frontiers of fusion materials science materials and fabrication methods that will establish ......

Frontiers of FusionMaterials Science

Presented by S.J. Zinkle,

Oak Ridge National Laboratory

Office of Fusion Energy SciencesBudget Planning meeting

March 13, 2001

Gaithersburg, MD

INTRODUCTION

¥The mission of the Fusion Materials Sciences programis to ÒAdvance the materials science base for the development ofinnovative materials and fabrication methods that will establishthe technological viability of fusion energy and enable improvedperformance, enhanced safety, and reduced overall fusion systemcosts so as to permit fusion to reach its full potentialÓÐResearch performed on structural materials (alloys and

ceramic composites), insulators, etc.

¥TodayÕs presentation: Materials science highlightsÐSimultaneous scientific excellence: research directly relevant

for fusion and of interest to the broader (materials) sciencecommunity

Fusion Materials Science ProgramTheory-Experiment Coordinating Group*

MicrostructuralStability

Physical &MechanicalProperties

Fracture &DeformationMechanisms

Corrosion andCompatibilityPhenomena

Fabricationand Joining

ScienceMaterials for AttractiveFusion Energy• Structural Alloys*

- Vanadium Alloys- F/M and ODS Steels- High T Refractory Alloys- Exploratory Alloys

• Ceramic Composites*- SiC/SiC, other CFCs

• Coatings• Breeder/multiplier

Materials• Neutron Source Facilities

Materials for Near-Term FusionExperiments• PFMs (Refractory

Alloys, etc.)• Copper Alloys• Ceramic Insulators• Optical Materials

*asterisk denotes Fusion Materials Task Group

Fusion Materials Sciences R&D Portfolio

¥ Large emphasis on mechanical properties

MicrostructurePhys./Mech. PropsDeformation/FractureCorrosion/CompatibilityFabrication/joiningIFMIF

Investigation of Thermal Creep Mechanisms in V-4Cr-4Ti

Diffusion-ControlledCreep Mechanisms

ε σkT

DGbA

b

d G

m n

=

Mechan ism D n A mClim b of Ed ge Disl oca tions DL 5 6x107 0Visco us Glid e (Mi cro creep) DS 3 6 0Low-Te mperatur e Climb Dd 7 2x108 0Harpe r-Dorn DL 1 3x10-10 0Nabarro- Herri ng DL 1 12 2Cobl e Db 1 100 3GBS (Supe rplasti city ) Db 2 200 2Nabarro-S ubg rai n DL 1 12 2Nabarro- Bardeen-H errin g DL 3 10 0 10- 1 2

10- 1 1

10- 1 0

10- 9

10- 8

10- 7

10- 6

10- 5

10- 4 10- 3 10- 2

873 Uniaxial923 Uniaxial973973 Uniaxial998 Uniaxial10731073 Uniaxial973 (V-3Fe-4Ti)1073 (V-3Fe-4Ti)

(dε/

dt)k

T/D

Gb

σ/G

Temperature, K

n = 7

n = 1

10- 6

10- 5

0.0001

0.001

0.01

0.1

0 0.2 0.4 0.6 0.8 1

Nor

mal

ized

She

ar S

tres

s,

τ /µ

(20˚

C)

Normalized Temperature, T/TM

Elastic regime(dε/dt<10-8 s-1)

Coble creep

Dislocation creep

N-Hcreep

Dislocation glide

Theoretical shear stress limit

20˚C 400˚C 700˚C

15

150

Uni

axia

l T

ensi

le S

tres

s, M

Pa

1.5

0.15

1500

10-8 s-1, L=20 µm

10- 6

10- 5

0.0001

0.001

0.01

0.1

0 0.2 0.4 0.6 0.8 1

Nor

mal

ized

She

ar S

tres

s,

τ /µ

(20˚

C)



Dislocation creep

N-Hcreep

Dislocation glide


20˚C 400˚C 700˚C

15

150

Uni

axia

l T

ensi

le S

tres

s, M

Pa

1.5

0.15

1500

10-4 s-1, L=20 µm

ε µ= =− −10 204 1s m, L

Deformation Mechanism Maps for V-4Cr-4Tiε µ= =− −10 208 1s m, L

Experimental Creep Data

PNNL / ORNL / ANL / UCSB collaboration

The R&D portfolio of the fusion materials scienceprogram has two general guiding features

¥Provide a valuable product for fusion energy sciences(build knowledge base on key feasibility issues)

¥Provide excellence in materials scienceÐThis also helps to build support for fusion energy within the

broad materials science community

Topic Fusion benefit Science aspectDisplacementcascades

Quantification of displacementdamage source term

• I s the concept of a liquid validfor time scales of only a fewlattice vibrations

• T ransient (ps) electron-phononcoupling physics

Defect migration Radiation damage accumulationkinetics

• 1 D vs. 3D diffusion processes• i onization-induced diffusion

(nonmetals)Structural materialoperating limits

Identify/expand operatingtemperature window andmechanical stress capabilities

• T hermal creep mechanisms• D islocation-defect interactions

V-4Cr-4Ti R&D Roadmap Snapshot1990 1995 2000 2005 2010

PHYSICAL/MECHANICAL PROPERTIES:Unirradiated:

Tensile propertiesThermal conductivityElectrical conductivitySpecific heatCoeff. thermal expansionFracture toughnessThermal creep

Irradiated (1-30 dpa)Tensile properties (100-600°C)

(600-750C)Thermal creep with fusion-relevant He

(He embrittlement) (?)Fracture toughness Tirr ≤400°C

400-700°CMicrostructural stability 100-600°CIrradiation creep - 200-500°C

500-700°CChemical compatibility with coolants

LithiumPb-LiHeliumSn-Li (?)Flibe (?)

