Dislocation glide driven interstitial shuffling of oxygen interstitials in titanium

Abstract

The bypassing of an oxygen interstitial by $\ensuremath{\langle}a\ensuremath{\rangle}$-type screw dislocations in Ti is studied as a function of the dislocation core structure using an empirical potential and the nudged elastic band method. It is shown that an interstitial oxygen will be pushed from the octahedral site into a new interstitial site in the dislocation core. From there, with the passage of a dislocation spread primarily on the prismatic plane there is a high energy barrier for oxygen to return to the octahedral site. Instead, it is likely to shuffle into the neighboring hexahedral site, a transition expected to lead to slip plane softening. For dislocations spread primarily within the pyramidal planes, the octahedral to hexahedral transition is much less likely as there is little to no barrier for the oxygen to return to the original octahedral site. This difference in barriers is then explained by a reduction in the attraction between the hexahedral site and the dislocation core, calculated within micromechanics, as the core transitions from a prismatic to a pyramidal state.