Title: Atomistic Investigations of Size and Strain Rate Dependence on the Mechanical Response of Nanoscaled Metallic Glass Structures
Presenter: Sara Adibi Sedeh
Abstract: Metallic glasses (MG) are interesting materials with a liquid like structure and metallic solid like properties. MGs can be used for coating protection since they show outstanding mechanical properties such as high strength and hardness. In this work, we used molecular dynamic simulations to investigate the mechanical behavior of Cu64Zr36 MG nanopillars under tensile loading. The MGs are prepared using a slow quench rate of 0.01 K/ps. We characterized the effects of the applied strain rate as well as the length and diameter of the nanopillars. For low strain rates (107s-1), plastic deformation in the nanopillars is generated at the yield point by nucleation of one or more shear bands. Results, for a nanopillar of 15nm diameter and aspect ratio 13, show a transition in deformation mode for increasing strain rate from 107s-1 to 109s-1, from a single shear band to multiple shear bands and increasing plastic flow and necking. Simulations with nanopillars with diameter in the range of 15 nm to 50 nm show essentially the same stress strain curves, plastic behavior, and failure implying low dependence diameter effects. On the other hand, simulations with nanopillars of different aspect ratios show very different strain to failure. Nanopillars with large aspect ratio, e.g. 13, fail at smaller strain (0.12), compared to nanopillar with small aspect ratios, e.g. 2.5 (0.42). Arguably, high aspect ratio nanopillars are able to store more elastic energy for a given strain enabling the full propagation of shear bands across the pillars at the yield point. These results explain and reconcile recent contradictory reports from simulations and experiments on the failure behavior of MG nanopillars.