JoiningThick plate lab welds (DBTT ≤0°C)Field welds (friction stir welding?)

MHD insulatorsInitial screeningChemical compatibility 400-700°CIn-situ formation/self-healing

Fusion Materials Science is Strongly Integrated withother Materials Science programs (research synergy)

¥ No one engaged in fusion materials research is supported 100% byOFES funding; all fusion materials scientists actively interact withother research communities

¥ BES (ceramic composites, radiation effects in materials, electron microscopy,deformation physics, nanoscale materials)

¥ NERI (deformation mechanisms in irradiated materials, damage-resistant alloys)¥ NEPO (mechanical behavior of reactor core internal structure)¥ EMSP program (radiation effects in nuclear waste materials, including modeling

relevant for SiC and other ceramics)¥ Naval programs (radiation effects in SiC/SiC, refractory alloys, cladding

materials)¥ NRC (fracture mechanics and radiation effects in pressure vessel alloys)¥ EPRI (stress corrosion cracking in alloys)¥ APT, SNS (effects of He and radiation damage on structural integrity of

materials)¥ Defense programs (stockpile stewardship materials issues)

Atomistic simulations model the unit interaction of anedge dislocation with a radiation-induced defect cluster

The simulations are in excellent qualitative agreement with experiments

Experimental TEM imageby Ian Robertson at UIUC

MD simulation by Brian Wirth at LLNL

Atomistic simulations supported by OFES and ASCI,In-situ TEM supported by OBES

Fusion Materials Scientists are Contributing tothe Resolution of Several Grand Challenges in

the General Field of Materials Science

¥ What are the maximum limits in strength and toughness formaterials?

Ð Dislocation propagation, interaction with matrix obstacles

¥ How are the ÒlawsÓ of materials science altered under nanoscaleand/or nonequilibrium conditions

Ð Critical dimensions for dislocation multiplicationÐ Nonequilibrium thermodynamics

¥ What is the correct physical description of electron and phonontransport and scattering in materials?

Ð Thermal and electrical conductivity degradation due to point, line and planardefects

¥ What is the effect of crystal structure (or noncrystallinity) on theproperties of matter?

Radiation damage is inherently multiscale with interacting phenomena ranging from ps-decades and nm-m

Nanoscience appears in numerous places in the fusionmaterials science program

3-D atom probe iso-composition contour(Y, Ti, O) for nanocomposited ferritic steel

Nanoscale self-organization of defectclusters in neutron-irradiated Ni

Atomic resolution analysis of crystal-amorphous transition in SiC

Crack-deflecting interfaces in ceramiccomposites give improved toughness

300 nm

SiC fiber

SiC SiC multilayersmultilayers

10 nm

Microcrack

Amorphousnanoscale

region

200 nm

Experimental evidence for nanoscale melting during atomiccollisions has been obtained

2400

2800

2000

1600

1200

800

400ZrO2 SiO2

20 40 60 80

ZrO2m+

ZrSiO4

ZrO2t+

ZrSiO4

ZrSiO4 + α-quartz

ZrSiO4 + β-quartz

ZrSiO4 + tridymite

ZrSiO4 + cristobalite

ZrO2t + SiO2liq

ZrO2t + cristobalite

liquidZrO2c+liquid

two liquids

ZrO2-SiO2 Phase Diagram

Mole Percent SiO2

Tem

pera

ture

(¡C

)

Nature, vol. 395, Sept 5. 1998, p. 565 nm

111

200

220

311

Microstructure of Zircon Irradiated at 800 °C

Tetragonal ZrO2

One of the Most Important Scientific Results From the US/Japan Collaborationson Fusion Materials has been the Demonstration of Equivalency of DisplacementDamage Produced by Fission and Fusion Neutrons

Fission(0.1 - 3 MeV)

A critical unanswered question is the effectof higher transmutant H and He

production in the fusion spectrum

5 nmPeak damage state iniron cascades at 100K

50 keV PKA(ave. fusion)

10 keV PKA(ave. fission)

MD computer simulations show that subcascades anddefect production are comparable for fission and fusion

Similar defect clusters produced by fission andfusion neutrons as observed by TEM

Fusion(14 MeV)

Similar hardening behavior confirms the equivalency

Displacement Damage Mechanisms are beinginvestigated with Molecular Dynamics Simulations

PKAs oriented in the close packedplanes produce enhanced damageefficiency at low energies compared toother orientations, due to a planardefect creation process

