^® STEMET is a trade name of MIFI-AMETO, Ltd.

Brazing as a process of making joints between different materials is implemented at temperatures lower than their melting points. In this case a state of local equilibrium is established at the boundary between material and liquid brazing filler metal (FM). This constitutes the significant difference and advantage of brazing in comparison with diffusion and pressure welding. Brazing provides an opportunity to make joints in hidden and hard-to-reach places of product, to connect many parts simultaneously and to braze together heterogeneous materials and materials with various wall thickness. Brazing is widely used in technologies for nuclear plants to make mock-up samples facing plasma and exposed to plasma impact [1-6]. To date, experiments of brazing beryllium with different materials such as: Cu - Be [2-5]; Be - TZM alloy, Be - C/C composite [4] have been carried out. However, despite the promising prospects for application of ductile thin foils made by rapid solidification (as pointed out earlier), the FMs in the form of powder, paste and rolled plates have often been used. Ribbon-type brazing FMs calibrated thickness and produced by rapid solidification have amorphous or microcrystalline structure with uniform composition and homogeneous phase state. Such peculiar FM features as narrow temperature interval of melting point, a short brazing time, and a high atom diffusion activity are found. All these peculiarities ensure a high ability of such FMs to penetrate into gaps between the components to be brazed. Homogeneous brazing zone is thus created. Using of thin brazing foils ensure saving of FMs and acceptable appearance of the brazed joint.

This paper discusses problems connected with the brazing of various materials using rapidly solidified (RS) ribbon-type FMs, together with investigations of the brazed zone and the tensile strength tests of brazed joints.

The aluminium- and silver-based brazing FMs are often used in the joining process of beryllium with beryllium and with other metals [6]. The first provides a high shearing strength of brazed joints at temperatures to 300 ^oC and retards recrystallization of beryllium because the brazing temperature is no more than 650 ^oC. The second provides the requisite strength in the joining of beryllium with various materials and offers the possibility of high working temperatures (to 600 ^oC). However, traditional brazing methods by aluminium- and silver-based FMs are very complex and multistep. These methods involve a tinning or coating on beryllium before brazing by electroplating and electrolytic modes [2,4]. Sometime Be-Ti-Zr alloys are used for brazing of beryllium [7].

The STEMET 1501 (Al-Si) was tested as the FM based on aluminium for brazing of beryllium, because Al and Si does not form brittle intermetallic phases with beryllium. The RS alloy of this composition has a microcrystalline structure.

As the result of phase diagram analyses and previously made investigations, the STEMET 1403 (Zr-Ti-Be-Fe) was chosen. The active titanium and zirconium make it possible to exclude a tinning or coating on the beryllium surface before brazing. The small thickness and amorphous structure of RS ribbons allow a decrease in the brazing temperature and brazing time over elevated diffusion activity and narrow melting interval. These will exclude forming a lot of intermetallic phases in the brazed seam.

The alloys of the Cu-Sn-In system were investigated as an alternative to silver-based FMs. The ductile ribbon with melting point less 750 ^oC can be obtained by the rapid solidification method in this system. In our opinion manganese and phosphorus can provide selt-flux property. As the result of this process, the preliminary treatment of the beryllium surface is excluded. The STEMET 1120 (Cu-Sn-Mn-In-Ni) and STEMET 1108 (Cu-Sn-In-Ni) were chosen because of the melting point estimates of this alloy system.