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Bulk Metallic Glasses: Atomic Modeling and Spark Plasma Sintering Synthesis

Petersen, Alexander
Thesis/Dissertation; Online
Petersen, Alexander
Poon, Joseph
The focus of this study was on further understanding bulk metallic glasses through the twofold path of theoretical modeling to predict elastic properties and experimental creation of large bulk metallic glass systems. In order to accurately predict the elastic properties of bulk metallic glass systems a reliable mathematical model had to be created. Existing elastic models for crystalline systems were explored with a focus given to the Voigt and Reuss models. The method selected for further investigation was the Coherent Potential Approximation (CPA) which proved to more accurately predict the elastic moduli. Beyond this, the short and medium range order was modeled and predicted based on the efficient packing of atomic clusters, as discussed by Miracle and others. In addition to geometric cluster modeling bonding priority and atomic arrangement were considered to predict the probable locations of specific elements during the metallic glass synthesis process. Through this adjustment the CPA model was allowed to reach a coefficient of determination in excess of 0.89 on a collection of 117 select experimental bulk metallic glass systems. The experimental creation was done on a variety of Nickel and Tungsten based systems with the goal of creating high density, highly compact, high hardness, and fairly ductile amorphous systems. This was done through optimization of amorphous system creation via synthesis of amorphous powder precursors and compaction. The sample compaction was conducted through the use of a spark plasma sintering system to ensure rapid temperature transitions, high pressure, and high compaction. The optimal path combined amorphous powders synthesized through a combination of methods including arc melting, melt spinning, annealing, and ball milling. The optimal systems created were Ni-based alloys constructed through a combination of multiple methods that retained their amorphous structure while demonstrating a hardness of 12.6 GPa, a density in excess of 11 g/cc, and ductility demonstrated through shear banding.
University of Virginia, Department of Engineering Physics, MS, 2015
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