Effect of C Doping Level and the Ratio of Mg to B on the MgB2 Wires Fabricated by Internal Mg Diffusion Method

Monofilament MgB2/Fe wires were fabricated by using internal Mg diffusion (IMD) process with ball milled crystalline boron powder. In this paper, the effect of C doping level and the ratio of Mg to B on these IMD-processed MgB2wires were investigated. It was found that the highest transport Jcvalue was 6.2 × 104A/cm2at 4.2 K and 10 T, when the carbon concentration was 4% and the ratio of Mg to B was 1:1.57. The microstructure results showed that a number of B-rich particles still remained in MgB2reacted layer, though B powder was ground by ball milling. Besides, there is residual Mg in the center of the MgB2wires because of the large wire diameter. The analysis of these results indicates that higher Jcdata can be achieved after further optimization of the B particle size, the wire diameter, and the ratio of Mg to B.