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Texture formation in superconducting BSCCO 2212/silver composite tapes: Effects of thermomechanical processing and laser float zone melting.

机译：BSCCO 2212 /银复合超导带中的纹理形成：热机械加工和激光浮区熔化的影响。

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摘要

An essential feature of BSCCO superconductors, required for large critical current densities {dollar}rm (Jsb{lcub}c{rcub}){dollar} is a high degree of crystallographic texture. In particular, since superconductivity occurs in the (001) planes of the orthorhombic unit cell, it is necessary that fabrication processes achieve a texture characterized by (001) planes lying parallel to the plane of conducting tape (c-axis) and thus to the direction of current flow. In addition, many major engineering applications of these new superconducting oxides require these materials to be fabricated in the form of tapes or wires with sufficient flexibility. However, the intrinsic brittleness of these ceramic superconductors imposes major difficulties in processing and bundling, and prohibits the use of conventional forming techniques. This problem, caused by the brittle nature of ceramic superconductors, can be greatly reduced by forming a composite of superconductor and some ductile metal.; In the present study, Bi-2212/Ag composite tapes were fabricated by the doctor blade casting method and then subjected to a thermomechanical process (cold rolling followed by heat treatment), and laser float zone melting process, in order to produce a dense and highly textured microstructure. For the thermomechanical process, the effects of cold rolling and subsequent heat treatment (solid-state sintering) on the texture development and growth of the Bi-2212/Ag composite tapes has been investigated. Experimental measurements of crystallographic texture and microstructure are presented as a function of the degree of deformation by using {dollar}Theta{dollar}-2{dollar}Theta{dollar} X-ray diffraction patterns, X-ray pole figures, and scanning electron microscopy. Based on these results, a mechanism during the cold rolling and heat treatment is suggested. For the laser float zone melting process, the effects of laser processing parameters on the 2212 phase formation and texture evolution of the Bi-2212/Ag composite tapes were studied. In order to analyze this relationship, various processing conditions, such as scanning rate, melted zone temperature, and melted zone width etc., were employed to determine what effect these conditions had on the 2212 phase formation and texture evolution. With these results, a mechanism for the 2212 phase formation from the melt, and texture development during the laser process are proposed. Finally, the deformation induced texture was compared with the texture formed by the laser float zone melting process.; It has been found that, although thermomechanical process yielded a moderate texture, the microstructure of a cold-rolled and solid-state sintered 2212/Ag tape shows the presence of pores and "weakly-linked" grains. Laser float zone melting process, on the other hand, resulted in much better c-axis alignment and a very dense microstructure with "strongly-linked" grains. Details of results, obtained with the above two different processing methods, are reported in this study.
机译：大临界电流密度{rm}（美元）所需的BSCCO超导体的基本特征是高度的晶体织构。特别是，由于超导电性发生在正交晶胞的（001）平面中，因此制造工艺必须获得一种纹理，该纹理的特征在于（001）平面平行于导电带的平面（c轴），因此平行于导电带的平面。电流方向。另外，这些新的超导氧化物的许多主要工程应用要求将这些材料制成具有足够柔韧性的带或线形式。但是，这些陶瓷超导体的固有脆性给加工和成束带来了很大的困难，并阻碍了常规成形技术的使用。由陶瓷超导体的脆性引起的这个问题，可以通过形成超导体和一些韧性金属的复合物而大大减少。在本研究中，Bi-2212 / Ag复合带通过刮刀铸造法制造，然后进行热机械处理（冷轧，然后进行热处理）和激光浮区熔化处理，以产生致密的高度纹理化的微观结构。对于热机械过程，已研究了冷轧和后续热处理（固态烧结）对Bi-2212 / Ag复合带织构发展和生长的影响。通过使用{美元} Theta {dollar} -2 {dollar} Theta {dollar} X射线衍射图，X射线极图和扫描电子，给出了晶体织构和微观结构的实验测量结果，作为变形程度的函数。显微镜检查。基于这些结果，提出了冷轧和热处理的机理。对于激光浮区熔化过程，研究了激光加工参数对Bi-2212 / Ag复合带的2212相形成和织构演变的影响。为了分析这种关系，采用了各种加工条件，例如扫描速率，熔融区温度和熔融区宽度等，以确定这些条件对2212相形成和织构演变有什么影响。利用这些结果，提出了一种由熔体形成2212相的机理，以及在激光加工过程中形成织构的机理。最后，将变形引起的织构与激光浮区熔化过程形成的织构进行比较。已经发现，尽管热机械过程产生适度的织构，但是冷轧和固态烧结的2212 / Ag带的微观结构显示出孔和“弱连接”晶粒的存在。另一方面，激光浮区熔化过程导致更好的c轴对准和具有“强链接”晶粒的非常致密的微观结构。通过上述两种不同的处理方法获得的结果的详细信息报告在这项研究中。

著录项

  • 作者

    Oh, Ilsung.;

  • 作者单位

    Michigan State University.;

  • 授予单位 Michigan State University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1995
  • 页码 173 p.
  • 总页数 173
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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