On the manufacture of silver-sheathed Bi-2212 high temperature superconducting wires

Abstract

High temperature superconductors (HTS) are presently being considered for a variety of defense and commercial applications. However, problems associated with low critical current density (Jc) in long length conductors still need to be addressed. It is realized that success in the fabrication of long lengths of wire and tape (up to 1 km) with optimum superconducting properties relies on improved manufacturing technologies. Unfortunately, there is no systematic study concerning the effect of processing parameters on the green properties of wires and tapes during the deformation processes. The focus of this investigation centered on silver (Ag) sheathed Bi-2212 wire forming processes and use of the two most common techniques, wire drawing and hydrostatic extrusion. Billets of 6.35 mm outside diameter were reduced separately by five different die sequences to a final diameter of 1.63 mm. Wires made by these procedures were characterized for properties such as Bi-2212 relative packing density, sheath material thickness, deformation force, elongation, drawing friction, and microstructural and mechanical properties. These results indicated that the amount of reduction per pass has a significant impact on the characteristics of non-heat treated wires and on the mechanical aspects of the wire drawing operations.