Microstructures and critical currents of single- and multi-filamentary MgB2 superconducting wires fabricated by an internal Mg diffusion process

作者：Togano K^*; Hur J; Matsumoto A; Kumakura H

来源：Superconductor Science and Technology, 2010, 23(8): 085002.

DOI：10.1088/0953-2048/23/8/085002

A single-filament wire and 7- and 19-filament wires of MgB2 superconductor were fabricated by an internal Mg diffusion (IMD) process. The wire is sheathed by a Cu-Ni alloy and each filament is composed of an outermost Ta, an intermediate B + SiC powder layer and an Mg core at the center. Despite the large total area reduction, the cross sections of all wires show uniform deformation of the composite. During the subsequent heat treatment, a reacted layer with a dense composite structure composed of a MgB2 matrix and fine particles is formed by Mg liquid infiltration and the reaction with the B + SiC powder. For all wires, the highest transport I-c was obtained at furnace temperatures of 640-645 degrees C, which is just below the melting point of Mg. In the single-filament wire, a fairly large amount of B + SiC remains outside the reacted layer, while the residual B + SiC is much reduced in the multi-filamentary wires, resulting in higher I-c, than that of the single-filament wire. However, the J(c), estimated for the reacted layer is not so different between the wires. When the heat treatment temperature exceeds 650 degrees C, the I-c value rapidly decreases, although the volume fraction of the MgB2 detected continues to increase. It is observed that the thickness of the reacted layer formed at higher temperatures becomes significantly inhomogeneous, which is thought to be responsible for the deterioration of transport I-c values. The highest J(c)(layer) estimated for the reacted layer is as high as 9.9 x 10(4) A cm(-2) at 4.2 K and 10 T and 3.3 x 10(5) A cm(-2) at 20 K and 1 T achieved for the multi-filamentary wires. The J(c)(core) estimated for the area including the hole and remnant B is about 1/3 of the J(c)(layer). From

• 出版日期2010-8