Production, Processing and Characterization of oxide dispersion strengthened W alloys for Fusion Reactors J. Martinez1, A. Muñoz1, M. A. Monge1, B. Savoini1, R. Pareja1 1University of Carlos III of Madrid, Spain
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
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.
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 Canning + Degassing (400 °C,24 h) HIP 1300 °C, 2h, 200 MPa. • Materials: • Powder metallurgy route: Mechanical alloying inAr atmosphere 20 h Blending
2 μm 25 nm V 0 nm 7 µm W 3- Microstructure W-2V W-2V 200 µm W-2VY W-2V J. Martinez B. Savoini, M.A. Monge, A. Munoz, R. Pareja Fusion Engineering and Design 86, 9-11, (2011) 2534-2537. J. Martinez B. Savoini, M.A. Monge, A. Munoz, D. E. J, Armstrong, R. Pareja Fusion Engineering and Design (2013)
W-M V 2 μm V-K 1μm 3- Microstructure W-4VLa W-2V W La W 20 µm 20 µm 20 µm 20 µm
3- Microstructure Martensític Phase WC Dispersoids
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.
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. W-2VY W-2V
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. W-2V W-2VY
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-0.5Y2O3alloy. • Q =21113 kJ/mol for W for micron-sized grain distribution [J. Almanstötter, Inter. J. of Refrac. And Mats. 15 (1997) 295–300].
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.
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.