Ceramic/metal connections and applications

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Although the special ceramic materials have excellent insulation (most ceramics), high temperature resistance, corrosion resistance and wear resistance, but their brittleness and machining performance are very poor, it is difficult to prepare large or complex structural parts. Metal materials have excellent room temperature strength, toughness, electrical conductivity and thermal conductivity, forming an obvious complementary relationship with ceramic materials in terms of performance. By using the connection technology to combine the two materials reliably, we can make full use of their respective excellent properties and produce complex components that meet the requirements.

Due to the fundamentally different chemical bond structure between ceramic materials and metal materials, as well as the special physical and chemical properties of ceramics themselves, there are many difficulties in the connection with metal or ceramic itself.
It is mainly reflected in the following two problems,
Firstly, ceramic materials are mainly composed of ionic bond and covalent bond, while metal materials are mainly composed of metallic bond, and the two are hardly infiltrated. Therefore, wettability of ceramic and metal materials should be considered.
Secondly, the linear expansion coefficient of the two is generally quite different. When heat sealing or mechanical connection is adopted, there will be a large residual stress at the joint between ceramic and metal, which will weaken the mechanical properties of the joint and even cause the joint to be damaged and cracked. Therefore, the problem of thermal stress relief at the joint should be considered.

The common way of connection is to use brazing process, using the metal or amorphous material whose melting point is lower than that of the welded material as the filler metal, heating to below the melting point of the base metal and above the melting temperature of the filler metal, and using the melting filler metal to wetting the base metal and filling the weld seam, so as to realize the connection of the welded material.

Solid phase diffusion connection is a high-temperature ceramic/metal connection mode that has been studied more. Its working principle is: two same or different materials are in close contact under high temperature and certain pressure, plastic deformation occurs on the surface, mutual diffusion is realized between atoms, and a good joint is formed.

The advantages of this process are that the joint quality is stable, the connection strength is high, the joint can be welded with larger section, more than one joint can be welded at one time, the efficiency is high, the middle layer can be added, the ceramic material does not need surface metallization. However, the process is complex and can meet the application requirements under high temperature and corrosion resistance conditions. High requirements for connecting surfaces and connecting devices.

Experimental steps:
1. Vacuum (10-2Pa);
2. Heating up (heating up to 1250℃, heating rate 15℃/min);
3. Heat preservation at 1250℃ for 100min (1 hour and 40min);
4. After 15min of heat preservation at 1250℃ (pressure), an additional force was applied for 6t, and the process lasted for 60min (temperature 1250℃).
5. After the addition of 6T, the pressure is maintained for 15min (the temperature is still 1250℃);
6. Unloading pressure, 10min unloading pressure to 0 (temperature is still 1250℃)
7. Pressure unloading is completed and the temperature drops automatically from 1250℃ to room temperature with the furnace.

Vacuum hot pressing sintering furnace perfectly meet the customer’s experimental process requirements, side door structure, very suitable for large size mold loading and unloading, easy to operate. During the experiment, the pressure and displacement control is accurate and precise, which ensures the pressing precision of diffusion connection technology. The furnace temperature uniformity throughout the working area is good, the pressed products are of high quality, and the metal substrate does not overheat and melt.

Learn More : Vacuum Hot Pressing Furnace