Speaker
Dr
Amir Kajbafvala
(Materials Science Center, University of Wisconsin-Eau Claire)
Description
High temperature superconductors (HTS) are an enabling technology for superconducting magnets generating magnetic fields greater than 25 T. The development of high field HTS magnets requires not only a conductor capable of carrying sufficient critical current density (Jc) at high magnetic field, but also one that is sufficiently strong to withstand the very large Lorentz forces and other stresses during fabrication, handling, and thermal cycling. Bi2Sr2CaCu2O8+x (Bi-2212) is the only HTS material available as round wire. Recently, significant progresses have been made to improve the Jc of Bi-2212 wire by use of over-pressure (OP) processing of the wire during heat treatment. This method has resulted in a more than doubling of the Jc of the wire to 640 A/mm2 at 4.2 K and 20 T. However, since Bi-2212 is a brittle material, the effect of these heat treatment changes on the mechanical properties of the material are not well understood.
In this study, a double-restack Bi-2212/AgMg wire was heat treated using a partial melt processing in both pure O2 and Ar/O2 atmosphere at various pressures including 1 bar, 50 and 100 bar (OP). The wires then experienced various amount of mechanical strains in both tension and compression. The Bi-2212 wire properties are investigated in various conditions, including green wire, 1 bar and OP-heat treated wires pre- and post-applying mechanical strains. A detailed and efficient polishing procedure is developed to prepare scratch-free specimens and to prohibit introducing filament damages caused during preparation method. The relationships between sample preparation techniques and the filament microstructure, distribution of secondary phases including AEC and Cu-free, and various filament damages are studied using optical, scanning electron and confocal microscopy.
*This work was supported by the DOE Award DE-FG02-13ER42036.*
Author
Dr
Amir Kajbafvala
(Materials Science Center, University of Wisconsin-Eau Claire)
Co-authors
Mr
Gavriel Lev DePrenger-Gottfried
(Materials Science Center, University of Wisconsin-Eau Claire)
Mr
James E. McFarlane
(Materials Science Center, University of Wisconsin-Eau Claire)
Prof.
Matthew C. Jewell
(Materials Science Center, University of Wisconsin-Eau Claire)
Ms
Sarah V. Sortedahl
(Materials Science Center, University of Wisconsin-Eau Claire)
