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Advanced Physical Metallurgy Advanced Physical Metallurgy
“ “ Amorphous Materials Amorphous Materials ” ”
Eun Eun Soo Soo Park Park
Office: 33-316
Telephone: 880-7221
Email: espark@snu.ac.kr
Office hours: by an appointment
2009 spring
03. 23. 2009
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Contents for previous class Contents for previous class
• Preparation of amorphous materials
Thermal evaporation Sputtering
Glow-discharge decomposition
Chemical vapor deposition Droplet quenching Injection casting Suction casting Squeeze casting
electrolytic deposition
Gas atomization
Melt-spinning Splat quenching
Irradiation
Pressure-induced amorphization
Solid-state diffusional amorphization
Surface coating Bulk type
: sphere, rod, plate
powder
thin film thin plate
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Glass Glass
Bonding type: covalent, ionic, metallic, van der waals, hydrogen bond Glass has one of those bonding
Glass has one of those bonding. .
Some examples which do not fit into any one category.
Some examples which do not fit into any one category.
Ex) Silica : some ionic + predominant covalent Ex) Silica : some ionic + predominant covalent
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Review of Chemical Bonds Review of Chemical Bonds
There are 3 forms of bonding:
There are 3 forms of bonding:
• • _________ _________ – – complete transfer complete transfer of of 1 or more electrons from one atom to 1 or more electrons from one atom to
another (one loses, the other gains) another (one loses, the other gains) forming oppositely charged ions that forming oppositely charged ions that attract one another
attract one another
• • _________ _________ – – some valence electrons some valence electrons shared
shared between atoms between atoms
• • _________ _________ – – holds atoms of a metal holds atoms of a metal together
together
Most bonds are Most bonds are
somewhere in between somewhere in between
ionic and covalent.
ionic and covalent.
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The type of bond can usually be calculated by finding the differ The type of bond can usually be calculated by finding the differe e nce in
nce in electronegativity electronegativity of the two atoms that are going together. of the two atoms that are going together.
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Electronegativity Difference
• If the difference in electronegativities is between:
– 1.7 to 4.0: Ionic Ionic
– 0.3 to 1.7: Polar Covalent Polar Covalent
– 0.0 to 0.3: Non- Non -Polar Covalent Polar Covalent
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Glass Glass
Bonding type: covalent, ionic, metallic, van der waals, hydrogen bond Glass has one of those bonding
Glass has one of those bonding. .
Some examples which do not fit into any one category.
Some examples which do not fit into any one category.
Ex) Silica : some ionic + predominant covalent Ex) Silica : some ionic + predominant covalent
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• • How does glass form? How does glass form? Glass transition
• • Why does glass form? Why does glass form? Better glass former than others Glass forming ability
Glass transition Glass transition
If liquid is cooled, two events can occur.
1) 1) CrystallizationCrystallization (solidification at T(solidification at Tm.p.m.p.))
2) Undercooled2) Undercooled below Tbelow Tm.p.m.p. More viscousMore viscous
(supercooled) (supercooled)
Glass Glass
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Normalizing as Tg
Difference of Cp at Tg depending on materials
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T
f= T
gT
g= fictive temperature, T
fthermodynamic property
thermodynamic property ?
Glass transition
: region over which change of slope occurs
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Schematic of the glass transition showing the effects of
temperature on the entropy, viscosity, specific heat, and
free energy. T
xis the crystallization onset temperature.
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400 500 600 700 800 900
(a) Ni
61Zr
22Nb
7Al
4Ta
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(b) Cu
46Zr
42Al
7Y
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(c) Zr
36Ti
24Be
40 (a)
(b)
(c)
(d)
(d) Mg65Cu
15Ag
10Gd
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Temperature (K)
Exothermic (0.5 w/g per div.)
Change of T
gs depending on alloy compositions
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• • T T
ggdepends on thermal history. depends on thermal history.
- T
gvs. cooling speed (v)
: v = v
oexp[-1/C(1/T
g-1/T
m)]
--from free-volume theory i.e., slower v Æ lower T
gTg (bulk : melt-quenched)
< T
g (film : vacuum vapor-deposited)37
DSC results DSC results
•• TTgg depends on thermal history depends on thermal history even in same alloy composition even in same alloy composition