Atomistic simulation study on twin orientation and spacing distribution effects on nanotwinned Cu films

Abstract

Affected by twin orientation and spacing distribution, different deformation and failure mechanisms of nanotwinned (NT) Cu films are discovered. For films with the same twin spacing, transition from brittle to ductile and ductile to localized necking with the increase of the slanted angle of twin boundary (TB) from 0° to 90° is examined. Two dominant slip mechanisms: (1) slip intersecting with the TBs; (2) slip parallel to the TBs can uncover the transition mechanisms with consideration of twin orientation. To maintain both relatively high strength and good ductility, the slanted angle can be set close to the ductile to localized necking transition border. Besides, the stress–strain curves obtained in this article show that the mechanical responses on both sides of the turning point 45° are asymmetric. On the other hand, the twin spacing distributions affect the ductility of NT Cu films and have almost no contribution to strengthening. The strength of the NT Cu films mainly depends on the twin density. NT Cu films with different twin spacing have worse ductility than equal twin spacing films due to the local twin spacing asymmetry. The failures can be predicted appearing at TBs adjacent to large twin spacing regions, and the failure propagation direction can also be predicted by knowing the obtuse angle decided by stacking faults and TBs.