Study on the Stability of Helium Clusters and Interstitials of Helium in Tungsten

In this paper, the molecular dynamics method was used to study the binding energy of a helium atom with the helium-vacancy cluster (HenV22) in tungsten. As a result, when the heliumvacancy ratio was less than 4.5 the binding energy decreased with the helium-vacancy ratio linearly. When the heliumvacancy ratio was larger than 4.5 the binding energy appeared vibrating extremely. After analyzing kinetic processes, it was found that the phenomenon was due to the helium-vacancy cluster extruding dislocation loop form the tungsten body randomly which leading to the energy of the system droping sharply. At the same time, the helium-vacancy cluster was surrounded by some metastable fcc-tungsten and hcptungsten. Trying to explain the phenomenon, we employed the firstprinciples calculation to study the phase transformation of tungsten under high-pressure. We found that the phase transformation can not occur under hydrostatic pressure. Moreover after analyzing the charge density difference, we found that the stability of the tetrahedral interstitial helium atom was higher than that of the octahedral interstitial helium atom in bcc-tungsten, whereas the stability of the tetrahedral interstitial helium atom was weaker than the stability of the octahedral interstitial helium atom in the fcc-tungsten