Deuterium trapping by deformation-induced defects in tungsten

Abstract

The influence of defects induced by plastic deformation of tungsten (W) on deuterium (D) retention has been studied. Recrystallized W samples were subjected to tensile deformations at temperatures of 573 K and 873 K to strains in the range of 3-38 %. The dislocation density measured by transmission electron microscopy (TEM) increased by about 40 times after deformation to the highest strain. The introduced defects were decorated with D by exposure to a low-flux D plasma at sample temperatures of 370 K and 450 K. D retention in the samples was studied using nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS). The trapped D concentrations after the plasma exposures were low (up to a few times 10 −4 at. fr.) and increased more slowly with strain than the dislocation density. Small vacancy-like defects and large vacancy clusters were detected in the samples by positron annihilation lifetime spectroscopy (PALS). Their concentrations also increased with strain more weakly than the dislocation density. It was concluded that these defects governed the D retention under plasma exposure at 450 K, while dislocations gave only a small contribution. It was also found that deformation already to the lowest strains significantly facilitates the formation of blister-like structures under D plasma exposure at 370 K. The defects associated with blister-like structures presumably gave a substantial contribution to D retention at 370 K.

Strain Dependence of Energetics and Kinetics of Vacancy in Tungsten

“…Here, the initial concentration of vacancy is set to be 10 −5 appm (77 monovacancies), and the monovacancies are randomly inserted in the simulation box. The simulation temperature is 573 K, which is consistent with the experiment [ 50 ]. The vacancy object is allowed to hop to one of the eight bcc nearest neighboring lattice sites with the vibration frequency of 6 × 10 12 /s.…”

“…Recently, Zibrov et al investigated the effects of plastic deformation on the performance of W exposed to D plasma [ 50 ]. It is found that the D retention is enhanced in the deformed W, which can be attributed to the formation of vacancy-type defects induced by deformation.…”

“…Twenty independent simulations were carried out for each case, and the average results are presented in the following parts. Here, in order to compare with the experimental results [ 50 ], the temperature was set to be 573 K.…”

Effect of statistically stored dislocations in tungsten on the irradiation induced nano-hardening analyzed by different methods

“…Samples were prepared from hot-rolled polycrystalline tungsten (W) with a purity of 99.97 wt.% manufactured by Plansee (Austria). The samples underwent the treatment described in [40,41] . In short, the samples were recrystallized at 1600 °C for 1 h in vacuum (2-5 × 10 −4 mbar) at Forschungszentrum Jülich.…”

“…This procedure led to a W grade, henceforth RX, with grain size in the range 10-50 μm with dislocation density (5.1 ±1.7) × 10 12 m −2 [40,41] . To increase the dislocation density in the grains, part of the samples were plastically deformed at 600 °C up to an engineering strain of 22% (see [40,41] for a detailed description) at SCK CEN. The obtained W grade, henceforth RX-22, has the same grain size as RX, but with increased dislocation density (8 ±3) × 10 13 m −2 .…”