The growth and coalescence of helium bubbles in bicrystal copper under tension

Molecular dynamics (MD) simulations are used to study the growth and coalescence of helium (He) bubbles in bicrystal copper (Cu) on an atomistic scale. The influences of He bubble positions, GB's characteristics, and initial temperatures on the coalescence mechanism are clarified. Our results reveal that the He bubbles distributed perpendicular to the loading direction are easier to coalesce than the parallel ones, and GB will accelerate this process due to the high diffusivity of the GB atoms. A spindle-shaped structure is observed during coalescence for the He bubbles in GB, due to the faster atomic diffusion along the GB plane. Three stages of He bubbles evolution are interpreted during tension loading. For He bubbles distributed in the GB plane, the GBs composed of fewer structural units show a reduced ability to promote the growth and coalescence of He bubbles. What's more, the temperature is found to accelerate the coalescence process due to the faster diffusion of surface atoms at higher temperatures.