William Stratton Ph.D. Thesis - MINDS@UW Home

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Acknowledgements This work could not have been done alone. During my tenure as a graduate student, I had the opportunity to work with several encouraging, enlightening, and entertaining people. A big thanks to: • The Perepezko Group at the University of Wisconsin, specifically Dr. John Perepezko, Seth Imhoff, and Joe Hamann for helpful discussions, nanocrystal counting statistics, DSC data, and providing me with high Al-content amorphous alloy samples. • The Kelton Group at Washington University for high Al-content amorphous alloy samples and helpful discussions. • Zhongyi Liu and Dean Miller for STEM support at Argonne National Laboratory. • The Abelson Group at the University of Illinois, specifically Dr. John Abelson, Lakshminarayana Nittala, and Stephanie Bogle for STEM support and helpful discussions. • Dr. Murray Gibson, Dr. Mike Treacy, and C.S. Webber for theoretical help with the development of the new FEM theory. • The Materials Science Center staff; Alex Kvit, Rick Noll, Rich Casper, John Jacobs, and Don Savage for equipment training and support. • Diana Rhoads for administrative support in the Materials Science Program. Whenever I had a question about the program, you always had an answer. • My fellow Materials Science Program graduate students for being both supportive collaborators and friends. • Members of the Voyles Group for always being ready to lend a hand and offer ideas. • My thesis advisor, Paul Voyles. Thank you for your time, your enthusiasm, your humor, and your guidance. With your help, my time as a graduate student was more enlightening than I ever expected. • Lastly, thank you to my wife Beth and my parents Ron and Gail for unwavering support and encouragement. I could not have accomplished this without your help. This research was supported by the National Science Foundation under Grant DMR-0347746. ii
Abstract High Al-content metallic amorphous alloys have an unusual devitrification behavior. Upon annealing, alloys made by a rapid quench develop a high density (>10 21 m -3 ) of pure Al nanocrystals. These alloys show a steadily decreasing heat flow signal in isothermal calorimetry and a steadily decreasing nucleation rate, suggesting heterogeneous nucleation. This data implies that a high density of nanoscale structural precursor sites is needed to account for the large number of nucleation events. One possible form of the precursor site in high Al-content amorphous alloys, and other amorphous materials, is atomic structure at the nanoscale (typically 1-3 nm), which is called medium-range order (MRO). This is to distinguish it from short-range order, typically first- and second-nearest neighbor atomic distances, and long-range order, typical of atomic spacing in crystals. MRO can be described as non-trivial three- or four-atom correlations or (in some cases) as small pockets of structural order in an otherwise disordered matrix. Fluctuation electron microscopy (FEM) is a quantitative electron microscopy technique that uses spatial fluctuations in diffraction from nanoscale volumes using the image variance to detect MRO in amorphous materials. To aid in interpretation of FEM results, we developed a new phenomenological theory which uses the assumed structure of a nanocrystal / amorphous composite for various amorphous materials to explicitly calculate the image variance as a function of experimental parameters. This model therefore connects the FEM signal to well-defined aspects of the material’s structure, iii
Page 1 and 2: MEDIUM RANGE ORDER IN HIGH ALUMINUM
Page 3: To my wife Elisabeth i
Page 7 and 8: Table of Contents List of Figures
Page 9 and 10: List of Figures Figure Page Figure
Page 11 and 12: Figure 2.8: V(Φ) at varying values
Page 13 and 14: electron beam exposure. The sharp f
Page 15 and 16: Figure 5.7: FEM data for Al88Y7Fe5
Page 17 and 18: Chapter 1. Introduction Amorphous m
Page 19 and 20: Material Type Tg ( o C) Reference P
Page 21 and 22: dH / dt (arb. units) time Figure 1.
Page 23 and 24: enough to avoid any nucleation onse
Page 25 and 26: nanocrystals are thermally stable u
Page 27 and 28: The structural difference between t
Page 29 and 30: Structures for various metallic gla
Page 31 and 32: ( , ) V k Q = ( r, , ) − ( r, , )
Page 33 and 34: of 1-3 nm is readily achievable in
Page 35 and 36: than the STEM FEM V 66,67,84 . This
Page 37 and 38: interesting behavior upon devitrifi
Page 39 and 40: Λ is a characteristic ordering len
Page 41 and 42: amorphous matrix crystal l R d R bi
Page 43 and 44: For a crystal oriented to a Bragg c
Page 45 and 46: number of crystals in a column will
Page 47 and 48: 3 d π 2 Rt max Zmax Φ = . (2.21)
Page 49 and 50: eciprocal lattice point 1 d hkl awa
Page 51 and 52: A hkl 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Page 53 and 54: V(C hklΦ,d) 0.4 0.3 0.2 0.1 0.4 0.
Page 55 and 56:
V(C 111 Φ) 0.12 0.10 0.08 0.06 0.0
Page 57 and 58:
Φ = 6π d ( 72 − 6π + π ρ) m
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V(t) 0.16 0.14 0.12 0.10 0.08 0.06
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⎛ 3 ⎛ 4 6tΩ⎞⎞ d = ⎜ Chkl
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Chapter 3. Experimental Set-up Prep
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A B 0.25 1/Å 0.25 1/Å Figure 3.1:
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〈IBF〉, to the bright field inte
Page 69 and 70:
Once the relative thickness is know
Page 71 and 72:
Given that FEM is a quantitative el
Page 73 and 74:
eam at a uniform intensity across t
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Low Filtering Limit ω l (Å -1 ) 0
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sample 101 . Much of the influence
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3.07 Thickness Dependant Thinning A
Page 81 and 82:
Residual XRD Intensity (arb. units)
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Intensity (arb. units) 0.30 Al 88 Y
Page 85 and 86:
3.08 Beam Induced Crystallization o
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Fraction of Atoms 0 120 keV 100 200
Page 89 and 90:
V(k) x10 -3 10 8 6 4 2 Al 92 Sm 8 P
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to produce an accurate FEM data set
Page 93 and 94:
Deformation Al 92Sm 8 sample: Rapid
Page 95 and 96:
intensity (arb. units) 3 4 {111} {2
Page 97 and 98:
Al2O3 Al hkl d (1/nm) hkl d (1/nm)
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easons. First, the as-spun V(k) for
Page 101 and 102:
atoms locally organized into an FCC
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in Figure 4.6. Still, this begs the
Page 105 and 106:
Φ 0.20 0.15 0.10 0.05 0.00 10 21 A
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Chapter 5. Al88Y7Fe5 and Al88Y7Fe4C
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diffracting condition through the m
Page 111 and 112:
increases the number of Al nanocrys
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Fraction of nanocrystals x10 -3 Fra
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Al 88 Y 7 Fe 5 Enthalpy (J/g) 0 -1
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Al 88Y 7Fe 5 100 nm Al 88Y 7Fe 4Cu
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5.04 Al88Y7Fe4Cu1 Discussion The de
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FEM is sensitive to both critical a
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devitrified structure has the possi
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fraction between the as quenched ma
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number, etc.) can give insight to t
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24. Liquid Metals Website, http://w
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66. Voyles, P. M., Gibson, J. M. &
Page 133:
105. Zuo, J. M. Electron detection
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William Stratton Ph.D. Thesis - MINDS@UW Home

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