Molecular dynamics simulations were performed to investigate the synergistic effects of stacking fault energy and twin boundary on the plasticity of a periodically twinned face-centered cubic metal nanowire subjected to tensile deformation. Circular nanowires containing parallel (111) coherent twin boundaries with constant twin boundary spacing were simulated in Au, Ag, Al, Cu, Pb and Ni using different embedded-atom-method interatomic potentials. The simulations revealed a fundamental transition of plasticity in twinned metal nanowires from sharp yield and strain-softening to significant strain-hardening as the stacking fault energy of the metal decreases. This effect was shown to result from the relative change, as a function of the unstable stacking fault energy, between the stress required to nucleate new dislocations from the free surface and that to overcome the resistance of coherent twin boundaries to the glide of partial dislocations. The relevance of the present predictions to realistic nanowires in terms of microstructure, geometry and accuracy in predicting the generalized planar and stacking fault energy curves was also addressed. The findings show clear evidence that the plastic flow of twinned nanowires under tension differs markedly between face-centered cubic metals, which could help to reconcile some conflicting past observations.

Fundamental Differences in the Plasticity of Periodically Twinned Nanowires in Au, Ag, Al, Cu, Pb and Ni. C.Deng, F.Sansoz: Acta Materialia, 2009, 57[20], 6090-101