Processing, Structure, and Properties of Amorphous Aluminum Alloys

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 Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ BMG in-situ by neutron diffraction.