Atomic-scale investigations on the interaction mechanisms of dislocations with {112¯1} and {112¯2} twinning

The interaction mechanisms of <c+a> dislocations with {$11\overline{2}1$} and {$11\overline{2}2$} twin boundaries (TBs) were systematically investigated at the atomic-scale in pure Ti via molecular dynamics (MD) simulations and transmission electron microscopy (TEM) characterizations. Results reveal that under pure shear loading, <c+a> dislocations dissociate into <a> dislocations, twinning dislocations (TDs) ${\stackrel{\rightharpoonup }{\mathit{b}}}_{2/2}^{\left(11\overline{2}1\right)}$, and an interfacial defect ${\stackrel{\rightharpoonup }{\mathit{b}}}_{10/12}^{\left(11\overline{2}1\right)}$, or into sessile <c> dislocation with TDs ${\stackrel{\rightharpoonup }{\mathit{b}}}_{-1/-1}^{\left(11\overline{2}1\right)}$ and $-{\stackrel{\rightharpoonup }{\mathit{b}}}_{-3/-3}^{\left(11\overline{2}1\right)}$ at migrating {$11\overline{2}1$} TBs, while interactions of <c+a> dislocation with {$11\overline{2}2$} TBs produce dislocations and TDs ${\stackrel{\rightharpoonup }{\mathit{b}}}_{1/1}^{\left(11\overline{2}2\right)}$ and $-{\stackrel{\rightharpoonup }{\mathit{b}}}_{3/3}^{\left(11\overline{2}2\right)}$. The introduction of normal stress perpendicular to TBs generates shear stress components in the basal slip system, promoting basal dislocation formation to alter interaction mechanisms. Stress evolution arises from localized stress transfer from <c+a> dislocations to reaction products, where pure shear retains residual stresses in interfacial defects (increasing fracture risks), while normal stress mitigates stress concentration by modifying dissociation pathways. TEM characterization confirms the interface defect configurations, validating the proposed mechanisms. This work provides atomic-level insights into <c+a>-TB interactions and establishes a theoretical foundation for regulating dislocation-twin dynamics in α-Ti alloys, emphasizing the critical role of stress-state control in optimizing the mechanical performance.