Doctor of Philosophy (PhD)
Materials Science and Engineering
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Ternary, Metallic Glass, Mechanical Behavior, Glass Forming Ability
Date of Defense
The vast demands for advanced materials have been putting tremendous pressure on materials scientists and engineers to discover and produce novel lighter and stiffer materials. This dissertation is devoted to the development and fundamental understanding of the strength and the structures within Aluminum ternary metallic glasses (MGs) and their composites, which have a low density and promising high strength. The dissertation focuses on the following content: The multi-objective optimization algorithm predicted the Al16.5Ni8Ce75.5 ternary metallic glass composition with an improved glass-forming ability (supercooled liquid region ∆𝑇𝑥=29K), based on the provided dataset. Inoue Criteria can predict the Al46Ni10Ce44 metallic glass concentration with the highest supercooled liquid region ∆𝑇𝑥=40K and best initial hardness 389(Hv). The highest hardness value, 853(Hv), was achieved when annealed Al46Ni10Ce44 at 573K for 30 mins. This value is significantly high compared to the published hardness of bulk MG systems, such as Zr-based, Pd-based and Mg-based metallic glasses, as well as conventional alloys such as stainless steel and super high strength steel. The relationship between the hardness of Al-Ni-Ce MGs and the annealing temperatures was investigated by high energy synchrotron X-ray diffraction (HEXRD) and Transmission Electron Microscopy (TEM). Obtained HEXRD and TEM results and microindentation values show that when the annealing temperature is close to the onset temperature of crystallization, the hardness reaches the highest value.
Annealing treatment of the Al23Ce75Si2 MG at a temperature above 473K introduced 30-40 nm AlCe3 crystalline precipitations, which enhanced the hardness of the annealed alloy. The number of such nano-precipitations increased with the annealing temperature within the range of 473K-563K. Consequently, the hardness increased with the annealing temperature. From transmission electron microscopy images, the mixed area of the crystalline and non-crystalline structure was identified, the increased density of grain boundary improved the mechanical property of the sample.
The pair distribution function (PDF) analyses based on the HEXRD of Al20Ni10Ce70, Al46Ni10Ce44, Al86.5Ni9.5Ce5, and Al85.8Ni9.1Ce5.1 were conducted, and the results demonstrate that there is an atom amount balance for Al atoms’ closest Ni and Ce. Also, this balance influenced glass forming ability (GFA). The PDF results from Al86.5Ni9.5Ce5 and Al85.8Ni9.1Ce5.1 indicate that a slight difference in concentration would not significantly affect the final GFA performance.
The current research suggests a possible way to design, synthesize, and improve Al-based bulk metallic glass (BMG).
Previously Published In
Liang, X., Chen, J., Mora, M. T., Urdaneta, J. F., & Zeng, Q. (2017). Effect of precipitation on the hardness of ternary metallic glass. Advances in Materials Physics and Chemistry, 7(06), 255.
Liang, Xue, "Mechanical Behavior of Ternary Metallic Glasses and Their Composites" (2019). FIU Electronic Theses and Dissertations. 4317.
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