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Tungsten Copper Contact Microwave Sintering

Except  conventional sintering process, microwave sintering as a new sintering  process is also gradually began to apply in the tungsten copper  material. It uses special microwave band has the fine structure coupled  with a basic material to generate heat, and material dielectric loss in  the electromagnetic field of the material as a whole it is heated to the  sintering temperature to achieve densification. Microwave sintering has  many advantages, such as volumetric heating, heat conduction from the  inside out and stepwise temperature distribution within the high outside  low, which are beneficial for heating rate, sintering time and energy  efficiency. For powder metallurgy industry, it is essential that lower  cost of production and lower energy consumption, so microwave sintering  has a broad prospect in tungsten copper contact.

 

Tungsten  copper (W-Cu) contact is a kind of psudoalloy that consist of W and Cu  immiscible and with a great difference in the melting point, which means  it is difficult to achieve higher density by conventional sintering  method and it has a bad influence on the electrical and thermal  conductivity, hermeticity and other mechanical properties. Compared with  conventional sintering process, microwave sintering can effectively  improve the density of tungsten copper contact materials to improve the microstructure and increase other comprehensive performance.

From  microwave sintering temperature and holding time point of view, the  sintering temperature rises to a certain temperature, density tungsten  copper contact materials increases, the relative density of up to 99.8%,  close to fully densification. This is due to the temperature rise  reduces the wetting angle, improved copper solution on a solid phase  wettability of tungsten, reducing the resistance of the particle  rearrangement process, the particles rearrangement sufficiently improve  the densification rate. Meanwhile, temperature increases can also reduce  the viscosity of liquid copper and increase in liquid copper capillary  force mobility, which will be conducive to densification. But thereafter  the temperature increased, lower relative density decreased, which is  due to the reduced coefficient of viscosity, the effect of gravity  copper deposited on the bottom of the fluid will gradually lead to the  formation of a new gas into the pores, thereby reducing the density.

 

The  sintering additive also has a great impact on the tungsten copper  contacts sintering densification. The experiments show that adding a  small amount of Co, Ni can significantly improve the solubility of W,  and help to improve the ability of densification. In the liquid phase  sintering process, W in solid solution reacted with sintering aid or  intermediate phase. And the product will form a continuous layer of  wrapping on W grains surface, which can significantly reduce the surface  tension between the liquid and the copper particles W and improve  wettability of the two phases.

In  addition, copper liquid under the action of capillary force, the gap  between the W particle flow and cause a rearrangement of W particles,  thereby significantly promoting compact shrink compact. However, copper  liquid flow too often will lead to the emergence of copper accumulation  pool, even reduce the uniformity of the sample. Overall, by analyzing  the experimental data, in the manufacture of tungsten copper alloy  contact process, the microwave sintering technology compared to  conventional sintering has a significant advantage in heating rate and  sintering cycle; sintering additive selection can promote the  densification of tungsten copper contactssamples of microwave sintering has more uniform microstructure and better mechanical properties.

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