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Viscosity and crystallization in a series of Zr-based bulk amorphous alloys

Citation

Waniuk, Theodore Andrew (2004) Viscosity and crystallization in a series of Zr-based bulk amorphous alloys. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06102004-214551

Abstract

The various influences on glass-forming ability and crystallization in a series of alloy compositions ranging along a tie-line from Zr41.2Ti13.8Cu12.5Ni10Be22.5 to Zr46.75Ti8.25Cu7.5Ni10Be27.5 are studied using multiple techniques. Both the kinetic and thermodynamic aspects of crystallization are examined experimentally and used to explain why, in this series, thermal stability is greatest in those alloys with the poorest glass-forming ability. Overall, the investigations reveal that a single criterion like thermal stability or high viscosity is an insufficient indicator of the glass-forming ability in certain complex bulk glass-forming systems. Instead, in these complex systems, multiple criteria must be combined to get a complete picture. The equilibrium viscosity of Zr41.2Ti13.8Cu12.5Ni10Be22.5 and three other alloys was determined for temperatures near the glass transition using three-point beam bending. The results of these measurements indicate that the alloys in this system are moderately strong liquids, and relaxation behavior is directly influenced by a chemical decomposition process which occurs in the supercooled liquid. This decomposition process also appears to affect the crystallization behavior in the same series of alloys. Critical cooling rates were determined by observing crystallization upon cooling from the molten state with different rates, and these were compared to thermal analysis performed under constant heating conditions. The latter measurements show that the supercooled liquid region is largest for compositions midway between the two endpoints; in contrast, the critical cooling rate increases continuously from 1.4 K/s to 28 K/s for each successive alloy in this series. In order to examine the crystallization process more closely, low temperature time-temperature-transformation diagrams for the alloy series were measured during isothermal annealing of initially amorphous specimens. For all investigated alloys, a primary quasicrystalline phase forms at a rate which varies substantially with alloy composition. Describing the complicated influences on crystallization required not only the previous thermal analysis but also constant heating measurements and x-ray diffraction data obtained after various states of annealing.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:bulk amorphous alloys; crystallization; metallic glass
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Johnson, William Lewis
Thesis Committee:
  • Johnson, William Lewis (chair)
  • Fultz, Brent T.
  • Ustundag, Ersan
  • Schroers, Jan
  • Haile, Sossina M.
Defense Date:21 May 2004
Funders:
Funding AgencyGrant Number
NASANAG8-1744
U.S. Department of EnergyDEFG-03-86ER45242
Record Number:CaltechETD:etd-06102004-214551
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-06102004-214551
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2538
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:11 Jun 2004
Last Modified:26 Dec 2012 02:52

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