Mechanical Property Changes in Metals due to Irradiationiramis.cea.fr/meetings/matgen4/Presentations/Zinkle-1.pdf) irradiation on the tensile properties of metals •Dose and temperature

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Mechanical Property Changes inMetals due to Irradiation

Steven J. Zinkle

Materials Science & Technology Division,Oak Ridge National Laboratory

Materials for Generation IV Nuclear ReactorsNATO Advanced Study Institute

Cargese, Corsica, FranceSept. 24-Oct. 6, 2007


Outline•Effect of low temperature (<0.3 TM) irradiation on the tensile

properties of metals• Dose and temperature dependence• FCC vs. BCC metal behavior

•Fracture toughness embrittlement in irradiated metals•High temperature He embrittlement of grain boundaries•Overview of deformation mechanisms in irradiated metals

(restricted to radiation hardening/embrittlement regime)• Microscopic flow localization observations (dislocation channeling)• Similarities and differences between flow localization phenomena in

unirradiated and irradiated metals• Practical consequences: e.g., structural design rules for uniform elongation <2%

• Not covered: hardness, fatigue, irradiation creep


Radiation Hardening Mechanisms

Radiation damage creates obstacles to dislocation motion- point defects ( ≡ solute strengthening in alloys)- small clusters and precipitates ( ≡ precipitates in alloys)- impenetrable clusters ( ≡ Orowan strengthening in alloys)

- all give ΔσY proportional to (dose)0.3-0.5

obstacles

dislocation

σOrowan loop


Dose Dependence of Radiation Hardening in Copper

• Fission and fusion neutron radiation hardening behavior are in good agreement• Hardening “saturation” occurs for doses above ~0.1 dpa (agrees with defect

cluster density behavior)

50

100

150

200

250

300

350

0.0001 0.001 0.01 0.1 1 10 100

Neutron Radiation Hardening of Copper

Kruglov et al (1969)El-Shanshoury (1972)Mohamed et al (1982)Vandermeulen (1986)Heinisch (1988)Fabritsiev et al (1994)Singh et al (1996)Zinkle&Gibson (1999)Singh et al. 1999

0.2

% Y

ield

Str

en

gth

(M

Pa

)

Damage Level (dpa)

Tirr=30 - 200˚C

50

100

150

200

250

300

350

0.00010.001 0.01 0.1 1 10 100

Neutron Radiation Hardening of Copper

0.2

% Y

ield

Str

en

gth

(M

Pa

)

Damage Level (dpa)

Tirr=30 - 200˚C

14 MeV neutrons: filled symbolsfission neutrons: open symbols


Radiation Hardening in Copper: Seeger vs.Friedel relationships

• Two general models are available to describe radiationhardening (∆σ) in metals:–Dispersed barrier model (Seeger, 1958)--valid for strong obstacles

Where M=Taylor factorα=defect cluster barrier strengthµ=shear modulusb=Burgers vector of glide dislocationN, d=defect cluster density, diameter

–Friedel 1963 (also Kroupa and Hirsch 1964) weak barrier model:

!

"# = M$µb Nd

!

"# =1

8MµbdN 2/3


!

"# = M$µb Nd

!

"# =1

8MµbdN 2/3vs.

0.1

1

10

1016 1017 1018 1019 1020 1021

Shear Strength of Cu Single Crystals Irradiated

and Tested Near Room Temperature

Blewitt et al 1960

Shear

Str

ength

(kg

f/m

m2)

Neutron Fluence (n/cm2)

n~0.33

0

2

4

6

8

10

0 0.2 0.4 0.6 0.8 1 1.2



Blewitt et al 1960

Shear

Str

ength

(kg

f/m

m2)

(!t)1/2 (1020 n/cm2)1/2

slope change

@3x1018/cm2

(3x10-4 dpa)?

0

2

4

6

8

10

0 0.2 0.4 0.6 0.8 1 1.2



Blewitt et al 1960

Shear

Str

ength

(kg

f/m

m2)

(!t)1/4 (1020 n/cm2)1/4

0

2

4

6

8

10

0 1 2 3 4 5



Blewitt et al 1960

Shear

Str

ength

(kg

f/m

m2)

(!t)1/3 (1018 n/cm2)1/3

Seeger; N~(φt)n, n=1–>1/2 Friedel; N~(φt)n, n=1/2


Effect of test temperature on irradiated strength• What is the effect of irradiation on the yield strength test

temperature dependence (athermal and thermal components)?

