Molecular dynamics studies of 〈a〉 -type screw dislocation core structure polymorphism in titanium

The atomic scale computation of dislocation core structures has become an essential tool in the development of models for the plasticity of metals. Competing dislocation core structures are often analyzed at $T=0$ K (with $T$ the temperature), and the dislocation core structure with the lowest energy is assumed to be the structure dictating the dynamics of the individual dislocation at finite temperatures. It is shown here that, for some hexagonal-close-packed (HCP) metals, this approach may be too simplistic. As a prototypical example, $\ensuremath{\langle}a\ensuremath{\rangle}$-type screw dislocations within HCP Ti modeled using an empirical interatomic potential are considered. It is shown using molecular dynamics simulations that, at room temperature and above, the core structure of the dislocation is remarkably complex and variable. The implications of this complexity for the dynamics of the dislocations are discussed.