Effects of twin and surface facet on strain-rate sensitivity of gold nanowires at different temperatures

We use classical molecular-dynamics simulations to examine the strain-rate sensitivity of single-crystalline and twinned Au nanowires (NWs) with a diameter of 12.3 nm deformed in tension at temperatures between 10 K and 450 K. It is found that the strain-rate sensitivity above 100 K is significantly smaller in twinned Au NWs with perfectly circular cross-section than in similar NWs without twins, while the activation volume remains in the same range of 1b(3)-15b(3) with b the magnitude of Burgers vector. This behavior is markedly different from that generally observed in bulk face-centered cubic metals where addition of nanoscale twins increases both strength and strain-rate sensitivity. Furthermore, our simulations show a threefold decrease in strain-rate sensitivity in twinned Au NWs with zigzag morphology constructed by assembly of {111} surface facets in comparison to the different types of circular Au NWs. The rate-controlling deformation mechanisms related to surface dislocation emission and twin-slip interaction, and their dependence on temperature and surface morphology are analyzed in detail. The combination of ultrahigh strength and decreased sensitivity to strain-rate predicted above 100 K in twinned Au NWs with faceted surface morphology holds great promise for creating metallic nanostructures with increased failure resistance to extreme loading conditions.