Gradient Porous Tungsten Manufacturing Process

Porous tungsten is widely used in power electronics, aerospace and other high temperature fields as a variety of components prepared by porous or porous matrix, such as porous cathode matrix with high current density, high temperature fluid filter, high temperature heater of rocket nozzle, etc.

With the development of technology, the requirement of pore characteristics of porous tungsten also extends from single pore characteristics to gradient porous tungsten. Some scholars have prepared porous tungsten products by pressing and sintering or hot pressing sintering. The main manufacturing processes are as follows:

1)Raw material powder: Raw material powder is one or several kinds of tungsten powder with different particle sizes. The particle size of raw material tungsten powder is 3-20 micron, and the purity of raw material tungsten powder is more than 99.9%.

2)Air grinding dispersion treatment: cleaning air grinding equipment, opening main control preheating, filling high purity nitrogen with 99.9% purity as working gas, reducing oxygen content to 0.1%, opening grinding valve, adjusting grinding pressure to 0.60-0.80 MPa, adding high purity tungsten powder into grinding chamber to grind, making its aggregate open and adjusting separating wheel to the highest rotation. Speed 6000r/min, start sorting wheel;

3) Classification treatment by air mill: according to the requirements, the speed of separating wheel is reduced to 0 r/min several times, and tungsten powder is collected in batches. By adjusting the speed of separating wheel, narrow particle size distribution tungsten powder with average particle size of 1-20 micron can be obtained.

4)Compression forming: select 3) two or more tungsten powders collected for multi-layer powder laying and compaction forming;

5) Sintering: Under the protective atmosphere of high purity hydrogen with purity higher than 99.9%, the forming billet was sintered at 1500-2200 ℃ for 60-240 min, and finally porous tungsten with porosity of 15%-30% and average pore size of 0.5-5 um was obtained.

For different size powder, the porosity and pore size of porous tungsten products are different after sintering by different sintering process. The pore size and pore size of gradient porous tungsten can be controlled by controlling the particle size, layer number and sintering process. Moreover, after the treatment of tungsten powder, the edges and corners of the powder particles disappear, the shape is regular or near spherical, without agglomeration, and the particle size distribution is uniform. The porous tungsten products prepared by sintering with the treated powder can effectively control the pore size, pore distribution, porosity and pore connectivity of the material, so as to avoid the occurrence of such defects. Porous tungsten products obtained by powder agglomeration have uniform microstructures due to uneven pore distribution, large number of closed holes and poor pore connectivity.

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