Helium nano-bubble bursting near the nickel surface

We have investigated the expansion and bursting of a helium nano-bubble near the surface of a nickel matrix using a molecular dynamics simulation. The helium atoms erupt from the bubble in an instantaneous and volcano-like process,which leads to surface deformation consisting of cavity formation on the surface, along with modification and atomic rearrangement at the periphery of the cavity. During the kinetic releasing process, the channel may undergo the "open" and"close" states more than once due to the variation of the stress inside the nano-bubble. The ratio between the number of helium atoms and one of vacancies can directly reflect the releasing rate under different temperatures and crystallographic orientation conditions, respectively. Moreover, a special relationship between the stress and He-to-vacancy ratio is also determined. This model is tested to compare with the experimental result from Hastelloy N alloys implanted by helium ions and satisfactory agreement is obtained.