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 contacts；samples of microwave sintering has more uniform microstructure and better mechanical properties.

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