Influence of grain boundaries on the loop-punching mechanism and shape of helium bubbles in tungsten

In the present work, the growth of helium bubble at Σ3(112)[110], Σ5(013)[100] and Σ13(015)[100] three grain boundaries in tungsten is studied using molecular dynamics simulation. The simulation results show that interstitial dislocation loops are pushed out earlier for the case He bubble growing at the Σ3(112)[110] and later for the case bubble growing at the Σ5(013)[100], while no prismatic interstitial dislocation loop is pushed out for the case bubble growing at Σ13(015)[100] by the end of the simulation. This is because the larger the excess volume per area of grain boundary, the later the prismatic interstitial dislocation loop pushed out. The shapes of helium bubbles are monitored by measuring bubbles sizes along three dimensions during their growing process. Helium bubble grows into a shape slightly deviating from the sphere at Σ3(112)[110] twin boundary; while grows into ellipsoid at Σ5(013)[100] and Σ13(015)[100] grain boundaries. Based on a two-dimensional model, the shapes of helium bubbles are then investigated quantitatively in terms of wetting theory. The theoretical shapes of helium bubbles at the three grain boundaries are in agreement with those obtained by molecular dynamics simulation method, indicating that the growth of helium bubble at grain boundaries obeys the wetting theory.