Strain Dependence of Energetics and Kinetics of Vacancy in Tungsten

Abstract

We investigate the influence of hydrostatic/biaxial strain on the formation, migration, and clustering of vacancy in tungsten (W) using a first-principles method, and show that the vacancy behaviors are strongly dependent on the strain. Both a monovacancy formation energy and a divacancy binding energy decrease with the increasing of compressive hydrostatic/biaxial strain, but increase with the increasing of tensile strain. Specifically, the binding energy of divacancy changes from negative to positive when the hydrostatic (biaxial) tensile strain is larger than 1.5% (2%). These results indicate that the compressive strain will facilitate the formation of monovacancy in W, while the tensile strain will enhance the attraction between vacancies. This can be attributed to the redistribution of electronic states of W atoms surrounding vacancy. Furthermore, although the migration energy of the monovacancy also exhibits a monotonic linear dependence on the hydrostatic strain, it shows a parabola with an opening down under the biaxial strain. Namely, the vacancy mobility will always be promoted by biaxial strain in W, almost independent of the sign of strain. Such unexpected anisotropic strain-enhanced vacancy mobility originates from the Poisson effect. On the basis of the first-principles results, the nucleation of vacancy clusters in strained W is further determined with the object kinetic Monte Carlo simulations. It is found that the formation time of tri-vacancy decrease significantly with the increasing of tensile strain, while the vacancy clusters are not observed in compressively strained W, indicating that the tensile strain can enhance the formation of voids. Our results provide a good reference for understanding the vacancy behaviors in W.

The promotion effect of uniaxial strain on hydrogen aggregation in tungsten

“…As seen in Table 1, when +1% and −1% uniaxial strain was applied, the formation energy of a single vacancy slightly increased and decreased, respectively. This suggests that the tensile (compressive) strain facilitated (suppresses) the vacancy formation in W, which originated from the electronic states variation of W atoms induced by the strain, as analyzed and discussed in previous studies (Hossain and Marian, 2014;Li et al, 2020). However, in comparison with the influence of H platelets, that of uniaxial strain on vacancy formation energy was negligible (≤0.11 eV), regardless of whether it was with or without planar H clusters.…”

Influence of helium on the evolution of irradiation-induced defects in tungsten: An object kinetic Monte Carlo simulation*

“…Our OKMC simulations were performed in a selfdeveloped code, which is suitable to investigate the defects evolution in nuclear materials. [40] Within the OKMC framework, all defects (i.e., vacancy, SIA, He and their complexes) are regarded as the objects at specific position with postulated reaction radii. In OKMC simulations, there are two different types of process that may occur, including the thermalactivated event and non-thermal-activated event.…”

“…The detailed information of our OKMC model are described in Refs. [34,40,41] and references therein.…”

Collaborative motion of helium and self-interstitial atoms enhanced self-healing efficiency of irradiation-induced defects in tungsten

“…As a stochastic computational method, the OKMC is an effective tool to explore the defects evolution in materials. Here, our OKMC simulation were performed in a self-developed code [32]. Similar with previous OKMC studies [17,33], many pre-defined events take place in the OKMC simulation inherently, and can be classified into four types, including the clustering (or recombination between vacancy and SIA), adsorption, migration and dissociation of defects.…”