Vacuum Brazing Of Ceramic And Metal Materials

For ceramic materials, everyone’s first impression is definitely its high melting point, high insulation performance and poor thermal stability. In the process of welding assemblies using ceramics and metals as connecting materials, these characteristics often add great difficulty to traditional welding methods. The resulting welded joints have poor performance and cannot meet process requirements. The application of vacuum brazing in the field of connecting ceramics and metal materials can effectively solve this problem. It can organically combine ceramics and metals to obtain composite components that have the advantages of both ceramics and metals.

Ceramic and stainless steel welded components (left); Ceramic and copper welded components (right)

Ceramics have such a high melting point and poor weldability. Is vacuum brazing the only way to connect ceramics to other metals?

In fact, this is not the case. Currently, the commonly used connection methods include the following categories: mechanical connection method, electrostatic connection method, hot isostatic pressing method, vacuum brazing method and solid-state diffusion connection method. However, during the production and scientific research process, scientific researchers comprehensively considered the joint performance, use cost, implementation difficulty and other factors of these connection methods and found that vacuum brazing is more suitable for connecting ceramics and metals than other connection methods. Other connection methods are available. Its obvious limitations prevent it from being widely and efficiently used in manufacturing.

Therefore, vacuum brazing is currently the most commonly used and most actively researched connection method for connecting ceramics and metals.

As the excellence of vacuum brazing in the welding of ceramics and metals has become known to more people, a large number of scientific researchers have invested in the development and research of related technologies, and more and more problems in the welding of metal materials and ceramic materials have been overcome.

Vacuum brazing of metals and ceramics

Al2O3  ceramics and 304 stainless steel are two common materials in our lives.Al2O3  ceramics are used in electronic components and substrates, high-temperature electrical insulators and other fields due to their high hardness and strong wear resistance.

Experimental study on vacuum brazing of 304 stainless steel parts and metallized alumina ceramics. First prepare a metallized ceramic surface, and apply molybdenum and manganese slurry on the ceramic surface that needs to be metalized by screen printing and coating. Then perform metallization and burning infiltration at 1500°C, and repeat the second coating and printing of molybdenum and manganese. slurry, burning and infiltration, then electroplating a nickel metal film, and hydrogen sintering at 1200°C; then the stainless steel brazing surface is prepared, that is, a layer of nickel is plated on the surface to be welded.

Vacuum brazing process: AgCu28Ni1.5 alloy powder is used as the brazing material, the brazing temperature is 830°C, and the heat preservation is 15 minutes; the obtained brazed joint can meet the high temperature test of 500°C × 48h, and the sealing performance of the joint after the test meets the helium leakage rate <4×10-4Pa·m3/s.

The vacuum brazing of surface-activated Al2O3 ceramics and 5005 aluminum alloy was studied. During the research process, Ag-Cu-Ti powder was used to evenly coat the

Al2O3  ceramic surface, and then the ceramic was subjected to active metallization treatment in a vacuum at a process condition of 880°C/10min. The obtained ceramic activation interface is as shown in the figure below.

Ceramic activation interface

Then grind the surface of the aluminum test plate to be welded with sandpaper to remove the oxide film on the surface. Place the Al-Si solder foil between the ceramic and 5005 aluminum alloy surfaces to be connected. The temperature rises at a rate of 15°C/min and reaches the brazing level. The temperature is maintained at 600~620°C for 5 minutes, then dropped to 300°C at a rate of 10°C/min, and then cooled with the furnace. The vacuum in the furnace is higher than 1.0×10−3Pa. The shear force of the brazed joint obtained under this process can reach up to 15MPa. The picture below is the metallographic diagram of the brazed joint.

Brazed joint appearance

In order to obtain a stable and strong joint between DD3 high-temperature alloy and Ti3 AlC2 ceramics, a series of vacuum brazing verification experiments were conducted using Ag-Cu-Ti as the filler metal. Finally, it was concluded that the brazing temperature is 850°C and the holding time is Under the condition of 10 minutes, the maximum shear strength of the brazed joint can reach 135.9MPa.

In addition to the development of vacuum brazing processes for ceramics and stainless steel, ceramics and aluminum alloys, and ceramics and DD3 single crystals, there are also more vacuum brazing processes for ceramics and metals.