Y2O3 Dispersion Strengthened Tungsten Prepared via APT for The Application of Plasma Facing Materials (PFMs)

Fusion power is considered as a promising candidate for future sustainable sources of energy. A major challenge for future fusion devices is the development of plasma facing materials (PFMs). The PFMs should be able to resist the harsh environment of fusion plasmas, e.g., high thermal loads, neutron irradiation, particle fluxes, etc. Therefore, the materials that could be used for PFMs are very limited. Tungsten is a very promising candidate for PFMs due to its high melting point, high temperature strength, good thermal conductivity, low erosion in fusion radiation environment, and low tritium retention.

To boost the properties of tungsten-based materials, yttrium oxide (Y2O3) was dispersed to strengthen tungsten targeting the application of plasma facing materials (PFMs). Ammonium paratungstate (APT) was used as the tungsten source. energy H/He neutrals were applied to investigate the erosion and cavity formation on the surface.

The W-1vol%Y2O3 alloys were prepared using a molecular-level liquid-liquid (L-L) mixing process. In this L-L doping, yttrium oxide (Y2O3) was firstly dissolved into aqueous solutions of nitrate (Y(NO3)3), and then ammonium paratungstate (APT, (NH4)10[H2W12O42] 4H2O) was added into the solution. After 90 min stirring at 80 °C, the spray drying was exploited to remove water and then was calcined at 550 °C for 1 h to decomposes these powders into tungsten oxide enclosing the yttrium oxide. These powders were immediately reduced into tungsten powder in flowing hydrogen, with Y2O3 embedded inside.

The powders were subsequently squeezed into a cylindrical mold (55 mm in diameter and 200 mm in height), and a cylinder with the diameter of 55 mm and the height of 50 mm could be got after sintered at 1800 °C for 2 h in vacuum with the pressure of 33 MPa. Subsequently, the cylindrical compact was thermo-mechanically processed into a disc with the diameter of 70 mm and the height of 26 mm by high-energy-rate forging at 1550 °C. Then the disc was cut into several small cylinders with diameters of 25 mm, followed by high-energy-rate forging at 1300 °C with a height reduction of about 75% (final thickness ∼6.5 mm), subsequently, the small discs were annealed at 1100 °C for 30 min in a dry hydrogen atmosphere to relieve residual stress and stabilize the microstructure. Finally, rectangular cuboid shapes cut from the small discs were brazed onto a copper heat sink with an internal channel of Ø 10 mm for active water-cooling during exposure in the HHF test facility GLADIS. Then the material was treated with high-energy-rate forging at 1550 °C. Elongated grains and a high density of microstructure defects can be observed in the deformed samples. Where after, deformed samples with different height were exposed to a 29 keV H/He mixed neutral beams.

In conclusion, yttrium oxide (Y2O3) was dispersed to strengthen tungsten targeting the application of plasma facing materials (PFMs). Ammonium paratungstate (APT) was used as the tungsten source. the as-prepared W-Y2O3 alloys has the advantages of high temperature machinability, high ductility, low ductile-brittle transition temperature (DBTT), and high irradiation-induced embrittlement, which makes it to be an promising material to be used as plasma facing materials.

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