Strain localization in a nanocrystalline metal: Atomic mechanisms and the effect of testing conditions

TL;DR

This study uses molecular dynamics to explore atomic mechanisms of strain localization in nanocrystalline metals, highlighting the influence of testing conditions and grain boundary behavior on failure modes.

Contribution

It provides new insights into atomic-scale processes driving strain localization and shear banding in nanocrystalline metals under various testing conditions.

Findings

Strain localization involves grain boundary deformation and dislocation activity.

Higher temperature and strain rate promote more uniform plastic flow.

No size effect observed for the tested grain and sample sizes.

Abstract

Molecular dynamics simulations are used to investigate strain localization in a model nanocrystalline metal. The atomic mechanisms of such catastrophic failure are first studied for two grain sizes of interest. Detailed analysis shows that the formation of a strain path across the sample width is crucial, and can be achieved entirely through grain boundary deformation or through a combination of grain boundary sliding and grain boundary dislocation emission. Pronounced mechanically-induced grain growth is also found within the strain localization region. The effects of testing conditions on strain localization are also highlighted, to understand the conditions that promote shear banding and compare these observations to metallic glass behavior. We observed that, while strain localization occurs at low temperatures and slow strain rates, a shift to more uniform plastic flow is observed when either strain rate or temperature is increased. We also explore how external sample dimensions influence strain localization, but find no size effect for the grain sizes and samples sizes studied here.