Production, Processing and Characterization of oxide dispersion strengthened W alloys for Fusion Reactors J. Martinez 1, A. Muñoz 1, M. A. Monge 1, B. Savoini 1, R. Pareja 1 1 University of Carlos III of Madrid, Spain York, June 2013

Outline 1-Introduction 2-Materials and experimental procedure 3-Microstructure 4-Thermal stability of the grain structure in the W-2V and W-2V-0.5Y 2 O 3 alloys 5-Conclusions 2

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. 3

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. 4

2-Materials and experimental procedure ▪Materials: ▪Powder metallurgy route: WW-ODSW-TiW-VW-Ti-ODSW-V-ODS W W-1La 2 O 3 W-2TiW-2VW-2Ti-1La 2 O 3 W-4V-0.5Y 2 O 3 W-2V-0.5Y 2 O 3 W-1Y 2 O 3 W-4TiW-4VW-4Ti-1La 2 O 3 W-4V-1La 2 O 3 Mechanical alloying in Ar atmosphere 20 h Blending Canning + Degassing (400 °C, 24 h) HIP 1300 °C, 2h, 200 MPa.

3- Microstructure 6 J. Martinez B. Savoini, M.A. Monge, A. Munoz, D. E. J, Armstrong, R. Pareja Fusion Engineering and Design (2013) W-2V W-2VY 200 µm W V 7 µm 0 nm 25 nm W-2V J. Martinez B. Savoini, M.A. Monge, A. Munoz, R. Pareja Fusion Engineering and Design 86, 9-11, (2011) μm

3- Microstructure 1μm1μm V-K W-M 2 μm 7 W LaW V 20 µm W-4VLa W-2V

3- Microstructure Martensític Phase WC Dispersoids 8

4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y 2 O 3 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. 9

4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y 2 O 3 alloys EBSD images for the W-2V and W-2V-0.5Y 2 O 3 alloys. Mackenzie boundary disorientation distribution function. Absence of any crystallographic texture in these alloys. 10 W-2V W-2VY

4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y 2 O 3 alloys ▪Grain size distribution: 1) The volume fraction of the submicron grains is significantly higher in W-2V-0.5Y 2 O 3 than in W-2V. 2) The volume fraction of the coarse grain population in W-2V-0.5Y 2 O 3 is lower than the corresponding to submicron grains  30 against 70%. 3) The micron-sized grains in W-2V-0.5Y 2 O 3 alloy appear not to coarsen for heat treatments at 1700 °C but it does in W-2V. 11 W-2VW-2VY

4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y 2 O 3 alloys ▪Correlation classic approach for the kinetics of normal grain growth induced by isothermal treatments: ▪Where D o is the initial size, D the size at time t, Q the activation enthalpy for isothermal growth, T temperature, k B the Boltzmann constant and K o a constant. ▪The fits of the experimental data of the submicron-sized grain distributions to eq. ▪Q= 183 ± 6 kJ/mol y K o = 4.7  10 –11 m 2 /s for W-2V alloy. ▪Q= 240 ± 11 kJ/mol y K o = 1.4  10 –9 m 2 /s for W-2V-0.5Y 2 O 3 alloy. ▪Q =211  13 kJ/mol for W for micron-sized grain distribution [J. Almanstötter, Inter. J. of Refrac. And Mats. 15 (1997) 295–300]. 12

4- Thermal stability of the grain structure in the W-2V and W-2V-0.5Y 2 O 3 ▪The effect of the thermal treatments on the microhardness values: ▪The values for W-2V-0.5 Y 2 O 3 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. 13

5- Conclusions ▪The powder metallurgy W-2V and W-2V-0.5 Y 2 O 3 alloys exhibited a bimodal grain size distribution. ▪ It has been found that the Y 2 O 3 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 Y 2 O 3 is significantly higher than in W-2V alloy. ▪The considerable enhancement of the microhardness in the W-2V-0.5 Y 2 O 3 appear to be associated to dispersion strengthening. 14

Thank you for your attention 15