Cluster-dynamics study on the evolution of dislocation loops in molybdenum: The role of defect diffusion coefficient and equilibrium concentration

Abstract

A cluster dynamics simulation based on rate theory was conducted to investigate the evolution of irradiation-induced dislocation loops in pure molybdenum ($\mathrm{Mo}$) irradiated with $30\mathrm{keV}$ $\mathrm{He}$⁺ at $673K$. The changes in number density and size of dislocation loops were analyzed, revealing rapid saturation of loop density with increasing dose, while the average loop radius grows and stabilizes at a maximum size. During the initial irradiation stage, significant nucleation leads to a rapid increase in loop density. The simulation results align well with in-situ transmission electron microscopy observations and clarify the kinetic mechanisms underlying key experimental features. It was found that the diffusion coefficients and thermal equilibrium concentrations of interstitial atoms and vacancies play critical roles in determining the evolution of loop density and size at elevated temperatures. This study provides insight into the microstructural evolution of irradiated molybdenum under helium ion exposure.