An upgraded brazing technique to manufacture ceramic-metal joints for UHV applications

• Published in: Vacuum 2002-12, Vol.68 (4), p.321-328
• Main Authors: Murari, A, Albrecht, H, Barzon, A, Curiotto, S, Lotto, L
• Format: Article
• Language: English
• Subjects: Active brazing; Applied sciences; Brazing. Soldering; Ceramic-metal joints; Exact sciences and technology; High-temperature feedthroughs; Joining, thermal cutting: metallurgical aspects; Metals. Metallurgy; UHV components
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/S0042-207X(02)00504-3

The properties of an upgraded active vacuum brazing procedure, explicitly developed to manufacture ceramic-metal joints, are presented and some of the most significant applications described. The essential feature of the technique is the use of AgCuTi as brazing material, which permits the joining of alumina (Al 2O 3) very reliably with various metals, including stainless steel. The careful control of the brazing cycle and the quality of the alumina, in terms of purity and density, play an essential role in determining the final performances of the components. With the technology presented, several vacuum components have been developed and manufactured, among which the most interesting are electrical feedthroughs compatible with commercially available signal connectors and capable of operating at temperatures of 500°C or higher. In particular, a completely new model of a signal feedthrough, to be used with the Minisnap-Plug of Odu and presenting an alumina–stainless steel joint, has been developed and thoroughly tested in the laboratory. Its performances have been verified at more than 700°C, with temperature variations of up to 10°/min. The latest version of these feedthroughs has shown good vacuum tightness and reliability up to 650°C and therefore presents better characteristics than most of the feedthroughs commercially available. In addition to being tested on the bench, some feedthroughs have been used in the nuclear fusion experiment Reversed Field eXperiment (RFX), without showing any sign of degradation or ageing.