Atomistic insight into the thermodynamic properties and the surrounding deformation of high-pressurized He bubbles in Al

Abstract

There exist a large number of nanoscale high-pressurized He bubbles in irradiated metal, and the microstructural property and mechanical effect of He bubbles have not been fully understood up to now. In this work, we investigate the high-pressurized He bubbles in Al via atomistic simulations, where the thermodynamic properties of He bubbles and the local deformation in Al are demonstrated by considering the initial size, the number ratio of He to vacancy, as well as the temperature. First of all, our simulations indicate that the He bubbles reach a saturated state when the He number density exceeds 47nm-3 for all the He bubble sizes at 300 K, which is in agreement with the experimental findings. As for the unsaturated state, the pressure in He bubbles increases with the number ratio of He to vacancy, with finite elastic deformation around the He bubbles. As for the saturated state, the pressure in He bubbles can be described as a function of volume and temperature. By considering the nanoscale interface effect, we propose an empirical pressure model for the saturated He bubbles, with a good coverage of our simulation points. At the same time, the mechanism of local hardening around the He bubble is discussed. Stacking fault octahedra on the {111} planes are found due to the expansion of high-pressurized He bubbles. Over-saturated He bubbles expand through the dislocation emission from sessile junctions, dependent on the maximal yield strength of Al. Moreover, with the increase of temperature, the shape of the He bubbles changes due to the reduction of stacking fault planes, and eventually develops into a sphere. At last, the shear stress distribution and the number of dislocation atom are also discussed.