Thermodynamic model for polymorphic dislocation core spreading within hexagonal close packed metals

Abstract

An exactly solvable thermodynamic model for the core structure of $\ensuremath{\langle}a\ensuremath{\rangle}$-type screw dislocations in $\ensuremath{\alpha}$-Ti is introduced and used to explore the role in which polymorphic core spreading contributes to the free energy of the dislocation. Each segment of the dislocation core is assumed to be in one of three possible configurations, and the free energy differences per segment between dislocation core spreadings are taken as parameters. It is shown that thermal fluctuations between the core spreadings should be common, even at room temperature, and that these fluctuations can contribute significantly to the free energy. It is also shown that under some circumstances, the core structures can display morphological switching wherein the stable core spreading changes morphology with a change in temperature. The implications for dislocation dynamics and for modeling finite temperature dislocation core properties using molecular dynamics simulations are considered.