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Microstructural CharacterizationMicrostructural Characterizationof of

MaterialsMaterials

EunEun SooSoo ParkPark

Office: 33-316 Telephone: 880-7221Email: espark@snu.ac.krOffice hours: by an appointment

2009 spring

03.04.2009

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Contents for previous classContents for previous classMicrostructure: structure inside a material

that could be observed with the aid of a microscope

OM, SEM, TEM, AFM, SPM

Observation of Microstructure: to make imagefrom the collection of defects in the materials

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Contents for previous classContents for previous class

Microstructure Properties

ProcessingPerformance

DesignDesign

““TailorTailor--made Materials Designmade Materials Design””

optimization of material properties through control of microstructure

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ex: hardness vs structure of steel• Properties depend on structure

Data obtained from Figs. 10.21(a)and 10.23 with 4wt%C composition,and from Fig. 11.13 and associateddiscussion, Callister 6e.Micrographs adapted from (a) Fig.10.10; (b) Fig. 9.27;(c) Fig. 10.24;and (d) Fig. 10.12, Callister 6e.

ex: structure vs cooling rate of steel• Processing can change structure

Structure, Processing, & PropertiesStructure, Processing, & Properties

Cooling Rate (C/s)

100

200

300

400

500

600

0.01 0.1 1 10 100 1000

(a)

30μm

(b)

30μm

(d)

30μm(c)

4μm

Ha

rdn

ess

(B

HN

)

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Contents for todayContents for today’’s classs class

-- Length Scale of MicrostructureLength Scale of Microstructure

1) Effect of atomistic length scale on material’s properties

including brief introduction for microstructural observation methods

--

2) Effect of defect structure on material’s propertiesincluding brief explanation of polycrystals and crystal

orientation

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Length Scale of MicrostructureLength Scale of Microstructure

<0.1 nm1 nm = 4x10-8 in

0.1-10 nm

HRTEM, STEM

AFM

1-1000 μm

Optical Microscope

SEM,TEM, XRD

>1 mm

Naked Eye

Nanostructure 0.1-100 nm

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Length Scales of MicrostructureLength Scales of Microstructure

• Many important intrinsic material properties are determined at the atomistic length scale.

• The Properties of materials are, how, often strongly affected by the defect structure. For example, polycrystals have different properties than single crystals just because of the variation of crystal orientation, combined with the anisotropy of the property. This immediately introduces the idea that the behavior of a material can vary from on location to another.

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• AmorphousAmorphous – from the Greek for “without form”not to materials that have no shape, but rather to materials with no particular structure

• grain boundaries

nearly random = non-periodic

• no grain boundaries

Building block: arranged in orderly, 3-dimensional, periodic array

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XX--ray diffraction resultsray diffraction results

Location and intensity of peaks~ location and arrangement of atoms

~analogous to a fingerprint

Diffuse halo pattern~summation of interference

Peak position

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XRD (XXRD (X--ray Diffraction)ray Diffraction)X선을 결정에 부딪히게 하면 그 중 일부는 회절을 일으키고 그 회절각과 강도는 물질구조상

고유한 것으로서 이 회절 X선을 이용하여 시료에 함유된 결정성 물질의 종류와 양에 관계되

는 정보를 알 수 있다.

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Recent BMGs with critical size Recent BMGs with critical size ≥≥ 10 mm10 mm

A.L. Greer, E. Ma, MRS Bulletin, 2007; 32: 612.

Zr47Ti8Cu8Ni10Be27 Johnson (Caltech)Vitreloy

Pd60Cu30Ni10P20 Inoue (Tohoku Univ.)

Fe48Cr15Mo14Y2C15B6 Poon (Virginia Univ.)Amorphous steel

Ca65Mg15Zn20 15mm Kim (Yonsei Univ.)Ca60Mg25Ni20 13mmMg65Cu20Ag5Gd10 11mmMg65Cu7.5Ni7.5Zn5Ag5Gd5Y5 14mm

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High fracture strength over 5 GPa in Fe-based BMGs

10 100 1000

10

100

1000

10,000

Young’s Modulus (GPa)

Stre

ngth

σy

(MPa

)

Lead alloysTin alloys

Al alloysMg alloys

Beryllium

Steels

Ti alloys

La50Al25Cu25

La55Al35Cu10

Mg65Cu25Al10

La50Al30Cu20

Zr65Ti17.5Ni10Cu17.5

Ti50Ni20Cu25Sn5

Ti60Be35Si5Metallic glasses

Fe81.1C13.8Si5.1

Fe80C7.5P12.5

Theoreticalstrength

Engineering alloys

Contours ofσy / E

Contours ofσy

2 / E

A.L. Greer, E. Ma, MRS Bulletin, 2007; 32: 612.

