MD Simulations of Compression of Nanoscale Iron Pillars

TL;DR

This study uses molecular dynamics simulations to explore how nanoscale iron pillars deform under compression, revealing buckling behaviors, slip mechanisms, and size-dependent yield stresses relevant to nanoscale plasticity.

Contribution

It provides new insights into the deformation mechanisms of nanoscale BCC iron pillars, including buckling modes and slip behavior, under different boundary conditions and geometries.

Findings

Buckling behavior depends on boundary conditions.

Slip occurs on <110> planes in <100>-oriented pillars.

Nanoscale pillars exhibit higher yield stresses than bulk materials.

Abstract

It is now possible to create perfect crystal nanowires of many metals. The deformation of such objects requires a good understanding of the processes involved in plasticity at the nanoscale. Isotropic compression of such nanometre scale micropillars is a good model system to understand the plasticity. Here we investigate these phenomena using Molecular Dynamics (MD) simulations of nanometre scale single crystal BCC iron pillars in compression. We find that pillars with large length to width ratio may buckle under high strain rates. The type of buckling behaviour depends sensitively on the boundary conditions used: periodic boundary conditions allow for rotation at top and bottom of the pillar, and result in an S shaped buckle, by contrast fixed boundaries enforce a C shape. Pillars with a length to width ratio closer to that used in experimental micropillar compression studies show deformation behaviour dominated by slip, in agreement with the experiments. For micropillars oriented along <100>, slip occurs on <110> planes and localized slip bands are formed. Pillars of this size experience higher stresses than bulk materials before yielding takes place. One might expect that this may be in part due to the lack of nucleation sites needed to induce slip. However, further simulations with possible dislocation sources: a shorter iron pillar containing a spherical grain boundary, and a similar pillar containing jagged edges did not show a decreased yield strength.