Superconducting and mechanical properties of Bi-2223/metal alloy wires composite bulk

Bi-2223 sintered bulk samples with addition of AgMg wires or Ag-plated Ni wires have been prepared to improve both the superconducting and the mechanical properties, simultaneously. When 24 AgMg wires of 0.4 mm in diameter were added into Bi-2223 bulk composite sample, the critical current density (J(c)) at 77 K increased from 2 A/mm(2) to 7 A/mm(2). The mechanical properties have been estimated by a three-point bending test. The maximum bending stress of 70 - 90 MPa at the rupture was obtained for Bi2223/metal wires composite bulk, regardless of the number of the wires. After the maximum bending stress, Bi-2223 bulk without metal wires fractured separately, while the composite did not fracture but fine cracks were induced only. The J(c) values of the composites just after the fracture were about half of the J(c) value in the composites without bending. It has been observed that the superconducting current flows even after cracking, in Bi-2223 bulk with metal wires. This is due to the fact that metal wires suppress progress of fine cracks just after the fracture, while the superconducting current flows in the uncracked region. This current still remaining after the fracture is a very important feature for the applications.