High Purity Niobium Tube

A vacuum brazing method for manufacturing a high purity niobium tube and a stainless steel tube comprises the following steps:

1. The former was chemically treated, and the latter was electroplated with Nickel after pretreatment.

2. The stainless steel tube is arranged on the outside of the high-purity niobium tube and the stainless steel lining is arranged on the inside of it.

3. A triangular groove is arranged on the contact surface of the two sides, and the solder of AgCu20 coated with titanium powder is placed in the triangular groove, and then the vacuum brazing is carried out in a vacuum brazing furnace for

4. After the vacuum brazing is finished, the stainless steel lining is removed to realize the welding.

5. The vacuum brazing method can not only make the filling material flow fully but also ensure the clean welding surface and avoid the oxidation of niobium plate in the process of heating rolling, the problem of replacing NB-TI flanges with stainless steel flanges due to the large difference between the two Coefficient of thermal expansion is overcome, thus solving the problem of vacuum sealing of superconducting cavity.

The manufacturing method belongs to the technical field of superconducting accelerating cavities. At present, the preferred material for superconducting cavity applications is the metal niobium, which has the highest critical point (9.26 K), the highest critical superheat field (about 200 MT), and excellent mechanical properties as a Superconductor classification, it is especially suitable for machining into various shapes of the superconducting cavity. High purity niobium tube-316L has become an urgent demand for high-performance superconducting cavity and cost.

Because of the big difference in expansion coefficient between two metals, the common welding method is easy to produce crack defects and lead to vacuum leakage. The AGÓN national laboratory has successfully used vacuum brazing to connect the two. The laboratory uses oxygen-free copper as a filler material, however, there are Fe-Nb compounds on the welding surface, which lead to a decrease in welding strength and possible vacuum leakage. Because the working temperature of the welding piece is liquid helium temperature (4.2 K), it needs to endure many times of cold and heat shocks from 4.2 K to 873 K and enough mechanical strength, the above technical requirements put forward very high requirements for the brazing seam of the two parts.

They were used as base materials, and titanium powder coated AGCU20 solder was used as filler material, the“High purity niobium tube” involved has a RRR value (the ratio of resistivity at 300K to resistivity at 10K) greater than 300 and a thickness greater than 3mm. 316L stainless steel tube for vacuum edge flange.

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