Single-core MgB 2 composite tapes were prepared by an in situ process with different metallic sheaths (Fe, Ta and Nb). Normal particles (10 wt% of W and SiC) were also added into the Nb sheathed samples. Critical currents measured in parallel and perpendicular field directions and angular dependences of critical currents have revealed I c anisotropy, which is influenced by the sheath material used and by the presence of normal particles as well. The observed differences are attributed to the coexistence of two dominant effects influencing J c (B) characteristics: the texture of MgB 2 close to the interface area and effective pinning (additions). Comparison of 'in situ' and 'ex situ' results indicates that final c-axis grain alignment is more expressive for the in situ process.

Addition of tungsten metallic particles has led to an improvement of the current carrying capacity of ex situ MgB2 wires, due to an improved internal stability. The best performance was observed for 5–10 wt% of W addition and therefore this content was also used for multi-core wires made by the rectangular wire-in-tube technique (RWIT). Transport current measurements show how the variable wire shape (rectangular, circular or tape) as well as additional mechanical deformations (twisting, bending and axial stresses) influence the critical current density of four-filament MgB2–W/Fe wires in external magnetic fields ranging up to 11 T. Critical current degradation by twisting, bending at room temperature and axial stresses at 4.2 K are discussed. It was found that the addition of W particles has no effect on the value of the irreversible strain limit.

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.

Multi-core MgB 2 wire reinforced by stainless steel (SS) has been made by an in situ approach and subjected to additional deformations and mechanical stressing. A critical current density J c of 10 4 A cm −2 at 4.2 K was measured in an external field of 9.45-10 T. The filament density of drawn wire was increased by cold deformation without axial tension, which resulted in an increased J c by approximately 17%. SS reinforced wire shows a high resistance to mechanical stresses. Only 10% I c degradation was measured for wire twisted with L t = 7.14 mm. The presented SS reinforced wire has the highest irreversible strain ε irr = 0.9% so far published.