Extraordinary strain hardening from dislocation loops in defect-free Al nanocubes

TL;DR

This study demonstrates that defect-free aluminum nanocubes exhibit extraordinary strain hardening due to dislocation loops, influenced by surface oxide layers, challenging traditional understanding of high SFE metal deformation.

Contribution

It reveals that surface oxide layers enable high strain hardening in defect-free Al nanocubes, a novel mechanism for strain hardening in high SFE metals.

Findings

High strain hardening rate of 4.1 GPa observed in Al nanocubes

Dislocation loops are stable and dominate deformation

Surface oxide layers significantly influence mechanical behavior

Abstract

The interaction of crystalline defects leads to strain hardening in bulk metals. Metals with high stacking fault energy (SFE), such as aluminum, tend to have low strain hardening rates due to an inability to form stacking faults and deformation twins. Here, we use in situ SEM mechanical compressions to find that colloidally synthesized defect-free 114 nm Al nanocubes combine a high linear strain hardening rate of 4.1 GPa with a high strength of 1.1 GPa. These nanocubes have a 3 nm self-passivating oxide layer that has a large influence on mechanical behavior and the accumulation of dislocation structures. Post-compression TEM imaging reveals stable prismatic dislocation loops and the absence of stacking faults. MD simulations relate the formation of dislocation loops and strain hardening to the surface oxide. These results indicate that slight modifications to surface and interfacial properties can induce enormous changes to mechanical properties in high SFE metals.