Atomistic mechanisms of helium–dislocation loop interactions in molybdenum: Insights from a machine-learning moment tensor potential

Molybdenum (Mo) is a key structural material for advanced nuclear systems, yet under irradiation, the formation of helium (He) bubbles and dislocation loops leads to severe degradation. Understanding He–dislocation loop interactions at the atomic scale is essential for predicting long-term performance. In this work, we develop a machine-learning Moment Tensor Potential and perform molecular dynamics simulations to systematically study the interactions between He atoms and the primary interstitial-type dislocation loops (1/2 ⟨111⟩ and ⟨100⟩) in BCC Mo. Our results show that dislocation loops act as strong trapping sites for He, modifying its spatial distribution and promoting heterogeneous nucleation of He clusters, with the ⟨100⟩ loop having a stronger effect. Conversely, He enhances loop growth by absorbing self-interstitial atoms, a process that intensifies with He concentration. A pronounced pinning effect of He on loop glide is observed, effectively immobilizing loops at 600 and 1200 K, though thermal activation at 1800 K partially releases this pinning. This study elucidates the mutual enhancement mechanism between He and dislocation loops, offering fundamental insights for designing radiation-resistant Mo alloys.