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 thermal properties of Bi-2223 tapes has been evaluated. Additions of Au, Pd, Mg 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 and 81.9(Hv), 236 MPa, respectively. On the other hand, the corresponding values of Ag were 55.4(Hv) and 135 MPa. In addition, microstructural observation showed that the additions of alloying elements to Ag significantly reduced 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 grain size and combined effects of solid solution hardening and dispersion hardening. Thermal conductivity of Ag alloys was measured by thermal integral method and observed to have decreased with increasing content of alloying elements.