MgB2composite wires with Fe, Nb and Ta sheaths

Single-core MgB2 composite wires have been made by the powder-in-tube method using commercial Mg, B and MgB2 powders (Alfa Aesar) in Fe, Nb and Ta tubes and both in situ and ex situ processes. Prepared wires were subjected to annealing at temperatures ranging from 600 °C up to 950 °C for 30 min in argon atmosphere. Resistive (R(T)) and transport current (Ic(μ0H)) measurements have shown how the sheath material that was used influences the critical temperature and critical current density. Inter-diffusion and reaction has been observed only for the iron sheath. Niobium has appeared as the best sheath material for MgB2 wires made by the in situ process but as the worst sheath material for the ex situ method. The reason is mainly due to the large transversal cracks generated in the fully Nb sheathed ex situ wires during the deformation, which are not healed by the subsequent heat treatment.