1 “Advanced Physical Metallurgy” ‐ Bulk Metallic Glasses ‐ Eun Soo Park Office: 33‐313 Telephone: 880‐7221 Email: [email protected] Office hours: by appointment 2014 Spring 04.08.2014
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“AdvancedPhysicalMetallurgy”
‐ BulkMetallicGlasses‐
Eun Soo Park
Office:33‐313Telephone:880‐7221Email:[email protected]:byappointment
2014Spring
04.08.2014
GlassFormation resultswhen
LiquidsarecooledtobelowTm (TL)sufficientlyfasttoavoidcrystallization.
Nucleationofcrystallineseedsareavoided
Growth ofNucleiintocrystallites(crystals)isavoided
Liquidis“frustrated”byinternalstructurethathindersbothevents
“Glass Formation”
Contents for previous class
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Contents for previous class
A.HomogeneousNucleationrate,I(byDavidTurnbull)
A.HomogeneousNucleationrate,I(byDavidTurnbull)
1) η ↑ (denserandompackedstructure)→I ↓
2) ForgivenTandη,α3β ↑ (σ solidinterfacialE&ΔSf ↑/ΔHf ↓)→I ↓
3) η~Trg (=Tg/Tl)&α3β ~thermalstabilityofsupercooled liquid
*metallicmelt의 경우 :αβ1/3 ~0.5
*ifαβ1/3 >0.9,어떤 cooling 조건에서도 균일 핵생성으로는 결정화 안됨.
*ifαβ1/3 ≤ 0.25,결정화 막기 어려움.
B.Growthrateofacrystalfromanundercooledliquid,U
1) η ↑ (denserandompackedstructure)→U ↓
2) ForgivenT,I&U ~η→Trg orα,β ↑ →GFA↑3) Local ordering 혹은 segregation 같은 atomic rearrangement 통해 f 값 ↓
→U ↓*metallicmelt의 경우 :αβ1/3 ~0.5/Trg >2/3~highGFA
*Puremetal:Rc ~1010‐12 K/s,butifTrg =0.5,Rc ~106 K/s
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C.
Nucleation and Growth Rates – Poor Glass Formers
• Strongoverlapofgrowthandnucleationrates
• Nucleationrateishigh
• Growthrateishigh
• Botharehighatthesametemperature
Tm
T
Rate
Growth Rate (m/sec)
Nucleation Rate (#/cm3-sec)
Nucleation and Growth Rates – Good Glass Formers
• Nooverlapofgrowthandnucleationrates
• Nucleationrateissmall
• Growthrateissmall
• Atanyonetemperatureoneofthetwoiszero
Tm
T
Rate
Growth Rate (m/sec)
Nucleation Rate (#/cm3-sec)
TTT curves and the critical cooling rate, Rc
T
Tm
time
Rc very fast Rc much slower
Poor glass formerBetter glass former
10Trg 1/4 1/2 2/3
Rc =1010 K/s
Rc =106 K/sRc =3x103 K/sRc =3.5x101 K/s
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A. Surface coating
2.6MethodstoSynthesizeMetallicGlasses2.6.1Vapor‐stateProcesses:expensive&slow,electronic&magneticapplications
J.KramerNonconductingmodificationsofmetals.Ann.Physik(Berlin,Germany) 19,37(1934)
FirstAmorphousMetals:evaporationmethod
Sbmetal→ Bi, Ga, and Sn-Bi alloys
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Surface coating
B.
2.6.1Vapor‐stateProcesses
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Surface coating
2.6.1Vapor‐stateProcesses
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Δd~very small
3 SiH4 + 4 NH3 → Si3N4 + 12 H2
C. Surface coating
2.6.1Vapor‐stateProcesses
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Surface coating
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Surface coating
2.6.1Vapor‐stateProcesses
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Surface coating
2.6.1Vapor‐stateProcesses
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Thin plate
2.6.2Liquid‐stateProcesses:RapidSolidificationProcess(RSP)mostidealwaytoobtainmetallicglasses,especiallythebulkvariety
105‐6 K/s
A.
