Pressure-induced property improvement of magnesium diboride wire

F Wan,M A Rindfleisch,E W Collings,M D Sumption

doi:10.1088/1757-899x/279/1/012024

Abstract

The 4.2 K non-barrier transport Jc values of the powder-in-tube (PIT) in-situ MgB2 wires have been enhanced by cold high pressure densification (CHPD). With respect to the control wire, the 1.5 GPa pressure induced the Jc improvement of the wire at 4.2 K and 10 T by 25 %. The Jc enhancement induced by the CHPD may result from two aspects. First, the CHPD resulted in the reduction of the transverse MgB2 core area. Second, the grain connectivity of the PIT in-situ MgB2 wire was improved by the CHPD, which is reflected by the reduced porosity.

Highlights

Compacted-powder pellets and the cores of powder-in-tube (PIT) wires are inherently porous
Shields et al [4] reported that hot isostatic pressing (HIP) induced the magnetic critical current densities as high as 1.3 × 106 A/cm2 at 0 T and 9.3 × 105 A/cm2 at 1 T of the MgB2 bulks at 100 MPa and 950 oC, 20 K
If the reduced transverse MgB2 core area is the unique factor to inducing the Jc enhancements of the MgB2 wires, the Jc of W20 will be improved by a factor no higher than 5.8 %

Summary

Introduction

Compacted-powder pellets and the cores of powder-in-tube (PIT) wires are inherently porous. Porosity in the starting powder fill (and staring porosity plus reaction in the case of in-situ material) impedes current flow and prevents the Jc of the bulk or wire from attaining its intrinsic intragranular value. Current transport between grains may be reduced by the presence of insulating partial coatings [2]. These effects can combine to yield very low connectivities [3], for example 20~40% [1] which would offer the possibility of transport Jc increases by factors of 5~2.5. Shields et al [4] reported that hot isostatic pressing (HIP) induced the magnetic critical current densities as high as 1.3 × 106 A/cm at 0 T and 9.3 × 105 A/cm at 1 T of the MgB2 bulks at 100 MPa and 950 oC, 20 K.

Findings

Published under licence by IOP Publishing Ltd

Conclusions