Investigations on the deformation mechanisms of single-crystalline Cu nanowires under bending and torsion

• We model 〈0 0 1〉/{1 0 0} single-crystalline Cu nanowires under bending and torsion.
• Fivefold deformation twins (FDTs) are formed at large bending angles.
• A reciprocal phase transformation is necessary for the formation of FDTs.
• An orientation change of stress is also essential for the formation of FDTs.

Molecular dynamics simulations are used to investigate the deformation behavior of 〈0 0 1〉/{1 0 0} single-crystalline Cu nanowires under bending and torsion. For 〈0 0 1〉/{1 0 0} Cu nanowires subjected to bending loadings, fivefold deformation twins are observed at large bending angles. The formation process can be understood by two dominate factors, i.e., the reciprocal phase transformation from atoms of other 12-coordinate lattice to hcp lattice and the annihilation of dislocations on adjacent slip planes to form a twin boundary. In addition, an orientation change of applied stress is essential for its formation. For 〈0 0 1〉/{1 0 0} Cu nanowires under torsion, the creation of full dislocations from the ends of nanowires is responsible for the plastic deformation mechanism. Moreover, damage is found to occur nearby the ends of nanowires, which is caused by the formation of dense network of dislocation jogs.