Damage efficiency saturates whensubcascade formation occurs

300 eV PKA

New Defect Reaction Kinetics for Mobile Clusters

vMD simulations show that INTERSTITIAL CLUSTERS formed incascades MIGRATE ONE-DIMENSIONALLY, but occasionally theyCHANGE DIRECTION!

vThese clusters follow a new kind of reaction kinetics.

vKinetic Monte Carlo computer simulations lead to anew analytical theory for reaction kinetics from 1-Dto 3-D vThe new defect reaction kinetics

applied in PBM rate theoryrationalizes

vDecoration of dislocations by loops

vEnhanced swelling at grainboundaries

vDependence of void swelling ontemperature, recoil energy, dose

vVoid lattice formation in pure metalsand complex alloys

L

Mixed 1-D/3-D migration, averagelength L between direction changes

km2 = 0.5 k12 1 + √ 1 + 4/(l2k1

2/4 + k14/k3

4 )

Sink strengthas a functionof 1-D pathlength.

Analyticalexpressioncompared toKMC results

3-D 1-D

U.S. Department of EnergyPacific Northwest National Laboratory

Experimental investigation ofstacking fault energies of BCC metals

1019

1020

1021

1022

1023

1024

100 200 300 400 500 600

Measured Defect Cluster Densities in V-4Cr-4Ti Neutron-irradiated to 0.5 dpa

Clu

ster

Den

sity

(m

-3)

Irradiation Temperature

faulted loops

perfect loops

Ti(O,C,N)precipitates 0

0.2

0.4

0.6

0.8

1

1.2

1.4

10 100 1000 104

Continuum mechanics calculation of dislocation loop energies in vanadium

Dis

loca

tion

loop

ene

rgy

(eV

/SIA

)Number of SIAs

Perfect loop

Faulted loop, γS F

=1.2 J/m 2

γS F

=0.8 J/m 2

d=1.2 nm d=2.5 nm

Determination of interstitial migration energies in ceramics

• S olve steady state rate eqns:

Dd C

dxC C D C C P

Dd C

dxC C D C C P

ii

i v i i s

vv

i v v v s

2

2

2

2

0

0

− − + =

− − + =

α

α

• F or sink-dominant conditions (CS>1014/m2),the defect-free zone width is related to thediffusivity (Di) and damage rate (P) by:

Di =L P

Cicrit Cs

Defect-free zones in ion-irradiated MgAl2O4

Defect-free grain boundaryzones in ion-irradiated Al2O3

10-9

10-8

10-7

10-6

10-5

10 15 20 25 30 35 40

Interstitial Diffusion Coefficient in Ion Irradiated Oxides Determined From Defect-Free Zone Widths at Grain Boundaries

Inte

rstit

ial D

iffus

ion

Coe

ffici

ent

(m2-s

-1)

1/kT (eV)-1

MgAl2O

4

Eim

~0.21 eV

Al2O

3

Ionizing Radiation can induce a myriad of effectsin ceramics

¥Defect productionÐRadiolysis (SiO2, alkali halides)ÐIon track damage (swift heavy ions)

¥Defect annealing and coalescence (ionization-induceddiffusion)ÐAthermal defect migration is possible in some materials

Highly ionizing radiation (dEioniz./dx > 7 keV/nm)introduces new damage production mechanisms

Swift heavy ions induce surfaceprotrusions and amorphizationIon tracks produce displacement

damage via inelastic atomic events

430 430 MeV MeV Kr –>MgAlKr –>MgAl 22OO44

430 430 MeV MeV Kr –>MgAlKr –>MgAl 22OO44

710 710 MeV BiMeV Bi –>Al –>Al22OO33

710 710 MeV BiMeV Bi –>Si –>Si33NN44

3.5 3.5 nm diamnm diam..amorphous coreamorphous core

Investigation of ionization-induced diffusion in ceramics

1017

1018

1019

1020

1021

1022

1023

10 100 1000 104

Loop

Den

sity

(m

-3)

Electron-hole pairs/dpa Ratio

ZrFe

Fe

Mg Al

Al

Mg

C C He He H

650˚C10- 6 to 10 - 4 dpa/s

Fe Al

C

He

H

H

Al2O

3MgAl

2O

4

Zr

Mg

Fe

MgOHe

H

Mg

0

10

20

30

40

50

10 100 1000 104 105

Loop

Dia

met

er (

nm)

Electron-hole pairs/dpa Ratio

Al

C

He

650˚C10-7 to 10-4 dpa/s

Fe

H

Al2O

3

MgAl2O

4

HHe

Mg

MgO

H (d~200 nm)

0.1 µm

Aligned cavities in Al2O3 ion-irradiated at 25˚C(Al/O/He ion irradiation, >500 eln.-hole pairs per dpa)

proj. [0001]proj. [0001]

Large interstitial loops in MgAl 2O4 ion-irradiated at25˚C for regions with >100 eln.-hole pairs per dpa

Irradiated materials undergo plastic instabilityand failure due to dislocation channel formation

Outstanding questions :• What governs the appearance of a yield point?• What governs the dose dependence of yield point onset?• What governs dislocation channel initiation?• What governs dislocation channel growth? (cross-slip in fcc metals is not well understood)• What controls channel width?

