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Designing bulk metallic glass matrix composites with high toughness and tensile ductility

Citation

Hofmann, Douglas Clayton (2009) Designing bulk metallic glass matrix composites with high toughness and tensile ductility. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-09102008-101837

Abstract

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Metallic glasses have been the subject of intense scientific study since the 1960s, owing to their unique properties such as high strength, large elastic limit, high hardness, and amorphous microstructure. However, bulk metallic glasses have not been used in the high strength structural applications for which they have so much potential, owing to a highly localized failure mechanism that results in catastrophic failure during unconfined loading. In this thesis, bulk metallic glass matrix composites are designed with the combined benefits of high yield strengths and tensile ductility. This milestone is achieved by first investigating the length scale of the highly localized deformation, known as shear bands, that governs fracture in all metallic glasses. Under unconfined loading, a shear band grows to a certain length that is dependent on the fracture toughness of the glass before a crack nucleates and fracture occurs. Increasing the fracture toughness and ductility involves adding microstructural stabilization techniques that prevent shear bands from lengthening and promotes formation of multiple shear bands. To accomplish this, we develop in-situ formed bulk metallic glass matrix-composites with soft crystalline dendrites whose size and distribution are controlled through a novel semi-solid processing technique. The new alloys have a dramatically increased room-temperature ductility and a fracture toughness that appears to be similar to the toughest steels. Owing to their low modulus, the composites are therefore among the toughest known materials, a claim that has recently been confirmed independently by a fracture mechanics group. We extend our toughening strategy to a titanium-vanadium-based glass-dendrite composite system with density as low as 4.97 g/cm[...]. The new low-density composites rival the mechanical properties of the best structural crystalline Ti alloys. We demonstrate new processing techniques available in the highly toughened composites: room temperature cold rolling, work hardening, and thermoplastic forming. This thesis is a proven road map for developing metallic glass composites into real structural engineering materials.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:amorphous metals; bulk metallic glasses; dendrites; ductility; fracture; matrix composites; metallic glass composites; processing; tensile ductility; toughness
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
  • Demetriou, Marios D.
Defense Date:23 July 2008
Author Email:dhofmann (AT) gmail.com
Record Number:CaltechETD:etd-09102008-101837
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-09102008-101837
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3438
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:23 Oct 2008
Last Modified:26 Dec 2012 02:59

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