Alignment and microstructural evolution in melt-processed Ag-clad Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} high {Tc} superconducting tape
The goal was to understand the behavior of non-superconducting phases and the development of alignment during melt processing so as to be able to develop a processing schedule that achieved a highly-aligned, homogeneous 2212 microstructure in fully-processed tape. During melt processing the 2212 phase melts incongruently into liquid, (Sr{sub 1-x}Ca{sub x})CuO{sub 2} (1:1) and Bi(Sr{sub 1-x}Ca{sub x}){sub 2}O{sub y} (Cu-free) phases and forms from the melt on cooling. Four distinct phase assemblages were observed in the melt between 869 and 921{degrees}C. It was found that the grain size of the Cu-free phase is minimized when tape is processed below 895{degrees}C. The 1:1 grain size can be reduced with extended annealing just below 865{degrees}C. 2212 alignment was quantified using the Dominant Orientation technique in which the length and orientation of individual grains were measured. The highest alignment was achieved by annealing just below the 2212 solidus temperature (870{degrees}C). An alignment mechanism based on grain growth of fortuitously aligned, plate-like 2212 grains within a mostly two-dimensional environment (Opportunistic Grain Growth) was proposed to explain the high alignment that can develop a melt-processed tape. Based on the non-superconducting phase and alignment data from this study, a heat treatment that used step-wise cooling (Step-Solidification) was developed yielding a microstructure consisting of highly-aligned 2212 and small non-superconducting grains.
- Research Organization:
- Wisconsin Univ., Madison, WI (United States)
- OSTI ID:
- 106971
- Country of Publication:
- United States
- Language:
- English
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