Date of Award

5-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Hahn Choo

Committee Members

Peter Liaw, Takeshi Egami, David Joy

Abstract

Although research has been conducted on amorphous aluminum-based alloys, most of the research has focused on melt-spun ribbons. There has been significantly less research on mechanically alloyed amorphous powder even though mechanically alloyed powder seems to have more potential for the production of bulk amorphous aluminumbased alloys. In addition, there has not been adequate research conducted on the local atomic structure of amorphous aluminum alloys, and a greater understanding of the relationship between processing, structure, and properties is necessary.

In the following thesis, multiple investigations have been performed to understand the structure, processing, and properties of aluminum-based amorphous alloys. These studies sought to develop a methodology for the production of amorphous aluminum alloys by mechanical alloying, understand how composition affects the glassforming ability, understand the crystallization and its effects on structure and properties, and consolidate the mechanically alloyed powder and examine the resultant structure and properties.

High-energy ball milling was used to synthesize aluminum-based alloys containing amorphous and nanocrystalline phases to investigate the compositional effects of transition metals (TM) on the amorphization and crystallization processes of the ballmilled Al85Y7Fe5TM3 alloys (TM = Ni, Co, Cu, and Fe) were investigated.

The local atomic structure of mechanically alloyed Al85Y7Fe8 and Al83Y7Fe8Ti2 were examined by high-energy synchrotron x-ray diffraction. Diffraction results showed that Al85Y7Fe8structure to be nanocrystalline, while Al83Y7Fe8Ti2is amorphous. The pair distribution function analyses revealed that local structure of Al85Y7Fe8was dominated by Al, Fe, and Al3Y short range ordered regions. On the other hand, the local structure of Al83Y7Fe8Ti2was comprised of Al, Al6Fe, and Al3Y short-range order regions, in which the order extended for about 8 angstroms.

Efforts to consolidate the mechanically alloyed amorphous powder were made by quasi-isostatic forging at different temperatures. Samples were also processed containing different levels of coarse grain crystalline aluminum to evaluate the production of bimodal composites.

In addition to the research performed on amorphous aluminum alloys, research on the mechanical behavior of the local atomic structure of a bulk metallic glass was performed. The internal strain was measured for a Zr57Nb5Cu15.4Ni12.6Al10 BMG in-situ by neutron diffraction.

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