Cryogenic deformation process of high temperature superconductors

A cryogenic deformation process has been developed and investigated for use in the processing of Ag/Bi-Pb-Sr-Ca-Cu-O superconducting wires. A typical cryogenic deformation process used comprised rolling or pressing the wires into tapes at 77 K and then heat treating the tapes at 838- for a period of 40-60 h. It was found that the cryogenic deformation improved the density, grain alignment, Ag/oxide core interface and critical current density. Critical current densities for cryogenically rolled and pressed Ag-clad mono- and multifilamentary tapes showed a 10 to 20% increase over those observed in normal processed tapes. In comparison with hot deformation and processed tapes, the cryogenic processed tapes showed improved flux pinning capability whereas the hot deformation was found to only improve weak links. During cryogenic deformation, the hardness of the silver sheath was significantly increased, which allowed a greater pressure to be applied during the deformation process. This large pressure was found to be the principal cause of the enhanced densification, texturing and increased dislocation densities.