Single-core wires were made via the powder-in-tube method, using commercial MgB2 powder. Using 2-axis rolling, composites were made in a Cu sheath. Energy dispersive X-ray mapping and scanning electron microscopy back-scattered electron observations proved that there was high elemental segregation (phase inhomogeneity) in as-rolled and as-sintered wires, although the wire after sintering was more inhomogeneous than was the as-rolled (non-sintered) wire. The X-ray diffractograms confirmed the presence of isotropy and the absence of texturization in the macroscopic phase within the MgB2 cores, in spite of their thermomechanical history. The observed decrease in the value of JC of the wire after sintering was attributed to macroscopic cracking and the worsening of intergrain connectivity. EDX line scans also revealed high anisotropy and high inhomogeneity in the distribution of elements within the MgB2 cores. Inhomogeneity in the final wire-product resulted from the high macroscopic inhomogeneity observed in the starting MgB2 powder. The Cu sheath was shown to be neutral (non-poisoning) for MgB2 cores made ex situ. However, due to its softness, it could not properly constrain the MgB2 core or provide the support required for adequate grain connectivity.

Structural Inhomogeneity of Superconducting ex situ MgB2/Cu Wires Made by the Powder-in-Tube Technique. W.Pachla, A.Presz, R.Diduszko, P.Kovác, I.Hušek: Superconductor Science and Technology, 2002, 15, 1281-7