microscopy (STEM). The deuterium was incorporated in damaged material by low-energy D plasma. The D concentration at radiation-induced defects in each sample was subsequently measured by nuclear reaction analysis allowing determination of the D concentration at depths up to 6μm. The total D retention was measured by thermal desorption spectroscopy. It was shown that pre-irradiation with self-ions led to rather high D concentration (⩾ 0.1at.%) in W even at high temperatures (⩾ 700K) due to formation of defects with high de-trapping energy for deuterium. The annealing of defects with low trapping energy for D occurs intensively in the temperature range between 300 and 700K. The radiation-induced defects with high de-trapping energy for D are thermally stable at least up to 1100K. The rearrangement and partial healing of dislocations as well as coalescence of small clusters in a big ones accompanied by a reduction of the total density of defects was observed by STEM after annealing of radiation-induced defects in recrystallized tungsten at 1000K. The D retention monotonically decreases in recrystallized W with increasing of annealing temperature up to 1100K that is in agreement with the reduction of radiation defect density observed by STEM. However, an increase of the D retention in ‘as received’ W pre-irradiated with self-ions at annealing temperature of around 1000K was found. The increase of the D retention at annealing temperature of ∼1000K was not observed in the case of recrystallized W pre-irradiated with self-ions. The mechanism of recovery of radiation-induced defects in dependence on the initial intrinsic defects (grain size, impurities, etc.) in W is discussed.