Superconducting Properties of Nb—Hf Alloys and the Effect of Mechanical and Heat Treatment on Their Structure and Properties

Bychkova, M. I.; Baron, V.V.; Savitskii, E.M.

doi:10.1007/978-1-4684-8220-1_13

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“…The Nb alloy follows the Ginzburg-Landau-Abrikosov-Gorkov (GLAG) theory [15,16]. This theory has motivated many microstructural studies of Nb alloys related to their superconducting properties, dating back to the 1960s [17][18][19][20][21][22]. The GLAG theory predicts the upper critical field (B c2 ) at 0 K to be given by B c2 (0) = 3.11 9 10 3 q n cT c , where q n , c, and T c are the normal state resistivity, electronic specific heat coefficient, and critical temperature, respectively [15,16].…”

Section: Graphical Abstract Introductionmentioning

confidence: 99%

High-temperature-tolerable superconducting Nb-alloy and its application to Pb- and Cd-free superconducting joints between NbTi and Nb3Sn wires

et al. 2021

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For more than 30 years, Pb–Bi alloy and Wood's metal (50% Bi, 26.7% Pb, 13.3% Sn, and 10% Cd) have been used as representative superconducting solder intermedia to establish superconducting joints between NbTi and Nb3Sn wires in high-field nuclear magnetic resonance magnet systems. However, the use of Pb and Cd has been severely restricted by environmental regulations, such as the Restriction of Hazardous Substances Directive. Herein, a novel method of forming a superconducting joint between NbTi and Nb3Sn wires without Pb and Cd has been proposed. This approach is based on metallurgical bonding processes using a superconducting Nb-alloy intermedium, whose fine microstructure is maintained even after exposure to temperatures higher than 650 °C. Further, fine crystal defects become sources of magnetic flux pinning centers. Among transition elements close to Nb, Hf is considered the most suitable additive for realizing high-temperature-tolerable (HTT) superconducting Nb-alloy intermedia. Utilizing the HTT characteristic of Nb–Hf, a superconducting joint between Nb3Sn filaments and one end of the Nb–Hf alloy core was created by forming a superconducting Nb3Sn layer at the interface through a chemical reaction. The other end of the Nb–Hf alloy core was cold-pressed with NbTi filaments, to connect their active new surfaces to each other in order to create a superconducting joint. Ultimately, a superconducting joint between NbTi and Nb3Sn wires was realized with a high critical magnetic field (Bc2) of more than 1 T. The formation of the superconducting joint was confirmed by current decay measurements. This method of forming a superconducting joint is promising for application in environmentally friendly nuclear magnetic resonance magnet systems. Graphical abstract

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