Rules of non-superconducting phase particles on crack propagation in YBCO coated conductors fabricated by the IBAD-MOCVD

Shen, Lei; Liu, Cong; Zhang, Xingyi

doi:10.1088/1361-6668/abad86

“…The slits or cracks caused by manufacturing process can weaken the delamination strength. And the experimental results show that the delamination can cause the cracks in the REBCO layer of CC [59], and the appearance of cracks in the REBCO layer may be one of the major reasons for the performance degradation. Based on the above conclusions, we assume that the performance degradation of coils can be positively associated with the extent of delamination in the coils and the number of cracks in the REBCO layer.…”

Section: Effects Of Electromagnetic Forces and Initial Localized Dama...mentioning

confidence: 99%

3D numerical investigation on delamination behavior of the epoxy impregnated REBCO pancake coil

Shen,

Chen,

Peng

et al. 2023

Supercond. Sci. Technol.

3

0

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Superconducting coils made of Rare-Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) exhibit superior electromagnetic performance. Employing epoxy impregnation can improve the structural integrity and mechanical property of the superconducting coils. However, due to the extreme work environment and weak adhesion strength of REBCO CC, the delamination induced by radial thermal stress and electromagnetic force significantly affects the electromagnetic property and the reliability of the superconducting coil. This study proposes a three-dimensional (3D) thermal-electromagnetic mechanical delamination model that incorporates the cohesive zone model (CZM) to investigate the delamination mechanisms in epoxy impregnated REBCO pancake coils during the cooling and coil operation processes. The simulation employs a three-parameter Weibull distribution to account for the inhomogeneity of transverse tensile strength in the CCs. The delamination behavior and mechanisms of the coils under different conditions are analyzed. The simulation results show that the model considering random adhesion strength proves to be more effective in representing the delamination behavior of the coil. And large tensile radial stresses caused by thermal stresses and electromagnetic forces lead to the delamination behavior of the coil during cooling and operation. The main reason for the tensile radial stress is the mismatch in the thermal contraction among components of the coils during cooling process. Furthermore, we investigate the influence of the thermal expansion coefficient (CTE) and thickness of the mandrel, the CTE and prestress of the overband and the initial localized damage. The results indicate that these factors significantly affect the tensile radial stress and the extent of delamination in the windings. And the extent and distribution of delamination is related to the stress release caused by delamination to a certain degree.

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“…One of the most serious technical problems is the degradation of REBCO performance observed after tape cabling, or during the winding of a magnet or in its operation. In these circumstances, mechanical loads often cause irreversible damage to the brittle REBCO layer [15][16][17][18]. Defects in the REBCO layer lead to critical current reduction and consequently to a decrease in the current transmission capacity of the cable.…”

Section: Introductionmentioning

confidence: 99%

Effect of off-axis bending on microstructural and transport properties of coated conductor tape

Ries¹,

Gömöry²,

Mosat³

et al. 2022

Supercond. Sci. Technol.

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In this work, the changes of microstructural and DC transport properties of coated conductor tape, deformed in helical form during manufacturing of a round cable, were studied. Superconducting layer experienced both outward (“OUT”) and inward (“IN”) bending with respect to the round core (rod) at various lay angles and former diameters. The microstructure of the REBCO surface was observed by using SEM. Direct transport measurements in liquid nitrogen were used to investigate the influence of bending parameters on DC transport properties. In “OUT” configuration, the cracks on the REBCO surface were formed at diameter of 9 mm and less at lay angle of 45°. The critical current of the tape started to degrade at diameter of 10 mm and less. The investigation showed that the cracks are formed in direction following the rod axis. In “IN” configuration, the measurements were performed at lay angles: 25°, 30°, 38°, 45°, 52° and 60°. The highest critical current retention and the lowest damage on the REBCO layer were observed at a lay angle of 30°, in particular: the critical current visibly degraded at diameter as small as 3 mm, and defects were visibly observed at diameter of 2 mm. At higher lay angles than 30°, the critical current degraded sooner (at higher diameters) and increased density of defects in the form of “protrusion lines” was observed. We found that protrusion lines followed preferential cleavage direction in approx. 80° to the tape length, independently on the lay angle used. By using a lower lay angle than 30°, the critical current degraded sooner, although no protrusion lines were observed, but the cracks were formed at the tape edges. For both bending configurations, the lower former diameters led to higher density of defects on the REBCO surfaces accompanied by degradation of superconducting properties.

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“…As the GdBCO superconducting film is located close to the neutral axis, it is better to be used in winding [20]. Zhang et al [24,25] found that with the increase in tensile strain, cracks first appeared in the YBCO layer on the side close to the buffer layer firstly and then expanded to the side close to the silver layer, pointing out the potential direction for improving the CC tension tolerance by improving the elastic properties or changing the elastic states of substrates of CCs.…”

Section: Introductionmentioning

confidence: 99%

Controllable rectification on the irreversible strain limit of 2G HTS coated conductors

Su

¹

,

Huang

²

,

Liu

³

et al. 2021

Supercond. Sci. Technol.

Self Cite

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The second generation high-temperature superconducting coated conductors (CCs) have excellent electrical and mechanical properties, and are extensively used in superconducting devices such as fault current limiters, magnets and motors. During the operation of these superconducting devices, superconducting CCs inevitably bear the combination of electromagnetic force and thermal mismatch stress, resulting in straining of YBa2Cu3O7− δ (YBCO) layer along the tape length. It is well known that the strains of superconducting CCs cause degradation of critical current (I c). Generally, the irreversible strain limit ( ε irr ) is used to characterize the phenomenon that I c of superconducting CCs degrades with axial strain. When the axial strain of superconducting CCs is less than ε irr , I c can be reversibly recovered by over 99% after being unloaded. Therefore, ε irr is a key parameter for the design and application of superconducting CC devices. For this reason, to carry out a practical engineering method for improving ε irr of superconducting CCs has become a challenge and aroused interests among researchers. This study is based on the idea of precompression. A 316LN stainless steel tape was pretensioned at 77 K to improve its elastic strain limit. Then, two superconducting CCs were soldered onto both surfaces of pretensioned stainless steel tape respectively. As a result, ε irr of the superconducting CCs can be controlled manually with different precompressions. Taking YBCO CCs produced by SuperPower Inc. as an example, the measurement results show that the ε irr of the YBCO CCs increased from 0.39% to 0.73%. Meanwhile, the thickness of the sample did not increase more than once.

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Rules of non-superconducting phase particles on crack propagation in YBCO coated conductors fabricated by the IBAD-MOCVD

Cited by 7 publications

References 38 publications

3D numerical investigation on delamination behavior of the epoxy impregnated REBCO pancake coil

3D numerical investigation on delamination behavior of the epoxy impregnated REBCO pancake coil

Effect of off-axis bending on microstructural and transport properties of coated conductor tape

Controllable rectification on the irreversible strain limit of 2G HTS coated conductors

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