Relationship between Microstructure and Mechanical Properties in ...

Centre of Excellence for Nuclear Materials

Workshop Materials Innovation for Nuclear Optimized Systems

December 5-7, 2012, CEA – INSTN Saclay, France

Yann De CARLAN CEA (France)

Relationship between Microstructure and Mechanical Properties in ODS Materials for Nuclear Application

Workshop organized by: Christophe GALLÉ, CEA/MINOS, Saclay – christophe.galle@cea.fr Constantin MEIS, CEA/INSTN, Saclay – constantin.meis@cea.fr

Article available at http://www.epj-conferences.org or http://dx.doi.org/10.1051/epjconf/20135101002

EPJ Web of Conferences 51, 01002 (2013) DOI: 10.1051/epjconf/20135101002 © Owned by the authors, published by EDP Sciences, 2013

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

Relationship between Microstructure and Mechanical Properties in ODS Materials for Nuclear Application Yann De CARLAN1 1

CEA-DEN-DMN, Service de Recherches Métallurgiques Appliquées, SRMA (Saclay, France)

Oxide Dispersion Strengthened ferritic/martensitic alloys are developed as prospective cladding materials for future Sodium-Cooled-Fast-Reactors (GEN IV) [1]. These advanced alloys present a good resistance to irradiation and a high creep rupture strength due to a reinforcement by the homogeneous dispersion of hard nano-sized particles (such as Y2O3 or YTiO). ODS alloys are elaborated by powder metallurgy, consolidated by hot extrusion and manufactured into cladding tube using the pilger cold-rolling process [2, 3]. ODS alloys present usually low ductility and high hardness. The aim of this talk is to present the specificity of the metallurgy of ODS materials in relationship with the main mechanical properties (tensile and creep properties, toughness, transition temperature…). Two types of alloys will be presented: Fe-9Cr martensitic ODS and Fe-14Cr ferritic ODS alloys. Mechanical properties of the materials depend on the metallurgical state (fine grains, recrystallized, martensitic) and very different behaviors are observed as a function of final microstructure. For example, for a Fe-9CrODS alloy, tempered martensite lets obtaining material with high strength whereas softened ferrite see figure 1 [4] tolerates high deformation levels.

Tempered martensitic structure

Softened ferritic structure Fig. 1: Electron Backscatter Diffraction maps for a Fe-9Cr ODS associated with the tensile properties at room temperature. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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

References [1] P. Dubuisson, Y. de Carlan, V. Garat, M. Blat, ODS Ferritic/martensitic alloys for Sodium Fast Reactor fuel pin cladding. Journal of Nuclear Materials 428 (2012) 6–12. [2] T. Narita, S. Ukai, T. Kaito, S. Ohtsuka, T. Kobayashi, Development of Two-Step Softening Heat Treatment for Manufacturing 12Cr–ODS Ferritic Steel Tubes. Journal of Nuclear Science and Technology, Vol. 41, No. 10, p. 1008–1012 (October 2004). [3] S. Ohtsuka, S. Ukai, M. Fujiwara, T. Kaito, T. Narita, Improvement of 9Cr-ODS martensitic steel properties by controlling excess oxygen and titanium contents. Journal of Nuclear Materials 329333(1): 372-376. [4] L. Toualbi, C. Cayron, P. Olier, R. Logé, Y. de Carlan. Relationships between mechanical behavior and microstructural evolutions in Fe 9Cr-ODS during the fabrication route of SFR cladding tubes. Submitted in Journal of Nuclear Materials, April 2012.

RELATIONSHIP BETWEEN MICROSTRUCTURE AND MECHANICAL PROPERTIES IN ODS MATERIALS FOR NUCLEAR APPLICATION

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

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

ODS FOR SODIUM FAST REACTORS

Beginning of the studies on the Fast Sodium Reactors to produce electricity

Rapsodie

Phénix

Superphénix

1960

1967

1973

1985

1987

Materials

First ODS (SCKCEN)

First irradiated tubes

Industrial Production (DourMetal)

ODS tubes in Phenix reactor

Optimization New reinforced of the ferritic alloys : austenitic ODS alloys steels

Forum Gen IV : reactors

SFR

2000

Need of optimized materials is still relevant ! SPX

PHENIX

L. Toualbi

2

Why ODS materials for Nuclear Applications ? SFR Dose > 150 dpa Stress ~ 100 MPa Temperatures : 400°C – 670°C

ODS materials (Oxide Dispersion Strengthened)

10

Average 15/15Ti

9

Average 316 Ti

5

Best lot of 15/15Ti

180 MPa – 650°C

4,5

8 4

6 5

Use limit for Phenix reactor

4

3 2,5 2 1,5

3

Ferritic-martensitic (F/M) steels ODS included

2 1 0 60

Conventional steel

3,5 Allongement (%)

Swelling (%)

7

70

80

90

100 110 120 130 140 150 160 170 180 190

ODS

1 0,5 0 0,0001

0,001

0,01

0,1

1

10

100

1000

10000

Temps (h)

dose (dpa)

Limited swelling under irradiation

Low thermal creep Nano dispersion 3

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 4

METALLURGY OF ODS MATERIALS Microprobe 1

Ex:ODS steel 18 Cr-1W Ti 0,5 Y2O3

0.85 W

0,8

0,6 Wt (%).