Glassformation:stabilizingtheliquidphase
Firstmetallicglass (Au80Si20)producedbysplatquenchingatCaltechbyPolDuwezin1960.
W. Klement, R.H. Willens, P. Duwez, Nature 1960; 187: 869.
20.* mix
mix
m
mm
TTTT
by I.W. Donald et al, J. Non-Cryst. Solids, 1978;30:77.
(where,,
=molefraction,
=meltingpoint)
imi
mixm TxT
ixi
mT
Au Si
0 10 20 30 40 50 60 70 80 90 100
100
300
500
700
900
1100
1300
1500
18.6
363
1064.4
1414
Liquid
Tem
pera
ture
(
°C)
deep eutectic
ΔT* = 0.679
Rapidsplatquenchingliquidmetaldroplet
lasertrigger
metalpiston
metalanvil
t=20μm
l=3cmw=2cm
Tmmix
Tm
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▣ Brief Definition of Melt SpinningA jet of liquid metal is ejected from a nozzle and impinges on the surface
of a rotating substrate, where a thin layer is formed from a melt puddle and
rapidly solidifies as a continuous ribbon.
▣ Several Types of Melt Spinning MethodFree Jet Melt spinning (FJMS)
Planar Flow Melt spinning (PFMS) Example (PFMS, Siemens)Outside of Wheel Inside of Wheel
Thin film
2.6.2Liquid‐stateProcesses
B.
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• Melt-spinning method Thin film
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Electroplating is a plating process in whichmetal ions in a solution are moved by anelectric field to coat an electrode. Theprocess uses electrical current to reducecations of a desired material from asolution and coat a conductive object witha thin layer of the material, such as a metal.Electroplating is primarily used fordepositing a layer of material to bestow adesired property (e.g., abrasion and wearresistance, corrosion protection, lubricity,aesthetic qualities, etc.) to a surface thatotherwise lacks that property. Anotherapplication uses electroplating to build upthickness on undersized parts. However,the limited size of the product formed inone experiment puts a limitation on theusefulness of this technique to producelarge quantities of metallic glasses
C.
Surface coating
2.6.2Liquid‐stateProcesses
2.6.2Liquid‐stateProcesses
C.Electro‐depositionMethods
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Powder
Gas Atomization
D.
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2.6.3Solid‐stateProcessesA. Mechanicalalloying/milling
:MA/MMperformedinahigh‐energyballmillsuchasashakermillorplanetarymillwillalsoinducesevereplasticdeformationinmetals.Duringmilling,particlesarefracturedandcoldweldedtogether,resultinginlargedeformation.
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2.6.3Solid‐stateProcesses
A. Mechanicalalloying/milling
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2.6.3Solid‐stateProcesses
A. Mechanicalalloying/milling
2.6.3Solid‐stateProcesses
B. Hydrogen‐inducedAmorphization
C. MultilayerAmorphization
Ex)
Solid-State Diffusional Amorphization
Alternate layers of crystalline metallic films (‘diffusion couples’) interdiffuse under isothermal conditions, with the eventual amorphization of the entire multilayer.
Couple: late transition metal with early transition metal ex. Au-La, Au-Zr, Au-Y, Cu-Zr, Cu-Er, Ni-Er, Ni-Ti, Ni-Hf, Fe-Zr,
Co-Zr, Ni-Zr
Low temperature annealing below the crystallization temperature (the nucleation or growth of crystalline phases cannot occur)
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* Diffusion in multiple binary system
A diffusion couple made by weldingtogether pure A and pure B
Draw a phase distribution and composition profile in the plot of distance vs. XB after annealing at T1.
Draw a profile of activity of B atom,in the plot of distance vs. aB after annealing at T1.
→ a layered structure containing , & γ.
What would be the microstructureevolved after annealing at T1 ?
A B
α β γ
A or B atom → easy to jump interface (local equil.)