Plastic flow localization in irradiated metals - An unresolved issue for >30 yrs

02

000

4000

Z( a)

02

000

4000

X(a

)

0 1 000 2 000 3000 4000Y (a)

b

225MPa

145MPa

Dislocation Dynamics (DD) is a new computer simulationmethod developed at UCLA for modeling fundamentalmicroscopic mechanical properties

New Understanding (dislocation-defect interactions):(a) Local heating destroys vacancy clusters;(b) Shape instabilities allow dislocations to overcomethe resistance of SIA clusters.

[-1 1 0] (a)

[-1-1

2]

(a)

-500 0 500-1200

-1100

-1000

-900

-800

-700

-600

bc

b

Leads to localized flow

Leads to yield drop

(1) N.M. Ghoniem, B. N. Singh, L. Z. Sun, and T. Diaz de laRubia, J. Nucl. Mater, 276: 166-177 (2000).(2) N.M. Ghoniem, S.- H. Tong, B.N. Singh, and L. Z. Sun,Phil. Mag., 2001, submitted

Broad Objectives of DD:1. Understand fundamental deformation mechanisms2. Provide a physical basis for plasticity3. Determine stress-strain behavior without assumptions.4. Design new ultra-strong and super-ductile materials.

Plastic flow localization in defect free bands appearsin the Dislocation Dynamics (DD) simulations

The implementation of cross-slip into DD gives rise to the formation ofdefect free bands (channels) with a width of 200-300 nm

Spreading of the channels isrestrained by the formationof dipole segments and theremaining radiation induceddefect distribution

Nature, August 24, 2000

Successful Applications in FusionMaterial Science (2) UCLA-RISO (Denmark) collaboration onlocalization of plastic flow

Computer Simulations Experiments on Irradiated Cu

0

100

200

300

400

500

600

700

0 0.05 0.1 0.15 0.2 0.25 0.3

Load-Elongation Curves for V-4Cr-4Ti Irradiated in HFBR to 0.5 dpa

Engi

neer

ing

Stre

ss, M

Pa

Normalized Crosshead Displacement, mm/mm

110˚C 270˚C

325˚C

420˚C

Tt e s t

~Tirr

100 nm100 nm

TTtesttest =T=Tirrirr =270˚C=270˚C

g=011g=011

Irradiated Materials Suffer Plastic Instabilitydue to Dislocation Channeling

0.3

Unirradiated

0.010.10.2

Unirradiated

0.01

0.1

0.20.3

Yield point formed

As-Irradiated Post-Irradiation Annealed350¡C/50 hrsPure Copper

Deformation Behavior in As-Irradiated and Post-IrradiationAnnealed Pure Copper (PNNL & Ris¿ National Laboratory)

Post-Irradiation Annealed Condition¥ Dislocation cell structure: material deforms

homogeneously at 0.01 dpa¥ Mixture of channeling and homogeneous

deformation at 0.3 dpa

As-Irradiated, 0.3 dpa¥ Cleared channels with little to no dislocation movement

between the channels; localized deformation¥ Large increases in strength (6 to 8x)¥ Loss of uniform elongation and work hardening capacity¥ Formation of a clearly defined yield point


PI Annealed, 0.01 dpa PI Annealed, 0.3 dpa

Deformation mechanisms in FCC metals

10-6

10-5

10-4

10-3

10-2

10-1

0 0.2 0.4 0.6 0.8 1

Deformation Map for 316 Stainless SteelIrradiated to 1 dpa

Nor

mal

ized

She

ar S

tres

s,

τ/µ(

20˚C

)



Coble creep

Dislocation creep

Dislocation glide


20˚C 300˚C 650˚C

24

240

Uni

axia

l T

ensi

le S

tres

s, M

Pa

2.4

0.24

2400

10- 8 s- 1, L=50 µm

N-H creep

Twinning

10-6

10-5

10-4

10-3

10-2

10-1

0 0.2 0.4 0.6 0.8 1

Deformation Map for 316 Stainless Steel

Nor

mal

ized

She

ar S

tres

s,

τ/µ(

20˚C

)


Elastic regime(dε/dt<10 -8 s-1)

Coble creep

Dislocation creepDislocation glide


20˚C 300˚C 650˚C

24

240

Uni

axia

l T

ensi

le S

tres

s, M

Pa

2.4

0.24

2400

10- 8 s- 1, L=50 µm

N-H creep

Twinning

Irradiation is a useful tool to producecontrolled microstructures fordeformation mechanics studies

Channeling (Disln glide) occurs at highertemperatures (~300ûC)

Twinning occursat lower

temperatures(<200ûC) and high

strain rates

Unir

Deformation Flow Instability-Localization¥ Understanding uniform strain loss-flow localization requires close integration of

mult iscale models & experiments. In many cases irradiation may enhancefunctional strength.