High strength of BMGsHigh strength of BMGs

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Limited Plasticity by shear softening and shear bandLimited Plasticity by shear softening and shear band

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Engi

neer

ing

Stre

ss (G

Pa)

0 2 4 6 8 10 12 14 16

Engineering Strain (%)

- low strength

- limited plasticity (0~2%) - catastrophic failure

20㎛

200㎛

Microscopically brittle fracture

Death of a material for structural applications

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SEM (Scanning Electron Microscopy)SEM (Scanning Electron Microscopy)SEM은 Electron beam이 Sample의 표면에 주사하면서 Sample과의 상호작용에 의

해 발생된 Secondary Electron를 이용해서 Sample의 표면을 관찰하는 장비이다.

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interrupt the localization of stress and deformation

• Prevent propagation of single shear band BMG matrix composites

• Multiple shear band formation

Plastic deformation in metallic glass•• No dislocation / No slip plane

• Inhomogeneously localized plastic flow in the shear band

Plastic deformation in metallic glassesPlastic deformation in metallic glasses

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1) Casting : hard/ductile particle

2) Extrusion : ductile powder

extrusion direction

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.100

500

1000

1500

2000

2500

3000

MGMC(20vol% brass)Max. compressive strength: 2.05 GPaTotal strain: 2.8 %Plastic strain: 0.8 %

MGMC(40vol% brass)Max. compressive strength: 1.64 GPaTotal strain: 4.7 %Plastic strain: 2.7 %

strain rate at room temp. = 6x10-5s-1

Stre

ss (M

Pa)

Strain

Monolithic BMGMax. compressive strength: 2.44 GPa

(Johnson et al., Acta Mater.,1999)

(Kim et al., J. Non-cryst. Solids, 2002)

ExEx--situ BMG matrix compositessitu BMG matrix composites

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1) Solidification : formation of primary ductile phase

(Johnson et al., Acta Mater., 2001)

2) Solidification : precipitation of ductile phase

InIn--situ BMG matrix compositessitu BMG matrix composites

(Cu60Zr30Ti10)95Ta5

Ta rich particle (Johnson et al., Acta Mater., 2001)

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TEM Image of a shear band

~20 nm

Shear bands are ~20 nm in width

Size of heterogeneitySize of heterogeneity

• Prevent propagation of single shear band

Micro- or nanometer scale heterogeneity

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TEM (Transmission Electron Microscopy)TEM (Transmission Electron Microscopy)

TEM은 electron beam이 통과할 수 있도록 ultrathin sections을 만들어 관찰할 수

있도록 하는 기능적 장치로 여러 가지 각각의 시스템으로 구성되어 있다.

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J. J. Lewandowski et al., Nature Mater. 5 (2006) 15

Melting of Sn coating on the surface of Vit. 1 on the compression side→ evidence for temperature rise (Tm, Sn = 232℃)

Observation of SBs after three point beam bend testObservation of SBs after three point beam bend test

212 nm

Width of shear band : 10 nmNo crystallization in the shear band

Branching shear bands

Crack propagation direction

Angle between split shear bands: 25~30º

Ti40Zr29Cu9Ni8Be14

Observation of shear bands after tensile testObservation of shear bands after tensile test

H.J. Chang et al. Unpublished. (2008)

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OM images for interruptions during compressionOM images for interruptions during compression

• Stress–strain curves and related OM images for each interruptions during compression test

(a)

(a)

(b) (c)

(b)

(c)

J. Y. Lee et al. Acta Mater. 54 (2006) 5271-5279

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Optical MicroscopeOptical Microscope OM과 TEM은 기본적인 구성 즉 렌즈의 배열은 같으나 렌즈를

무엇을 사용하느냐 하는 차이 이다. OM은 유리(glass)를 EM은

magnetic lens를 사용한다. 광원은 OM이 시광을 EM이 전자

(빔)를 사용하므로 전자현미경은 칼라 상을 볼 수 없는 것이다.

