Tungsten Copper Electrode Densification Problems II

Under normal infiltration, sintering conditions between tungsten and copper are two metals are immiscible and invasive low, which also makes the two powder densification process by certain obstacles, making it difficult to achieve high densification and the desired structure. But only by increasing the pressure and sintering temperature, although to some extent, can increase the density of the final product, but brought a lot of problems in the process conditions and comprehensive performance assurance, the following aspects in general:

2. Composition description

In the process of sintering, the composition controlling precision of tungsten copper is lower, although it calculated by accurate copper infiltration. In addition, the falling and overflow of copper liquid will have an effect on the composition offset and bring some difficulties to the surface machining of parts with complex shape during the liquid-phase sintering. Generally, due to the shrinkage ratio of liquid sintering reaches 15%-20%, the distortion and dimensional accuracy controlling is more difficult than solid-phase sintering. It is not conductive to parts with complex shape machining directly, especially to powder injection molding (PIM).

Thus, in order to achieve densification, we should ensure that the composition and size will be effective controlled, which is beneficial for machining parts with complex shape by PM and PIM. According to the present research, improving the activity of powder, such as choosing ultrafine powder and high energy-storing powder, can achieve densification rapidly, decrease the amount of copper overflowing and the size precision will remarkably improved. It is the most beneficial for composition controlling that sintering can be in solid phase state. This is due to liquid-phase sintering has some difficulties in distortion and size controlling, especially for the high volume fraction.

3. Size distribution

The study on the size controlling of liquid-phase sintering shows that the macroscopic deformation and micro structure has some internal connection, such as solubility, contact angle, grain size, coordination number and the volume fraction of solid. Tungsten copper (W-Cu) system has low solubility and high dihedral angle. Relevant scholars through calculations show that the three-dimensional grain contiguity of more than 3:00 to avoid collapse and deformation resistance critical solid volume fraction is 0.2. It is clear that the structure of complex parts, the only requirement without deformation is not enough, which also needs to have a certain size range of accuracy requirements. It is similar to component controlling, sintering in solid phase state is beneficial for size precision sintering and high densification.

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