Mechanism of deformation and ''sandwich'' rolling process in Ag-clad Bi-based composite tapes

The mechanism of deformation was studied by stress-strain state analysis in Ag-clad Bi-based superconducting composite tapes prepared by the powder-in-tube method. The sausaging morphology was investigated and compared in tapes produced by different deformation processes. A new deformation process called ''sandwich'' rolling was developed to prevent the formation of sausaging and cracks in the longitudinal direction. In this ''sandwich'' rolling, the tape is deformed between two steel sheets. The stress-strain state of the tape in ''sandwich'' rolling is the same as that of uniaxial pressed tape because the deformation of steel sheets is negligible in comparison to that of Ag-clad Bi-2223 tape. The stress-strain distribution of the superconducting oxide core can be controlled by the curvature and hardness of the steel sheets. The critical current density of the sandwich rolled tape is improved in comparison with the flat rolled tape.