Wedge-shaped twins and pseudoelasticity in fcc metallic nanowires under bending

Molecular dynamics simulations were performed to study the deformation mechanisms of 〈110〉-oriented, faceted Cu and Au nanowires under bending along three different crystallographic directions. Independent of the bending direction, the stress field is characterized by a highly nonlinear elastic response, leading to a shift of the neutral fiber away from the central wire axis. The nanowires show ultra-high yield strengths, and the achievable large elastic strains directly influence the dislocation nucleation through the change of the unstable stacking fault energy. In agreement with theory and experiments on face-centered cubic 〈110〉 nanowires under uniaxial load, the tensile part of the wires exhibit deformation twinning, while plastic deformation in the compressed part takes place by slip of perfect dislocations. Independent of the bending direction, wire size, temperature and bending rate, all wires showed the formation of wedge-shaped twins. Upon instantaneous load removal, wires bent in two of the three directions showed spontaneous, pseudoelastic unbending. The findings of this study could be relevant for the design of flexible electronics and mechanical energy storage applications at the nanoscale.