The fracture behaviour of (Bi,Pb)2Sr2Ca2Cu3O10+x polycrystals clad with silver sheets

Mechanical deformation including rolling and pressing is widely used to produce grain-aligned BSCCO superconductors. However, the microstructural changes of the polycrystalline superconductors and the fracture behaviours of the Bi2223 oxide have not been clearly understood. The present work investigates the deformation and fracture behaviours of the silver clad Bi2223 compound. The results indicate that the randomly aligned crystals cleave and slip along the a-b plane. and rotate to the 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 mechanical deformation, multi-step deformation feature has been observed in many crystals, which is believed to result from sliding along the a-b planes of the Bi2223 compound. With a low deformation ratio. the compressive force is not large enough to cause fracture of the Bi2223 crystals. The dominant deformation feature is the sliding of the top layers on the crystals, which is believed to result from the plastic deformation of Ag sheet. This understanding is useful in controlling the microstructure of high temperature superconductors in order ttl improve their properties. (C) 1998 Elsevier Science B.V.