Enhanced vacancy-interstitial annihilation via sliding, rotation and emission of the interstitial in tungsten

Experimental studies have demonstrated that introducing alloying elements into bulk tungsten effectively mitigates radiation-induced swelling. This improvement is attributed to enhanced annihilation between vacancies and self-interstitial atoms (SIAs) facilitated by alloying elements. However, the precise atomic-scale mechanisms governing this process remain unclear. In this work, we investigated the dynamic annihilation mechanisms of vacancies with both free and alloying-elements-pinned SIA clusters through combined molecular statics and dynamics simulations. Motivated by the high-energy intermediate state of a SIA cluster motion, we analysed the relevant atomic trajectories and energy landscapes, and identified three key processes driving SIA-mediated vacancy annihilation: sliding, rotation and emission of the interstitial. These processes collectively extend the effective annihilation region of SIAs beyond the limited spatial range predicted by static lattice stability calculations. Crucially, the dynamic coupling between vacancy hopping and these SIA behaviours further amplifies the annihilation volume, offering a mechanistic basis for the large annihilation radii hypothesized in rate theory. This work provides atomic-level insights into vacancy annihilation dynamics and reveals that the radiation-induced SIA clusters, when stabilized by alloying elements, act as efficient vacancy scavengers. These findings establish a framework for optimizing radiation-resistant materials through synergistic strategies of alloy design and grain refinement.