Note: Effective measurement of retained <i>I</i>c in evaluating electromechanical properties of high temperature superconductor tapes by the voltage tap clipping technique

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Development of a coated conductor tape joint with good quality and low joint resistivity, Rsj, in terms of transport and mechanical properties, was attempted by direct bonding at the interface of the Cu–Cu stabilizers in overlapped GdBCO CC tapes. In this study, we attempted to achieve a low Rsj by introducing hybrid joining, soldering and ultrasonic welding (UW), and its mechanism was analyzed theoretically. Coated conductor tapes were experimentally joined using various methods of soldering, UW, and combinations of the two. As a result, a much lower Rsj of about 57 nΩ · cm2 was obtained for RCE-DR-processed GdBCO CC tape joints using the hybrid joining method. The mechanical properties of the jointed CC tapes were also evaluated at room temperature and 77 K under self-field. Load–displacement curves of joined CC tapes followed the curve of the single CC tape. Critical current and joint resistance, Rj, of hybrid-joined CC tape were retained after double bending at room temperature up to 20 mm bending diameter.

Section: Double-bending Test Results At Rtmentioning

confidence: 99%

Pursuing low joint resistivity in Cu-stabilized REBa₂Cu₃O_δcoated conductor tapes by the ultrasonic weld–solder hybrid method

Shin¹,

Kim²,

Dedicatoria

2015

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“…When UW CC bridge-joints are fabricated, no I c degradation should occur, and the R j should be as low as possible so that the cooling capacity needed to counteract the resistive Joule heating in the stacked HTS coils is minimized. Measurement of retained I c in the CC joints were done using a technique employing a Cu voltage tap clipping method, as shown in figure 5(b) [19] where the CC joints were gripped between the Cu terminal blocks of the sample holder and each pair of Cu voltage clips was attached to the sample 5 mm away from the opposing ends of the joint. The retained I c of CC joints was measured at 77 K and self-field with an electric field criterion of 1 µV cm −1 .…”

Section: Joint Resistance Measurement and Tensile Bending Test Methodsmentioning

confidence: 99%

Joint characteristics of ultrasonic welded CC bridge joints for HTS coil applications

Shin

Jung

Nisay

2020

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Long lengths of second-generation REBCO coated conductor (CC) tapes must be joined together when power cables, coils, and magnets requiring kilometer-scale lengths are fabricated. Various resistive joining techniques of CC tapes, such as soldering and diffusion reaction, have been studied. The joint method should provide good adhesion, low joint resistance (R j), no critical current (I c) degradation, cost effectiveness, and simplicity in processing. An ultrasonic welding (UW) process was developed and used to form various types of CC joint structures, such as lap- and butt-joints, using differently stabilized REBCO CC tapes. In this study, the UW process was used to form various bridge-joints of CC tapes for high-temperature superconducting coils. A mechanical-controlled soldering method which has provided a low contact resistance was also adopted for comparison. CC joints of various structures were fabricated using UW and soldering, and the retained I c and R j were measured at 77 K and self-field in each. The electromechanical properties of the CC bridge-joints were evaluated using a bending test. Results showed that R j varied in the CC joints depending on the structure type and joint area. Moreover, the additional Sn layer in Cu-stabilized CC tapes improved R j in each joint structure because it provided a solder-like bond at the joint interface. The bridge-joints formed using UW showed comparable bending diameter tolerances for irreversible I c degradation to those formed using mechanically controlled soldering. The multiple 4 mm wide CC bridges provided more flexibility at the joint part due to gaps between bridges and resulted to a better tolerance to tension bending than the single 12 mm wide ones.

“…Our previous studies described the details [19,36,37]. The four-probe method with voltage clipping was used to measure the R j of CC joints fabricated by various methods at 77 K and to determine whether I c degradation occurred after the joining processes [47,48]. The voltage clips were located 5 mm from both ends of the joint part, allowing a complete current transfer during the measurements.…”

Section: Joint Fabrication and Electrical Measurementmentioning

confidence: 99%

Performance characteristics of REBCO coated conductor joints fabricated by flux-free hybrid welding

Nisay,

Shin

2023

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Recently, the joining of rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes using ultrasonic welding (UW) has demonstrated outstanding potential in the in-line fabrication of longer tapes required for superconducting device applications. The UW method can produce CC joints by applying ultrasonic vibration in less than one second, and hybrid welding (HW) has been adopted to improve further the joint resistance (Rj) and electromechanical properties of the UW CC joints. However, conventional methods for preparing the HW and soldered CC joints involve applying solder flux to remove the oxide film, which can cause corrosion to the surface of the CC tapes and affect the joint's lifespan during device operation. Therefore, this study aims to fabricate a robust HW CC joint of pre-solder insertion without solder flux and compare its joint strength and electromechanical properties with the traditional cases with the solder flux. While similar Rj can be obtained from both cases of HW CC joints, the flux-free HW CC joint has slightly higher joint strength and superior adhesive characteristics than those with flux. The difference in fracture mechanisms after lap-shear and T-peel tests between flux-free HW and with flux was extensively discussed. Additionally, the study investigates the correlation between a decrease in Rj with longer joint length in differently stabilized and processed CC tapes for flux-free HW. Overall, this study demonstrated that the flux-free HW method could efficiently produce robust CC joints with a lesser risk of corrosion and enhanced joint characteristics.