Features of ceramic connection

    Due to the essential difference between the atomic structure of ceramic materials and metals, coupled with the special physical and chemical properties of the ceramic itself, there are many problems in the welding of ceramic materials or the welding of ceramics and metals. Ceramic material welding mainly has the following characteristics and difficulties:

    1) Ceramic materials mainly have ionic bonds and covalent bonds, which show very stable ionic coordination. It is usually impossible to fuse ceramics and metals through fusion welding, and it is also difficult to be wetted by molten metal. Therefore, it is necessary to metallize ceramics or braze with active brazing filler metal during brazing to obtain a reliable brazed joint.

    2) The linear expansion coefficient of ceramics is small, which is quite different from the linear expansion coefficient of metal. When ceramic and metal are heated and welded, residual stress will be generated in the joint area, which will weaken the mechanical properties of the joint; when the residual stress is large, it will also cause the joint at the joint. Cracks are produced, and even fractures are caused. Therefore, when connecting ceramics to metal or connecting ceramics with metal as an intermediate layer, the problem of thermal stress in the joint area must be considered.

    3) Due to the low thermal conductivity of ceramics and weak resistance to thermal shock, cracks are prone to occur during concentrated heating (especially when high-energy density heat sources are used for fusion welding). Therefore, during welding, the temperature gradient of the welded joint area should be reduced as much as possible, and the heating and cooling rate should be controlled.

    4) Ceramics have high melting point, high hardness and strength, and are not easy to deform. Therefore, direct diffusion welding of ceramics is very difficult. The surface requirements of the welded parts are very strict and the diffusion time is also very long. Usually an intermediate layer is used to reduce the connection temperature, and the plastic deformation of the metal can reduce the processing requirements for the ceramic surface.

    5) The conductivity of most ceramic materials is very poor or basically non-conductive. It is difficult to connect by arc welding, and some special measures must be adopted.

    No matter which welding process is used, the performance of ceramic and metal welded joints must meet the following basic requirements:

    1) The welded joint of ceramic and metal must have high strength, which is the basic requirement for welded structural parts;

    2) The welded joint must have vacuum airtightness;

    3) The residual stress of the joint should be minimized, and the welded joint should have corrosion resistance and thermal stability during use;

    4) The welding process should be as simplified as possible, the process is stable, and the production cost is low.

(Huiputech)