Intrinsic deformation behaviour in pressed Bi-Sr-Ca-Cu-O tapes

Abstract

It was reported that the critical current density of superconducting tapes can be improved using cryogenic processing. The present paper studies the intrinsic grain alignment characteristics of cryogenically pressed and room-temperature-pressed Bi-Sr-Ca-Cu-O tapes. The grain alignment mechanisms of the two processed tapes were found to be different. The cryogenically pressed tapes showed a step-like increase in grain alignment at approximately 30% deformation, while the increase in grain alignment for the room-temperature-pressed tapes was gradual. The results indicate that the behaviour is reproducible and independent of annealing time and therefore, intrinsic to the deformation steps of each process. The effects of deformation on the alignment are suggested to occur due to two factors:(1) the point at which fracturing of the grains occurs and (2) rotation or movement of these grains into the preferred alignment. The differences observed between the two processes are due to the combined effects of these two factors. The significance of this study is that better grain alignment can be achieved in cryogenically pressed tapes at lower deformation ratios.