SEM investigation of the critical current degradation onset in BSCCO-2223 multifilamentary tapes submitted to bending

M. T. MALACHEVSKY; C.D'OVIDIO

SUPERCONDUCTOR SCIENCE AND TECHNOLOGY

Año: 2005 vol. 18 p. 289 - 293

0953-2048

The applicability of superconducting tapes is evaluated employing the definition of an irreversibility strain
irr, attained at a critical current density
irr, attained at a critical current density Jc of 98% of its initial value. Before reaching this limit, the Jc decreases slowly. In order to determine the microstructural changes responsible for this behaviour, we investigated the mechanical response of 19-filament BSSCCO-Ag tapes with different ceramic microstructures, when bent without exceeding
irr. After chemically removing a rectangular-shaped area of the silver sheath to expose the ceramic filaments, the samples were subjected to three-point bending inside an SEM chamber. Thus, we were able to follow the microstructural changes produced by the formation and propagation of cracks at the same time that we recorded on a PC the force versus deflection curves. We identified three different regions representing the response of the tapes to increasing bending. After the elastic region, the pre-existing microstructural faults determined the plastic behaviour. At higher deflections, we measured several stress drops coincident with the observation of micro-cracks that grew slowly across the filaments. Twin samples were employed to control the critical current density decay as a function of the bending deflection introduced at ambient temperature. We investigated the correlation between the bending induced defects and the critical current degradation.c of 98% of its initial value. Before reaching this limit, the Jc decreases slowly. In order to determine the microstructural changes responsible for this behaviour, we investigated the mechanical response of 19-filament BSSCCO-Ag tapes with different ceramic microstructures, when bent without exceeding
irr. After chemically removing a rectangular-shaped area of the silver sheath to expose the ceramic filaments, the samples were subjected to three-point bending inside an SEM chamber. Thus, we were able to follow the microstructural changes produced by the formation and propagation of cracks at the same time that we recorded on a PC the force versus deflection curves. We identified three different regions representing the response of the tapes to increasing bending. After the elastic region, the pre-existing microstructural faults determined the plastic behaviour. At higher deflections, we measured several stress drops coincident with the observation of micro-cracks that grew slowly across the filaments. Twin samples were employed to control the critical current density decay as a function of the bending deflection introduced at ambient temperature. We investigated the correlation between the bending induced defects and the critical current degradation.
irr. After chemically removing a rectangular-shaped area of the silver sheath to expose the ceramic filaments, the samples were subjected to three-point bending inside an SEM chamber. Thus, we were able to follow the microstructural changes produced by the formation and propagation of cracks at the same time that we recorded on a PC the force versus deflection curves. We identified three different regions representing the response of the tapes to increasing bending. After the elastic region, the pre-existing microstructural faults determined the plastic behaviour. At higher deflections, we measured several stress drops coincident with the observation of micro-cracks that grew slowly across the filaments. Twin samples were employed to control the critical current density decay as a function of the bending deflection introduced at ambient temperature. We investigated the correlation between the bending induced defects and the critical current degradation.