Molding Pressure Effect on Tungsten Copper Composite Materials

Except powder granularity, the molding pressure is also one of main influencing factors of tungsten copper composite materials density. The experiments show that with the increasing molding pressure, the density of sintered blank is increasing. On the one hand, it due to the increasing pressure promotes the densification in the third stage of the compaction, that is when the pressure exceeds a certain value continues to increase, if it continues to increase pressure on the powder by the pressing force and the frictional force is greater than the elastic stress. Particles have plastic deformation and fill in the gap of powder, which will further increase the density; on the other hand, due to nano-crystalline copper particles themselves have a very large surface free energy, if the pressing pressure is further increased, the copper particles are plastically deformed again, i.e., the copper particle surface free energy is further increased to further reduce the melting point, which make it infiltrate tungsten particle at low temperature and promote the densification process.

In addition, it is inevitable that copper evaporation in the process of tungsten copper manufacturing. The researcher found that when the particle size of Cu grain reaches nano scale, it will be volatile at 450℃. So under the optimum holding temperature of 1350℃, Cu phase will be easily consumed by evaporation. since tungsten copper material is a versatile material, after copper volatile, not only because of the disappearance of the binder phase becomes loose, reduce the density and strength of the material, it will make the physical as well as electrical and thermal conductivity coefficient of linear expansion and other materials significant performance degradation. There is an experiment uses two kinds of pressure 300MPa and 800MPa pressed found that with the increase of molding pressure, the material density increased wettability of liquid copper has been significantly improved, while the loss of copper in the case of the high temperature phase has also been in control. This is due to:

1. Increasing molding temperature reduces the spacing of W grains and improves the strength of W skeleton, which also make it difficult to form a copper material inside the material loss of external channels, slow volatile speed of copper particles within the material;
2. Large molding pressure increases the surface contact area of the copper, so that the original surface free energy with increase in the melting process of the copper particles and copper particles easier contact between adjacent and fused together to form larger particles, thereby reducing the fine particles volatile chance of high temperature phase, maintaining the stability of copper content.

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