Microstructure and critical current densities of MgB2/Cu wires

Cu sheathed MgB₂ wires with a diameter of 2.50 mm and 0.93 mm have been fabricated by the In-Situ Powder-in-Tube PIT method. We have studied three subjects; the morphology of the wire core affected by the fabrication process of cold rolling, compounds in the core produced by the heat-treatment and effect of the microstructure on critical current densities Jc. The value of Jc is 10³ A/cm² in 2 T at 25 K for the wire of 2.50 mm diameter. This value is three times higher than that of the wires of 0.93 mm diameter. EDS analysis and X-ray diffraction patterns have shown that in the wire with a diameter of 0.93 mm Cu and Mg diffusion on heat-treatment process, leading to formation of Cu-Mg compounds. We have paid attention to texture change of the wire core from granular to filamentary by the cold rolling process. It has been supposed that this filamentary texture gives an effect on the formation of MgB₂ and Jc value.