Numerical and theoretical study on shock-induced coalescence of He bubbles

As an important irradiation defect, the behavior of helium (He) bubble is very important to understand the mechanical properties of irradiated metals. In this work, the coalescence mechanism of He bubbles in Al under shock compression is revealed with atomistic simulations and theoretical analysis. Our simulations show two coalescence modes caused by ligament failure and interface deformation. The former is driven by the pressure difference, occurs when the kinetic energy of the shocked He bubble is sufficient to break through the ligament; the latter is driven by the surface tension, characterized as the contacting at one point and the subsequent smoothing of a neck connecting the two He bubbles. For the He bubbles with short spacing, the coalescence is easily dominated by the ligament failure, while the He bubbles with large spacing have the opportunity to contact each other after shock migration, resulting in the coalescence dominated by the interface. Furthermore, the Frenkel-like model based on the balance of the surface tension and viscous forces is successfully used to predict the time required for coalescence. The time required for coalescence is proportional to the bubble radius and the matrix viscosity. In terms of reproducing the morphological evolution, the real-time radius of the MD results is slightly smaller than that of the theory result in the later stage due to the observed smoothing of the local curvature in the MD simulation.