Fabrication of high-performance MgB2wires by an internal Mg diffusion process

We succeeded in the fabrication of high- J c (critical current density) MgB 2 /Fe wires applying the internal Mg diffusion (IMD) process with a pure Mg core and SiC addition. A pure Mg rod with a diameter of 2 mm was placed at the center of a Fe tube with an outer diameter of 6 mm and an inner diameter of 4 mm, and the space between the Mg and the Fe tube was filled with B powder or a powder mixture of B–(5 mol%) SiC. The composite was cold worked into a wire with a diameter of 1.2 mm and finally heat treated at temperatures above the melting point of Mg (∼650 °C). During the heat treatment, liquid Mg infiltrated into the B layer and reacted with B to form MgB 2 . X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB 2 . Scanning electron microscopy (SEM) analysis shows that the density of the MgB 2 layer is higher than that of the usual powder-in-tube (PIT) processed wires. The wires with additional 5 mol% SiC heat treated at 670 °C showed J c values higher than 10 5 A cm −2 in 8 T and 41 000 A cm −2 in 10 T at 4.2 K. These values are much higher than those of the usual PIT processed wires, even compared to those with additional SiC. The higher density of the MgB 2 layer obtained by the diffusion reaction is the major cause of these excellent J c values.