RELATIONSHIP BETWEEN MICROSTRUCTURE AND MECHANICAL ...

MINOS Workshop, Materials Innovation for Nuclear Optimized SystemsDecember 5-7, 2012, CEA – INSTN Saclay, France

RELATIONSHIP BETWEEN MICROSTRUCTURE

AND MECHANICAL PROPERTIES IN ODS

MATERIALS FOR NUCLEAR APPLICATION

Yann de Carlan et al., CEA , DEN, SRMA, 91191 GIF/YVETTE FRANCE

2

ODS FOR SODIUM FAST REACTORS

Rapsodie

Beginning of the

studies on the Fast

Sodium Reactors to

produce electricity

First ODS (SCK-

CEN)

Phénix

First irradiated

tubes

Superphénix

Industrial

Production

(DourMetal)

ODS tubes in

Phenix reactor

Forum Gen IV : reactors

1967 1973 1985 1987 20001960

Materials

Optimization

of the

austenitic

steels

New reinforced

ferritic alloys :

ODS alloys

PHENIXPHENIX

SPXSFR

L. Toualbi

Need of

optimized

materials is still

relevant !

3

Why ODS materials for Nuclear Applications ?

ODS materials

Limited swelling under irradiation Low thermal creep

Nano dispersion

(Oxide Dispersion Strengthened)

0

1

2

3

4

5

6

7

8

9

10

60 70 80 90 100 110 120 130 140 150 160 170 180 190

dose (dpa)

Average 316 Ti

Ferritic-martensitic (F/M) steels ODS included

Average 15/15TiBest lot of 15/15Ti

Use limit for Phenix reactor

Sw

ellin

g(%

)

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

0,0001 0,001 0,01 0,1 1 10 100 1000 10000

Temps (h)

Allo

ngem

ent

(%)

180 MPa – 650°C

Conventional steel

ODS

SFRDose > 150 dpaStress ~ 100 MPaTemperatures : 400°C – 670°C

4

METALLURGY OF ODS MATERIALS

nano-phases (~2-4nm)

Complex manufacturing� ODS steels present low ductility and limited consolidation at room temperature

� Low deformability

� Intermediate heat treatments needed for stress relief purpose

5


Ex:ODS steel18 Cr-1W Ti 0,5 Y2O3

Uniform distribution ofnano oxides

0

0,2

0,4

0,6

0,8

1

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1D in mm

Wt (

%).

0.46 Y

0.3 Ti

0.85 W

Microprobe

Homogeneous microstructureFine ferritic grains

elongatedin extrusion direction

Longitudinal direction Transverse direction

TEM

nano-oxides

50 nm

TEM

SANS

TAP

Optical

DSM – LLBOrphée

0

0,2

0,4

0,6

0 1 2 3 4 5 6 7 8 9 10

Rayon moyen (nm)

H(r

) *

fp

90×14×14 nm3

Y,YO and O

Clusters

Ti, TiO

8 1023 m-3

1,8 nm

Texture

8 1022 m-3 φ 3 nm

1, 2 µm - 300nm 400 nm - 200 nm

fp 1,1%

GPM RouenO. Kalokhtina, B. Radiguet, Ph. Pareige

Plate

EFTEMHRTEM

6


0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7

ODS metallurgyConventional metallurgy

Temperature /°C

Time / h

7

� Ferritic grades

Fe -12/20Cr

� Martensitic grades

Fe - 9 Cr

Large differences between both type of alloys as a function of their finalmicrostructure but generic creep behavior is noticed.

Fe-9Cr Fe-12/20Cr


8


Ferritic Fe-14Cr ODS :Extruded at 1100°C + 1h at 1050°C (very difficult to recrystallize)

Typical microstructures

10µm

Martensitic Fe-9Cr ODS :Tempered martensite(very high critical cooling rates)

L. Toualbi, Phd Thesis

9

austenite + ferrite

austenite + martensite

� Martensitic grade: Fe-9Cr-1W-0.2Ti-0.3Y2O3

� CCT diagram

- Transformation temperatures

- Critical cooling rates ~ 1°C/s



10

MECHANICAL PROPERTIES OF ODS

� Tensile properties

� Creep properties

� Impact properties

11

TENSILE PROPERTIES OF ODS ALLOYS

� Ferritic (Fe-14 Cr ODS)

A. Alamo et al. Journal of Nuclear Materials 329–333 (2004) 333–337

As-extruded

12


0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8 9 10Allongement rationnel (%)

Con

trai

nte

vrai

e (M

Pa)

7.10-4 s-1

10-5 s-1

Extruded and annealed ferritic ODS (Fe-18Cr), tensile test at 650°C in the transvers direction, large decrease of the ductility when the deformation rate is decreasing.

