The solder material used has a decisive impact on the technological properties of the joint. The filler metal can be applied as wire, foil, or paste, depending on the geometry of the parts to be brazed. Solders based on silver, which are particularly suitable for joining copper-parts, as well as nickel-based solders, suitable for brazing heavy-duty joints of stainless steels and super alloys, are widely used in vacuum brazing technology. However, active brazing alloys are also used increasingly for joining ceramic materials such as Al2O3 or Si3N4.
The function of the hard and high-temperature filler metals described is based on their ability when in the molten state to dissolve elements of the materials to be joined, thus creating a strong metallurgical bond similar to a welded joint. In contrast to welding, however, the base materials do not melt because the melting ranges of the solder alloys are much lower than those of the base materials.
The fact that the joining process is carried out in a vacuum atmosphere prevents any interaction between the solder and base materials with the surrounding atmosphere. This means that the use of highly-corrosive fluxes can be avoided on the one hand, while the vacuum atmosphere in the joining process means that the physical properties of the base materials are not influenced on the other.