When 12:00 PM - 1:30 PM Jul 21, 2023
Where 1017 HH Dow or virtual
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PhD defense: "Leveraging Advanced Characterization Techniques to Study Eutectic Pattern Formation in 4D"

Paul Chao
Shahani group

The solid ordered patterns forming from a disordered liquid state are ubiquitous throughout nature. Eutectics in particular show various types of patterns, including: lamellae, rods or labyrinthine, which are governed by growth laws determining their periodicity. Unfortunately, these laws may not adequately predict arrangement in eutectic systems containing a faceted or intermetallic phase, e.g. Si, Al2Cu or Al3Ni. These non-metal phases have an anisotropy of interfacial energy and/or mobility with respect to the liquid and/or solid phases and may lead to a faceted growth front. These effects have been hypothesized to influence the coupling of the solute diffusion fields ahead of the composite eutectic growth front and thus modify the resulting two-phase pattern that solidifies. 

This thesis examines three binary aluminum-containing eutectic alloys containing a faceted nonmetal phase: Al-Si, Al-Al2Cu and Al-Al3Ni. Each alloy system exhibits a unique eutectic microstructure: coral-like, labyrinthine or lamellar, and aligned rod-like, respectively. I explore how the pattern selection mechanisms are governed by crystalline anisotropy and growth velocity using state-of-the-art experimental techniques. The self-organization process is characterized in three dimensions using destructive slice-and-view scanning electron microscopy and also in four dimensions using non-destructive synchrotron-based X-ray transmission microscopy. 

I leverage these available tools and techniques and also develop novel reconstruction, processing, visualization, and analysis methods, to explore solidification dynamics of eutectics in unprecedented detail. The high-dimensional imaging data opens the doors to a wealth of information on the kinetics of eutectic solidification in highly anisotropic materials. The experimental results can be used to test the predictions of existing theory and set new directions for the refinement of theory. 

To the best of my knowledge, I am the first to characterize and experimentally measure the interfacial dynamics of eutectic growth in 4D in the sub-micrometer regime and under realistic growth conditions (e.g., directional solidification). The findings in my thesis provides a clearer understanding of the mechanism governing pattern selection during eutectic solidification, with attention to anisotropic systems.