Response of copper nanowires in dynamic tensile deformation

Abstract

Molecular dynamics (MD) simulations with an embedded atom method (EAM) potential are carried out to analyse the size and strain rate effects in the tensile deformation of single-crystal copper nanowires. The cross-sections of the wires are squares with dimensions of between 5 and 20 lattice constants (or 1.8-7.2nm). Deformations under constant strain rates between 1.67 × 107 and 1.67 × 1010s−1 are analysed. It is found that the yield stress decreases with specimen size and increases with loading rate. On the other hand, ductility increases with specimen size and strain rate. The influence of specimen size is due to enhanced opportunities for dislocation motion at larger sizes. The influence of strain rate is due to the dynamic wave effect or phonon drag which impedes the motion of dislocations. The analysis also focuses on the variation in deformation mechanisms with specimen size and strain rate. Slip along alternating (111) planes is observed in small wires, while multiple cross-slips are primarily responsible for the progression of plastic deformation in larger wires. As strain rate is increased, a transition of the deformation mechanism from sequential propagation of slip along well-defined and favourably oriented slip planes to cross-slip, and then to amorphization, is observed.