Flo

w S

tre

ss

Test Temperature

!athermal

!thermal

BCC metals: large τthermal component

FCC metals: small τthermal component

Hardening models (Seeger, Fleisher, etc.):Thermal component of flow stress iscontrolled by radiation-induced hardeningcenters


Early Work on BCC Metals such as Fe led to Conclusions that theTest Temperature Dependence was not Affected by NeutronIrradiation

• These early studies were limited to low doses <1019 n/cm2), where the magnitude ofradiation hardening (and radiation-induced defect sizes) is relatively small

200

300

400

500

600

700

800

900

1000

0 100 200 300 400 500 600

Effect of Test Temperature on the Yield Strength of

Mild Steel Irradiated with Fission Neutrons at 60 C

Lo

wer

Yie

ld S

tren

gth

(M

Pa)

Test Temperature (K)

Unirrad.

2.3e18 n/cm2

Little (1970)


Comparison of the Yield Strength Behavior ofAnnealed and (low-dose) Irradiated Iron

10

20

30

40

50

60

70

50 100 150 200 250 300


Polycrystalline Iron Irradiated with Fission Neutrons at 60 CL

ow

er

Yie

ld S

tren

gth

(kg

/mm

2)


Unirrad.1.2e16 n/cm

2

Ohr (1969)


Comparison of the Yield Strength Behavior ofAnnealed and Irradiated Iron at Higher Doses

0

10

20

30

40

50

60

50 100 150 200 250 300


Single Crystal Iron Irradiated with Fission Neutrons at 75 CL

ow

er

Yie

ld S

tren

gth

(kg

/mm

2)


Unirrad.

1.8x1017

Kitajima (1968)1.3x1018

1x1019

n/cm2 (E>1 MeV)

} 60 MPa

200 MPa


Comparison of the Yield Strength Behavior ofAnnealed and Irradiated Iron at Higher Doses

0

50

100

150

200

250

300

350

100 150 200 250 300 350 400 450

Lo

we

r Y

ield

Str

en

gth

(M

Pa

)


unirradiated

irradiated

2.8x1021

/m2

J. Diehl et al. (1968)Single crystal Fe

Tirr

~350 K

!"

=2

10

MP

a

!"=60 MPa


Radiation Hardening in Eurofer97 Steel irradiated at300oC

400

500

600

700

800

900

1000

1100

0 50 100 150 200 250 300 350

Yie

ld S

tren

gth

(M

Pa)

Test Temperature (oC)

!"=540 MPa

!"=460 MPa

J. Rensman (2005)

9 dpa, Tirr

=300oC

25 mm plate


Effect of Test Temperature on the Yield Strength ofPolycrystalline Copper, Neutron Irradiated at 60˚C

0

100

200

300

400

500

0 100 200 300 400 500

Yie

ld S

tre

ng

th (

MP

a)


Unirrad.9.5e16

4.1e17

3.6e18

5.9e18

1.3e19

2.3e20n/cm2

(E>1 MeV)

Makin (1967)

• Change in test temperature dependence from unirradiated behavior occurs for fluencesabove ~0.5 to 1x1018 n/cm2, E>1 MeV (Makin 1967, Koppenaal 1965)

• Similar range of test temperature dependence occurs in as-irradiated vs. postirradiationannealed Cu (Rühle, Makin, Howe, Koppenaal, etc.)

180 MPa

410 MPa

Radiationhardeningcontrolled primarilyby SFTs


Effect of Electron Irradiation on the YieldStrength Behavior of Single Crystal Copper

1

1.5

2

2.5

3

3.5

4

4.5

0 50 100 150 200 250 300 350

Re

so

lve

d S

he

ar

Str

en

gth

(M

Pa

)


unirradiated

1.0x1020

e/m2

3.4x1021

e/m2

2 MeV electron irrad. Cu

Tirr

=300 K

K. Kamada et al. (1973)

Radiation hardening controlledprimarily by dislocation loops


Comparison of the Yield Strength Behavior ofAnnealed and Quenched Aluminum

0

5

10

15

20

25

30

35

40

50 100 150 200 250 300

Yie

ld S

tre

ng

th (

MP

a)


slow cooled from 600oC

quenched from 607oC

n=4x1020

/m3

Loop d=23 nm

AluminumK.H. Westmacott (1966)