Nano MacroMicroσcrss

0.00

0.05

0.10

0.15

0.20

0.25

200 300 400 500 600 700 800 900

σy

φt

n =0.2

n =0.4

n =0.5 n σy

-0.2

0

0.2

0.4

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

n

hp/Loo

V unirradiated

V irradiated

strain softening?

0

100

200

300

400

500

600

700

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

nv-newp1/VNC02d

Nom

inal

Str

ess

F/A o (

MP

a)

Nominal Strain, u/lo

Tensile test

FEA

0

100

200

300

400

500

600

700

800

0 0.05 0.1 0.15 0.2nvnewp2/nvnewd

σ (M

Pa)

ε

Tensile test 3-Dshape imaging andFEA modeling

True σ−ε

Irr

Multiscale Physics

Eng s-e

Engr s-e Instability Theory

flow channel

Exp.

FEA

nP

∆

Beam Bend Tests

FEAIrr

Unirr

Hardness Pile-up/n

Unirr

Irr

εhard

εsoft

σ

ε

s

eFEA

0

-

+

σy

Macro

εu

Confocal microscopy

Recent work at ORNL suggests that thermodynamicsmay be significantly altered at the nanoscale

Atomic analysis of new nanocompositedferritic steel provides clues to itsoutstanding creep strength (6 orders ofmagnitude lower creep rate thanconventional steels at 600-900ûC)

Atomic composition of nanoclusters

Discovery of Unprecedented Strength Properties in IronBase Alloy

0

50

100

150

200

250

300

350

400

450

22000 24000 26000 28000 30000 32000 34000 36000

12YWT

9Cr-WMoVNb Steel

12Y

LMP T(25+logt), (K-h)

Str

ess

(MP

a)

700¡C, 530h, Stop

800¡C, 931h, Stop

900¡C, 1104h

800¡C, 9000h

800¡C, 817h

650¡C, 9000h

600¡C, 9000h

650¡C, 1080h, Rupt.

¥ Time to failure is increased by several orders of magnitude

¥ Potential for increasing the upper operating temperature of ironbased alloys by ~200¡C

Multiphysics - Multiscale Fracture Modeling - I10 m

10-10 m

10-2 m

10-3 m

Macroscopic Scale

structure

Mesoscopic Scale

FEM: blunting fields

FEM: load-displacement

Large scale bridging

Trigger particle mechanicsσ* = Kmicro/C√πa

Elastic-plastic deformation and fracture of acracked body as a function of temperatureand loading rate as characterized bymaterial macro constitutive and fracturetoughness properties.specimen

Local multiaxial plasticityat blunting macro-crack tipresulting in stress-strainfield concentrations thatcrack mm-scale brittletrigger particles. Manymicro-cracks arrest atparticle-ferrite interfaces,lath packets, and grainboundaries. Ultimateprocess zone damagedevelopment and collectiveinstability cause macro-cleavage.

Fracture involves multiple processes interacting from atomic tostructural scales. UCSB is developing multiscale physical fracturemodels and new engineering methods of fracture control using small-scale tests. Research combines theory, models, measurements andcharacterization of key processes at all pertinent length scales.

Multiscale Research on Fracture Mechanisms, Mechanicsand Structural Integrity Assessment

δ = 68µm δ = 70µm δ = 72µm

δ = 74µm δ = 76µm δ = 78µm

200µm

Theoretical vs. Observed Master Curve MC Embrittlement Shifts in F82HSize-Corrected Minitest K(T) Data

Tomographic Imaging of Cleavage FEM Simulations of Crack Fields

Multiscale Research on Fracture Mechanisms, Mechanics, Models and Structural Integrity Assessment Methods

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

No

rmal

ized

Str

ess

(S

irr/S

ave)

Cross Head Displacement (mm)

UnirradiatedStress (MPA), S

aveFiber type

292 (3 tests)Regular Nicalon™359 (7 tests)Hi-Nicalon™416 (2 tests)Type-S Nicalon™

Type-S NicalonComposite

High NicalonComposite

Ceramic Grade Nicalon Composite10 mm

20 mm

2.3 x 6 x 30 mm

FCVI SiC Matrix, C-interphase, Plain Weave Composite~ 1 dpa, HFIR irradiation

ORNL / Kyoto U.

A science-based program involving tailored nanoscalemicrostructures is producing remarkable advances inradiation-stable ductile ceramic composites (SiC/SiC)

Ceramic fiber 0.5 µm

SiC-interlayerThin C-interlayer

SiC-interlayer

Bulk SiC

Crack Growth in Ceramic Composites is a Potential Lifetime-Limiting Mechanism Controlled by Microscale Phenomena

Analytical modeling of internal stresses

fiberinterphasematrix

abc

σ r AB

r dpa= −

[ ( )]2

σθ = +AB

r dpa[ ( )]2

ldeb 2u loxlox

matrix

fiber

σapp σapp

u P Pf fl

f fn

f= +( )Φ Φ x

y

c0

dPCrackTip

dP

a

2u(x, a)2rf+ =

mic

rosc

ale

mac

rosc

ale

unirr

adia

ted

irrad

iate

d

Fiber Displacement (1 µm/div)

0.0

0.1

0.2

0.3

0.4

Load

(N) 25 min 60 min 90 min

120 min

Experimentally determined, semi-empirical,bridging-compliance relations Micromechanical

model forpredictingsubcritical crackgrowth due tomicroscalemechanisms.