→ μAα = μA
β, μAβ = μA
γ at interface
(aAα = aA
β, aAβ = aA
γ)
β
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Solid-State Diffusional Amorphization
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Two Main Attributes
2.6.3Solid‐stateProcesses
D. Pressure‐inducedAmorphization
e. AmorphizationbyIrradiation
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Mechanism of irradiation amorphization:
• The kinetic knock-off of atoms from their lattice positions• Very high temperature is expected in a very small volume
during a short time (ps), which causes melting of material in a local small point.
Two opposing radiation-induced processes can be operative:
• Radiation-induced chemical disordering of atoms on lattice sites will tend to promote amorphization;
• Radiation-induced defect migration will tend to restore ordering.
The irradiation be carried out at sufficiently low temperatureto suppress the defect migration.
고에너지 입자 충돌에 의해 발생되는 가장 기본적인 결함 :Vacancy&Interstitial
*Aprimaryknock‐onatom(PKA)displacesneighbouring atoms,resultinginanatomicdisplacementcascade,leadingtoformationofpointdefectsanddefectclustersofvacanciesandinterstitialatoms
Seegeretal.,Proc.Symp.Radiat.DamageSolidsReact.1(1962)101‐1056.
20keVFedisplacementcascadeinbccFeat 600K http://www.youtube.com/watch?v=0btHd_8JFV4
(Frenkel pair)
방사선 결함: 고에너지 입자와 재료의 충돌에 의한 결함
방사선 결함: 고에너지 입자와 재료의 충돌에 의한 결함
S.Zinkle,Defects,deformationanddamageinstructuralmaterials,2012
AmorphizationDislocation loops
Voids
Helium cavitiesin grain boundary
Precipitates
solute segregation
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Sample Preparation : Surface Damage
250eV Ar+5 keV Ar+
Y.W. Kim, Metals and Materials International, 7, 499 (2001)
Ion beam induced amorphous formation in Silicon (100)
The schematic diagram of High Energy Electron beam accelerator
Electron beamHeat
radiation
X-ray
Thermal conduction
Backscattered electrons
Secondary electronsKinetic energy of accelerated electron
Collided with electrons of materials
To transform thermal energy
TT1000 prototype picture
Surface : Amorphous alloySurface gloss, Hardness, corrosion resistance,
Substrate : Cu(or Ti, Fe) alloy
Ductility, limited size of amorphous materials,
It is possible to make mass production and reduce weight
Electron beam irradiation is heating the mixture of powder.
The temperature of substrate is so low that surface is super-cooling.
The making method of amorphous materials by Irradiation
2.6.3Solid‐stateProcesses
f. SeverePlasticDeformation:Intensedeformationatlowtemperatures
equalchannelangularextrusion(ECAE)
BentintoanL‐shapedconfiguration→Uniformsimpleshearthroughoutbulksample
(SPDmethods)
Torsionunderhighpressure→ verylargetruestrainbysimpleincreasingthe#ofrotations
Billetdiameter~Notexceedingabout20mm
Typically10mmindia.and<1mminheight
WonPercyBridgmanthe1946Nobelprize→ metalprocessing~morerecentin2003
Developedinthe1970s
0 1 2 3 4
0
100
200
300
400
500
600
700
800
Equ
ival
ent s
train
Distance from center (mm)
N=50
N=20
N=10
N=5
N=1
806
322
161
81
16
Equivalent straint3
Nr2=
πε
HPT: severe plastic deformation, but Inhomogeneous process
HPT process: Equivalent strain induced on sample
2.6.3Solid‐stateProcesses
f. SeverePlasticDeformation:Intensedeformationatlowtemperatures(SPDmethods)
2.6.3Solid‐stateProcessesg. AccumulativeRollBonding(ARBprocess)
:2sheetsofthesamematerialarestacked,heated(tobelowtherecrystallizationtemperature),androlled,bondingthe2sheetstogether.Thissheetiscutinhalf,the2halvesarestacked,andtheprocessisrepeatedseveraltimes.ComparedtootherSPDprocesses,ARBhasthebenefitthatitdoesnotrequirespecializedequipment.However,thesurfacestobejoinedmustbewellcleanedbeforerollingtoensuregoodbonding.