Radiation hardening controlledprimarily by dislocation loops


Effect of Strain Rate and Temperature onYield Strength Behavior of Unirradiated V-4Cr-4Ti

180

200

220

240

260

280

300

320

340

360

20°C300°C400°C500°C600°C700°C750°C800°C850°C

10-6 10-5 10-4 10-3 10-2 10-1 100

Lo

we

r Y

ield

Str

ess (

MP

a)

Strain Rate (s-1)

"10 MPa

Negative strain rate exponent correspondsto dynamic strain aging regime

180

200

220

240

260

280

300

320

340

360

380

400

420

440

0 100 200 300 400 500 600 700 800 900

Lower Yield StressFlow Stress

Str

es

s (

MP

a)

Temperature (°C)

O mobile (in V-5Ti alloy)

Ti mobile

V mobile

HomogeneousDeformation

InhomogeneousDeformation

CreepDeformation

Engin

eering S

tress (

MP

a)

Normalized Crosshead Displacement

10-3/s

20°C

200°C

300°C

500°C

600°C

400°C

700°C

750°C800°C

850°C

100

0.05


Effect of Strain Rate and Temperature onYield Strength Behavior of Irradiated V-4Cr-4Ti

Strain rate exponent becomes negative in irradiated alloys at Ttest>300oC even whendynamic strain aging serrations are not visible in stress-strain curves

500

550

600

650

700

750

10-5

0.0001 0.001 0.01 0.1

Lo

we

r Y

ield

Po

int

(MP

a)

Strain rate (s-1

)

V-5Cr-5Ti400˚C, 4 dpa, EBR-II

V-4Cr-4Ti (50%CW+1000˚C,2h)200˚C, 0.5 dpa, HFBR

Ttest

~Tirr

CR+1050˚C TWCA/1050˚C


What are the consequences of radiationhardening?

• Increased strength (good!)•Decreased tensile elongation (bad!)

– Practical impact/consequences: need to use more conservative structural designrules for uniform elongation <2%

• For BCC metals, increase in the ductile-brittle transition temperatureand decrease of toughness in the “ductile” regime (can becatastrophic!)– Radiation hardening also tends to reduce the fracture toughness of FCC metals


Examples of tensile curves for pure metals irradiated at ~330 K

Al0.35TM

Ni0.19TM

V0.15TM

Mo0.11TM


V

0

200

400

600

800

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Str

ength

, M

Pa

YS

UTS

0.0

0

10

20

30

40

50

60

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Elo

ng

atio

n,

%

UE

TE

0.0

Mo

0

200

400

600

800

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Str

ength

, M

Pa

YS

UTS

0.0

0

10

20

30

40

50

60

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Elo

ng

atio

n,

%

UE

TE

0.0

Ni

0

200

400

600

800

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Str

ength

, M

Pa

YS

UTS

0.0

0

10

20

30

40

50

60

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Elo

ng

atio

n,

%

UE

TE

0.0

Al

0

200

400

600

800

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Str

ength

, M

Pa

YS

UTS

0.0

0

10

20

30

40

50

60

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Elo

ng

atio

n,

%

UE

TE

0.0

Effect of neutron irradiation near 70˚C on tensile properties

K. Farrell et al.

Ni V Mo

Ductile FCC metal Ductile BCC metal Low-ductility BCC metalReduction of uniform elongation to <2% typically occurs within 0.001 to 1 dpa


Low uniform elongations occur in many BCC and FCCmetals after low-dose irradiation at low temperature

Uniform elongation of neutron-irradiated V and Nb

-2

0

2

4

6

8

10

12

0 100 200 300 400 500 600 700

Un

ifo

rm E

lon

ga

tio

n (

%)

Test Temperature (˚C)

0.5 dpa

0.1 dpa

Test Temperature isIrradiation Temperature

0

2

4

6

8

10

0.0001 0.001 0.01 0.1 1 10

Fabritsiev et al (1996)Heinisch et al (1992)Singh et al. (1995)

Un

ifo

rm E

lon

ga

tio

n (

%)

Damage Level (dpa)

Unirradiatedelongations

Tirr=36-90˚C

Uniform elongation of neutron-irradiated GlidCop Al25 and CuCrZr

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350 400

Un

ifo

rm E

lon

ga

tio

n (

%)

