Coarse crystal ammonium paratungstate as white crystals, is flake or needle, slightly soluble in water, the solubility in water less than 2% at 20℃, insoluble in alcohol. Coarse grain ammonium paratungstate (APT) as a raw material of powder metallurgy industry, with the continuous increasement of subsequent product performance and quality requirements, domestic and foreign requirements increase by year, and thus it has become a hot seller in recent years.

Coarse ammonium paratungstate features
Coarse grain ammonium paratungstate (APT) as a raw material of powder metallurgy industry, has the features like simple production process, high purity finished products, high density, good flowability, easy storage and so on. With the continuous development of new carbide and filament varieties, its excellent performance makes people come to realize that it will have a profound impact on the performance of the subsequent productions tungsten powder and tungsten carbide products as the physical appearance of the raw material APT.

Except tungsten copper electrode, there are some copper alloy electrodes, such as pure Cu, CrCu, BeCu and so on.

3. BeCu: Be (Beryllium) as the main part, which also called beryllium bronze. It has the best elastic in copper alloy, high strength, high hardness, good fatigue resistance, small elastic hysteresis, corrosion resistance, wear-resisting, high electrical conductivity, non-magnetic and some excellent physical, chemical and mechanical properties. The density is 8.3g/cm³, tensile strength ≥ 100MPa, thermal conductivity ≥ 105w/m·k20℃.

4. W-Cu: Tungsten copper, it is manufactured by powder metallurgy (PM), which suitable for tungsten carbide molding. Tungsten copper has low wastage of electrode and high material removal rate (MRR), which is the most widely used in EDM. The density reaches 14 g/cm³, the hardness is HV184, the electrical conductivity is 42%IACS.

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Except tungsten copper electrode, there are some copper alloy electrodes, such as pure Cu, CrCu, BeCu and so on.

1. Cu (also called red Cu, pure Cu): It has high purity, uniform distribution, lower oxygen content, no porosity, excellent thermal and electrical conductivity, etc. After heating treatment, the electrode has no direction and the molding precision has been improved. Despite heat pressing or cold pressing process, tungsten copper can be widely used in wires, cable, electric brush and some occasions requires high thermal and electrical conductivity. Cu≥99.95%, oxides ≤ 0.003%, the electrical conductivity ≥ 57%IACS, the hardness ≥ HV85.2.

2. CrCu: The hardness ＞ HRB75, the electrical conductivity ＞ 75%IACS, it has high strength and hardness at 400℃, excellent abrasion resistance and anti-attrition. After aging and hardening treatment, its thermal and electrical conductivity will be remarkably improved and easily for welding and brazing. CrCu has good corrosion resistance in the water or atmosphere, and good antioxidation at high temperature, can well withstand the pressure processing in the cold and hot states, but its drawback is a strong sensitivity to the gap in the gaps and corners causing stress concentration, prone to mechanical damage.

Tungsten copper electrode is one of the most widely used in Electrical Discharge Machining (EDM). Due to EDM uses pulsed spark between tool and workpiece, which ablate the metal by partial high temperature of discharging. Therefore, it is necessary that the electrode of EDM requires ablation resistance and excellent conductivity. What’s more, its distribution should be uniform.

Some researchers find that the measured conductivity is generally lower than the theoretical value by theoretical model of thermal conductivity value (also applied in analyzing conductivity). The influencing factors of conductivity of tungsten copper electrode are impurities, porosity and micro structure. Among them, impurity is the main factor, which trace will remarkably decrease the thermal conductivity and electrical conductivity of tungsten copper.

The source of impurities in the following areas: 1. activator, for improving the densification of tungsten copper, will form the solid solution with Cu and has an effect on the electrical conductivity. 2. The purity of raw material is lower, probably lead in impurities from outside during the preparation.

Except that the density and hardness of tungsten copper electrode, the effect of adding nickel (Ni) on the electrical conductivity of tungsten copper electrode is also can not be neglected. The effect of content of Ni on the electrical conductivity of tungsten copper electrode diagram as follow:

The diagram visually shows that the electrical conductivity of tungsten copper electrode dramatically decreases after adding nickel (Ni). (When the content of Ni is 0%, the electrical conductivity is 34.5%IACS, and the electrical conductivity decreases to 17.5%IACS after the content of Ni reaching 0.2 %.) Afterwards, with the increasing content of Ni, the electrical conductivity decreases constantly. The principle is similar to the adding cobalt (Co) that tungsten dissolved in nickel (Ni), which promoted the sintering densification. A large number of solid tungsten particles bonded contact with each other to form a continuous skeleton, limiting the role of liquid Cu infiltration, resulting in tissue tungsten copper alloy electrode uneven. In addition, external Ni atom enlarges the resistance through electrons of tungsten and copper scattering after adding active element Ni.

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. According to the phase diagram of Cu-Ni and Ni-W as follow:

From the Cu-Ni and Ni-W phase diagram can visually see the nickel (Ni) and copper (Cu) is infinitely miscible, and tungsten W can be dissolved in Ni. Therefore, when tungsten copper composite powder mixed with Ni element, the porosity will decrease and the density and the hardness of tungsten copper electrode is improved. In addition, in the process of sintering, tungsten particles rearranged by the liquid Cu, which shortens the distance among the particles and further enhances the densification. Through SEM (Scanning Electron Microscope), we can find that the particle of skeleton is uniform and the granularity is finer. However, with the increasing content of Ni, the connectivity of tungsten skeleton will be better.

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