Magneto-optical and electromagnetic studies of core connectivity and weak-link behaviour in Cu/MgB2 and Ni/MgB2 wires and tapes
Magneto-optical and electromagnetic studies of core connectivity and weak-link behaviour in Cu/MgB2 and Ni/MgB2 wires and tapes
复制标题
Cu/MgB2 和 Ni/MgB2 线材和带材中芯连接性和弱连接行为的磁光和电磁研究
DOI：
10.1088/0953-2048/17/3/013
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发表时间：
2004
影响因子：
3.6
通讯作者：
E. Hellstrom
中科院分区：
文献类型：
--
作者：
A. Polyanskii;V. Beilin;I. Felner;M. Tsindlekht;E. Yashchin;E. Dul’kin;E. Galstyan;M. Roth;B. J. Senkowicz;E. Hellstrom
利用临界电流密度、交流磁化率（实部）和磁光成像（MO）对预反应MgB2粉末制成的圆线和带进行了表征。磁化率测量表明，变形后的Ni/MgB2和Cu/MgB2导线和带芯中存在大规模的弱链网络。作为带芯薄弱环节的证据，as -变形样品显示了两步过渡。变形带的第一次热处理（HT）导致了急剧的磁化率转变，带芯中的连接非常强，如MO图像所示，以及高临界电流。第二次轧制烧结带，在脆芯中形成缺陷网络，并导致曲线展宽，但没有导致两步转变。这些数据表明，变形引起的裂缝不是弱连接行为的主要来源。在该样品中也记录了传输电流的大量减少。第二次高温持续30分钟，恢复了剧烈的磁跃迁和高输运电流。在MO图像上观察到带芯中强弱连接的交替区域。在最高温度下，对变形带进行快速加热和冷却，不需要停留时间，从而产生具有急剧转变和传输电流增加的牢固连接芯。快速高温处理后，MO图像未见机械缺陷。这种快速转变可以用高应变MgB2晶粒的快速烧结来解释。
Critical current density, ac susceptibility (real part ) and magneto-optical (MO) imaging were used to characterize round wire and tapes made from pre-reacted MgB2 powder by the powder-in-tube method. Magnetic susceptibility measurements indicated the existence of large-scale weak-link networks in the cores of as-deformed Ni/MgB2 and Cu/MgB2 wires and tapes. As-deformed samples showed a two-step transition in versus T traces as evidence of weak links in the tape core. The first heat treatment (HT) of as-deformed tapes led to a sharp susceptibility transition, very strong connection in the tape core as seen in MO images, and high critical current. A second rolling of an as-sintered tape induced a network of defects in the brittle core and gave rise to curve broadening, but did not result in a two-step transition. These data show that deformation-induced cracks are not the primary source of weak-link behaviour. A large decrease in transport current was also registered in this sample. The second HT, for 30 min, restored the sharp magnetic transition and high transport current. Alternating areas of strong and weak connection in the tape core have been observed on MO images. Fast heating and cooling of the as-deformed tape with no dwell time at the maximum temperature resulted in a strongly linked core with a sharp transition and increased transport current. After fast HT, no mechanical defects were observed in MO images. Such fast transformation could be explained by rapid sintering due to highly strained MgB2 grains.