Atomic-scale modeling of the deformation of nanocrystalline metals

TL;DR

This paper uses atomic-scale simulations to study how nanocrystalline metals deform, revealing dominant mechanisms and the impact of impurities on their mechanical properties.

Contribution

It presents molecular dynamics simulations of nanocrystalline copper, analyzing deformation mechanisms and the effects of impurity atoms in grain boundaries.

Findings

Grain boundary sliding dominates deformation at studied sizes.

An optimal grain size exists for maximum hardness.

Impurity atoms in grain boundaries influence mechanical properties.

Abstract

Nanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display technologically interesting properties, such as dramatically increased hardness, increasing with decreasing grain size. Due to the small grain size, direct atomic-scale simulations of plastic deformation of these materials are possible, as such a polycrystalline system can be modeled with the computational resources available today. We present molecular dynamics simulations of nanocrystalline copper with grain sizes up to 13 nm. Two different deformation mechanisms are active, one is deformation through the motion of dislocations, the other is sliding in the grain boundaries. At the grain sizes studied here the latter dominates, leading to a softening as the grain size is reduced. This implies that there is an ``optimal'' grain size, where the hardness is maximal. Since the grain boundaries participate actively in the deformation, it is interesting to study the effects of introducing impurity atoms in the grain boundaries. We study how silver atoms in the grain boundaries influence the mechanical properties of nanocrystalline copper.