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Elementary flow event in an metallic glasses

Size of heterogeneitySize of heterogeneity

σ

σ

v>v*atomic volume

free volumefluctuation

ε0

Ω

defect volume shear strain

atomic scale heterogeneity

Probability )*

exp(fv

vA

average free volume

⎪⎪⎭

⎪⎪⎬

⎫

⎪⎪⎩

⎪⎪⎨

⎧

=f

VV

A 00expηη

Flow governed by localized defect (~10 atoms) and creates defects

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Enhancement plasticity in BMGs with atomic scale heterogeneity

Effect of quenched in Effect of quenched in quasicrystalquasicrystal nuclei nuclei

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Effect of quenchedEffect of quenched--in in quasicrystalquasicrystal nucleinuclei

Fully amorphous structureβ-Zr particle(~70 nm) in amorphous matrix

50 nm200 nm(a)

β-Zr

(b)

(b) Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5(a) Zr63Ti5Nb2Cu15.8Ni6.3Al7.9

2 mm rod

200 nm

I5 I3 I2

I-phase

3 mm rod

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0 2 4 6 8 10 120

500

1000

1500

2000

[b][a]

d = 2mminjection-cast

Uniaxial CompressionStrain Rate = 1 x 10-4s-1

[a] [b]

Stre

ss (M

Pa)

Strain (%)

σf = 1.70 GPa, εf= 2.37 %σf = 1.71 Gpa, εf= 4.64 %

σf = 1.72 Gpa, εf= 2.05 %

5 nm

HRTEM image in [b] alloy

Compression test

Effect of quenchedEffect of quenched--in in quasicrystalquasicrystal nucleinuclei

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1 2 3 4 5 60.0

0.5

1.0

1.5

2.0

FT

[k3 ·χ

(k)]

r(A)

alloy (2) rib. alloy (2) 1 mm alloy (2) 2 mm alloy (2) 3 mm

(c)

1 2 3 4 5 60.00

0.05

0.10

0.15

0.20

r(A)

FT[k

2 ·χ(k

)]

alloy (2) rib. alloy (2) 1 mm alloy (2) 2 mm alloy (2) 3 mm

(a)

Zr-K edge

Ni-K edge

1 2 3 4 5 60.0

0.5

1.0

1.5

2.0

2.5

r(A)

FT[k

3 ·χ(k

)]

alloy (2) rib. alloy (2) 1 mm alloy (2) 2 mm alloy (2) 3 mm

(b)

Cu-K edge

EXAFS analysis

Distinctive structural change around Ni atom

Intensity change due to microstructural change

(b) Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5

Effect of quenchedEffect of quenched--in in quasicrystalquasicrystal nucleinuclei

Extended X-ray Absorption Fine Structure

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EXAFS AnalysisEXAFS Analysis

Extended X-ray Absorption Fine Structure (EXAFS)는 고체를 통과한 X-선

의 흡수 spectrum을 분석하여 원자단위의 구조를 분석하는 방법으로 그 동안 전

이금속을 포함한 분자, 촉매, 비정질 재료, 초전도재료 등 다양한 재료들에 있는

특정 원소 주위의 local structure 분석하기 위하여 많이 사용되어 왔다.

포항방사광가속기

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T ( )캜-200 -100 0

Cu + 3.32 at%Ni

Cu + 2.16 at%Ni

deformed Cu + 1.12 at%Ni

1

2

3

4

5

6

Re

sist

ivit

y, ρ

(1

0-8

Oh

m-m

)

0

Cu + 1.12 at%Ni

ure?Cu밣

• Electrical Resistivity of Copper:

• Adding “impurity” atoms to Cu increases resistivity.• Deforming Cu increases resistivity.

Adapted from Fig. 18.8, Callister 6e.(Fig. 18.8 adapted from: J.O. Linde,Ann Physik 5, 219 (1932); andC.A. Wert and R.M. Thomson,Physics of Solids, 2nd edition,McGraw-Hill Company, New York,1970.)

ELECTRICAL PropertiesELECTRICAL Properties

pure Cu

(oC)

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Composition (wt%Zinc)Th

erm

al C

on

du

cti

vity

(W

/m-K

)

400

300

200

100

00 10 20 30 40

Adapted from Fig. 19.4, Callister 6e.(Fig. 19.4 is adapted from Metals Handbook: Properties and Selection: Nonferrous alloys and Pure Metals, Vol. 2, 9th ed., H. Baker, (Managing Editor), American Society for Metals, 1979, p. 315.)

THERMAL PropertiesTHERMAL Properties

• Thermal Conductivity of Copper:--It decreases when you add zinc!

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• Transmittance:--Aluminum oxide may be transparent, translucent, or

opaque depending on the material structure.

Adapted from Fig. 1.2,Callister 6e.(Specimen preparation,P.A. Lessing; photo by J. Telford.)

single crystalpolycrystal:low porosity

polycrystal:high porosity

OPTICAL PropertyOPTICAL Property

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Grain growth

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