Size-dependent deformation mechanisms of Al nanopillars

Abstract

The dynamical mechanical properties of Al nanopillars, <1 µm in diameter and with aspect ratios ranging from 2 : 1–6 : 1, have been evaluated in real-time by uniaxial compression testing inside a transmission electron microscope. The compressive deformation mode of the Al pillars is observed to be dependent on the diameter/aspect ratio of the pillar under test. For comparable height pillars and increasing aspect ratio, the compressive deformation mode of the Al pillars changes from deformation via discrete slip bands on multiple slip systems (900 nm diameter, aspect ratio ∼2 : 1), to localized bulging at the apex of the pillar, followed by slip band initiation (450 nm diameter, aspect ratio ∼4 : 1), to a full pillar buckling mode (250 nm diameter, aspect ratio ∼6 : 1). Al pillar buckling is observed to initiate a new pillar deformation sequence, comprising lateral slip of the pillar across the compressing diamond probe and generation of a 90° pillar kink. Extreme deformation close to the 90° kink results in sudden major strain bursts and lateral shear events, with dynamic recrystallization of the displaced Al volume occurring to form new grains.