An atomistic study of the thermal and anti-thermal behavior of incoherent twin step migration under an elastic energy driving force

The migration of Σ3{112} incoherent twin boundaries (ITBs) leads to the occurrence of twinning or detwinning of nanotwinned face-centered-cubic metals, however, its temperature dependence of migration behavior is still an open issue. In the present work, the migration of Σ3{112} ITB step driven by an elastic energy driving force in Cu and Ni was investigated using the molecular dynamics simulation method. The driving force originates from the strain energy imbalance between the two sides of the twin boundary under normal-shear strains coupling conditions. The simulation results show that both thermally activated and anti-thermally activated migrations occur in Cu; however, only anti-thermally activated migration occurs in Ni. Further investigation reveals that there exists a critical temperature (T_c) determined by the ITB step migration energy barrier. When temperature is lower than T_c, the ITB step displays thermally activated migration; the ITB step otherwise conducts anti-thermally activated migration. The elastic energy driving force method and present theoretical analysis can likely be extended to explain the thermally activated and anti-thermally activated migration of general grain boundaries, will shed light on both Σ3{112} ITBs migration and general grain boundaries migration.