Thermal kinetics of micro-defects in He-ion implanted W and W5Re alloys

To investigate the thermal evolution of vacancy-type defects in He-ion irradiated W and W5Re alloy, different isochronal annealing treatments from 373 to 1273 K were conducted on the irradiated materials. Positron annihilation spectroscopy including positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy were mainly used to characterize the micro-defects evolution. The results showed that the thermal evolution characteristics of defects in both W and W5Re were similar. After He-ion irradiation, mono-vacancies with positron annihilation lifetime of ~ 190 ps were detected in W, together with a large amount of dislocation loops with positron annihilation lifetime of ~ 150 ps in W5Re alloys. The coarsening of vacancy clusters at the expense of small vacancy clusters was the main thermal evolution feature of vacancy-type defects in both W and W5Re when annealing temperature increased to 1073 K. In this progress, the positron annihilation lifetime increased to ~ 350 ps (clusters composed of 4 –8 mono-vacancies) in both W and W5Re. As the temperature increased to 1273 K, the positron annihilation lifetime decreased to ~ 240 ps, which was attributed to a significant population reduction of the dislocation loops, the dissociation of large HenVm complexes and the annealing of micro-voids in both W and W5Re. The vacancy-type defects in W5Re were more susceptible to the annealing temperature because of the formation of vacancy cluster-Re complexes. Re clusters in irradiated W5Re alloy could serve as the nucleation sites of He bubbles, which promoted the swelling and protrusion formation on the surface.

Change in the Positron Annihilation Lifetime of Vacancy Clusters Containing Hydrogen Atoms in Electron-Irradiated F82H

The change in the positron annihilation lifetime (PAL) of vacancy clusters before and after electrolysis hydrogen charging was determined using PAL measurements in electron-irradiated F82H. The experimental change indicated 8 hydrogen atoms were trapped in vacancy clusters; whereas the theoretical calculation resulted in approximately 14 atoms. As the samples were left at room temperature for 5 min until the start of the PAL measurements, the de-trapping effect of hydrogen atoms was also considered; approximately 13 hydrogen atoms were captured at each vacancy cluster. The PAL decreased after annealing at 148 K, which could not be explained theoretically. Therefore, further experiments and discussions are needed to obtain a precise change in the PAL of vacancy clusters containing hydrogen atoms in F82H.

Irradiation resistance mechanism of the CoCrFeMnNi equiatomic high-entropy alloy

When face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE) are irradiated by high-energy particles or deformed at high speed, stacking fault tetrahedra (SFTs), which are a type of vacancy cluster defect, are often formed. Therefore, SFTs were expected to form in the CoCrFeMnNi equiatomic high-entropy alloy (HEA). However, no SFT was observed in the CoCrFeMnNi HEA with high-speed plastic deformation even after annealing at 873 K. To elucidate this mechanism, the binding energy of vacancy clusters in the CoCrFeMnNi HEA was calculated based on first principles. The binding energy of the di-vacancy cluster was positive (average of 0.25 eV), while that of the tri-vacancy cluster was negative (average of − 0.44 eV), suggesting that the possibility of formation of a tri-vacancy cluster was low. The inability to form a cluster containing three vacancies is attributed to the excellent irradiation resistance of the CoCrFeMnNi HEA. However, if an extra vacancy is added to a tri-vacancy cluster (with negative binding energy), the binding energy of the subsequent tetra-vacancy cluster may become positive. This suggests that it is possible to form vacancy clusters in the CoCrFeMnNi HEA when high-energy ion or neutron irradiation causes cascade damage.

Vacancy cluster-induced local disordered structure for the enhancement of thermoelectric property in Cu2ZnSnSe4

Local disorder induced by vacancy clusters containing cation and intrinsic Se vacancies servers as thermoelectric performance booster in cation-deficient Cu2ZnSnSe4.

Numerical Interpretation of Hydrogen Thermal Desorption Spectra for Iron with Hydrogen-Enhanced Strain-Induced Vacancies

We obtained thermal desorption spectra of hydrogen for a small-size iron specimen to which strain was applied during charging with hydrogen atoms. In the spectra, a shoulder-shaped peak in the high-temperature side was enhanced compared with the spectra of the specimen to which only strain was applied. We also observed that the peak almost disappeared by aging processes at ≥ 373 K. Then, assuming that the shoulder-shaped peak results from hydrogen atoms released by vacancies, we simulated the thermal desorption spectra using a model incorporating the behavior of vacancies and vacancy clusters. The model considered up to vacancy cluster $${{V_9}}$$ V 9 , which is composed of nine vacancies, and employed the parameters based on atomistic calculations, including the H trapping energy of vacancies and vacancy clusters that we estimated using the molecular static calculation. As a result, we revealed that the model could, on the whole, reproduce the experimental spectra, except two characteristic differences, and also the dependence of the spectra on the aging temperature. By examining the cause of the differences, the possibilities that the diffusion of clusters of $${V_2}$$ V 2 and $${V_3}$$ V 3 is slower than the model and that vacancy clusters are generated by applying strain and H charging concurrently were indicated.