Improvement of Jc by cold high pressure densification of binary, 18-filament in situ MgB2 wires

Abstract

Cold high pressure densification (CHPD) has recently been foundto be a promising way to improve the critical current density,Jc, insingle-core MgB2 wires prepared by in situ processing. In this work, the CHPD process was also applied to multifilamentary,binary MgB2 wires, leading again to a strong enhancement of the transportJc. The fields and where the transport Jc at4.2 K reaches the value 1 × 104 A cm − 2 for parallel and perpendicular fields were determined as 8.5 and 8.2 T, respectively (0.1 µV cm − 1 criterion). Thebehaviour of Jc versus B at 20 and 25 K was almost isotropic, the corresponding values being 4.7 and 3 T, respectively. The observed enhancement ofJc by a factor 2.3 at 4.2 K at all applied fields up to 10 T in densified samples isdirectly correlated with the observed enhancement of the mass density andmicrohardness. The decrease of the electrical resistivity of the densified wirereflects improved grain connectivity in the filaments. The improvement ofJc by CHPD was still observed after sequential pressing with overlapping regions, up to atotal wire length of 150 mm. This result is promising as regards practical applications.