Vacuum brazing

Vacuum brazing is a thermal joining method, which makes it possible to fabricate high-quality joints between similar and dissimilar materials. Decisive for the technological properties of the joint is the used filler metal. Basically, the filler metal can be applied as wire, foil or paste, depending on the geometry of the parts to be brazed. Filler metals based on silver, suitable especially for the joining of copper-parts and also nickel-based filler metals, suitable for the brazing of high-loaded joints of stainless steels and super alloys are widely spread. Moreover, so-called active brazing alloys are more and more used for joining ceramic materials such as Al₂O₃ or Si₃N₄. High-temperature brazed joints, fabricated in a vacuum furnace, generally show very good mechanical and chemical properties which are in some cases similar to those of the base materials.

The mechanism of brazing is based on the ability of the filler metals to dissolve elements of the bulk material thus creating a strong metallurgical bond. The characteristic of those bonds depends on the combination of filler metal and bulk material. For stainless steel parts, brazed with nickel base filler metals, the achieved metallurgical bond is similar to a welded joint. In contrast to welding, melting of the base materials does not take place due to the melting ranges of the filler metals, which are located significantly below those of the base materials.

High-vacuum as brazing atmosphere prevents the interaction between the filler metals and the base materials with the surrounding atmosphere. The use of high-corrosive fluxes can thereby be avoided. On the other hand there is no influence of the vacuum atmosphere on the physical properties of the base materials.

In the vacuum furnace the whole part is heated to brazing temperature. Thereby distortion, which occurs by using local heating methods like flame-brazing or induction-brazing, can be avoided. Furthermore parts with a complex joint design can be brazed.