Comparison of Production Technology of Tungsten Copper Alloy
Conventional tungsten copper alloy is generally prepared by copper infiltration and liquid sintering method, but because of tungsten copper incompatibility of its sintering performance is poor, it is difficult to achieve complete sintering densification, it is difficult to form a uniform microstructure, Adjust the composition of tungsten and copper composite materials. In addition, Ni, Co, Fe and Pd can be used to improve the sintering properties of tungsten-copper alloy, and the effect of sintering can be improved by using the powder with ultra-fine copper dispersion. On the conductance, thermal conductivity have a negative impact). However, it is still very important to explore the new preparation technology to obtain more reasonable and better performance of the new tungsten-copper alloy in the research and development of tungsten-copper alloy. Tungsten is very high melting point, so the preparation of tungsten copper alloy can only be prepared by powder metallurgy method, roughly as follows:
1, melting method
The melting method is to prepare a certain density, strength of the porous matrix skeleton, and then infiltration of the lower melting point of the metal, filling the skeleton method. The mechanism is mainly in the metal liquid wetting porous matrix, in the capillary force under the review of the first chapter of the literature, the metal liquid flow along the particle gap filled porous pores, to obtain a comprehensive performance of the material, the advantage is the density High, good sintering performance, good thermal conductivity and conductivity performance; the shortcomings of the need to melt after the removal of excess metal copper, an increase of machining costs, reducing the yield. However, the melting method is still the most widely used method for the preparation of tungsten and copper alloys. ]. Because of the high melting point of tungsten, the sintering shrinkage is small at the general high temperature (<1700 ℃), it is difficult to densify, and because of the high hardness of the tungsten powder itself, the poor formability is difficult to achieve the high skeleton density required for high tungsten content, The key technology for the preparation of tungsten-copper alloys by leaching is to obtain a dense tungsten skeleton. With the development of powder plasticizing near net forming technology and the complexity of parts and components, the preparation of tungsten skeleton has been developed by a single traditional powder metallurgy molding to extrusion molding and injection molding. It mainly includes high temperature sintering and extrusion Forming and injection molding.
2, high temperature liquid sintering method
As the melting point of W and Cu is very different, tungsten copper alloy can be prepared by high temperature liquid phase sintering method, which can be densified by high temperature liquid sintering above the melting point of copper. The advantage is that the production process is simple and easy to control, the disadvantage is high sintering temperature, sintering time is long, sintering performance is poor, low sintering density (only theoretical density of 90% -95%), can not meet the requirements. In order to improve its density, after the liquid phase sintering need to increase the post-processing process: pressure, hot pressing, hot forging and so on. But this increases the complexity of the process and limits its application. A.K.Bhalla et al. The tungsten copper alloy prepared by the explosion compaction method has a good high temperature liquid sintering effect.
3, activated liquid phase sintering method
As the high temperature liquid phase sintering method can not get close to the theoretical density of tungsten copper alloy, the use of sintering treatment is to increase the complexity of the process and production costs. The sintering method not only reduces the sintering temperature, shortens the sintering time, but also makes the sintering density greatly improved. J.L.Johninson and R. M. German et al. Studied the activation of transitional elements Pd, Ni, Co, Fe. The results show that the activation effect of CO and Fe is the best, and the densification of tungsten and copper alloy can be improved obviously. When the CO content is 0.35%, the sintering performance is good after sintering at 1300 ℃ for 1h; the activation effect of Ni and Pd is not obvious , Which is worse than that in pure w powder. The reason is that Ni, Pd and Cu can form infinite solid solution, which can not achieve the activation effect, while CO, Fe and Cu form only finite solid solution, which is formed during the sintering process. The second phase in the grain boundary precipitation, the formation of intermetallic compounds, to promote the densification of tungsten. However, the addition of activator affects the conductivity and thermal conductivity of Cu in high conductivity phase, which significantly reduces the conductivity and thermal conductivity of the composite material. The conductivity, thermal conductivity, High thermal conductivity requirements of microelectronic materials is detrimental, so the preparation of the material is only applicable to the preparation of conductive, thermal conductivity requirements are not high occasions.
4, fiber alternative particle method
The use of fibers with a certain direction to replace refractory metal powder particles (such as tungsten powder) made by the composite material is not only conductive, high thermal conductivity, and can control the refractory metal at high temperature oxidation splash, with a high corrosion resistance Sex.
5, arc melting method
Arc melting method is the first use of traditional powder metallurgy method (mixed powder a sintering) the required alloy made of electrodes, and then in the consumption of electric arc furnace melting, resulting in small grain size, density segregation is small High density and good corrosion resistance of tungsten copper alloy.
6, fixed structure method
For tungsten copper alloy, while exploring its different production processes, but also from the change in structural design research, trying to form a fixed structure of the technical direction. That is based on different service conditions, designed into a dedicated component, so as to ensure the quality and use requirements. If the current use of hollow electric contacts, because the contact body there is a hollow area, the contact in the contact arc, the heat fast, burning small, long life.