THE FRACTURE-BEHAVIOR OF (BI,PB)(2)SR2CA2CU3O10+X POLYCRYSTALS CLAD WITH SILVER SHEETS

Mechanical deformation including rolling and pressing is widely used t o produce grain-aligned BSCCO superconductors. However, the microstruc tural changes of the polycrystalline superconductors and the fracture behaviours of the Bi2223 oxide have not been clearly understood. The p resent work investigates the deformation and fracture behaviours of th e silver clad Bi2223 compound. The results indicate that the randomly aligned crystals cleave and slip along the a-b plane. and rotate to th e rolling plane, forming a-b plane aligned texture microstructure. The results also indicated that the deformation behaviours under high or low deformation rates are quite different. Under a medium or high mech anical deformation, multi-step deformation feature has been observed i n many crystals, which is believed to result from sliding along the a- b planes of the Bi2223 compound. With a low deformation ratio. the com pressive force is not large enough to cause fracture of the Bi2223 cry stals. The dominant deformation feature is the sliding of the top laye rs on the crystals, which is believed to result from the plastic defor mation of Ag sheet. This understanding is useful in controlling the mi crostructure of high temperature superconductors in order ttl improve their properties. (C) 1998 Elsevier Science B.V.