Tungsten Steel Functionally Gradient Materials

In the future, the refractory tungsten metal and structural material steel need to be joined together in the divertor part of fusion equipment. Due to the huge difference of thermal expansion coefficient between tungsten and steel, the joint of tungsten and steel obtained by conventional welding method has large residual stress and working pressure, which will lead to deformation and cracking.

tungsten steel functionally gradient materials image

The preparation of tungsten steel functionally gradient materials is an important way to solve this problem. However, the melting point of tungsten differs greatly from that of iron and steel, and tungsten and steel react at high temperatures. It is difficult to obtain tungsten-iron divertor with good performance and low cost in one step by common methods. Therefore, the FGM of tungsten steel with high relative density of 98% and excellent mechanical properties can be prepared by electric sintering under ultra-high pressure. The sintering time is short, the sintering process is completed in one step, the cost is reduced and the efficiency is greatly improved. The process includes the following steps:

A.Preparation of raw materials: tungsten powder with fineness of 1-10 micron is selected, and steel powder/iron powder with fineness of 45-150 micron is selected. The tungsten powder and steel powder iron powder are mixed evenly according to the designed volume fraction.

B.Forming of green billet: laminated moulding of the above-mentioned mixed powders with a forming pressure of 50_300 MPa;

C.Sintering: Place the formed green billet in a pyrophyllite mould, put it into the press, apply 1-10 GPa pressure, the pressure is bidirectional pressure or hexahedral pressure; then apply 2 6 kW alternating current at both ends, the current is 1000A 3000A, the sintering time is 15 seconds 100 seconds, and keep the pressure for 30 180 seconds; By grinding and polishing, the relative density of tungsten-steel functionally gradient materials is 98 99.9%, which is consistent with the design composition.

The above process can make FGM from two materials with different physical properties, such as tungsten-steel (iron), at one time, with less time-consuming and low cost. By cold pressing, the thickness of each layer can be well controlled while eliminating the residual gas in the green body, so as to make it consistent with the design components. The prepared FGM has good mechanical properties and thermal shock resistance. It is suitable for thermal deposition materials and high temperature plasma erosion components, such as filter materials in nuclear fusion devices.

 

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