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

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TTT DSC Isothermal Figure 1.3: Representative TTT, DSC and isothermal calorimetry for nucleation control versus growth control. Nucleation control amorphous alloys will show a distinct Tg in DSC, while growth control amorphous alloys do not. Figure from 31 . transformation curve is nose shaped, with the fastest transformation kinetics occurring at the apex. Figure 1.3 compares representative TTT, DSC, and isothermal curves for a nucleation versus a growth controlled material 31 . When we form a rapidly quenched amorphous alloy, we are following a decreasing temperature versus time (cooling) contour line on the TTT diagram. If the cooling contour line does not intersect the transformation curve, the disordered liquid structure will be preserved in the solid state. This is because the material was quenched rapidly 6
enough to avoid any nucleation onset or crystal growth during solidification. Therefore, if heated, this sample would crystallize by homogeneous nucleation, since there were no phases formed during the quench to act as nucleation sites for crystal growth. The DSC would show a distinct Tg and the isothermal trace would first increase then decrease 25,30 . On the other hand, if the cooling contour did intersect the transformation contour, then a fraction of our quenched material would have undergone crystallization. These small proto- crystals, formed by the rapid quench, would not grow because of the rapidly rising viscosity of the material due to the high cooling rate 9,14,25 . Proto-crystals could then act as nucleation sites for crystal growth on post-quench annealing. The DSC would not show a distinct Tg and the isothermal calorimetry trace would be monotonically decreasing 25,30 . Based on DSC and isothermal calorimetry results, typically BMGs are nucleation controlled materials 14,15 , while marginal glass formers are typically growth controlled amorphous materials 11,12,19,25,31-33 . Since marginal glass formers are growth controlled, this leads to a very special type of devitrification reaction which improves the mechanical properties of the material. 1.02 High Al-Content Amorphous Alloys High Al-content amorphous alloys 16,34 are amorphous alloys that contain greater than 80 atomic percent Al. These amorphous alloys are marginal glass formers which require an RE element, a TM element, or both to solidify to an amorphous state 15 . The amorphous structure is metastable, with the eutectic concentration of the alloy usually having the highest glass forming 7
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 and 20: Material Type Tg ( o C) Reference P
Page 21: dH / dt (arb. units) time Figure 1.
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
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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
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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
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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
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Φ 0.20 0.15 0.10 0.05 0.00 10 21 A
Page 107 and 108:
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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