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 (MTP) and perform molecular dynamics simulations to systematically study the interactions between He atoms and the primary interstitial-type dislocation loops (1/2 and ) 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 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 K 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.