Activation volume and incipient plastic deformation of uniaxially-loaded gold nanowires atvery high strain rates

Abstract

Uniaxial tensile loading is investigated by the molecular dynamic (MD) method on Aunanowires at ultra-high strain rates. The activation volume is used to comprehensivelycharacterize the incipient plastic deformation during this process. For lower strain rates such as6.287 × 108 s−1, the movingvelocity, V, of the atom planes due to uniaxial loading is two orders ofmagnitude smaller than the phonon wave propagation speed,V0, and the coherence between atoms is always maintained with a larger activation volume. Inthis case, plastic deformation is initiated mainly by collective atomic slipping, and thusonly lower flow stress is needed. On the other hand, for higher strain rates such as6.287 × 1010 s−1,V is elevated to thesame magnitude as V0, the atom coherence is broken, their individual behavior is dominated by extraordinarilysmall activation volume, and atom diffusion becomes the main mechanism for plasticdeformation. As a result, the yield strength is improved substantially. A higher temperaturemay weaken this strain-rate-dependent mechanical behavior because of the enhanced atomactivity.