Irradiation and Test Temperature (˚C)

CuCrZr

ODS Cu

GlidCop Al25

V-4Cr-4Ti

0.3TM

0.3TM

0

10

20

30

40

50

0.0001 0.001 0.01 0.1 1 10 100

Te

nsile

Elo

ng

atio

n (

%)

Displacement Damage (DPA) 0

1 dpa = 2x1021 n/cm2 (E>0.1 MeV)

Wiffen (1978)

UniformElongation

TotalElongation

Nb-1Zr Tirr=40-60˚C

Cu alloys

Low uniform elongation is induced aftervery small doses at low temperatures

0.4TM


Radiation hardening in V-4Cr-4Ti

0

200

400

600

800

1000

0 100 200 300 400 500 600 700

Effect of Dose and Irradiation Temperature onthe Yield Strength of V-(4-5%)Cr-(4-5%)Ti Alloys

Yie

ld S

tre

ng

th (

MP

a)

Irradiation Temperature (˚C)

Ttest~Tirr

unirradiated

0.1 dpa

0.5 dpa5-50 dpa

V-4Cr-4Ti

0.3 TM


Neutron Irradiation Data Show Low Ductility and HighHardening of Mo-Re alloys up to 1070 K (0.37 TM)

0

500

1000

1500

2000

0

1

2

3

4

5

6

7

8

600 700 800 900 1000 1100

Summary of Tensile Properties of Fast Neutron-Irradiated Mo-Re alloys

Hasegawa et al (1995)Fabritsiev&Pokrovsky (1998)

Ult

ima

te T

en

sil

e S

tre

ng

th (

MP

a)

Un

ifo

rm e

lon

ga

tio

n (

%)

Temperature (K)

Unirrad. UTS

Irrad. UTS

Irrad. eUIrrad. UTS

(brittle fracture)

0.3 TM


Summary of Tensile Properties of Neutron-irradiated Nb-1Zr in Li-bonded capsules

0

100

200

300

400

500

600

700

0

5

10

15

20

25

30

35

200 400 600 800 1000 1200 1400 1600

Summary of Tensile Properties of Neutron-Irradiated Nb1Zr in Li-bonded CapsulesU

ltim

ate

Te

ns

ile

Str

en

gth

(M

Pa

)

Un

ifo

rm e

lon

ga

tio

n (

%)

Temperature (K)

Unirrad. UTS

Irrad. UTS

Irrad. eU

0.3 TM


Fracture surface of Irradiated Nb-1Zr shows ductilebehavior, despite low uniform elongation value

F.W. Wiffen, unpublished results


The issue of localized flow (planar slip) has beenthe subject of numerous materials scienceinvestigations (unirradiated metals)

• Three general parameters may be considered to influence planarslip (e.g., Gerold & Karnthaler Acta Met. 39 (1989) 2177; Basinskiet al. Phil Mag. A 76 (1997) 743):– Stacking fault energy (weak effect)– Value of yield stress (weak effect)– Occurrence of short range ordering (solid solution alloys) or ordered

precipitates that are shearable (generally dominant effect)


Plastic deformation mechanisms for dispersion hardenedmaterials containing work-softening obstacles

Macro

scopic

pla

sti

c s

train

, ! p

/(1

-f)

cluster annihilation resistance, {2E"/f(1-f)µA}0.5

Uniform slip

Uniform slip

T. Mori and T. Mura, Mat Sci Eng. 26 (1976) 89

Hetero

gene

ous s

lip

Ee=elastic energystored by one obstacleρ=obstacle densityf=vol. fraction ofobstacles


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

Eng

inee

ring

Str

ess,

MP

a

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=270˚̊CC

g=011g=011

Irradiated Materials Suffer Plastic Instability(due to Dislocation Channeling?)


Overview of dislocation channeling

• Dislocation channeling is a viable mechanism to locally worksoften the matrix– Shearable obstacles

• Channeling involves localized flow and therefore inhibitsdislocation multiplication– Limited interaction between dislocation sources

However, …………….• It is not generally established that the catastophic reduction in

tensile elongation is directly due to dislocation channeling– High tensile elongations and significant work hardening rates can occur in

irradiated metals that exhibit dislocation channeling


Localized deformation (and dislocationchanneling) occurs in many irradiated materialsystems

Vanadium

316 SS316 SS

A533BA533B

Zircaloy-4

MolybdenumMolybdenum

CopperCopper


Dislocation channel interactions in Fe deformedfollowing neutron irradiation at 70˚C to 0.8 dpa

g.b.

