Abstract
Both strengthening and weakening trends with decreasing diameter have been observed for metallic glass nanowires, sometimes even in the samples with the same chemical composition. How to reconcile the results has reminded a puzzle. Since the detailed stress state and microstructure of metallic glass nanowires may differ from each other significantly depending on preparation, to discover the intrinsic size effect it is necessary to study metallic glass nanowires fabricated differently. Here we show the complex size effects from one such class of metallic glass nanowires prepared by casting using molecular dynamics simulations. As compared with the nanowires of the same composition prepared by other methods, the cast nanowires deform nearly homogeneously with much lower strength but better ductility; and also show strengthening in tension but weakening in compression with decreasing wire diameter. The subtle size dependence is shown to be related to the key factors including internal and surface stress state, atomic structure variation, and presence of various gradients. The complex interplay of these factors at decreasing size leads to the different deformation behaviors.
Highlights
The size effect of metallic glasses (MGs) is still a controversial topic
We will investigate the size effect of the MG nanowires prepared by the procedure mimicking casting liquid into glass nanowires through molecular dynamics (MD) simulations
Our results demonstrate that deformation of incredible ductile cast nanowire with much loose atomic packing and gradients of density and chemical composition is still governed by the similar mechanisms found in FIB nanowires, that is, the interplay between the internal and surface stress
Summary
The size effect of metallic glasses (MGs) is still a controversial topic. Unlike crystalline materials, bulk MG materials possess high strength, hardness and elastic limit, but poor ductility. The systematic study is, expected to shed light on the deformation mechanisms in metallic glass nanowires in general whose response is sensitively dependent on the subtle structural change and internal and surface stress. Strengthening is found under tension at decreasing wire size in cast wires but absent in FIB wires; and the same failure mechanism observed in cast wires initiates from the interior when under compression but from surface when under tension, despite the presence of complex gradients and subtle structural changes. Besides these highlights, we shall present more detailed results below
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