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 5 10 15 20 25 30

INTERNAL STRESSES40Vf Hi-Nicalon SiC

f/1 micron C/CVI-SiC

m 1000˚C

radial stress:fiber/interphaseradial stress:interphase/matrixaxial stress: fiberaxial stress:interphase

Str

ess

(MP

a)

dpaU.S. Department of Energy

Pacific Northwest National Laboratory

Micromechanical Modeling Allows Prediction ofComponent Lifetime of Ceramic Composites

0

0.002

0.004

0.006

0.008

0.01

0 5 104 1 105 1.5 105 2 105

Mid

po

int

Dis

pla

cem

en

t (m

m)

T ime(s)

Fiber Creep OnlyNon-linear, time dependent compliance

Oxidation-InducedRecession Plus Fiber Creep:linear, time-dependent compliance

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 5 104 1 105 1.5 105 2 105

Mid

po

int

dis

pla

cem

en

t (m

m)

Time (s)

1200°C

202 Pa O2 + argon

argon (< 2 Pa O2)

expe

rimen

tm

odel

Oxygen atmosphere investigated inconjunction with DOE office of Basic

Energy Science Program

0.0018

0.002

0.0022

0.0024

0.0026

0.0028

0.003

0 2 105 4 105 6 105 8 105 1 106

CrackLength

(m)

Time (s)

1473K

1373K

1323K1273K

1173K 1073K

At 1323K thermal and irradiation creep rates are roughly equal

T > 1323K Thermal Creep DominatesT < 1323K Irradiation Creep Dominates

Crack Velocity = 1.7 x 10-10 m/sat 800-900 C (1073-1173K)

105

106

107

108

10-12

10-11

10-10

10-9

10-8

0.1 1 10 102 103

Time to grow a bridged crack 0.5 mmat 800˚C in 10 ppm O2 (1.01 Pa)

Time (s)

Avg.V

C

(m/s)

PO2 (Pa)

Cracksgrow less

than 0.5 mmin this region

Cracksgrow more

than 0.5 mmin this region

AverageCrack

Velocity

Estimatedlife at 1.01 Pa(10 ppm O

2)

is 2 x 107 s(230 days)

Model verification Predictive capabilities

Irradiation-enhanced creep of

fibers controlscrack growth below

≈ 1073 K

Model predictscrack velocity and

crack length

NOTE: Lifetime predicted for oldergeneration material properties.

More recent materials haveenhanced lifetimes.


Physics of phonon transport & scattering arebeing investigated in neutron-irradiated ceramics

K TK T K T K Ku gb d rd

( )( ) ( )

[ ] = + + +

−1

0

1 1 1 1

K

K

h

K C

h

K Cirr

unirr D unirr v D unirr v

=

−−

2

18

2

18

2

2

1 2

12

2

1 2υ

πυ

πΩΘ ΩΘ

/ /

tan

Thermal resistance of different phonon scatteringcenters can be simply added if their characteristicphonon interaction frequencies are well-separatedfrom one another

Thermal resistance due to radiation-induced defects(vacancies, dislocation loops, etc.) is proportional totheir concentration

Thermal Conductivity of 2D SiC/SiC Composites

0

2 0

4 0

6 0

8 0

1 0 0

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0

The

rmal

con

duct

ivity

(W

/mK

)

Temperature (°C)

2D-SA Tyrannohex(unirradiated)

(50% parallel fibersand 50% interfaces)

(100% transverse fibersand 100% interfaces)

0

10

20

30

40

50

0 200 400 600 800 1000 1200

Temperature ( oC )

The

rmal

Con

duct

ivity

(W

/mK

) fiber: Tyranno SAmatrix: CVI-SiC

Vf = 0.4

(enhanced f/m bonding)

(degraded interface)

(typical interface)

5000

500

50

Interfaceconductance

(W/cm2K)

0

10

20

30

40

50

400 600 800 1000 1200

Temperature, K

The

rmal

Con

duct

ivity

, W

/mK

fiber: Tyranno SAmatrix: CVI-SiCV

f = 0.4, t = 200 nm

(anisotropic PyC)

(isotropic PyC)

(degraded PyC)

20 W/mK

0.2 W/mK

2.0 W/mK

Coating Conductivity

¥ Number and quality of interfacesimportant

¥ Fibers parallel to conductionpath useful (3D architecture)

¥ Samples currently beingirradiated

Experimental:

NERI Program

¥ Strong bonding due to fibersurface treatment useful

¥ Degraded interface due toirradiation or fiber/matrixmismatch

Model 1: Thin Interface Conductance¥ Preferred orientation of

graphitic crystallites

¥ Strong interface cohesion

¥ Degraded interphase due toirradiation or oxidation

Model 2: Interphase Conductivity

Fusion Materials Program


Thermodynamic Stability, Microstructure Characterization, andProperty Evaluation of In-situ Formed ÒCaOÓ Insulating Coating onVanadium Alloys

