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Atomic-level Structure and Deformation in Metallic Glasses

Citation

Chen, David Zhaoyue (2016) Atomic-level Structure and Deformation in Metallic Glasses. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z95Q4T2B. http://resolver.caltech.edu/CaltechTHESIS:05252016-155624343

Abstract

Metallic glasses (MGs) are a relatively new class of materials discovered in 1960 and lauded for its high strengths and superior elastic properties. Three major obstacles prevent their widespread use as engineering materials for nanotechnology and industry: 1) their lack of plasticity mechanisms for deformation beyond the elastic limit, 2) their disordered atomic structure, which prevents effective study of their structure-to-property relationships, and 3) their poor glass forming ability, which limits bulk metallic glasses to sizes on the order of centimeters. We focused on understanding the first two major challenges by observing the mechanical properties of nanoscale metallic glasses in order to gain insight into its atomic-level structure and deformation mechanisms. We found that anomalous stable plastic flow emerges in room-temperature MGs at the nanoscale in wires as little as ~100 nanometers wide regardless of fabrication route (ion-irradiated or not). To circumvent experimental challenges in characterizing the atomic-level structure, extensive molecular dynamics simulations were conducted using approximated (embedded atom method) potentials to probe the underlying processes that give rise to plasticity in nanowires. Simulated results showed that mechanisms of relaxation via the sample free surfaces contribute to tensile ductility in these nanowires. Continuing with characterizing nanoscale properties, we studied the fracture properties of nano-notched MGnanowires and the compressive response of MG nanolattices at cryogenic (~130 K) temperatures. We learned from these experiments that nanowires are sensitive to flaws when the (amorphous) microstructure does not contribute stress concentrations, and that nano-architected structures with MG nanoribbons are brittle at low temperatures except when elastic shell buckling mechanisms dominate at low ribbon thicknesses (~20 nm), which instead gives rise to fully recoverable nanostructures regardless of temperature. Finally, motivated by understanding structure-to-property relationships in MGs, we studied the disordered atomic structure using a combination of in-situ X-ray tomography and X-ray diffraction in a diamond anvil cell and molecular dynamics simulations. Synchrotron X-ray experiments showed the progression of the atomic-level structure (in momentum space) and macroscale volume under increasing hydrostatic pressures. Corresponding simulations provided information on the real space structure, and we found that the samples displayed fractal scaling (rd ∝ V, d < 3) at short length scales (< ~8 Å), and exhibited a crossover to a homogeneous scaling (d = 3) at long length scales. We examined this underlying fractal structure of MGs with parallels to percolation clusters and discuss the implications of this structural analogy to MG properties and the glass transition phenomenon.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:metallic glass, nanomechanics, molecular dynamics, percolation, dimensionality
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Greer, Julia R.
Thesis Committee:
  • Greer, Julia R. (chair)
  • Johnson, William Lewis
  • Goddard, William A., III
  • Miller, Thomas F.
Defense Date:3 May 2016
Funders:
Funding AgencyGrant Number
National Science Foundation Graduate Research FellowshipDGE-1144469
Department of Energy, Basic Energy SciencesUNSPECIFIED
Department of Energy National Nuclear Security AdministrationDE-FC52-08NA28613
National Science FoundationDMR-0520565
National Science FoundationDMR-1436985
NASA Space Technology Research Grants ProgramUNSPECIFIED
Record Number:CaltechTHESIS:05252016-155624343
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05252016-155624343
DOI:10.7907/Z95Q4T2B
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/nl402384rDOIArticle adapted for ch. 2
http://dx.doi.org/10.1063/1.4907773DOIArticle adapted for ch. 3
http://dx.doi.org/10.1021/nl5027869DOIArticle adapted for ch. 4
http://dx.doi.org/10.1021/acs.nanolett.5b01034DOIArticle adapted for ch. 4
http://dx.doi.org/10.1126/science.aab1233DOIArticle adapted for ch. 5
ORCID:
AuthorORCID
Chen, David Zhaoyue0000-0001-5732-5015
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9759
Collection:CaltechTHESIS
Deposited By: David Chen
Deposited On:31 May 2016 18:59
Last Modified:18 May 2017 17:15

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