Abstract: The stabilities and migration behaviors of 1/2<110> perfect vacancy loops in various FCC metals are studied by molecular dynamics (MD) simulations. Compression strain can suppress the spontaneous structural transformation from perfect vacancy loops to sessile stacking fault tetrahedra (SFTs). Instead, an intermediate stable structure containing four stacking faults and exhibiting one-dimensional (1-D) fast migration is formed. The migration is essentially enhanced with the compression strain, the corresponding migration barrier can be as low as 0.002 eV for perfect loop containing 100 vacancies in Cu under 4 % compression strain. Furthermore, the stabilities and mobilities of intermediate structures are increased with the decrease of stacking fault energy (SFE) for Au, Cu, Ni and Al. Two different migration modes, including collective glide and change of habit planes, are observed, the dominant migration behavior depends on the loop size and compression strain. The energetics of 1/2<110> perfect vacancy loops and SFTs, as well as the energy landscapes of two 1-D migration modes, are calculated to interpret its structural transformation and migration behaviors. This study first reveals the fast migration behaviors of perfect vacancy loops in FCC metals and the underlying mechanisms, especially the important role of compression strain, which would provide important clues for understanding the variations of microstructures and properties related with vacancy behaviors.

Key words: Molecular dynamics, Perfect vacancy loops, Stacking fault tetrahedra, Migration behaviors, Compression strain