Argonne National Laboratory

• Calculated thermodynamic stability of candidateoxides in lithium as function of oxygen content

• Composition from EDS analysis vs depth for in-situ formed "CaO" coating on V-alloy

-140

-135

-130

-125

-120

-115

500 600 700 800 900

Free

Ene

rgy

(kca

l/g-a

tom

-O)

T¡K

O in Li (wppm)

100

10

1

Y/Y2O3

Ca/CaO

Be/BeO

Li/Li2O

• Microstructure of “CaO” coating on V-alloy

• In-situ resistance of “CaO’ coating in lithium

BASE METAL HEAT AFFECTED ZONE

Research performed byM. K. Miller, Oak Ridge National Laboratoryand A. J. Bryhan, Applied Materials

GIE (atoms m -2)Zr 7.6 x 10 13

B 7.3 x 10 12

C 1.1 x 1013

O -3.9 x 1012

GIE (atoms m -2)Zr 1.3 x 10 13

B 9.9 x 10 14

C 9.9 x 1011

O 1.1 x 1013

•B, Zr (and C) segregation inhibits O embrittlement of grain boundaries–Etot~20%, transgranular fracture mode instead of typical e tot~3%,intergranular fracture for Mo welds

•Bulk alloy composition: 1600 appm Zr, 96 appm C, 53 appm B, 250 appm O

FIM FIM

APT atom maps

Atom Probe Tomography Reveals Zr, B and C Segregationto Grain Boundaries Produces Improved Mo Weldments

LASER-INDUCED SURFACEDEFORMATION MECHANISMS

¥ Single Shot Effects on LIDT:• Laser Heating Generates Point Defects

• Coupling Between Diffusion and Elastic Fields Leadto Permanent Deformation

• Progressive Damage in Multiple Shots• Thermoelastic Stress Cycles Shear Atomic PlanesRelative to one Another (Slip by Dislocations)

• Extrusions & Intrusions are Formed whenDislocations Emerge to the Surface

Computer SimulationExperiment

Focused laser-induced surface deformation (Lauzeral,Walgraef & Ghoniem, Phys. Rev. Lett. 79, 14 (1997) 2706)

Focused Laser-inducedSurface Deformation

SINGLE-SHOT LASER DAMAGEEXPERIMENTS & MODELING

Deformation instability mechanisms

Physical Mechanism of Feedback in PointDefect GDDI: Laser Intensity Distribution

Newly Developed Techniques Allow Greater MaterialsScience Output From Smaller Irradiation Volumes

3 mm TEM disk isirradiated in fission reactor

Shear punch test yields mechanical properties datathat correlate with tensile data and can be correlatedwith data on conventional (full size) specimens

He and H analyseson outer rim

Bonded into unirradiated disk to reduceradioactivity levels and waste generation in

evaluation of microchemistry and microstructures

Fe54-F82H

0

100

200

300

400

500

600

700

800

900

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Displacement (mm)

Eff

ecti

ve S

hear

Str

en

gth

(M

Pa) FN91

FN92

FN93

FN51

FN52

C603

C601

C605

C609JP17 p1

250 C, 2.4 dpa142-406 appm H

4.5 appm He

JP22 p5300 C, 34 dpa352 appm H

65.3 appm He

Unirradiated

500 C, 8 dpa

300 C, 8 dpa

400 C, 8 dpa

639-1280 appm H

10.2 - 11.2 appm He

Hydrogen and Helium analysis results

0

500

1000

1500

2000

2500

0 5 10 15 20 25 30dpa

H, ap

pm

250 300

300

400

500

Calculated

0

20

40

60

80

100

0 10 20 30 40

dpa

He

, a

pp

m

54Fe

54Fe+55Fe

NFe


The fusion materials program is participating inground-breaking remote microscopy investigations

DOE/JAERI remote microscopyanalysis of irradiated SiC/SiCcomposite, July, 2000

Groundwork laid by DOE 2000Materials MicrocharacterizationCollaboratory initiative (OASCR)

Precipitate stabilityknowledge derived from

radiation effects studies canbe used to develop highly

creep resistant alloys(microturbine recuperator)

Microstructure-Mechanical property knowledge derived from FusionMaterials Science investigations is being transferred to US Industry

Conclusions

¥The Fusion Materials Sciences program is pursuingsimultaneous scientific excellence (fusion energy andmaterials science)ÐResearch portfolio is determined by fusion energy needs

(guided by fusion materials roadmap key feasibility issues)Ðresearch results are of interest to broader materials science

community

Backup viewgraphs

0

100

200

300

400

500

600

700

800

0 200 400 600 800

Ulti

mat

e T

ensi

le S

tren

gth

(MP

a)

Temperature (˚C)

CuCrZr, ITER SAA

CuNiBe, HT1 temper

CuNiBe, AT

GlidCop Al25 (IG0)

