Improvement of the fracture toughness and trapped field of bulk high temperature superconductors by controlling the microstructure

通过控制微观结构提高块体高温超导体的断裂韧性和俘获场

基本信息

批准号：
12650012
负责人：
IKUTA Hiroshi
金额：
$ 2.11万
依托单位：
Nagoya University, Associate Professor, Research Associate
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

The superconducting properties of bulk high temperature superconductors, such as the trapped field, had already reached a very high level. However, it has been commonly observed that the samples are easily broken by the magnetic pressure of the trapped fluxes or by an abrupt heat cycling. The microstructure of melt processed.bulk superconductors is influenced by the contents of each phase as well as by the preparation condition, which in turn affects the fracture toughness. Therefore, we prepared samples by varying the composition and preparation condition, and examined the microstructure and the fracture toughness. The major results are summarized in the following.We succeeded in the preparation of a single-grain, c-axis aligned, Nd-based bulk superconductor that is 30 mm in diameter for the first time. The trapped field was larger than that of a Sm-based sample that contains the same amount of Ag. We also studied the relation between the atmosphere during the melting and the formatio … More n of voids, and succeeded in the elimination of voids by melt-processing the samples in an oxygen-gas flowing atmosphere or vacuum. It was also confirmed that the samples show high performance if the atmosphere were switched to an Ar-gas flowing one during the growth process. The average particle size of the Sm211 phase in a sample prepared with 211-phase powders that were treated with ball-milling was 0.7 ^m, and the trapped field increased compared to samples prepared with the same condition using 211-phase powders that were not ball-milling treated.We also studied the oxygenation process of Sm- and Y-based samples to establish an efficient oxygen treatment for dense samples. It was found that the diffusivity of oxygen is influenced by the difference in the microstructure rather than the difference of the system, Ag-added samples require a longer oxygen treatment because of the less amount of voids, and a low temperature treatment below 350aC is important for Sm-based samples. We established the melt-processing conditions of the Nd-Eu-Gd system up to 36 mm in diameter, for which the trapped field was 1.4 T at liquid nitrogen temperature and 8.2 T at 20 K. For the Dy-based system, the trapped field reached 5.7 T at 18 K even with a small sample whose diameter was 18 mm, and the trapped field of a CeO2-added Y-based sample that is 18 mm in diameter reached 6.2 Tat25K. Less

大量高温超导体（例如被困场）的超导特性已经达到很高的水平。但是，通常观察到，样品很容易被捕获通量的磁压或突然的热循环打破。熔体加工的微观结构。Bulk超导体受到每个阶段的内容以及制备条件的影响，从而影响断裂韧性。因此，我们通过改变组成和制备条件来制备样品，并检查了微结构和断裂韧性。主要结果总结在以下内容中。我们成功地制备了单个元素，C轴对准，基于和基于ND的散装超导体，直径为30 mm。被困的场大于包含相同数量Ag的基于SM的样本的场。我们还研究了熔化和格式化的大气之间的关系……更多的空隙，并通过在流动大气或真空吸尘器中融化样品来成功消除空隙。还可以证实，如果在生长过程中将大气切换为流动的AR-GA，则样品表现出很高的性能。用211期粉末制备的样品中SM211相的平均粒径为0.7 ^m，与使用未经球磨相同的样品制备的样品相比，被捕获的领域增加了。发现氧气的难度受微观结构的差异而不是系统差异的影响，由于空隙量较小，因此Ag添加的样品需要更长的氧处理，而低于350AC的低温处理对于基于SM的样品很重要。我们建立了直径不高达36毫米的ND-EU-GD系统的融化处理条件，在液态氮温度下，被困的场为1.4 t，在20 K时为20K。对于基于DY的系统，被困的磁场在18 K处达到5.7T。 tat25k。较少的