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Study of the origins of toughness in amorphous metals

Citation

Garrett, Glenn Robert (2013) Study of the origins of toughness in amorphous metals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9JD4TRM. http://resolver.caltech.edu/CaltechTHESIS:05252013-065528171

Abstract

Amorphous metals that form fully glassy parts over a few millimeters in thickness are still relatively new materials. Their glassy structure gives them particularly high strengths, high yield strains, high hardness values, high resilience, and low damping losses, but this can also result in an extremely low tolerance to the presence of flaws in the material. Since this glassy structure lacks the ordered crystal structure, it also lacks the crystalline defect (dislocations) that provides the micromechanism of toughening and flaw insensitivity in conventional metals. Without a sufficient and reliable toughness that results in a large tolerance of damage in the material, metallic glasses will struggle to be adopted commercially. Here, we identify the origin of toughness in metallic glass as the competition between the intrinsic toughening mechanism of shear banding ahead of a crack and crack propagation by the cavitation of the liquid inside the shear bands. We present a detailed study over the first three chapters mainly focusing on the process of shear banding; its crucial role in giving rise to one of the most damage-tolerant materials known, its extreme sensitivity to the configurational state of a glass with moderate toughness, and how the configurational state can be changed with the addition of minor elements. The last chapter is a novel investigation into the cavitation barrier in glass-forming liquids, the competing process to shear banding. The combination of our results represents an increased understanding of the major influences on the fracture toughness of metallic glasses and thus provides a path for the improvement and development of tougher metallic glasses.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:bulk metallic glass; amorphous metal; fracture toughness; damage tolerance; configurational disorder; annealing; microalloying; cavtitation
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)
  • Goddard, William A., III
  • Fultz, Brent T.
  • Ravichandran, Guruswami
  • Demetriou, Marios D.
Defense Date:27 September 2012
Record Number:CaltechTHESIS:05252013-065528171
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05252013-065528171
DOI:10.7907/Z9JD4TRM
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7752
Collection:CaltechTHESIS
Deposited By: Glenn Garrett
Deposited On:30 May 2013 16:38
Last Modified:05 Oct 2016 23:12

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PDF (Full Thesis) - Final Version
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PDF (Title, Contents, Ch.1: Introduction) - Final Version
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PDF (Ch.2: Damage Tolerant Pd Glass) - Final Version
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PDF (Ch.3: Configurational Disorder and Toughness) - Final Version
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PDF (Ch. 4: Microalloying Effect on Toughness) - Final Version
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PDF (Ch.5: Cavitation in BMG Liquids) - Final Version
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PDF (Ch.6: Summary, Future Directions) - Final Version
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PDF (Appendices) - Final Version
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