Controlling Deformability in Metallic Glass Nanopillars and Nanolattices

Citation

Liontas, Rachel (2017) Controlling Deformability in Metallic Glass Nanopillars and Nanolattices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9028PHX. https://resolver.caltech.edu/CaltechTHESIS:09132016-104159178

Abstract

Metallic glasses offer desirable mechanical properties, including high strength, hardness, and elasticity. In bulk, they suffer from catastrophic failure upon mechanical loads. However, ductility may emerge upon (1) reducing the characteristic dimension of the metallic glass to the nanoscale or (2) irradiating the metallic glass. These two methods of controlling metallic glass deformability are investigated through a host of mechanical experiments on metallic glass nanopillars and nanolattices before and after irradiation. The mechanical experiments are conducted inside a scanning electron microscope to allow simultaneous mechanical loading and visualization of nanoscale deformation behavior.

Such experiments reveal that helium irradiation of electrodeposited Ni₇₃P₂₇ metallic glass tensile nanopillars increases plasticity by a factor of two with no sacrifice in strength. Other tensile experiments on Zr-Ni-Al metallic glass nanopillars in as-sputtered and annealed states reveal substantial ductility, highly dependent upon both the nanopillar size and processing conditions. Molecular dynamics simulations, transmission electron microscopy, and synchrotron x-ray diffraction are used to explain the observed mechanical behavior through changes in free volume and short-range order.

Larger nanolattice structures are fabricated to contain hollow beams of metallic glass, with beam wall thicknesses in the nanoscale size range that may allow proliferation of the beneficial “smaller is more ductile” size effect observed in metallic glass nanopillars. Compression experiments on Zr-Ni-Al metallic glass nanolattices reveal enhanced deformability as the nanolattice wall thickness is reduced and upon irradiation. This work points to metallic glass nanolattices as promising candidates for radiation-intensive applications and demonstrates that by fabricating the metallic glass in a nanolattice architecture the beneficial nanoscale size effect in deformability can be preserved.

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