Superconducting MgB2 wires were made by the powder-in-tube processing of commercial MgB2 powder in Fe, stainless steel and composite metallic sheaths by annealing (850 to 1100C). Technologically interesting JC values of some 106A/cm2 in self-field at 4.2K were achieved. However, as the annealing temperature was increased, substantial chemical reaction was observed at the MgB2/sheath interface. A detailed study was made, using electron probe microanalysis, of the reaction products in the interfacial region and of the distribution of O in the core. Borides of Fe and Cr were formed at the core/sheath interface in Fe and stainless steel sheaths, respectively, with a consequent depletion of B from the superconducting core. A similar effect was caused by the formation of a solid solution of B in Nb sheaths. Milling the starting powder before wire manufacture resulted in a very significant increase in the O content of the core, which probably explained the relatively poor performance of these wires.

Interfacial Reactions and Oxygen Distribution in MgB2 Wires in Fe, Stainless Steel and Nb Sheaths. C.R.M.Grovenor, L.Goodsir, C.J.Salter, P.Kovac, I.Husek: Superconductor Science and Technology, 2004, 17, 479-84