Vacancy clustering to faulted loop, stacking fault tetrahedron and void in fcc metals

An atomistic step of growth to a faulted loop, a stacking fault tetrahedron (sft) and a void by clustering of vacancies in fee metals was studied by molecular dynamics computer simulation with an isotropic EAM potential due to Daw and Baskes [1]. In aluminum, a tri-vacancy relaxes to the Damask-Dienes-Weizer structure (3v-sft). A penta-vacancy relaxes to an octahedral 6v in which an atom is included. The relaxed 5v is stable so that a 6v grows to doubly linked relaxed 5v. This is a critical step of faulted loop formation. By further absorption of vacancy, a cluster grows to an array of relaxed 5vs on a (1 1 1) plane and finally collapses to a faulted loop. In gold, a stable structure of vacancy cluster below 15v is a void. A tri-vacancy in gold does not relax to the Damask-Dienes-Weizer structure. Above the size of 6v, partial relaxation of 3v-sft type was observed. The relaxation of a micro-void to a sft is the thermal activated process. In nickel, a void is the most stable cluster below 20v and a sft is the most stable structure above the size of 20v. In Ni, a micro-void grows to a large void due to the difficulty of relaxation to a sft. Vacancies in Ag grow to a sft in the similar way as vacancy clustering in Au.