Strain effects in high temperature superconductors investigated with magneto-optical imaging

Abstract

Abstract-In order to determine the influence of intermediate deformation steps on the mechanical behavior of Bi-based tapes, the effect of longitudinal applied strain is investigated by means of magneto-optical imaging. The strain is applied in a helium flow-cryostat. Cracks appear soon after the critical current in Bi-based tapes is degraded. All filaments form multiple cracks that grow into tape-wide cracks, running from one filament to the next. The crack location is not caused by stress concentrations in the matrix, but by the mechanically weak colony boundaries. Because of the absence of intermediate rolling steps in the production of Bi 2 Sr 2 CaCu 2 O tapes, a different crack structure is observed compared to Bi 2 Sr 2 Ca 2 Cu 3 O tapes. The relation between the critical current and the formation of cracks is studied. The degradation in critical current before the critical strain is reached may be caused by microcracks that remain undetected by magneto-optical imaging. The influence of strain on the microstructure of YBa 2 Cu 3 O coated conductors is also investigated with magneto-optical imaging. The formation of cracks is believed to be determined by the nickel substrate and related to the Ni-grain size.

Effect of tensile strain on grain connectivity and flux pinning in Bi2Sr2Ca2Cu3Ox tapes

“…8 The sample was zero-field cooled to 30± 1 K on the cold finger of a helium flow cryostat. An external magnetic field of 25 mT ͑2% accuracy͒ was applied perpendicular to the surface of the tape to visualize the spatial variation in critical current density of the filaments.…”

Distribution of normalized critical current of bent multifilamentary Bi2223 composite tape

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Under no applied strain, the critical current is different from specimen to specimen and from position to position within a specimen. [18][19][20][21][22][23][24] Under applied strain, the damage evolution behavior is also different from specimen to specimen and from position to position within a specimen, resulting in wider distribution of critical current.…”

Limits to the critical current inBi2Sr2Ca2Cu3OxLaan1, Schwartz2, Haken3 et al. 2008Phys. Rev. BSelf Cite230140View full textAdd to dashboardCite

“…It has been shown that transport current in high-quality Bi-2223 tapes flows in part along pathways where grain boundaries form no significant barrier and where dissipation occurs within the grains. [20][21][22][23] The grains that make up this strongly linked backbone are connected at angles smaller than about 4°. Apart from this backbone, a number of other current paths also contribute to the overall critical current of the tape.…”