M. Ratti, PhD thesis

13


� Martensitic (Fe-9Cr ODS)


Tensile properties in different metallurgical state :- J95-M3, tempered martensite- J95- M5, Softened ferrite

Tempered martensite

Softened ferrite

14

CREEP PROPERTIES OF ODS ALLOYS

� Ferritic (Fe-18 Cr ODS)

Extrusion direction

ODS plateExtruded and annealed

Extrusion direction

SL ST S45

200 nm

Bamboo like microstructure

M. Ratti, Phd Thesis

15


� Ferritic Fe-18 Cr ODS at 650°C 250 MPa

M. Ratti, Phd Thesis

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

0 1000 2000 3000 4000 5000 6000 7000

Temps (heures)

Allo

ngem

ent

(%)

Very low deformation rates (Long-250 MPa : 7.10-8 h-1).

almost no tertiary domain .

Different order of magnitude on the rupture time as a function of the orientation of the sample / texture of the microstructure

Transvers

45°°°°

Long (in progress)

16

Inoué et al.

17


� Ferritic ODS


0

100

200

300

400

500

10-1 100 101 102 103 104 105

Str

ess

(MP

a)

Rupture Time (h)

MA957 - Fine grains 650°C

9Cr2MoVNb (EM12) 650°C

MA957 - Recryst. 700°C


15/15Ti 700°C

Aust.15/15Ti 650°C

0

100

200

300

400

500

10-1 100 101 102 103 104 105

Str

ess

(MP

a)

Rupture Time (h)

MA957 - Fine grains 650°C

9Cr2MoVNb (EM12) 650°C



15/15Ti 700°C

Aust.15/15Ti 650°C

18


M. Praud, J.Malaplate et al., creep 2012

Higher performances of Fe-14Cr ODS alloys (fine grains) in the longitudinal direction compared to Fe-9Cr ODS (softened ferrite)

19

� Martensitic Fe-9 Cr ODS

17104.1 −−⋅= sIIε&

110101.1 −−⋅= sIIε&


M. Praud, J.Malaplate et al., creep 2012

20


• Creation of cavities • Decohesion along the grain boundaries

INTERGRANULAR mechanismConsistent with the macroscopic observations

ODS 9%Cr

ODS 14%Cr

In situ relaxation tests at 550°C

• Dislocation still pinned on oxides

• Viscous motion

• Activation of sources of dislocations at the grain boundaryM. Praud, J.Malaplate et al., creep 2012

21

IMPACT PROPERTIES OF ODS ALLOYS

Fine grain


� Ferritic Fe-14 Cr ODS alloys

22


DBTT (°C) USE (J)LT TL LT TL

rod Ø36 -29 108 7.6 3.8

� anisotropic impact behaviourfor the rod : higher USE and lower DBTT under LT loading

extrusion direction

TL

LT

diameter: 36mm

Fe-14Cr 1W ODS“Fine grain microstructure”


AL Rouffié et al. http://dx.doi.org/10.1016/j.jnucmat.2012.08.050 22

23


AL Rouffié et al. http://dx.doi.org/10.1016/j.jnucmat.2012.08.050

DBTT (°C) USE (J)LT TL LT TL

rod Ø36 -29 108 7.6 3.8

� anisotropic impact behaviourfor the rod : higher USE and lower DBTT under LT loading

ED

notch

expected propagation

plane

effective propagation plane

For different samples, tendency to delamination


24


AL Rouffié et al. http://dx.doi.org/10.1016/j.jnucmat.2012.08.050

� Ferritic Fe-9Cr ODS alloys (thick plate)

Quasi-isotropicbehaviour

25

CONCLUSIONS

The mechanical properties of nuclear F/M alloys depend stro ngly on the chemical compositionand the microstructure of the product

�Tensile properties- Large dependence on the grain size / morphology / dislocation density / nano-precipitation

- Collapse of the strength from 400°C

- Strain rate effect on the ductility

� Creep properties- No tertiary creep but high performances

- Reduced fracture strain

- Damage more severe at high temperature low strain rate / low stress => Intergranularmechanism of failure

� Impact properties- Low toughness and in general “low” Upper Shelf Energy and sometimes tendency to

delamination

- Very important impact of the microstructure (morphological texture) on the impact properties

The fabrication route of ODS materials with the appropriatemicrostructure is a key issue for the nuclear applications

RELATIONSHIP BETWEEN MICROSTRUCTURE AND MECHANICAL ...

Documents

Transcript of RELATIONSHIP BETWEEN MICROSTRUCTURE AND MECHANICAL ...