Compression of Nanoporous Au Nanopillars in Molecular Dynamics Simulations

We study the compressive deformation of nanoporous gold nanopillar and the effect of pillar and ligament diameters on the deformation using Molecular Dynamics simulations. Atomistic nanoporous nanopillars are carved from a single crystal FCC lattice with the aid of an algorithm proposed by Soyarslan et al. [1]. The atomic structures are first relaxed, so as to obtain a stable ligament shape and diameter. Then, nanopillars of different diameters with different ligament size are compressed at a constant rate and the stress-strain curves are calculated. The deformation exhibits three typical stages: elastic, a plastic “plateau” and a rapid hardening. Within the elastic regime, we employ a novel technique to identify the average number of load-bearing ligaments, showing that compression of ligaments is predominant. Based on the simulations, we modified the Gibson-Ashby model to account for the size of the nanopillar on the effective elastic constant. In addition, we found that the stress at which the nanopillars yield is size-dependent, explained by the nucleation of dislocations and evolution of stacking faults within the ligaments in the plastic “plateau”. Finally, the coalescence of ligaments is observed during the rapid hardening stage. During the densification processes, dislocations are nucleated from the interface until the grain boundary is removed between the two coalesced ligaments.

1. C. Soyarslan, S. Bargmann, M. Pradas, J. Weissmüller, Acta Mater. 149 (2018) 326-340.