Effects of initial cold work conditions on the deformation and current capacity of monofilamentary and multifilamentary Bi-2223 conductors

The influences of initial cold work conditions on the deformation characteristics and the current-carrying capability of Bi-2223 powder-in-tube conductors have been investigated by varying the working friction and the amount of reduction per pass. The results demonstrate that deformation of the conductors can be very inhomogeneous depending on the working parameters. Specifically, dead zones are found within the transverse cross-sections of the tapes close to the tools-sample interfaces such that the bulk of the deformation is restricted to the central portions of the conductors. Since the core of monofilamentary tape is located outside the dead zones, it is highly densified when deformed under high friction condition resulting in the largest J(c). On the other hand, a large number of filaments in multifilamentary tape reside within the dead zones such that high working friction does not result in optimum J(c). Instead, a combination of low friction and large reduction per pass resulted in the most homogeneous deformation and highest current capacity.