Atomistic investigation of the evolution of He cluster-loop complex in fcc nickel

The evolution of He bubble-loop complexes in fcc Ni is studied using atomistic simulations. The influences of temperature, He concentration and formation sequence (He bubbles formation cooperatively with or after a faulted dislocation loop) on the evolutions are systematically calculated and analyzed. Results show He bubbles nucleate at the edges of dislocation loops rather than inside them in all conditions, leading to a reduction of the formation energy of loops. We reveal two growth processes of the complexes, depending primarily on the formation sequence. When bubbles and loops grow cooperatively, the loop lines can bend around to enclose bubbles, creating complexes containing bubbles both at the loop edge and within the loop plane. When a bubble forms after a dislocation loop creation, the resulting complex contains bubbles only at the loop edge. The size of the bubble-loop complex increases with He concentration owing to additional SIAs kicked out by the He bubble, irrespective of its formation sequence. This study provides atomistic insights into He-enhanced nucleation and growth of dislocation loops in fcc metals and will help in developing a better understanding of the microstructure evolution in irradiated Ni materials.