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

18

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