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

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probably the commercially available Vitreloy alloy (Zr41.2Ti13.8Cu12.5Ni10Be22.5). Vitreloy is marketed as having excellent impact and wear mechanical properties along with high biocompatibility 24 , so this material is used in sporting equipment, electronics casings, and bioimplants. Marginal glass formers do not form the amorphous structure so readily, so they require a much higher cooling rate than BMGs (~ 10 5 K/s) 25 . High Al and Fe-content amorphous alloys are examples of marginal glass formers. At this point the only commercially available marginal glass former is Metglass (Fe80B20) 26 a high Fe-content amorphous alloy, which is used in low-loss power distribution transformers because of its excellent magnetic properties 27,28 . Metals can be made amorphous either by nucleation control or growth control. Experimentally, calorimetry is typically used to tell the difference between these two mechanisms. Calorimetry measures the energy loss or gain associated with a phase transformation from a sample with temperature changes 6,29 . There are different types of calorimetry experiments. Isothermal calorimetry holds the temperature constant while measuring the energy change, thus measuring the energy difference measured as a function of time. DSC increases the temperature at a constant heating rate, therefore measuring the energy difference as a function of temperature. The DSC and isothermal calorimetry signal for growth controlled amorphous alloys are different than those for a nucleation controlled. Nucleation controlled amorphous alloys should show a distinct Tg below the onset of primary crystallization (Tx) in the DSC trace, and the isothermal trace should show an increasing and then decreasing signal indicating first the formation of nuclei (increase dH/dT), then their subsequent growth (decrease in dH/dT) 25,30 . Growth controlled amorphous alloys should not show a distinct Tg in 4
dH / dt (arb. units) time Figure 1.2 : Isothermal calorimetry traces for a nucleation (a) versus growth control glass (b). Since energy is first needed to form then grow nuclei in a nucleation controlled material, the dH / dt (arb. units) isothermal signal first increases and decreases. Since nuclei already exist in a growth controlled material, the isothermal signal only decreases. Figure adapted from 30 . DSC, rather it will be at the same temperature as Tx 25 . Also, the isothermal trace will only show a steadily decreasing evolved heat, indicating that nuclei already existed in the material, and we are only seeing their subsequent growth 30 . A schematic isothermal calorimetry trace for these two mechanisms is seen in Figure 1.2. (a) (b) time To explain these differences in DSC and isothermal calorimetry results requires using a time-temperature-transition diagram (TTT). A TTT diagram plots the change in structure (e.g. nucleation onset) as a transformation curve on axes of time versus temperature. This 5
Page 1 and 2: MEDIUM RANGE ORDER IN HIGH ALUMINUM
Page 3 and 4: To my wife Elisabeth i
Page 5 and 6: Abstract High Al-content metallic a
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: Material Type Tg ( o C) Reference P
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
Page 59 and 60: V(t) 0.16 0.14 0.12 0.10 0.08 0.06
Page 61 and 62: ⎛ 3 ⎛ 4 6tΩ⎞⎞ d = ⎜ Chkl
Page 63 and 64: Chapter 3. Experimental Set-up Prep
Page 65 and 66: A B 0.25 1/Å 0.25 1/Å Figure 3.1:
Page 67 and 68: 〈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
Page 75 and 76:
Low Filtering Limit ω l (Å -1 ) 0
Page 77 and 78:
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)
Page 83 and 84:
Intensity (arb. units) 0.30 Al 88 Y
Page 85 and 86:
3.08 Beam Induced Crystallization o
Page 87 and 88:
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
Page 91 and 92:
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)
Page 99 and 100:
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
Page 107 and 108:
Chapter 5. Al88Y7Fe5 and Al88Y7Fe4C
Page 109 and 110:
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
Page 117 and 118:
Al 88Y 7Fe 5 100 nm Al 88Y 7Fe 4Cu
Page 119 and 120:
5.04 Al88Y7Fe4Cu1 Discussion The de
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FEM is sensitive to both critical a
Page 123 and 124:
devitrified structure has the possi
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fraction between the as quenched ma
Page 127 and 128:
number, etc.) can give insight to t
Page 129 and 130:
24. Liquid Metals Website, http://w
Page 131 and 132:
66. Voyles, P. M., Gibson, J. M. &
Page 133:
105. Zuo, J. M. Electron detection
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