Tungsten Copper Electrode Infiltration

Infiltration is kind of process that uses the metal or alloy which has lower melting point than the product to fill in the pores of products in molten state. For tungsten copper electrode, copper solution has lower melting point and it fill in the porous tungsten skeleton, which has excellent density and strength so that tungsten copper material has better properties, such as thermal conductivity, electric conductivity and high hardness.

 The process is: Tungsten powder (W) + shaping agent (or adds Cu-induced powder) → tungsten skeleton (suppressing + degreasing + sintering) → copper infiltration (Cu) → after treatment. And the most research focus on:

1. Powder granularity

2. Tungsten skeleton

3. Infiltration process

4. After treatment.

Powder granularity: It stresses that tungsten powder granularity has an effect on tungsten copper electrode and other properties. Generally, the higher sintering temperature, the larger average granularity and the better strength of tungsten skeleton. However, if the granularity of tungsten powder exceeds a certain degree, the contact area among tungsten powder will be reduced and the tungsten powder can not be necking, which decreases the strength and hardness of tungsten skeleton and material.Some scientists do some researches about tungsten powder granularity and volume fraction effects on density of tungsten copper electrode, they thought it depends on original grain size of tungsten powder and this effect will decrease by the increasing temperature of sintering temperature.

Other experiment uses three different granularity of tungsten powder (8.7μm, 23.2μm and 65.2μm) for W-15Cu tungsten copper electrode. They thought different process parameters and tungsten powder granularity accounts for obturator or the changing of W-W adjacency rate, which has an effect on the density and resistivity. Nowadays, tungsten copper contacts made of 4-8μm (tungsten powder) granularity is widely used worldwide, which has good molding, contraction, low coefficient of thermal expansion and it is easily to be controlled in size or the porosity of tungsten blank.In order to achieve that corrosion ratio and the efficiency of machining in electrical discharge machining (EDM) with tungsten copper electrode by diverse granularity of tungsten powder, researchers use 1.0-3.0μm five kinds of tungsten powder as tungsten copper electrode. It demonstrates that 2.0 μm average granularity of tungsten copper has better properties in 80WC-20Co tungsten carbide machining.

Besides, mixed with light of Cu-induced powder will improve the corrosion ratio and the efficiency. Chinese scholars use 0.8-3.0μm tungsten powder for mixing, the result shows that despite small average granularity of tungsten powder, the density of sintering blank is still lower and the micro-structure is maldistributed.Viewed from tungsten skeleton, it is a key of high density tungsten copper electrode manufacturing by infiltration. Due to tungsten (W) has high melting point, high hardness and low contraction, it is difficult to be machining and densifying, which becomes the major part of scholars study. The study of tungsten skeleton can be divided into two types, one is the shaping properties of tungsten skeleton, and the other is the sintering properties of tungsten skeleton.