Need well-engineered materials tomitigate neutron radiation effects

Clearedslipchannel

~200 nm~200 nmoffsetoffset

}}~80 nm~80 nmoffsetoffset}}

Zinkle & Singh, J. Nucl. Mater. 351 (2006) 269


Summary of Dislocation Channeling ParametersMaterial Dose

(dpa)Irrad.Temperature

TestTemperature

Channelwidth (nm)

Channelspacing

Reference

Cu ~0.001-0.5 313-323 K 295 K ~50-200 0.5-2.3 µm 9 research groups

Cu ~0.5 ~50˚C 50 K77 K295 K

5070100

0.8-1.2 µm Howe 1974

CuCrZr 0.3 323 K 323 K 100-300 Singh & Stubbins fatigue

Cu-0.8%Co ~0.001 ~50˚C 295 K 160 1.2-2.3 µm Sharp 1974

Cu-0.05%Al ~0.001 ~50˚C 295 K 240 1.2-2.3 µm Sharp 1974 (channels notobserved in Cu-4%Al)

Au ~0.003 20˚C 295 K ~100 Okada 1989

Ni ~50˚C 295 K ~300 Noda 1977

Pd 0.3 ~50-100 Victoria et al 2000

304L SS 5 (ions)“

500˚C“

563 K295 K

1550-200 (twins)

Brimhall 1995

Fe-10%Cr-30%Mn

~0.005 300˚C ~100? F. Abe 1992

!-Fe ~0.38 323 K 323 K 50-200 Singh et al.;Victoria et al 2000

Nb ~0.002 ~400 Tucker 1969

V 0.1-0.8 330 K 295 K 20-80 0.5-2.5 µm Arsenault 1977; Farrell 2002

V-4Cr-4Ti 0.5-5 500-673 K 295-673 K ~50-100 Rice&Zinkle 1998, Gazda 1998

Mo ~0.2 323 K 323 K ~500 Luft 1991; Singh et al.

TZM ~0.2 373 K 373 K 100-200 Singh et al.

Re Pitt 1980

Zircaloy-2,4 425-563 K 293-573 K 40-100 Coleman 1972, Onchi 1980

Au quenched 160-500 Yoshida 1968, Bapna 1974

Al quenched 650-1000 Mori 1969; Tokuno 1987

Dislocation channel width is ~100 nm for a wide range of experimental conditions


Investigation of dislocation interactions with SFTsSFT annihilation by a single dislocation (remnant apex)

Y. Matsukawa, ORNL


Dislocation interaction with SFTs in quenched Au

• Type 1 interaction (Frank loop formation) at room temperatureMatsukawa, Stoller, Osetsky & ZinkleJ. Nucl. Mater. 351 (2006) 285



• Type 2 interaction at room temperature (superjog creation with noSFT remnant)

Matsukawa, Stoller, Osetsky & ZinkleJ. Nucl. Mater. 351 (2006) 285



• Types 1(a) & 2(b) interactions also occur at 100 K




• Type 3 interactions at room temperature (SFT apex remains);not observed at 100 K



Interaction of a screw dislocation with 78-vacancy SFT and 91-intersitital cluster in Cu thin foil

300 K

Cooperative effects may be important for annihilation of sessile defectclusters by gliding dislocations during deformation

Yu.N. Osetsky


Effect of Irradiation Dose and Strain onDeformation Modes of FCC Metals

0

5

10

15

20

0.0001 0.001 0.01

Deformation Mode Diagram for Neutron-irradiated Au

Elo

ng

ati

on

(%

)

Displacement Damage (dpa)

Uniform elongation limit

Dislocationchannels

Cell Structure

Au14 MeV n irrad.

Tirr=T test=295 K

~0.5 µm

~0.3 µm

~0.3 µm

0

2

4

6

8

10

12

14

16

0.0001 0.001 0.01

Deformation Mode Diagram for Neutron-irradiated Ni

Elo

ng

ati

on

(%

)

Displacement Damage (dpa)

Uniform elongation limit

Dislocationchannels

Cell Structure

Ni14 MeV n irrad.

