The effects of chemical short-range order on crystallization pathway in ternary marginal glass forming alloys

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Emel Erdal MSc Thesis.pdf

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2021-9-08

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Erdal, Emel

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Among all the metallic glass-forming systems, Al-based marginal glass-forming alloys (Al-RE or Al-TM-RE) have been recently received significant attention due to their unusual devitrification behavior. The population of nanocrystals developed in the amorphous matrix can reach up to 1024 m-3 upon crystallization, which cannot be explained by classical nucleation theory. Our previous studies on binary Al90RE10 (RE: Sm, Tb, Y) systems have shown that the topological medium-range order, which is inherited from the liquid state, is effective in the formation of nanocrystals upon devitrification. In this study, we have examined the effects of chemical order on devitrified ternary metallic glass systems. Particularly, Al90Sm5Tb5 and Al90Y5Tb5 ternary metallic glasses were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), atom probe tomography (APT), and high energy synchrotron X-Ray diffraction (HEXRD) methods. It was observed that although the total amount of RE is constant, the substitution of Tb with 5% of Y or Sm has changed the devitrification path compared to Al90RE10 (RE: Sm, Tb, Y) binary systems. The traditional fcc-Al nanocrystallization event observed in binary Al-RE metallic glass systems was found to be altered in Al90Sm5Tb5 glassy alloys. Instead, the formation of intermetallic phases with fcc-Al nanocrystals embedded inside is observed in TEM analysis. This behavior is also supported by DSC results, where a sharp exothermic transformation peak with a significant enthalpy change replaced the traditional low intensity and broad fcc-Al nanocrystallization peak. This work has been supported by AFOSR under contract number FA9550-20-1-0261.

Subject Keywords

Marginal glass formers, Devitrification, APT, HEXRD, TEM

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https://hdl.handle.net/11511/93180

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

E. Erdal, “The effects of chemical short-range order on crystallization pathway in ternary marginal glass forming alloys,” M.S. - Master of Science, Middle East Technical University, 2021.