Tungsten-Based Plasma Facing Components

Tungsten materials are considered to be plasma facing components (PFC) for the preparation of the International Thermonuclear Experimental Reactor (ITER) due to its high melting point, high sputtering threshold, high thermal conductivity, low vapor pressure, and low hydrogen isotope retention.

However, the brittleness of tungsten is an important factor limiting its application in plasma facing components of a fusion reactor. It is generally believed that there are three main sources of brittleness:

1. A number of dislocation movements in tungsten often require high temperature to activate.

2. In the industrial production process, low solubility impurities in tungsten are often difficult to eliminate, and O, N, H, etc. are harmful. The impurity element is concentrated at the tungsten grain boundary to weaken the grain boundary, which often leads to the brittleness of tungsten.

3. The high heat flux loading and high energy neutron irradiation environment of PFC in the fusion reactor tend to make tungsten easy to recrystallize embrittlement and irradiation embrittlement. Therefore, the brittleness of tungsten will reduce the service life of PFC and threaten the safety of fusion devices. Improving the toughness of tungsten-based materials is one of the important topics in the field of fusion materials.

Some researchers have proposed a tungsten-based plasma facing components, which is characterized by: tungsten powder and tungsten fiber are used as raw materials, and tungsten powder is selected according to the ratio of tungsten fiber to matrix volume of tungsten powder of about 10%-30%. The tungsten powder is uniformly mixed with the tungsten fiber by a method of mixing powder which does not damage the tungsten fiber, and then the mixture is sinterd by hot isostatic pressing. The tungsten powder used is pure tungsten powder or tungsten-rhenium alloy powder, and the tungsten fiber is chosen to be pure tungsten fiber or tungsten-rhenium.

The preparation process is as follows:

1) Purchase high-quality commercial doped tungsten wire and reduced tungsten powder. The requirements are: the recrystallization temperature of doped tungsten wire should reach 2000K, the diameter should be about 10-300μm, and the tensile strength should be above 2.5GPa. The content should be as low as possible (purity >99.5 wt%) and the grain size should be as small as possible (<3 μm) to improve the sintering quality;

2) In order to improve the interfacial properties of tungsten fiber and tungsten matrix, it is necessary to prepare intermediate film such as ZrO2, La2O3, Y2O3, C, etc. on the tungsten wire by physical (chemical) vapor deposition or sol-gel method. ;

3) Short-cut the tungsten wire with a diameter of about 10-300μm into a length of 1-5mm, and then select the tungsten powder according to the ratio of the fiber to the volume ratio of the matrix of about 10%-30% and mix it evenly in the low-energy ball mill. After the mixing is finished, the resulting powder was degassed in a vacuum of the order of 10-3 Pa at 500-800 ° C for 0.5-1 h.

4) The uniformly mixed powder is sintered by hot isostatic pressing method, the sintering temperature should be about 1700K, the pressure is about 200MPa, the working gas is argon gas, and the titanium material is selected as the sheath.

5) According to the design requirements of the fusion reactor PFC, parts of different shapes and sizes can be directly sintered by hot isostatic pressing process, or the Wf/W material prepared by sintering can be processed into required parts.

6) The obtained product maintains the advantages of commercial tungsten: high melting point, high thermal conductivity, low hydrogen isotope retention, etc. At the same time, the performance isotropic is superior to CVD prepared tungsten continuous long fiber composite material; The raw material and powder sintering method is low in cost; the three-point bending test shows that the material can exhibit the inelastic deformation ability that commercial polycrystalline tungsten does not have, because cracks appear along the fiber and matrix interface expansion and debonding interface during loading. Relative frictional sliding further dissipates energy, greatly improving the toughness of the brittle tungsten-based material.

In summary, the tungsten-based plasma facing components (Wf/W) prepared by the method is a promising plasma facing material.

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