Spatial distribution of local elastic moduli in nanocrystalline metals

TL;DR

This study uses molecular dynamics simulations to analyze how local elastic moduli vary spatially within nanocrystalline metals, revealing grain boundary effects and size-dependent elastic properties.

Contribution

It provides a detailed analysis of local elastic moduli distributions in nanocrystalline metals and models the overall elastic behavior as a weighted average of grain and boundary contributions.

Findings

Grain boundary shear modulus distribution is wide and size-independent.

Grains have a peaked shear modulus distribution that sharpens with size.

Total elastic modulus decreases with smaller grain sizes, mainly due to increased grain boundary atoms.

Abstract

Elastoplastic properties of nanocrystalline metals are non-uniform on the scale of the grain size, and this non-uniformity affects macroscopic quantities as, in these systems, a significant part of the material is at or adjacent to a grain boundary. We use molecular dynamics simulations to study the spatial distributions of local elastic moduli in nano-grained pure metals and analyze their dependence on grain size. Calculations are performed for copper and tantalum with grain sizes ranging from 5-20nm. Shear modulus distributions for grain and grain-boundary atoms were calculated. It is shown that the non-crystalline grain boundary has a wide shear-modulus distribution, which is grain-size independent, while grains have a peaked distribution, which becomes sharper with increasing grain size. Average elastic moduli of the bulk, grains, and grain boundary are calculated as a function of grain size. The atomistic simulations show that the reduction of total elastic moduli with decreasing grain size is mainly due to a resulting larger grain-boundary atoms fraction, and that the total elastic moduli can be approximated by a simple weighted average of larger grains elastic moduli and a lower grain-boundary elastic moduli.