Quantitative tracking of grain structure evolution in a nanocrystalline metal during cyclic loading

TL;DR

This study uses molecular dynamics simulations to quantify how cyclic loading affects grain structure and deformation mechanisms in nanocrystalline aluminum, revealing temperature-dependent structural evolution and strengthening effects.

Contribution

It introduces a grain tracking algorithm to measure deformation mechanisms and structural changes during cyclic loading in nanocrystalline metals.

Findings

Cyclic loading induces twin boundary formation and grain coalescence.

Higher temperatures accelerate structural evolution.

A temperature-dependent cyclic strengthening effect is observed.

Abstract

Molecular dynamics simulations were used to quantify mechanically-induced structural evolution in nanocrystalline Al with an average grain size of 5 nm. A polycrystalline sample was cyclically strained at different temperatures, while a recently developed grain tracking algorithm was used to measure the relative contributions of novel deformation mechanisms such as grain rotation and grain sliding. Sample texture and grain size were also tracked during cycling, to show how nanocrystalline plasticity rearranges overall grain structure and alters the grain boundary network. While no obvious texture is developing during cycling, the processes responsible for plasticity act collectively to alter the interfacial network. Cyclic loading led to the formation of many twin boundaries throughout the sample as well as the occasional coalescence of neighboring grains, with higher temperatures causing more evolution. A temperature-dependent cyclic strengthening effect was observed, demonstrating that both the structure and properties of nanocrystalline metals can be dynamic during loading.