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Production, Processing and Characterization of oxide dispersion
strengthened W alloys for Fusion Reactors
J. Martinez1, A. Muñoz1, M. A. Monge1, B. Savoini1, R. Pareja1 1 University of Carlos III of Madrid, Spain
York , 24-26 June 2013
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Outline
1-Introduction
2-Materials and experimental procedure
3-Microstructure
4-Thermal stability of the grain structure in the W-2V and W-2V-0.5Y2O3 alloys
5-Conclusions
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1-Introduction▪ Tungsten-base alloys are very promising materials for making
plasma facing components (PFC) in the future fusion reactors.
▪ The properties required to be a plasma facing materials (PFM) are:▪ High melting temperature.
▪ Thermal shock resistance.
▪ Good thermal conductivity.
▪ Creep strength.
▪ Minimal tritium retention.
▪ High temperature strength.
▪ Low sputtering and erosion rates.
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1-Introduction▪ Problems related with tungsten:
▪ The ductile–brittle transition temperature (DBTT) and Recrystallization temperature (RCT).
▪ The ductile–brittle transition temperature and recrystallization temperature have to be enhanced in order to widen the operating temperature window (OTW).
▪ The DBTT and RCT as well as the ductility of tungsten depend on the microstructure, alloying elements and production history.▪ Reinforcement by oxide dispersion strengthened (ODS).
▪ W-Ti or W-V alloys.
2-Materials and experimental procedure▪ Materials:
▪ Powder metallurgy route:
W W-ODS W-Ti W-V W-Ti-ODS W-V-ODS
WW-1La2O3 W-2Ti W-2V W-2Ti-1La2O3
W-4V-0.5Y2O3
W-2V-0.5Y2O3
W-1Y2O3 W-4Ti W-4V W-4Ti-1La2O3 W-4V-1La2O3
Mechanical alloying in Ar
atmosphere 20 hBlending
Canning+
Degassing(400 °C, 24 h)
HIP1300 °C, 2h,
200 MPa.
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3- Microstructure
J. Martinez B. Savoini, M.A. Monge, A. Munoz, D. E. J, Armstrong, R. Pareja Fusion Engineering and Design (2013)
W-2V
W-2VY200 µm
W
V
7 µm
0 nm
25 nm
W-2V
W-2V
J. Martinez B. Savoini, M.A. Monge, A. Munoz, R. Pareja Fusion Engineering and Design 86, 9-11, (2011) 2534-2537.
2 μm
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3- Microstructure
1μm
V-K
W-M
2 μm
W
LaW
V
20 µm 20 µm
20 µm 20 µm
W-4VLaW-2V
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3- Microstructure
MartensíticPhase
WC Dispersoids
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4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y2O3 alloys▪ Objectives:
▪ Study of the ultrafine grained structure.
▪ The mechanical behavior of these alloys at high temperature.
▪ Isothermal annealing for 1 h:• Samples of the alloys were vacuum sealed.
• Temperature was in the range 800 − 1700 °C.
• Followed by water quenching.
▪ Microstructure of the samples was examined by:▪ Electron backscatter diffraction (EBSD).
▪ Electron channeling contrast imaging (ECCI) in SEM.
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4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y2O3 alloys
• EBSD images for the W-2V and W-2V-0.5Y2O3 alloys.
• Mackenzie boundary disorientation distribution function.
• Absence of any crystallographic texture in these alloys.
0 10 20 30 40 50 600
5
10
15
DISORIENTATION ANGLE (º)
PR
OB
AB
ILIT
Y (%
)
C)
0 10 20 30 40 50 600
5
10
15
DISORIENTATION ANGLE (º)
PR
OB
AB
ILIT
Y (%
)C)
W-2V W-2VY
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4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y2O3 alloys
▪ Grain size distribution:• 1) The volume fraction of the submicron grains is significantly higher in
W-2V-0.5Y2O3 than in W-2V.• 2) The volume fraction of the coarse grain population in W-2V-0.5Y2O3
is lower than the corresponding to submicron grains 30 against 70%.• 3) The micron-sized grains in W-2V-0.5Y2O3 alloy appear not to
coarsen for heat treatments at 1700 °C but it does in W-2V.
2468
10
T=as-HIP
2468
10
T=1273 K
2468
10 T=1573 K
Vol
ume
fract
ion
(%)
2468
10
T=1773 K
102 103 1040
5
10
15
20 T=1973 K
Grain size (nm)
5
10
15
20
T=as-HIP
5
10
15
20
T=1273 K
5
10
15
20T=1573 K
Vol
ume
fract
ion
(%)
0
5
10
15
20
T=1773 K
102 103 1040
5
10
15
20T=1973 K
Grain size (nm)
W-2V W-2VY
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4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y2O3 alloys
▪ Correlation classic approach for the kinetics of normal grain growth induced by isothermal treatments:
▪ Where Do is the initial size, D the size at time t, Q the activation enthalpy for isothermal growth, T temperature, kB the Boltzmann constant and Ko a constant.
▪ The fits of the experimental data of the submicron-sized grain distributions to eq.
▪ Q= 183 ± 6 kJ/mol y Ko = 4.710–11 m2/s for W-2V alloy.
▪ Q= 240 ± 11 kJ/mol y Ko = 1.410–9 m2/s for W-2V-0.5Y2O3 alloy.
▪ Q =21113 kJ/mol for W for micron-sized grain distribution [J. Almanstötter, Inter. J. of Refrac. And Mats. 15 (1997) 295–300].
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4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y2O3
▪ The effect of the thermal treatments on the microhardness values:
▪ The values for W-2V-0.5 Y2O3 are between 2.5 and 3 times higher than the corresponding values for W-2V.
▪ A recovery onset at 1300 °C is observed for both alloys in coincidence with the submicron grain growth.
800 1000 1200 1400 1600
3,63,84,04,24,44,64,85,05,2
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10
12
14
16
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W-2V W-2V-0,5Y2O3
Mic
roha
rdne
ss (G
Pa)
Temperature (ºC)
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5- Conclusions
▪ The powder metallurgy W-2V and W-2V-0.5 Y2O3 alloys exhibited a bimodal grain size distribution.
▪ It has been found that the Y2O3 addition inhibit growth of the coarse grains at T<1700 °C, at least.
▪ Although the activation enthalpy for submicron grain growth in W-2V-0.5 Y2O3 is significantly higher than in W-2V alloy.
▪ The considerable enhancement of the microhardness in the W-2V-0.5 Y2O3 appear to be associated to dispersion strengthening.
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Thank you for your attention