Fabrication of high-performanceMgB2 wires by an internal Mg diffusion process

Abstract

We succeeded in the fabrication ofhigh-Jc (criticalcurrent density) MgB2 /Fe wires applying the internal Mg diffusion (IMD) process with a pure Mg core and SiCaddition. A pure Mg rod with a diameter of 2 mm was placed at the center of a Fe tubewith an outer diameter of 6 mm and an inner diameter of 4 mm, and the spacebetween the Mg and the Fe tube was filled with B powder or a powder mixture ofB–(5 mol%) SiC. The composite was cold worked into a wire with a diameter of1.2 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 formMgB2. X-ray diffraction analysis indicated that the major phase in the reacted layer isMgB2. Scanning electron microscopy (SEM) analysis shows that the density of theMgB2 layer is higher than that of the usual powder-in-tube (PIT) processedwires. The wires with additional 5 mol% SiC heat treated at670 °C showedJc valueshigher than 105 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 processedwires, even compared to those with additional SiC. The higher density of theMgB2 layer obtained by the diffusion reaction is the major cause of these excellentJc values.