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 –
[email protected] Constantin MEIS, CEA/INSTN, Saclay –
[email protected]
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
METALLURGY OF ODS MATERIALS
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
METALLURGY OF ODS MATERIALS
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
METALLURGY OF ODS MATERIALS
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
METALLURGY OF ODS MATERIALS
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
TENSILE PROPERTIES OF ODS ALLOYS
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
TENSILE PROPERTIES OF ODS ALLOYS
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
CREEP PROPERTIES OF ODS ALLOYS
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
CREEP PROPERTIES OF ODS ALLOYS
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
CREEP PROPERTIES OF ODS ALLOYS
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
CREEP PROPERTIES OF ODS ALLOYS
Martensitic Fe-9 Cr ODS
ε&II = 1.4 ⋅10 −7 s −1
ε&II = 1.1 ⋅10 −10 s −1
M. Praud, J.Malaplate et al., creep 2012
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
M. Praud, J.Malaplate et al., creep 2012
• 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
IMPACT PROPERTIES OF ODS ALLOYS
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
IMPACT PROPERTIES OF ODS ALLOYS
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
AL Rouffié et al. http://dx.doi.org/10.1016/j.jnucmat.2012.08.050
ED 23
IMPACT PROPERTIES OF ODS ALLOYS
Ferritic Fe-9Cr ODS alloys (thick plate)
Quasi-isotropic behaviour
AL Rouffié et al. http://dx.doi.org/10.1016/j.jnucmat.2012.08.050
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