Bending strain study of Bi-2223/Ag tapes using Hall sensor magnetometry

The influence of room temperature bending on critical current (Ic) of Bi-2223/Ag tapes is studied by Hall sensor magnetometry, four-point method and scanning electron microscopy. Hall sensor magnetometry allows us to assess tape homogeneity and the amount of mechanical damage caused by bending. The microstructure of the Bi-2223 ceramic is found to strongly affect the tape behavior under bending strain. In a tape with moderate Ic = 6.1 A at 77 K and a porous ceramic core, crack propagation took place normal to the Ag-ceramic interface, whereas in tapes with dense core, Ic above 10 A at 77 K, cracks propagated in the tape plane. In monofilamentary tapes core homogeneity correlated with good bending strain performance. In multifilamentary tapes crack propagation between filaments was prohibited by the Ag matrix, thus leading to enhanced strain tolerance. In the high Ic tapes studied, bending to 25 mm radius resulted in 1%-2% Ic degradation.