Sintering Process Effect on Tungsten Copper Electrode Properties

Except the effect of tungsten copper powder itself granularity and distribution and the impurities on tungsten copper electrode properties, the parameters of sintering process control will affects the performance, which mainly from two aspects: one is effects of molding pressure, the other is the influence of sintering atmosphere. In the process of molding, the sample usually has three changing steps: 1. sliding stage, the compacts density increased rapidly at this time; 2. on the basis of the first stage and pressing, the porosity decreased, the compacts density almost not change; 3. when the pressure exceeds a certain value continues to increase, as the pressure continues to rise, the relative green density continues to increase. On the one hand it is due to increase in pressure increases the degree of densification material in the press of the third stage, i.e. when the pressure exceeds a certain value continues to increase, if the pressure continues to increase, the powder is subjected to the pressing force and the friction of its elastic stress, plastic deformation of the particles to produce a powder filling the gap, to further increase its density; on the other hand, since nano grain has high free energy, if the compaction pressure further increases, the particles will pass plastically deformed and the surface free energy is further increased, the melting point is further reduced. This makes it at lower temperatures can be effectively infiltrate W particles.

In the tungsten-copper composite milling process, with the milling time goes by, there would inevitably bring in impurity metal elements, vacuum sintering can effectively exclude impurity element or an oxide, played the role of purification; and vacuum sintering is also beneficial for removing the absorbed gas, which promote the shrinkage effect at the end of sintering. In addition, to a certain temperature sintering furnace charge time should be protected by inert gas. However, the timing of inert gas is a critical issue. If charging too early, Cu grain on the surface not completely melted and closed, Ar will enter through the gap between the particles of material filling the body had been evacuated holes increases when liquid copper tungsten particles were infiltrated and filling the gap resistance, after the copper melting and closing the material surface to form pores; if charging too late, material surface appeared cracks, and then filled with an inert gas also missed the best time. 

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