Hydrogen retention and diffusion in tungsten beryllide

Abstract

Beryllide compounds are often used in various domains because they are more resilient to oxidation than pure beryllium and at the same time they keep some of the properties of this metal. Nevertheless, the data about their properties during atomic hydrogen exposure are very scarce: numerous experiments have been conducted in the past few years on solid hydride deposition under beryllium-seeded plasma action or on energetic hydrogen implantation into metallic beryllium; many others have been devoted to hydrogen retention and diffusion in tungsten. There have been fewer studies about hydrogen interaction with the alloys of these metals, although the beryllium-tungsten mixed compounds have been experimentally detected in laboratory experiments. This article reports on calculations carried out using first-principles density functional theory (DFT) on tungsten beryllide crystal (Be12W) taken as a model alloy. The formation and reactivity of atomic vacancies are investigated in the domain of temperature ranging from 0 to 500 K, together with atomic hydrogen retention and diffusivity in the bulk and in/out vacancies.

Valence Electron and Chemical State Analysis of Be12M (M = Ti, V) Beryllides by Soft X-ray Emission Spectroscopy

“…Previous theoretical studies by density functional theory (DFT) calculations reported defect formation energies for various types of defects in metallic Be and beryllides. , The calculated vacancy formation energies at Be i ( i = 1,2, 3) sites in Be 12 Ti and Be 12 V were in the range 1.43–1.64 eV, which were significantly higher than that in metallic Be (1.09 eV). Such increases of Be vacancy formation energy have also been reported for Be 12 W . D. V. Bachrin et al predicted that Be 12 Ti has a lower hydrogen isotope binding energy compared with that of Be, by at least 0.4 eV .…”

“…14,15 The calculated vacancy formation energies at Bei (i = 1,2, 3) sites in Be 12 Ti and Be 12 V were in the range 1.43-1.64 eV, which were significantly higher than that in metallic Be (1.09 eV). Such increases of Be vacancy formation energy have also been reported for Be 12 W. 16 D. V. Bachrin et al predicted that Be 12 Ti has a lower hydrogen isotope binding energy compared with that of Be, by at least 0.4 eV. 17 Burr et al reported that the Be-Fe(-Al) intermetallics have much lower oxygen affinity than metallic Be by calculating solution energies of oxygen.…”

Effects of the Be 22 W phase formation on hydrogen retention and blistering in mixed Be/W systems

“…This lower diffusivity for H atoms in Be 22 W can impede the movement of H atoms. 1.03 Be 12 W W 3.00 [14] Be 1.14-1.48 [14] Pure W W 3.26, 3.33, [10] 3.25 [14] Pure Be Be 1.09, 0.95, [9] 1.11 [28]…”

“…[8] However, the corresponding research on H behavior in Be-W materials is still lacking. [14] From a more fundamental point of view, it is interesting to analyze the influence of the secondary element (W) with rich electrons on the solubility and diffusion of H in the poor-electron element (Be). Furthermore, the physicochemical properties of the mixed materials and alloys are essential input data needed for the modeling of erosion, transport, and deposition in large-scale codes.…”

“…However, it will be a big challenge to employ first-principles calculations because of the large mismatch in the constants at the interfaces. As Allouche et al [14] did for Be 12 W, here we restrict our study on Be 22 W, mainly including the effects of Be 22 W phase formation on hydrogen retention and blistering in the mixed Be/W phase. When high-energy hydrogen ions are implanted into the solid, it inevitably generates Frenkel pairs and cascades of atoms and vacancies, so we will consider H solubility in both interstitial sites and near vacancies.…”