Plasticity of Nano- and Micro-pillars

We review unique mechanisms of plastic deformation in nanoand micropillars. At the nanoscale, it is shown that plastic deformation is asymmetric with respect to direction of mechanical loading, as a result of specific relationships between the normal and resolved shear stress on active slip planes. This is attributed to the dependence of shear wave speed on the stress state acting on slip planes. Plastic deformation of nano-twinned copper pillars show a mechanism transition from dislocation nucleation to twin boundary migration. The flow strength σf of micropillars is shown to be size-dependent, and scales with the diameter, D as: σf ∝ D , in agreement with experiments. For micropillars of diameter larger than ≈ 100 nm, a ‘weakestlink’dislocation activation mechanism accounts for the size effect. Aspects of work-hardening in discrete steps can be explained to result from cross-slip and sub-division of screw segments.