Tungsten Copper Properties Comparison of Different Process

The commonly used molding technologies are molding process, extrusion molding and injection molding, wherein the molding process and injection molding process widely used in tungsten copper materials. Molding process is also known as compression molding or press molding, it is a kind of processes that put first powdered, granular or fibrous plastic into the mold cavity at a molding temperature, and then close the mold to shape and solidify. Molding process has many advantages, such as less raw material wastage, low cost of equipments, one-step forming, suitable for plate with large size. But it has long lead time, low efficiency, not suitable for products with complex structure or shape, the size is limited by the compressor.

The injection molding process here refers specifically to metal powder injection molding (MIM), it is a kind of new near net shape powder metallurgy technology that introduce from modern plastic injection molding technology into the field of powder metallurgy. The basic process is that Firstly, the solid powder with an organic binder uniformly kneaded, granulated after heating under plasticized state (~ 150 ℃) with an injection molding machine into the mold cavity solidifying-forming, and then by chemical or thermal decomposition method of forming the blank the binder removal, the final densification to give the final product. While the advantages of MIM are high density, high product consistency, a wide range of applications and can be formed smaller in size and shape of the structure of complex products. However, it has high requirements for the injection, high cost of mold design and only suitable for small batch production.

Take W-Cu tungsten copper product as a example to compare molding process with injection molding of tungsten copper material properties. W-Cu theoretical density is 17.28g / cm3, the trend of relative density and relative density. As we can see from this graph above, With increasing sintering temperature, density of the obtained two processes copper tungsten composites are showing trend of increased first and then decreased. The difference is the temperature of the maximum density, the highest density  of molded samples at 1350 ℃, reaches 17.16g / cm3, while the sample injected at 1400 ℃ highest density is 17.17 g / cm3. After the further increase in temperature, both the density began to decrease. This is due to the sample over-burnt, Cu phase inside of tungsten copper exudates to surface and the pores and defects left in side. Under the optimum sintering temperature, the density of injected sample reaches 99.31%, molded samples reaches 99.78%. In addition, the hardness of tungsten-copper composite material (HRB) was positively correlated to its density, the greater the density, the hardness of the respective materials is also greater.

Besides, we also compare the micro-structure of tungsten copper with different processes. The specific procedure is that milled, polished tungsten copper composite sample after etching with FeCl3 salt solution for 2 minutes, with water to clean the surface of the etching solution, then wipe the surface with alcohol cotton, and then drying, Finally placed under microscope observation of the metallurgical microstructure. By comparing the SEM photomicrographs and photographs can be found that tungsten copper molded sample of W, Cu two-phase distribution is more uniform, uniform grain size, but segregation occurs at a constant temperature inside, causing a regional copper-rich, there are some porosity. While tungsten copper sample by injection molding, W and Cu distribute uniform and does not exist W-rich phase and Cu-rich phase of the phenomenon and Cu phase forms net structure around tungsten grains.