Current densities and strain tolerances of filamentary MgB2 wires made by an internal Mg diffusion process

Engineering current densities and tensile strain effects in filamentary MgB2 wires manufactured by the diffusion of magnesium into boron (IMD) process have been examined at a 4.2 K and with an external field of 6–7.5 T. MgB2 wires with 6 or 7 filaments, Nb or Ti barriers and Monel®, GlidCop® and HITEMAL® outer sheaths were examined and compared with commercially produced MgB2 conductors. IMD wires allow for higher engineering current densities in comparison to commercial wires produced by the powder-in-tube (PIT) process, but a uniform Mg/B ratio in the as-formed IMD wires is extremely important for long-length homogeneity. IMD and PIT wire samples were loaded progressively to determine the irreversible strain limit (εirr) and stress limit (σirr) defined as the maximum loaded strain or stress where the critical current (Ic) is still reversible. It was found that the strain tolerances of the tested MgB2 wires are affected by the metallic components used. The wire with the lowest content of metallic elements (Nb/Monel®) led to the lowest strain tolerance (εirr = 0.30%). Alternately, the wire with stronger GlidCop®/Monel® sheath resulted in the best strain tolerance (εirr > 0.50%).