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

Monofilament MgB
₂
/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 MgB
₂
wires were investigated. It was found that the highest transport J
_c
value was 6.2 × 10
⁴
A/cm
²
at 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 MgB
₂
reacted layer, though B powder was ground by ball milling. Besides, there is residual Mg in the center of the MgB
₂
wires because of the large wire diameter. The analysis of these results indicates that higher J
_c
data can be achieved after further optimization of the B particle size, the wire diameter, and the ratio of Mg to B.