In Situ TEM Investigation of the Mechanical Behavior of Micronanoscaled Metal Pillars

Abstract

In this article, our most recent progress on applying a unique quantitative transmission electron microscope deformation technique on micronanoscaled metal pillars will be reviewed. We found that single-crystal pillars fabricated through focused ion beam always contain high density of defects. However, if the sample size is small enough, then both face-centered-cubic metals and body-centered-cubic metal pillars can experience “mechanical annealing,” i.e., a phenomena referring to the reduction of dislocation density in the deforming volume, when dislocation generation is outweighed by dislocation annihilation through the free surface. We also found that when the sample size was reduced below 1 μm or so, stress saturation and deformation mechanism transition occurred in a hexagonal-close-packed Ti alloy. Unlike crystalline materials, metallic glasses do not allow the presence and movement of dislocations or deformation twinning. However, we demonstrated the metallic glasses also follow the well-established tenet for crystalline materials: i.e., smaller is stronger and can reach its theoretical elastic limit under appropriate testing conditions. In addition, for the tested size regime, we found that high-energy electron beam has no obvious effect on the mechanical properties of materials with metallic bond. However, for materials with covalent bond and ionic bond, significant electron beam effects have been confirmed.