Investigations on High Temperature MgB2 Superconductor Wires and Tapes with New Sheath Materials and the Correlation of Their Microstructures and Properties

Long superconducting MgB2 wires and tapes were produced by the "powder in a tube" method (PIT) using a mechanically alloyed nano-powder consisting of Mg, B and MgB2 as the precursor material. Both single-core (SC) and multi-core (MC) conductors were made by swaging and wire drawing the powder contained within a new type of sheath material (ODS-Cu) which, amongst others, also has the advantage of thermally stabilising the conductor. Metallographic investigations on specimens of the conductors in the as-drawn condition and after heat treatment were carried out both to monitor the manufacturing process as well as to gain information regarding important parameters such as the changes in hardness and ductility of the sheath and filament occurring during the forming process and the effect which they have on the final properties of the conductors. The metallographic and scanning electron microscopic (SEM) investigations of the microstructures were carried out on longitudinal (LS) and cross (XS) sections of the conductors which made it possible to understand the correlation between the microstructures and properties of the conductors and to draw important conclusions in order to be able to achieve the optimum design and best electrical properties for the finished conductors. By heat treating the cold formed conductor in the temperature range 500-650 degrees C, very good superconducting properties were able to be produced with critical temperatures (Tc) of 36 K and critical current densities (jc) of 10(4) A/cm(2) in fields of 11 T (parallel to the tape surface), measured at 4.2 K. Using this new sheath material, a conductor of over 100 m in length was able to be manufactured.