METAL-CERAMIC INTERFACE RESPONSE TO BENDING AND FATIGUE CYCLES IN SUPERCONDUCTING AG-BI2223 COMPOSITES

M.T. MALACHEVSKY; D.A. ESPARZA

PHYSICA C - SUPERCONDUTIVITY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1999 vol. 324 p. 153 - 160

0921-4534

Bending cycles in superconducting composites lead to degradation of their transport properties. We had studied this effect on Ag-Bi2223 composites, in the form of tapes with 1, 7 and 19 ceramic filaments. The samples were subjected to increasing bending-straightening strains, measuring the critical current density Jc at 77 K, 0 T after each cycle, in order to determine the maximum allowed strain (max) before degradation of the Jc occurs. Fatigue tests were performed by cycling the tapes on bending to a fixed radius. For this purpose, two mandrels with different diameters were selected: one resulting in strains  < max and the other in  > max . The behavior of Jc as a function of the number of cycles was observed for the three composites, indicating that multifilamentary tapes withstand cycling better. As the transport properties in composite superconductors are mainly characterized by their metal-ceramic interface, the silver sheath was chemically removed after the last cycle to investigate the interfacial microstructure. The exposed ceramic was observed with a SEM to identify the crack formation mechanism: mainly intergranular cracks in the face subjected to tension and transgranular cracks in the face subjected to compression.