Development and characterization of sheath alloys for Bi-(Pb)-Sr-Ca-Cu-O superconductor tape

The effect of alloying element additions to Ag sheath on mechanical and the rmal properties of Bi-2223 tapes has been evaluated. Additions of Au, Pd, M g and Al to Ag increased hardness and strength, while reducing workability and thermal conductivity. Hardness and tensile strength of Ag0.92Pd0.06Mg0. 02 and Ag0.973Au0.025Mg0.002 sheath alloys improved to 92.5(Hv), 397 MPa an d 81.9(Hv), 236 MPa, respectively. On the other hand, the corresponding val ues of Ag were 55.4(Hv) and 135 MPa. In addition, microstructural observati on showed that the additions of alloying elements to Ag significantly reduc ed grain size from 240 mu m to 10 similar to 100 mu m. The improvements in hardness and strength of Ag alloys are believed to be due to the smaller gr ain size and combined effects of solid solution hardening and dispersion ha rdening. Thermal conductivity of Ag alloys was measured by thermal integral method and observed to have decreased with increasing content of alloying elements.