Extraordinary Strain Hardening from Dislocation Loops in Defect-Free Al Nanocubes

The complex interaction of crystalline defects leads tostrain hardening in bulk metals. Metals with high stacking fault energy(SFE), such as aluminum, tend to have low strain hardening rates dueto an inability to form stacking faults and deformation twins. Here, weusein situscanning electron microscopy (SEM) mechanicalcompressions tofind that colloidally synthesized defect-free 114 nmAl nanocubes combine a high linear strain hardening rate of 4.1 GPawith a high strength of 1.1 GPa. These nanocubes have a 3 nm self-passivating oxide layer that has a large influence on mechanical behaviorand the accumulation of dislocation structures. Postcompressiontransmission electron microcopy (TEM) imaging reveals stableprismatic dislocation loops and the absence of stacking faults. MDsimulations relate the formation of dislocation loops and strainhardening to the surface oxide. These results indicate that slight modifications to surface and interfacial properties can induceenormous changes to mechanical properties in high SFE metals