Enhanced Superconducting Performance of MgB₂ Wires via Cold High-Pressure Densification and Drawing Process

Abstract

MgB₂ wires fabricated by the advanced magnesium infiltration process (AMIP) were subjected to different drawing steps and cold high-pressure densification (CHPD) at 0.8 GPa. Four samples were compared: as-drawn A1 and further-drawn A2, together with their CHPD-pressed counterparts, AP1 and AP2. X-ray diffraction confirmed the phase purity of MgB₂, with lattice parameters of (a = 3.0882) Å and (c = 3.5261) Å. SEM analysis revealed a substantial reduction in porosity and improved grain compaction following CHPD. The wire-core area decreased by 19% from A1 to AP1 and by 6.5% from A2 to AP2, confirming effective densification. Magnetization measurements showed nearly identical superconducting transition temperatures (T_c approx 36.6 K) for all samples, indicating that CHPD modified the microstructure without affecting the phase composition. Drawing alone enhanced the low-field critical current density (J_c) by improving grain connectivity. At 0 T and 20 K, A2 exhibited a J_c of 2.51 × 10⁵ A/cm², representing a 19% improvement over A1. Combining drawing with CHPD produced a further enhancement, with AP2 reaching 2.7 × 10⁵ A/cm² at 0 T and 20 K, corresponding to an overall improvement of 28%. At 3T, J_c increased from (1.52 × 10⁴) to (1.83 × 10⁴) A/cm², representing a 20% improvement in field performance compared with the unpressed wires. The irreversibility field (H_irr) remained nearly unchanged at approximately 5.8 T, confirming that the observed performance gains originated primarily from improved grain connectivity and reduced porosity. The optimized combination of drawing and CHPD therefore provides a practical route toward industrial-grade MgB₂ wires for high-field applications operating near 20 K.