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Amorphous metallic foam: synthesis and mechanical properties

Citation

Veazey, Chris (2007) Amorphous metallic foam: synthesis and mechanical properties. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01212007-235934

Abstract

Bulk metallic glass alloys were processed into foam by several synthesis routes. These methods utilize the thermodynamic stability and thermoplastic formability of the supercooled liquid state to produce low-density homogeneous foams. The cellular structure is shown to evolve by growth of randomly distributed spherical bubbles towards polyhedral-like cells separated by microscopic intracellular membranes exhibiting random orientations and aspect ratios. The ability of amorphous metals to develop such random cellular morphologies is attributed primarily to the high ductility exhibited by their softened state, which enables large superplastic membrane elongations during foaming.

Upon loading, moderate porosity foams are known to deform plastically by recurring non-linear yielding transitions followed by non-catastrophic collapse events. The ability of these foams to yield non-catastrophically is a result of the plastic deformability of amorphous metals in sub-millimeter dimensions. Nonlinear yielding is found to be accommodated by clusters involving 4–6 cells, which yield by intracellular membrane buckling and ultimately collapse plastically to produce a localized plastic collapse band. By comparison, high-porosity foams deform plastically by multiple recurring non-catastrophic collapse events without undergoing macroscopic failure. The numerous minor collapse events are associated with localized ligament collapse, and the few major collapse events are associated with the cooperative collapse of several adjacent ligaments and the formation of a collapse band. On average, the serrated flow responses between major events appear to be self-similar and resemble the recurring nonlinear yielding responses exhibited by moderate porosity foams.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:amorphous alloy; bulk metallic glass; metal foam
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Johnson, William Lewis
Thesis Committee:
  • Johnson, William Lewis (chair)
  • Fultz, Brent T.
  • Ravichandran, Guruswami
  • Atwater, Harry Albert
Defense Date:6 July 2006
Author Email:veazey (AT) caltech.edu
Record Number:CaltechETD:etd-01212007-235934
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-01212007-235934
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:262
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:22 Feb 2007
Last Modified:26 Dec 2012 02:28

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