Helium bubbles diffusion in aluminum: Influence of gas pressure

The influence of helium pressure on the mechanisms of diffusion of the He-filled nanobubbles in fcc Al is investigated by the classical molecular dynamics. It is shown that at pressures < 20 kbar gas sup-presses self-diffusion, while the concentration of adatoms, rather than their mobility, plays a key role. However, as the pressure increases to values at which the bubble emits self-interstitial atoms, the sur-face self-diffusion and bubble diffusion coefficients begin to increase. It is shown that the bubble diffusion coefficient is proportional to the concentration of self-interstitial atoms in the surface layer. At higher gas pressures, self-interstitial atoms form dislocation loops around the bubble and bubble diffusion coeffi-cient drops significantly. The effect of surface self-diffusion suppression by gas pressure cannot explain the experimental data, while they can be explained by dislocation loops formation around bubbles. Two interatomic interactions models for Al-He system are considered. It is shown that the main findings of this work do not depend on the choice of the model.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The influence of helium pressure on the diffusion mechanisms of He-filled nanobubbles in fcc Al is investigated using classical molecular dynamics. It is found that at pressures below 20 kbar, gas suppresses self-diffusion by affecting the concentration of adatoms. However, at higher pressures, bubble diffusion coefficients increase due to the emission of self-interstitial atoms. The formation of dislocation loops around the bubble leads to a significant drop in the bubble diffusion coefficient at higher gas pressures. The effect of surface self-diffusion suppression cannot explain the experimental data, while the formation of dislocation loops can.