Size effects in Al nanopillars: Single crystalline vs. bicrystalline

The mechanical behavior of bicrystalline aluminum nano-pillars under uniaxial compression reveals size effects, a stochastic stress–strain signature, and strain hardening. Pillar diameters range from 400 nm to 2 μm and contain a single, non-sigma high angle grain boundary oriented parallel to the pillar axes. Our results indicate that these bicrystalline pillars are characterized by intermittent strain bursts and exhibit an identical size effect to their single crystalline counterparts. Further, we find that the presence of this particular grain boundary generally decreases the degree of work hardening relative to the single crystalline samples. These findings, along with transmission electron microscopy analysis, show that nano-pillar plasticity in the presence of a grain boundary is also characterized by dislocation avalanches, likely resulting from dislocation nucleation-controlled mechanisms, and that at these small length scales this grain boundary may serve as a dislocation sink rather than a dislocation source.