1-2x10- 3 s- 1

CuCrNb

10- 6

10- 5

0.0001

0.001

0.01

0.1

0 0.2 0.4 0.6 0.8 1

Deformation Map for CuNiBe (Brush-Wellman Hycon 3HP)

Nor

mal

ized

She

ar S

tres

s,

τ /µ

(20˚

C)


Elastic regime(dε/dt<10 -8 s-1)

Coble creep

Dislocation creep

Dislocation glide


20˚C 300˚C 500˚C

14

140

Uni

axia

l T

ensi

le S

tres

s, M

Pa

1.4

1400

10-8 s-1, L=30 µm

N-H creep

10- 6

10- 5

0.0001

0.001

0.01

0.1

0 0.2 0.4 0.6 0.8 1

Deformation Map for Oxide Dispersion-strengthened Copper (GlidCop Al25)

Nor

mal

ized

She

ar S

tres

s,

τ /µ

(20˚

C)


Elastic regime(dε/dt<10 -8 s-1) Coble creep

Dislocation creep

Dislocation glide


20˚C 300˚C 500˚C

14

140

Uni

axia

l T

ensi

le S

tres

s, M

Pa

1.4

1400

10-8 s-1, L=5 µm

N-H creep

Applications to US industry (e.g.,USCAR) as well as fusion energysciences program

Mechanical behavior of copper alloys can be understood onthe basis of current materials science models of deformation

A focussed, science-based welding program hassuccessfully resolved one of the key feasibility issues for V

alloys

Ð Results are applicable to other Group V refractory alloys (Nb, Ta)

-200

-100

0

100

200

300

1992 1994 1996 1998 2000 2002

DB

TT

(ûC

)

Year

V-4Cr-4Ti base metal

GTA welds (no heat treatment)

Fi gure 3 Transm i ssi on el ect r onmicr og raph showin g tw i ns i n wel d GTA 1 7f ollow i ng r em oval o f hydrogen.

Success is due to simultaneous control of impurity pickup,grain size

Dose (dpa)0.1 0.2 0.30

50

100

150

200

250

300

∆σ 0.0

5(M

Pa )

φc=158o

φc=165o

φc=170o

Experiment

OFHC-Cu

Successful Applications in Fusion MaterialScience (2) Quantitative predictions of hardening with only oneadjustable parameter

Measurements at PNNL& RISO

Simulations at UCLA.

Dislocation Dynamics (DD) is a new computer simulationmethod developed at UCLA for modeling fundamentalmicroscopic mechanical properties

0

2

4

[01

0 ](µ

m )

0

2

4

[01

0 ](µ

m )

024

[001 ]

(µm )

024

[001 ]

(µm )

0 2 4

[100] (µm)

0 2 4

[100] (µm)

024

[ 00 1]

( µm)

024

[001 ]

(µm )

0 2 4

[100] (µm)

0 2 4

[100] (µm)

0

2

4

[01

0 ](µ

m )

X

Y

Z

0

2

4

[010] (µ m)

0

2

4

[001

](µ

m)

0

2

4

[1 00] (µ

m)

0

2

4[ 00 1

]( µ

m)

0

2

4[1 00](µ

m)

0

2

4[01

0] (µ m)

XY

Z

Frame 001 01 Jun 2000Frame 001 01 Jun 2000

TEM-Slice

0

2

4[01 0] (µ

m)

0

2

4[ 00 1]

( µm)

0

2

4

[100] (µ m)

0

2

4

[001 ]

(µm )

0

2

4[100] (µ m)

0

2

4

[01 0] (µ

m)

Y

X

Z

Broad Objectives of DD:

1. Understand fundamental deformation mechanisms

2. Provide a physical basis for plasticity

3. Determine stress-strain behavior without assumptions.

4. Design new ultra-strong and super-ductile materials.

(1) N. M. Ghoniem, L. Sun, Phys. Rev. B,60(1): 128-140 (1999).

(2) N.M. Ghoniem, S.- H. Tong, and L. Z.Sun Phys. Rev. B, 61(1): 913-927 (2000).

Colloidal metal nanoclusters can be created in MgAl2O4

Energy loss (eV)

Inte

nsity

(co

unts

)

15 2510

PEELS spectrum for implanted MgAl2O4

Energy-filtered TEM used to quantify colloid distribution

Matrix plasmon peak

colloid peak

Advanced Analytical Electron Microscopy Techniquesare being used to Examine Precipitates in V alloys

Dark Field STEM ImageDark Field STEM Image

20 nm20 nm

0200400600800

10001200

0 1 2 3 4 5 6 7 8

Titanium K αChromium K β

Inte

nsi

ty

Position (nm)

Enriched 3X

Solute Segregation Was Detected in V-4Cr-4Ti FollowingNeutron Irradiation to 0.5 dpa at Elevated Temperatures

Analytical microscopyreveals Ti-rich precipitateswith Fm3m space group(Baker-Nutting precipitate-matrixorientation)

frontiers of fusion materials science materials and fabrication methods that will establish ......

Documents