Simulation study of helium bubble coalescence in tungsten at various temperatures relevant to fusion conditions

J Zhan and T Okita and MY Ye and D Kato and K Suzuki, COMPUTATIONAL MATERIALS SCIENCE, 187, 110076 (2021).

DOI: 10.1016/j.commatsci.2020.110076

Molecular dynamics (MD) methods are used to study nanosized helium (He) bubble coalescence process in tungsten (W) at various temperatures relevant to fusion conditions, on an atomistic scale. Bubble coalescence in W is observed at a higher temperature and He/V ratio, while the calculated internal bubble pressure due to virial stress increases with the increase in the He/V ratio; bubble coalescence is significantly dependent on the bubble distance. In these MD simulations, coalescence occurs, only when the surface distance between the two bubbles is equal to 1a(0), where a(0) denotes the lattice constant and is approximately 0.317 nm at 2100 K. On the other hand, a bubble diameter between 1a(0) and 3a(0) may have relatively limited effect on the coalescence, although largersized bubbles may have higher migration energy. Local stress profile calculated indicates that initial bubbles can interact with each other, which may enhance the He atoms diffusion between bubbles and their coalescence. Physical contact at the initial stage of coalescence may occur between two nearby bubbles accompanied by W lattice distortion because of the limited displacement of W atoms near the bubbles and rapid migration of He atoms within the two bubbles. These results are beneficial for understanding the evolution of He bubbles in bulk W.

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