Tirr=T test=295 K

~0.5 µm

~0.5 µm

~2 µm

~2 µm

A. Okada et al. Mater. Trans. JIM 30 (1989) 265


Tensile Deformation Behavior in Irradiated Cu

40

60

80

100

120

140

160

0 100 200 300 400 500

Tensile Deformation Behavior in Irradiated Cu

Cri

tic

al

Re

so

lve

d S

he

ar

Str

es

s (

MP

a)

Temperature (K)

No channels

!t=4x1024/m2, E>1 MeV (~0.5 dpa)L.M Howe, Rad. Eff. 23 (1974) 181

As-irradiated

0.25 h, 723 K1 h, 723 K

5 h, 723 K

Similar behavior observed in quenched Au(S. Yoshida, Trans. JIM 9 suppl. (1968)83)

Engineering and true stress-strain tensile curves for stainlesssteel before and after spallation irradiation at ~100˚C

HTUPS316 Stainless Steel

Unirradiated

1.2

2.8

4.0 dpa

0.40.6

1.1

0

200

400

600

800

1000

0 10 20 30 40 50 60 70

Elongation, %

Engin

eering S

tress, M

Pa

HTUPS316 Stainless Steel

Unirr.

1.22.8

4.0 dpa0.4

0

200

400

600

800

1000

1200

1400

0.0 0.1 0.2 0.3 0.4 0.5 0.6

True strain

Tru

e s

tre

ss,

MP

a

EC316LN Stainless Steel 10.7 dpa

3.6

2.5

1.1

0.5 Unirr.

0

200

400

600

800

1000

0 10 20 30 40 50 60 70

Elongation, %

En

gin

ee

rin

g S

tre

ss,

MP

a

EC316LN Stainless Steel

Unirr.10.7 dpa

1.12.5

3.6 0.5

0

200

400

600

800

1000

1200

1400

0.0 0.1 0.2 0.3 0.4 0.5 0.6

True strain

Tru

e s

tress, M

Pa

T.S. Byun et al., J. Nucl. Mater. 298 (2001) 269


Radiation Effect in True Stress-True Strain Curve (FCC)

EC316LN

unirradia

ted

10.7 dpa

1.12.5 3.6

0.5

0

200

400

600

800

1000

1200

0 0.1 0.2 0.3 0.4 0.5

True strain

Tru

e s

tre

ss

True stress-true straincurves for EC316LNstainless steel; the curves ofirradiated specimens areshifted in the positivedirection by strains of 0.14,0.18, 0.23, 0.28, and 0.385,respectively, to superimposeon the curve of unirradiatedmaterial. Irradiation-induced increases in yieldstress were 305, 358, 421,485, and 587 MPa,respectively.

T.S. Byun & K. Farrell, Acta Mater. 52 (2004) 1597

Further work is need to determine importance of dislocation channeling in observedexhaustion of initial strain hardening capacity


A533B

unirr

adia

ted

0.003 0.015 dpa

0

200

400

600

800

1000

0 0.03 0.06 0.09 0.12 0.15

True strain

Tru

e s

tre

ss,

MP

aRadiation Effect on True Stress-True Strain Curve (BCC)

True stress-true straincurves for A533B steel; thecurves of irradiatedspecimens are shifted inthe positive direction bystrains of 0.035 and 0.09,respectively, tosuperimpose on the curveof unirradiated material.Irradiation-inducedincreases in yield stresswere 132 and 235 MPa,respectively.


• True stress- true strain curve for irradiated material coincides withunirradiated curve, after translation to account for radiation hardening– Suggests main effect of radiation hardening is to partially exhaust strain

hardening capacity

132 MPa235 MPa


Plastic Instability Stress (σPI) of BCC Metals

• Plastic Instability Stress (σPI) = the true stress version of Ultimate Tensile Stress• Plastic Instability Stress is independent of dose when yield stress < σPI.• Yield stress can be > σPI, which is defined only when uniform deformation exists.• σPI is considered to be a material constant, independent of initial cold-work or radiation-

induced defect clusters

σML=true stress at maximum load

0

200

400

600

800

1000

1200

1400

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Str

ess,

MP

a

A533B (HFIR)a A533B (HFIR)a

A533B (HFIR)b A533B (HFIR)b

A533B (HFIR)c A533B (HFIR)c

? ML ? YS

? ML????IS ?ML????YS

?YS

?ML????IS = ? YS

Prompt

necking

at yield

Uniform

deformation

exists before

necking DC

0

σML=σUTS =σPI σML=σYS

σYS σML=σIS =σYS

σYSσML


400

600

800

1000

1200

1400

1E-05 0.0001 0.001 0.01 0.1 1 10 100

dpa

Str

ess, M

Pa

3Cr-3WV (HFIR) 3Cr-3WV (HFIR)

