Interface irregularity and texture evolution of Bi-Sr-Ca-Cu-O superconductor tape processed by PIT method

We evaluated the degree of texture and the interface irregularity between the Ag sheath and the superconductor core of Bi-Sr-Ca-Cu-O (BSCCO) superconductor tape during drawing and rolling processes. The degree of texture and the interface irregularity were characterized by pole figure analysis and the coefficient of variation in thickness (COV) factor, respectively. It was observed that the interface became gradually irregular during the drawing and rolling processes. On the other hand, the degree of texture improved significantly during rolling process, but little during the drawing process. The critical current of the tape depended remarkably on the combined effects of the interface irregularity and the degree of texture. As the dimension of the wire/tape was changed from a diameter of 3.25 mm to a thickness of 0.20 mm, the critical current increased by 10 times. Microstructural investigation showed that grain alignment was locally degraded by the existence of both second phases and interface irregularity. It was observed that larger grain size and better texturing developed near the relatively straight interface compared to those inside the superconducting core.

I. Introduction

For many industrial applications of high superconductors such as power systems, including transformers, cables, motors and energy storage systems (SMES), the development of long lengths of superconductors with good electrical properties and mechanical reliability is critical. Since the development of the powder-in-tube (PIT) process by Heine et al. [1], the PIT process has become one of the most promising techniques for making long length superconductor tapes with good producibility and high electrical and mechanical properties. Recently, it was reported that Ag-sheathed Bi-Sr-Ca-Cu-O (BSCCO) tape made by PIT process has been fabricated to 1.2 km long with a critical current of 30 A at 77K [2].