STUDIES ON THE THERMOMECHANICAL PROCESSING IN THE PREPARATION OF MULTIFILAMENTARY TAPES OF (BI, PB) - 2223 / AG FOR HTS CURRENT LEADS

摘要

The effects of heat treatment schedule and the uniaxial pressure applied prior to the last stage sintering for the preparation of (Bi,Pb) -2223/Ag multifilamentary tapes for use as HTS current leads were studied. The phase assemblage of the tapes prior to the last stage sintering is found to play a crucial role in governing the microstructure, phase purity and Jc of the finished tapes. It is observed that tapes with higher amount of Bi-2223 prior to the last stage sintering and deformation produced better sintered density, Jc and' microstructure in the finished tapes. A pressure of 500 MPa applied prior to the last stage sintering was found to be optimum for obtaining better microstructure, higher sintered density and Jc. The level of Jc and Jc homogeneity along* the length of the tape as well as Jc-B characteristics of the pressed tapes are much superior compared to the rojjld tape. The observed scattering in Jc along the length of the pressed tape is only 0.3 percent of the maximum measured, while that of a rolled tape is -4 percent of the maximum. Eventhough uniaxial pressing is not suitable for the preparation of long length tapes, laboratory scale samples of length -20 cm can be successfully prepared by uniaxial pressing applied prior to the last stage sintering.