Properties of Multifilamentary MgB2 Wires Fabricated by Internal Magnesium Diffusion Using Amorphous and Crystalline Boron Powders

MgB
₂
/Nb/Monel multifilamentary wires were fabricated using amorphous and crystalline boron powders by an internal Mg diffusion (IMD) process. The microstructure, morphology, and the critical current density (J
_c
) of the reacted MgB
₂
layers in the multifilamentary wires made using different boron powders were analyzed and compared. The purity of boron powder influences greatly the transport properties of MgB
₂
wires. The J
_c
as high as 6.1 × 10
⁴
A cm
^-2
at 4.2 K, 10 T is obtained in the seven-core MgB
₂
wire made using amorphous boron powder. The IMD-processed seven-core MgB
₂
wire fabricated using high-purity crystalline boron powder has also a high J
_c
of 4.9 × 10
⁴
A cm
^-2
at 4.2 K and 10 T. However, the seven-core MgB
₂
wire prepared using low-purity crystalline boron powder has a relatively low J
_c
compared with the others, which is expected to allow the fabrication of large-scale and low-cost superconducting wires for practical application. The further improvement of layer J
_c
, nonbarrier J
_c
and engineering critical current density J
_e
is necessary because of the irregular subfilaments and the inhomogeneous thickness of the reacted MgB
₂
layer in multifilamentary wires.