Single-core MgB2 wires and tapes were made by using the powder-in-tube method and commercial MgB2 powder. Composites were made, by using 2-axis rolling, in Cu and/or Fe/Cu sheaths. Alternative deformation by wire-drawing, rotary swaging and cold isostatic pressing were applied to powder-in-tube wires and tapes. Current–voltage characteristics and transport current densities in the self-field and external fields were measured. It was found that the grain connectivity of ex situ MgB2 was affected by the applied sheath, and the mode of deformation. Two-axis rolling generated the highest powder density, resulting in the best grain connectivity. The highest transport current densities, of 8700 and 55830A/cm2, were measured for Cu and Fe/Cu sheathed square wires, respectively. Cold isostatic pressing at 1.5GPa increased the current density and n-exponent. This implied an improvement in grain connectivity. It was found that external pressure improved inter-grain connectivity but decreased pinning in MgB2 cores.

Structure, Grain Connectivity and Pinning of As-Deformed Commercial MgB2 Powder in Cu and Fe/Cu Sheaths. P.Kovác, I.Hušek, W.Pachla, T.Melišek, R.Diduszko, K.Fröhlich, A.Morawski, A.Presz, D.Machajdik: Superconductor Science and Technology, 2002, 15, 1127-32