Except cobalt (Co) element, Nickel (Ni) is also a kind of common additives, and the density, the hardness, the electrical conductivity and other comprehensive properties of tungsten copper electrode will be influenced by the content of Ni. The effect of content of Ni on the density and hardness of tungsten copper W-25Cu electrode as follow:

The diagram shows that the density and the hardness of tungsten copper electrode is sensitive to the adding Ni element. When the content of Ni is 0.3%, the density rapidly increases 14.9g/cm³ to 17.0g/cm³. Therefore, adding Ni element will improve the density and the hardness of tungsten copper products.

Since the large part of tungsten copper electrode is used for EDM (Electrical Discharge Machining), the measure of its electrical conductivity is crucial. However, the electrical conductivity is sensitive to the impurities and porosity so that the adding cobalt (Co) has an large effect on the electrical conductivity of tungsten copper electrode. The effect of different content of Co on the electrical conductivity of tungsten copper electrode diagram as follow:

The diagram shows that the adding Co element dramatically decreases the electrical conductivity of tungsten copper electrode. Before adding Co element, the electrical conductivity is about 34.5%IACS, while adds 0.2% Co element, the electrical conductivity greatly decreases 34.5%IACS to 16.4%IACS. With the constant increase of Co content, the electrical conductivity decrease constantly. However, tungsten dissolving in Co improves the sintering densification, a large number of solid phases connected with each other to form the continuous tungsten skeleton, the infiltration of liquid phase copper has been restricted, which leads to the maldistribution.

Use cobalt (Co) powder as activator can greatly promote the solid phase sintering of tungsten skeleton. Some studies have shown that due to the existence of W₆CO₇ phase or Co atom on the surface of tungsten particle, it has better wettability and improve the rearrangements of particles in sintering. Although the effect of Co additives can not be removed, the high phase boundary diffusion and the transformation of material are enhancing. In the process of tungsten skeleton sintering, W dissolved in Co, firstly formed "carrier phase" on the surface of tungsten particle and then the tungsten atom by spreading the opposing Co phase, when liquid phase sintering is preferentially formed in connecting skeleton. Co-W and Co-Cu binary phase diagram as follow:

During the infiltration, viscous Cu liquid flows and fills the pores in, which further improve the densification. When the Co content exceeds 0.2%, the pores in the material substantially eliminated, and a large number of solid phase tungsten particles is connected with each other to form continuous skeleton, which limit the flow of liquid Cu, block the increase of densification, and decrease the density because of the growth of tungsten particle.

Sintering additives, which can dissolve tungsten, can be used for decreasing the porosity of tungsten copper electrode. The most common method is to add active elements, which takes advantage of active elements to dissolve tungsten and improve phase precipitation, round and accumulation, to obtain a high density. It can remarkably improve the properties of tungsten copper, decrease the sintering temperature and shorten the sintering time. The effect of different content of Co element on the hardness of tungsten copper electrode as follow:

We can learn from the graph that the effect of Co element on the hardness of tungsten copper electrode is similar to the density of tungsten copper electrode, which remarkably increases at the beginning and tends to stabilization or decrease. When the content of cobalt is about 0.3%, the density and hardness of tungsten copper electrode reaches the maximum 16.69g/cm³, and HB311.6.

More infomations about Co-doped effects on tungsten copper electrode, click here:

http://news.chinatungsten.com/en/tungsten-information/81018-ti-10447 
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Adding activate element to promote tungsten dissolution, and of the solid phase sintering and liquid phase diffusion densification during sintering tungsten particles dissolved in the liquid phase precipitation, round and accumulation, to obtain a high density. Its addition can remarkably improve the material properties, reduce the sintering temperature and shortening the sintering time.

However, the addition of these elements will be activated in a certain extent, reduce the thermal conductivity and electrical conductivity of tungsten copper electrode. Therefore, this kind of method is suitable for the occasions, which has lower demands of thermal conductivity and electrical conductivity. The effect of different content of Co on the density of tungsten copper electrode as follow:

The graph shows that the reaction of tungsten copper electrode density is sensitive to the adding Co element, which increases at the beginning, 14.9g/cm³ rapidly increases to 16.6g/cm³. Afterwards, the content of Co increases constantly, the density of tungsten copper electrode changes a little and has a decreasing trend.