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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Comparison of Metal-Ceramic Brazing Methods

Advanced ceramic materials have excellent characteristics such as high hardness, high strength, high temperature resistance, good wear resistance, corrosion resistance, and oxidation resistance, and broad application prospects, especially in the fields of electronic energy, transportation, engine manufacturing, and aerospace. However, the toughness value of ceramics is low, which is a brittle material. It is difficult to prepare components with large sizes and complex structures by mechanical processing. In order to overcome the brittleness and difficult processing of advanced ceramics and broaden their further application and development, Connect ceramics and metals to form a complementary relationship in performance, making it an ideal structural and engineering material to meet the application of modern engineering. Vacuum brazing or diffusion welding is commonly used in production to connect ceramics and metals (ceramics). With the in-depth research on connection technology, new methods have been developed (neutral atom beam welding, laser welding, ultrasonic welding, microwave Welding and combustion synthesis technology, etc.).

1 Vacuum brazing connection technology

Vacuum brazing uses a material whose liquidus temperature is lower than the solidus temperature of the base metal as the solder, heats the solder to a molten state, and has good wettability to the base metal, fills the joint gap, and then the liquid solder Crystal solidification, so as to realize the connection of parts. A small wetting angle of the solder on the ceramic is a prerequisite for metallurgical joining. From a thermodynamic point of view, the wetting of the solder refers to the process of reducing the free energy of the system after the liquid solder contacts the base metal; from an energy point of view, increasing the surface energy of the ceramic is beneficial to the wetting and bonding of the solder. spread out. Wetting is divided into adhesion wetting, spreading wetting and immersion wetting. For the vacuum brazing of ceramics and metals, in addition to the above wetting forms, there is also reactive wetting. The nature of this wetting is liquid The metal brazing filler metal is first adsorbed on the surface of the ceramic and the metal, and then dissolves, and further chemical reactions occur to realize the connection between the brazing filler metal and the base metal. In order to make the solder wet the surface of ceramics, the majority of scientific research workers through the treatment of the ceramic surface (surface growth of carbon nanotubes, surface growth of graphene, surface epitaxial growth of whiskers, surface metallization, etc.), or add to the solder Active metal elements (Ti Zr, Hf, V) and other methods to solve it.

2 Effect of ceramic surface metallization on vacuum brazing

The main methods of ceramic surface metallization are Mo-Mn method, vapor deposition, ion implantation and electroless plating. Among them, the Mo-Mn method was proposed earlier, but it consumes time and energy in the process, so it is rarely used now. Vapor deposition methods include chemical vapor deposition, physical vapor deposition and plasma reaction methods. The purpose of metallization is to improve the wettability of the solder to the ceramics, and to protect the ceramics from decomposition and voids during high-temperature vacuum brazing.

Ceramics and metals are two different materials with large differences in thermal expansion coefficients, and residual stress is easily generated during the connection process. Ceramic materials are mainly composed of ionic bonds and covalent bonds, with strong binding force, and it is difficult to release stress by their own plastic deformation. A large stress concentration is formed at the interface, which reduces the connection strength of the joint and is prone to fracture during use. Therefore, how to accurately measure and calculate the size and distribution of residual stress is an important issue in the connection of ceramics and metals.

The connection method of ceramics and metals has been developed and researched, and the results show that the problem of connectability has been solved, but the strength and heat resistance of the connection joint still have a large gap compared with the use requirements. From the analysis of the current literature and practical application, the methods that can realize the connection of ceramics and metals are mainly concentrated in vacuum brazing and diffusion bonding, and the application range is the widest.