Control of core structure in MgB2 wire through tailoring boron powder
Control of core structure in MgB2 wire through tailoring boron powder
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DOI：
10.1016/j.jallcom.2015.02.151
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发表时间：
2015-07
影响因子：
6.2
通讯作者：
M. Maeda;D. Uchiyama;S. A. Hossain;Zongqing Ma;M. Shahabuddin;Jung Ho Kim
中科院分区：
文献类型：
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作者：
M. Maeda;D. Uchiyama;S. A. Hossain;Zongqing Ma;M. Shahabuddin;Jung Ho Kim
一种常见的制备镁B2线材的工艺，即管内粉末法，在线芯内形成大量的空洞，空洞的形成是无法完全避免的。然而，当使用韧性粗镁粉作为前驱体时，取向或多或少地沿电流流动方向排列，进一步的定制方法可能为提高传输临界电流密度开辟道路。在这里，我们使用了不同粒度的硼粉，结合粗大的镁粉，评估了它们的尺寸对相组成、微观结构和传输性能的影响。粗大的镁粉和大尺寸的硼粉在线芯中混合，经过冷加工和烧结，形成颗粒状。相反，在用细小的硼粉制备的线材的还原过程中，出现了取向的核心。在烧结过程中，特别是在镁几乎不会蒸发的低温下，会产生沿丝方向取向的结构，主要由MgB2相组成。这些发现表明，起始材料的初始尺寸对于定制结构至关重要。
A common fabrication process for MgB2wire, namely, thein situpowder-in-tube process, forms numerous voids within the wire core, and void formation cannot be completely avoided. The orientation is, however, known to be aligned more or less along the current-flow direction when ductile coarse magnesium powder is used as a precursor, and further tailoring approaches could open up the way to improving the transport critical current density. Herein, we have used boron powders with different particle sizes, in combination with the coarse magnesium powder, and evaluated their size effects on the phase composition, microstructure, and transport properties. A mixture of the coarse magnesium powder with large-sized boron powder in the wire core, after cold working and sintering, forms a granular morphology. In contrast, an aligned core appears during the reduction process for wire which is prepared by using fine boron powder. The sintering process, especially at a low temperature, where magnesium evaporation hardly occurs, yields an aligned structure, mainly consisting of MgB2phase, along the wire direction. These findings demonstrate that the initial size of the starting materials is critical for the tailored structure.