Optical

0.46 Y

0,4

Uniform distribution of nano oxides

Plate

0,2

0.3 Ti

0 0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

D in mm

TEM

Texture

Homogeneous microstructure Fine ferritic grains elongated in extrusion direction 1, 2 µm - 300nm

400 nm - 200 nm

Longitudinal direction

TEM

Transverse direction TAP

0,6

Ti, TiO SANS H(r) * fp

0,4

fp 1,1%

0,2

Y,YO and O

DSM – LLB Orphée

Clusters 50 nm

nano-oxides EFTEM 22 8 10 m-3 φ 3 nm HRTEM

0 0

1

2

3

4

5

6

Rayon moyen (nm)

7

8

9

10

90×14×14

nm3

GPM Rouen

8 1023 m-3 1,8 nm

O. Kalokhtina, B. Radiguet, Ph. Pareige

5


Conventional metallurgy ODS metallurgy

Temperature /°C 1400 1200 1000 800 600 400 200 0 0

1

2

3

4

5

6

7

Time / h 6


Ferritic grades

Fe -12/20Cr

Martensitic grades

Fe - 9 Cr

Fe-9Cr Fe-12/20Cr

Large differences between both type of alloys as a function of their final microstructure but generic creep behavior is noticed. 7


Typical microstructures

10µm

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

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

L. Toualbi, Phd Thesis 8


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

Transformation temperatures

-

Critical cooling rates ~ 1°C/s

austenite + ferrite

austenite + martensite

L. Toualbi, Phd Thesis

9

MECHANICAL PROPERTIES OF ODS

Tensile properties

Creep properties

Impact properties

10

TENSILE PROPERTIES OF ODS ALLOYS

Ferritic (Fe-14 Cr ODS)

As-extruded

A. Alamo et al. Journal of Nuclear Materials 329–333 (2004) 333–337 11


600

500

Contrainte vraie (MPa)

-4 -1

7.10 s

400

300

200

-5 -1

10 s

100

0 0

1

2

3

4 5 6 Allongement rationnel (%)

7

8

9

10

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

12


Martensitic (Fe-9Cr ODS)

Tempered martensite

Tensile properties in different metallurgical state : - J95-M3, tempered martensite - J95- M5, Softened ferrite L. Toualbi, Phd Thesis

Softened ferrite 13

CREEP PROPERTIES OF ODS ALLOYS

Ferritic (Fe-18 Cr ODS) Extrusion direction

ODS plate Extruded and annealed Bamboo like microstructure 200 nm

SL

ST

S45

Extrusion direction

M. Ratti, Phd Thesis

14


Ferritic Fe-18 Cr ODS at 650°C 250 MPa 2

almost no tertiary domain .

1,8 1,6

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

1,4 Allongement (%)

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

1,2 1

Transvers

0,8

45° °

0,6

Long (in progress)

0,4 0,2 0 0

1000

2000

3000

4000

5000

6000

7000

Temps (heures)

M. Ratti, Phd Thesis

15

Inoué et al. 16


Ferritic ODS 500 MA957 - Fine grains 650°C

Stress (MPa)

400

Aust.15/15Ti 650°C

MA957 - Recryst. 650°C

300 200

15/15Ti 700°C

MA957 - Recryst. 700°C

100

9Cr2MoVNb (EM12) 650°C

0 -1

10

0

10

1

2

3

4

5

10 10 10 10 10 Rupture Time (h) A. Alamo et al. Journal of Nuclear Materials 329–333 (2004) 333–337

17


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

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

18


Martensitic Fe-9 Cr ODS

ε&II = 1.4 ⋅10 −7 s −1

ε&II = 1.1 ⋅10 −10 s −1


19

CREEP PROPERTIES OF ODS ALLOYS In situ relaxation tests at 550°C • Decohesion along the grain boundaries • Creation of cavities

ODS 9%Cr

ODS 14%Cr

INTERGRANULAR mechanism Consistent with the macroscopic observations


• Dislocation still pinned on oxides • Viscous motion • Activation of sources of dislocations at the grain boundary 20

IMPACT PROPERTIES OF ODS ALLOYS

Ferritic Fe-14 Cr ODS alloys

Fine grain

A. Alamo et al. Journal of Nuclear Materials 329–333 (2004) 333–337 21


Ferritic Fe-14 Cr ODS alloys anisotropic impact behaviour for the rod: higher USE and lower DBTT under LT loading extrusion direction

TL

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

LT

rod Ø36

DBTT (°C) LT TL -29 108

USE (J) LT TL 7.6 3.8

diameter: 36mm

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

22

22


Ferritic Fe-14 Cr ODS alloys anisotropic impact behaviour for the rod: higher USE and lower DBTT under LT loading

rod Ø36

DBTT (°C) LT TL -29 108

USE (J) LT TL 7.6 3.8

For different samples, tendency to delamination effective propagation plane notch expected propagation plane


ED 23


Ferritic Fe-9Cr ODS alloys (thick plate)

Quasi-isotropic behaviour


24

CONCLUSIONS The mechanical properties of nuclear F/M alloys depend strongly on the chemical composition and 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 => Intergranular mechanism 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 appropriate microstructure is a key issue for the nuclear applications

25