The effect of coherent twin boundary migration on the deformation mechanism of Fe-Ni nanowires: molecular dynamics simulation.

Fe-Ni nanowires (NWs) containing coherent twin boundaries (CTBs) have received widespread attention in recent years owing to their unique chemical properties. It is important to understand the influence of CTBs on the deformation mechanism of Fe-Ni alloy NWs to develop functional materials based on Fe-Ni alloy NWs. The deformation process of BCC Fe-Ni NWs containing several CTBs under uniaxial stretching was simulated using the molecular dynamics method. It is shown that the NWs of CTBs exhibit two deformation mechanisms under uniaxial stretching. The first mechanism shows that CTB migrates and then completely merges and disappears after yielding the NWs. In this case, if dislocations occur, only few dislocation lines are generated. During the stretching process, the potential energy of atoms within grains increases slowly, while the potential energy of atoms on the CTB increases rapidly. Thus, the whole CTB has a huge activation energy, which leads to its migration. The second mechanism is that during deformation, CTBs of NWs do not migrate. In this case, the potential energy of almost all atoms in the NWs increases. Thus, the local energy of the NWs jumps to a higher level. The higher local energy changes their structure near the CTB from the BCC phase to amorphous structural phases, and the nucleations of deformation twins and those of dislocation lines occur in these regions. Furthermore, the twins and dislocations grow within the grains. These grown twins and dislocations impede the migration of CTB. These findings are beneficial for the better application of alloy nanowires containing coherent twin boundaries.