By means of an ab initio plane-wave pseudopotential method, monovacancy, divacancy and self-interstitials in hexagonal close-packed titanium were investigated. The calculated monovacancy formation energy was 1.97 eV, which was in excellent agreement with other theoretical calculations, and agrees qualitatively with published experimental results. The relaxation of the atoms around a single vacancy was observed to be small. Two divacancy configurations, the in-plane and the off-plane, have also been shown to be equally stable. With regards to the interstitials, of the eight configurations studied, two (octahedral and basal octahedral) have relatively lower formation energies and are, thus, the most likely stable configurations. Small energy differences were found between them, suggesting their possible co-existence. It was also observed that the tetrahedral configuration decays to a split dumbbell configuration, whereas both the basal tetrahedral and the basal pseudo-crowdion interstitials decay to the basal octahedral configuration. Using the nudged elastic band method, a possible minimum energy path was determined for the diffusion of self-interstitial titanium atoms from an octahedral site to the nearest octahedral site. The energy barrier for this migration mechanism was shown to be about 0.20eV.

Ab initio Pseudopotential Study of Vacancies and Self-Interstitials in HCP Titanium. A.T.Raji, S.Scandolo, R.Mazzarello, S.Nsengiyumva, M.Härting, D.T.Britton: Philosophical Magazine, 2009, 89[20], 1629-45