Effect of ultrasonic-vibration drawing process on Bi-2212 round wires
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Effect of ultrasonic-vibration drawing process on Bi-2212 round wires Xueqian Liu1, Shengnan Zhang1,* , Qingbin Hao1, Guoqing Liu1, Gaofeng Jiao1, Chengshan Li1, Jianqing Feng1, and Pingxiang Zhang1 1
Superconducting Materials Research Center, Northwest Institute for Nonferrous Metal Research, Xi’an 710016, China
Received: 6 July 2020
ABSTRACT
Accepted: 1 October 2020
Bi2Sr2CaCu2O8?d (Bi-2212)/Ag round wires were fabricated by imposing ultrasonic-vibration drawing (UVD) technique during both the single-filament and multi-filament cold-drawing processes. The frequency of ultrasonic-vibration was set fixed at 20 kHz and different output power density levels had been altered by varied amplitudes. The influence of ultrasonic-vibration on the deformation process of Ag metal sheath, filament density, Ag/superconductor ratio, wire dimension, drawing force reduction, and the superconducting properties of final wires has been systematically studied. Softening effect of ultrasonic-vibration on the Ag metal can be deduced with the decreasing drawing flow stress and drawing force under certain amplitude. It was found that powder densification could be promoted and higher filament volume fraction as well as high wire diameter uniformity had been reached with the introduction of UVD process, leading to the enhancement of Jc and JE after proper heat treatment. Such technique could be considered in fabrication of Bi2212 long wires as well as other superconducting materials.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
1 Introduction Bi2Sr2CaCu2O8?d (Bi-2212), firstly discovered in 1988 [1], has become one of the most promising hightemperature superconductor (HTS) candidates for practical applications. With attractive intrinsic characters such as its high irreversibility field (Hirr[ 100 T) and upper critical field (Hc2), Bi-2212 can maintain high superconducting current capacity under low temperature and ultrahigh magnetic field [2]. In particular, Bi-2212 can be fabricated into isotropic round wires, retaining stable electromagnetic
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https://doi.org/10.1007/s10854-020-04587-x
performance regardless of the magnetic field directions. Besides, the well-developed winding, cabling, and insulation techniques [3] also make it easier for massive production and application in magnets insert coils [4], accelerators, and current leads. Abundant researches had been conducted to study the behavior of Bi-2212 single crystals [5] as well as introducing doping into Bi-2212 system [6, 7]. As for fabrication of Bi-2212 long wires, currently, the most feasible and commercially used fabrication technique for Bi-2212 HTS wires is the powder-in-tube (PIT) method. Within this process, many crucial factors are
J Mater Sci: Mater Electron
involved, including the stoichiometry [8] and phase composition [9] of precursor powders, deformation processing, wire configuration [10], and final heat treatment parameters [11, 12]. Doping is an effective way to enhance flux pin
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