9Cr-1MoVNb (HFIR) 9Cr-1MoVNb (HFIR)

9Cr-2WV (HFIR) 9Cr-2WV (HFIR)

9Cr-2WVTa (HFIR) 9Cr-2WVTa (HFIR)

9Cr-1MoVNb (LANSCE) 9Cr-1MoVNb (LANSCE)

9Cr-2WVTa (LANSCE) 9Cr-2WVTa (LANSCE)

?ML ? YS

0

σML σYS

A533B pressure vessel steel Ferritic/martensitic steels


Plastic Instability Stress (σPI) ofFCC Metals irradiated near 70˚C


0

200

400

600

800

1000

1200

1400

1600

1800

1E-05 0.0001 0.001 0.01 0.1 1 10 100

dpa

Str

ess,

MP

a

EC316LN (LANSCE) EC316LN (LANSCE)

HTUPS316 (LANSCE) HTUPS316 (LANSCE)

AL6XN (LANSCE) AL6XN (LANSCE)

316 (HFIR)a 316 (HFIR)a

316LN (HFIR) 316LN (HFIR)

316 (HFIR)b 316 (HFIR)b

?ML ?

YS

0

σML σYS

0

200

400

600

800

1000

1E-05 0.0001 0.001 0.01 0.1 1 10

dpa

Str

ess,

MP

a

Ni (HFIR) Ni (HFIR)

Cu (HFIR) Cu (HFIR)

? ML ? YS

0

σML σYS

Type 316 austenitic stainless steel Pure Cu, Ni

Ni

Cu


Plastic Instability Criterion for BCCmetals irradiated near 70˚C

V

0.00120.0001

0

100

200

300

400

500

600

700

0 10 20 30 40

Elongation, %

En

gin

ee

rin

g s

tre

ss,

MP

a

0.012

0.12 dpa

0.69

PIS = 390 MPa

A533B

Unirradiated

0.015

0.054

1.2 dpa

0.003

0

200

400

600

800

1000

1200

0 5 10 15 20 25

Elongation, %

En

gin

ee

rin

g s

tre

ss,

MP

a

PIS =670 MPa

• Prompt plastic instability at yield occurs when yield stress > σPI.• σPI is constant for unirradiated and irradiated conditions; implies that σPI is acriterion for plastic instability

σPI=670 MPaσPI=390 MPa


Plastic Instability Criterion (FCC & HCP) irradiated at ~70˚C

EC316LN

10.7 dpa

3.6

2.5

1.1

0.5 Unirradiated

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60

Elongation, %

En

gin

ee

rin

g S

tre

ss,

MP

a

PIS = 890 MPa

Zircaloy-4

unirradiated0.001

0.1

0.80 dpa

0.01

0

200

400

600

800

0 10 20 30 40

Elongation, %

En

gin

ee

rin

g s

tre

ss,

MP

a

PIS=510 MPaσPI=510 MPa

σPI=890 MPa


Deformation mechanisms in stainless steel

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

No

rma

lize

d S

he

ar

Str

es

s, !/µ

(20˚C

)

Normalized Temperature, T/TM

Elastic regime

(d"/dt<10-8 s-1)

Coble creep

Dislocation creep

Dislocation glide

Theoretical shear stress limit

20˚C 300˚C 650˚C

24

240

Un

iax

ial

Te

ns

ile

Str

es

s,

MP

a

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

No

rma

lize

d S

he

ar

Str

es

s, !/µ

(20˚C

)


Elastic regime

(d"/dt<10-8 s-1)

Coble creep

Dislocation creep

Dislocation glide


20˚C 300˚C 650˚C

24

240

Un

iax

ial

Te

ns

ile

Str

es

s,

MP

a

2.4

0.24

2400

10- 8 s- 1, L=50 µm

N-H creep

Twinning

Irradiation induces changes incontrolling deformation mechanisms

Channeling (Disln glide) occurs at highertemperatures (~300˚C)

