Effect of boron particle size on microstructure and superconducting properties of in-situ Cu addition MgB₂ multifilamentary wire

In previous studies, the secondary (impurity and non-reactive) phase and voids were observed in MgB₂ matrix after the heat treatment, and then these are the lowering factors of critical current density (J_c) property. In order to improve J_c property by microstructure control of MgB₂ matrix, the fine elemental boron powder as the raw material was carried out using the high-speed vibrated milling with tungsten carbide (WC) jar. The average particle size of metal boron powder was decreased from 1.14 μm to 0.20 μm by the high-speed vibrated milling. The various fine particle boron powders as the function of milling time were also prepared, and in-situ Cu addition MgB₂ multifilamentary wires using these fine boron powders were fabricated. Critical transition temperature (T_c) value of Cu addition MgB₂ wire using fine boron powder obtained to about 37 K. No change of the T_c property by the different particle sized boron powders was confirmed. In this paper, the comparisons of microstructure and superconducting properties between the different boron particle sizes were investigated.