Defect clustering upon dislocation annihilation in α-titanium and α-zirconium with hexagonal close-packed structure

Abstract

The annihilation of vacancy- and interstitial-type dislocation dipoles is investigated employing atomistic simulations and metadynamics in hexagonal close-packed (hcp) metals α-titanium and α-zirconium, with a variety of dipole heights, orientations and annealing temperatures. Molecular dynamics simulations reveal that depending on the dipole type, height, orientation, etc., dipolar configurations transform into specific reconstructed configurations at low temperature, while vacancy or interstitial clustering occurs at high temperature. The time of clustering and the lifetime of the resulting clusters are estimated through the search of the lowest-energy paths. Compared with previous knowledge on face-centered cubic (fcc) metals, the general processes of dislocation annihilation and point defect clustering are similar, however, due to the varied lattice symmetry: (1) the atomic structures of the reconstructed configurations at low temperature and the clusters at high temperature in hcp systems are different from those in fcc systems; and (2) in hcp systems the clustering process is shortened and the stability of the resulting clusters is enhanced compared with fcc systems.