Characterization of edge damage induced on REBCO superconducting tape by mechanical slitting

Abstract

Rare-earth barium-copper-oxide (REBCO) superconductors are high-field superconductors fabricated in a tape geometry that can be utilized in magnet applications well in excess of 20 T. Due to the multilayer architecture of the tape, delamination is one cause of mechanical failure in REBCO tapes. During a mechanical slitting step in the manufacturing process, edge cracks can be introduced into the tape. These cracks are thought to be potential initiation sites for crack propagation in the tapes when subjected to stresses in the fabrication and operation of magnet systems. We sought to understand which layers were the mechanically weakest by locating the crack initiation layer and identifying the geometrical conditions of the slitter that promoted or suppressed crack formation. The described cracking was investigated by selectively etching and characterizing each layer with scanning electron microscopy, laser confocal microscopy, and digital image analysis. Our analysis showed that the average crack lengths in the REBCO, LaMnO3 (LMO) and Al2O3 layers were 34 μm, 28 μm, and 15 μm, respectively. The total number of cracks measured in 30 mm of wire length was between 3000 and 5700 depending on the layer and their crack densities were 102 cracks mm−1 for REBCO, 108 cracks mm−1 for LMO, and 183 cracks mm−1 for Al2O3. These results indicated that there are separate crack initiation mechanisms for the REBCO and the LMO layers, as detailed in the paper. With a better understanding of the crack growth behavior exhibited by REBCO tapes, the fabrication process can be improved to provide a more mechanically stable and cost-effective superconductor.

Numerical analysis of the mechanical and electrical properties of (RE)BCO tapes with multiple edge cracks

“…However, a severe problem is the microcracks induced during this process. Random micro-cracks at the edges were observed with the help of SEM [21,23]. These cracks have a minimal size and oblique angle and are mainly distributed in the (RE)BCO layer.…”

“…The length and angle of the oblique cracks on the edge of the (RE)BCO layer vary erratically [21,23]. A parametric crack model was developed to overcome the limitations of the theoretical solution and consider the interaction between cracks comprehensively, as shown in figure 10.…”

“…As a fundamental verification of the above results, SCS6050 tape manufactured by SuperPower ® Inc. is used for destructive tensile experiments. Based on current observations of microscopic photographs of cracks [21,23], conducting experiments with realistic crack parameters to study the interaction between cracks is challenging due to difficulties in both sample preparation and experimental process supervision. For this reason, the tensile experiments in this paper qualitatively investigate the effect of crack geometry and crack geometric mutation on crack propagation at the macroscopic scale [29].…”

“…Several recent studies have been carried out to describe the geometry and distribution pattern of the edge cracks in (RE)BCO tapes. Hartnett et al [23] quantified the density and length of the edge cracks inside the tape by scanning electron microscopy (SEM) and scanning laser confocal microscopy. One result is that micro cracks with varying lengths and angles are scattered in the (RE)BCO layer and the adjacent buffer layer (Al 2 O 3 ).…”

Enhancement of electro-mechanical behaviors in RE–Ba–Cu–O composite superconducting tapes with laser slit edges

“…In order to improve production efficiency and reduce cost, 2G-HTS tapes are commonly fabricated at a certain width, such as 10 mm, 12 mm, and even 40 mm. Prior to the end products, the 2G-HTS tapes are slit to typically 4 mm width, sometimes other width, between 1 and 6 mm for various applications [9].…”