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

Abstract

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%).

High critical current properties of multi-filamentary MgB2 superconducting wires fabricated using an internal Mg diffusion method

“…The superconducting transition of our multi-filamentary wires is significantly better than the magnetic results of previous seven-filament IMD-MgB 2 wires [21]. And the magnetic T c value is similar to that of other seven-filament MgB 2 wires calculated from resistance measurements [39]. These results suggest high purity and good uniformity of the MgB 2 phase.…”

Low‐purity Cu and Al sheathed multi‐core MgB2 wires made by IMD process

“…But, larger volumes of the fine-grain structure Al + Al 2 O 3 sheath (62.7%) with the ultimate tensile strength of 230-260 MPa [17], a lower filament area (14.3%) and also the presence of a thin and strong Al 3 Ti phase at Ti/Al interfaces can be responsible for presented electro-mechanical properties of 6Al wire. It should be noted that the observed stress tolerance of 6Al wire is even better than for Monel sheathed wires and comparable to Glid-Cop sheathed wires [24]. Such high tolerances to tension stress can be interesting for possible applications where low mass and mechanically strong MgB 2 superconductors are desired.…”