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Ceramic-To-Metal Vacuum Brazing Services

With the development of science and technology and people’s increasing requirements for various properties of materials, metal-ceramic assemblies have developed rapidly in recent years and have been widely used in various fields such as national defense and aerospace. In nuclear power and solar equipment, ceramic-metal assemblies are often required to convert nuclear energy and solar energy into electrical energy. In the outer structure of the space station P2, ceramics can play an important role in heat preservation and radiation protection. In space vehicles, it is often necessary to use the corrosion resistance and high temperature protection properties of metal-ceramics to make structural parts. In addition, it is also widely used in vacuum tubes, high-voltage ceramic guide holes, transistor packaging, and ceramic booster warrants. Vacuum brazing is the most common and important method in the production, processing and maintenance of metal-ceramic composite parts. On the one hand, it is difficult to successfully fire high-quality ceramic bulk materials with complex shapes and large volumes. On the other hand, high-performance ceramics like alumina and zirconia often require complex comprehensive properties, which not only need to use the characteristics of high temperature resistance and oxidation of ceramics, but also need to have the ductility of metals. Therefore, it is often necessary to connect them directly with other metal materials or ceramic materials. Metal-ceramic assembly is an important functional structural material, so it is a meaningful work to study its vacuum brazing technology.

The most widely used metal-ceramic assembly is the assembly formed by the interconnection of various iron alloys, copper and copper alloys, nickel and nickel alloys and ceramics, as shown in Figure 1. In this society where metal-based materials are the main industrial application materials, the application range and function of ceramic materials largely depend on the quality of its connection with metal-based materials.

1 Application principle and research status of vacuum brazing in metal-ceramic welding

In general, the purity of the base metal and alloy is low, and the uniformity and performance of the material structure are higher than those of ceramics. The most widely used welding application between ceramics and metals is vacuum brazing. Brazing is to use a metal material with a lower melting point than the base metal as the solder, heat the weldment and the solder to a temperature between the melting point of the solder and the melting point of the base metal, use the liquid solder to wet the base metal, fill the gap between the joints and A welding method in which base metals interdiffuse to achieve a connection.

By selecting the appropriate solder, the brazing between metal and ceramic can be effectively realized, and a good welding structure and a welded joint with high mechanical properties can be obtained.

Vacuum brazing process conditions, such as welding temperature and vacuum degree of welding environment, are important factors affecting the structure of welded joints. The working temperature of vacuum brazing joints is generally 200-300 degrees lower than the melting point of the brazing alloy, and the vacuum degree of the brazing environment is also relatively high. When the vacuum degree is not high enough, it is easy to produce welding cracks, and if it contains Al, When easily oxidized elements such as Cr and Fe are used, it is easy to form oxide particles and holes in the welding connection, which seriously affects the connection strength. Welding temperature is an important factor affecting the composition of the intermediate layer, the wetting effect of the intermediate layer and the mechanical properties of the welded joint. If the temperature is too low, the intermediate layer cannot be melted and the intermediate compound with good connection performance cannot be formed. If the temperature is too high, it is easy to Pores or some other impurities will seriously affect the mechanical properties of welded joints. During the brazing welding experiment of AIN ceramics and Cu, it was found that when the thickness of the newly formed intermediate layer TiN was below 850 degrees during the welding process, it became thicker with the increase of temperature. When the welding temperature increased to 900 degrees , the thickness of the intermediate layer decreases instead.

2 Outlook for metal-ceramic vacuum brazing

Due to the poor ductility of ceramics, it is easy to generate a lot of stress and even cracks due to temperature fluctuations during the heating and cooling process of welding. Therefore, the majority of scientific researchers have come up with a lot of good methods in the actual welding process. : Add foam metal layer as a buffer at the joint. Someone has done such an experiment: it was found that after vacuum brazing, the welding material without a buffer layer could not withstand cyclic thermal stress at all, but after adding a buffer layer, it still retained a certain degree of stability after several cycles of heat treatment. Tensile strength and shear strength. The difficulty of ceramic vacuum brazing technology lies in the design of the intermediate layer, the elimination of residual stress, the oxidation of the intermediate layer and the prevention of the diffusion of defects such as dislocations, that is, the strength and service life of ceramic welded parts are very important evaluation criteria. The chemical reactions of the intermediate layer and their influence on the welding quality need quantitative analysis. The establishment and improvement of the welding model of ceramic-metal welding and the theoretical calculation of welding strength may be the focus of ceramic-metal welding and improve the welding quality. The direction of the effect.