Effects of deformation radius during rolling on the properties of Bi-2223/Ag superconductor tapes

摘要

Superconducting Bi-2223/Ag tapes were manufactured using rolling processes with deformation radii in the range of 0.8-42cm for constant reduction rates of 15% strain per pass. The effect of the variation of the radius on the development of work instability in these tapes was studied. Longitudinal and transverse "sausaging" were observed for large and small radii, respectively. At intermediate radii, a square "biscuit" morphology was observed. The severity of these non-uniformities was significantly reduced for small radii. Cracks in the unsintered powder core at approximately 90° to the tape plane were observed, and are indicative of a tensile fracture mode in the core. This fracture mode is suggested to be a contributor to the development of non-uniformities such as sausaging. The formation of work instabilities is attributed to hardening of the oxide core due to high levels of hydrostatic stress in some rolling configurations.