Properties of multifilamentary MgB2 wires fabricated by internal magnesium diffusion using amorphous and crystalline boron powders

MgB₂/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 MgB₂ 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 MgB₂ wires. The J_c as high as 6.1 × 10⁴ A cm^-2 at 4.2 K, 10 T is obtained in the seven-core MgB₂ wire made using amorphous boron powder. The IMD-processed seven-core MgB₂ wire fabricated using high-purity crystalline boron powder has also a high J_c of 4.9 × 10⁴ A cm^-2 at 4.2 K and 10 T. However, the seven-core MgB₂ 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 MgB₂ layer in multifilamentary wires.