Twinning occursat lower

temperatures(<200˚C) and high

strain rates


Calculated irradiated Ashby deformation mapfor V-4%Cr-4%Ti

10-6

10-5

10-4

10-3

10-2

10-1

0 0.2 0.4 0.6 0.8 1No

rma

lize

d S

he

ar

Str

es

s, !/

µ(2

0˚C

)


Elastic regime

(d"/dt<10-10 s-1)

Coble creep

Dislocation creep

Dislocation glide


14

141

Un

iax

ial

Te

ns

ile

Str

es

s,

MP

a

1.4

0.14

1410

10-10 s-1, L=30 µm

N-H creep

20˚C 400˚C 700˚C

Irrad. creep

Damage rate = 10-6 dpa/s


Tensile toughness is not a reliable indicator offracture toughness in BCC metals

• Magnitude of radiation hardening (overall matrix strength) is most importantparameter for fracture toughness in BCC metals

0

200

400

600

800

1000

0 2 4 6 8 10

Effect of Test Temperature on the Tensile Stress-Strain Curve of V-4Cr-4Ti Irradiated to 4 dpa at 400˚C

En

gin

ee

rin

g S

tre

ss (

MP

a)

Engineering Strain (%)

Ttest

=20˚C

Ttest

=390˚C

! ! d"=26 MPa

! ! d"=66 MPa

0

5

10

15

20

-200 0 200 400

Effect of Neutron Irradiation at ~400˚C on the Charpy Impact Properties of V-4%Cr-4%Ti

Ab

so

rbed

En

erg

y (

J)


4 dpa,Tirr=400˚C

V-4Cr-4Ti

unirradiated

0.5 dpa,Tirr=420˚C

Charpy V-notch

Fracture Toughness of BCC Metals:Master Curve Approach

• Ludwig-Davidenkov relation providesa rough estimation of embrittlementdue to radiation hardening

• The measured DBTT depends on numerous parameters,including strain rate and amount of physical constraint incracked sample

• Important parameters such as constraint andstrain rate are included in recent advancedapproaches (Master curve)

0

200

400

600

800

1000

-200 0 200 400 600

Yie

ld S

tre

ng

th,

MP

a

Temperature, °C

unirradiated

irradiated

!*/M

UCSB

0

100

200

300

400

500

Ke (

MP

a!m

)

-250-150 -50 50 150 250 350 450

T (°C)

!T ! 145°C


Low temperature radiation hardening causesfracture toughness embrittlement in BCC metals

0

200

400

600

800

1000

1200

-200 -100 0 100 200 300 400 500 600

Effect of Irradiation Temperature and Doseon the Yield Strength of V-4%Cr-4%Ti Alloys

Yie

ld S

trength

(M

Pa)

Irradiation and Test Temperature (˚C)

~0.5 dpa

~4-15 dpa

!f*

DBTT0.5 dpa DBTT4 dpaDBTTunirr.

unirradiated

0

5

10

15

20

-200 0 200 400

Effect of Neutron Irradiation at ~400˚C on the Charpy Impact Properties of V-4%Cr-4%Ti

Ab

so

rbe

d E

ne

rgy

(J

)


4 dpa,Tirr=400˚C

V-4Cr-4Ti

unirradiated

0.5 dpa,Tirr=420˚C

Charpy V-notch


•Macroscopic Mode I fracture is composed ofcoordinated Mode III shear displacements at the crack tip

TEM in-situ deformation studies can be used to provideinsight on fundamental fracture processes

Atomic resolution imaging of ductile crack propagation (plane stress)

2 nmY. Matsukawa, ORNL


Summary and Conclusions•Low temperature (<0.3 TM) irradiation causes rapid

hardening and reduction in uniform elongation of metals•When radiation hardening increment becomes a significant fraction of the

unirradiated strength, new dependencies on test temperature and strainrate may occur

•Uniform elongation is typically reduced to <1% after doses of ~0.1 dpa•Responsible mechanisms for loss of tensile ductility (dislocation

channeling, radiation hardening) are currently being investigated•Radiation hardening causes fracture toughness embrittlement

and increases in the ductile-to-brittle-transition temperature inirradiated BCC metals•Can be mitigated by alloying additions that reduce radiation hardening or

increase σ*

Documents

Mechanical Property Changes in Metals due to Irradiationiramis.cea.fr/meetings/matgen4/Presentations/Zinkle-1.pdf) irradiation on the tensile properties of metals •Dose and temperature