To harness "smaller is more ductile" behavior emergent at nanoscale and to proliferate it onto materials with macroscale dimensions, we produced hollow-tube Cu60Zr40 metallic glass nanolattices with the layer thicknesses of 120, 60, and 20 nm. They exhibit unique transitions in deformation mode with tube-wall thickness and temperature. Molecular dynamics simulations and analytical models were used to interpret these unique transitions in terms of size effects on the plasticity of metallic glasses and elastic instability.
TEM sample preparationTEM samples of notched and unnotched metallic glass nano-cylinders were prepared through a focus ion beam (FIB) free process that resulted in minimal damage to the nanostructures. Nano-cylinders with poor adhesion to the growth substrate were attached using
In addition to the tensile experiments discussed in detail, we also examined the mechanical properties of the as-sputtered Zr-Ni-Al metallic glass via uniaxial compression experiments on cylindrical nanocompression specimens. Specimen were fabricated by FIB milling of the same ~4.5 µm thick sputtered film analyzed by TEM in Figure 2. The specimens were fabricated with diameters ranging from 225 nm to 1560 nm, and corresponding heights such that the aspect ratio was ~1:3 so as to avoid buckling during compression. The specimens were compressed at a strain rate of 1×10 -3 s -1 using the Hysitron PI-85 nanomechanical testing instrument in-situ in the Versa 3D scanning electron microscope. The resultant compression data is displayed in Figure A.1. These specimens exhibited two very distinct regimes of mechanical behavior depending on their size: ductile behavior and homogeneous flow was observed for "small" specimens with initial diameters ≤ 555 nm, while shear banding and localized failure was observed for "large" specimens with initial diameters ≥ 890 nm. These differences in mechanical response are apparent from the stress-strain curves, which show uniform plastic loading for the "small" specimens ( Figure A.1 (a)), and many strain bursts from the catastrophic shear banding events for the "large" specimens ( Figure A.1 (b)).The post-compression images of the specimens also illustrate the differences in mechanical response with the "small" specimens exhibiting homogeneous deformation near the top of the specimens ( Figure A.1 (c), (d)) and the "large" specimens exhibiting clear shear bands ( Figure A.1 (e), (f)). Overall, the compression data indicates a transition from homogeneous-like flow to shear banding at a specimen diameter between 555 and 890 nm.
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