Diffusion of helium in tungsten-based refractory alloys by molecular dynamics simulations

Refractory tungsten-based medium- and high-entropy alloys have emerged as promising radiation-resistant candidates for fusion applications. Understanding the behavior of helium (He) in refractory metals and alloys is critical for the development of fusion reactors, as He accumulation can lead to material degradation and failure. Based on a machine-learned tabulated Gaussian approximation potential for WTaVMoNb and a pair potential for He-He, we present a new interatomic potential to model the interaction between He atoms and WTaVMoNb. We calculate the binding energies of He-He and vacancy-He clusters as well as the migration energies of He in pure metals and various alloys. We find that the chemical environment strongly influences the migration of He. In pure metals and alloys without V, the migration energy of a single He atom is much smaller than the migration energy of a single vacancy, which is, in turn, smaller than the binding energy of a He atom to a vacancy. Moreover, in these alloys, we do not observe an overlap of the distributions of these energies. In contrast, in alloys containing V, there is a large degree of overlap between these energies, indicating weaker He clustering. We also directly simulate the diffusion of He and nucleation of He clusters in various alloys containing vacancies and vacancy clusters. The results show that only a small proportion of He atoms combine with vacancies to form clusters in V-containing alloys and that He atoms are easier trapped in voids than in vacancy dislocation loops.