Effect of Bending Before Annealing on Current-Carrying Properties of Iron-Based Superconducting Tapes

The iron-based superconductor (IBS) is a good candidate for high field magnet applications. The bending effect and properties of IBS tapes were systematically investigated in this work. The bent Ba
_1-x
K
_x
Fe
₂
As
₂
(Ba122/Ag/AgSn) 7-filamentary tapes with different bending diameters (D = 10, 15, 20, 25, 30 mm) were prepared by bend-and-react method. A special mechanical structure was used to prevent the heat-treated IBS tapes from being damaged during joint soldering and performance test. The critical current (
I
_c
) performances of all the bent samples have been tested at 4.2 K and 6-10 T. When the bending diameter is smaller than 30 mm, the transport
I
_c
of bent IBS tapes decreases with smaller bending diameters. The average ratio of
I
_c
(bent tape) and
I
_c
(straight tape) was also calculated. The Optical Microscope Images (OMI) show a lot of cracks that appear regularly in the outermost superconducting core away from the bending center, especially in D10 bent IBS tapes. The magnitude, type, and distribution of the stress in the bent tapes during the bending process were simulated and compared. The causes of the crack formation and the
I
_c
reduction in bent IBS tapes were also discussed in detail.