High critical current of Ti-sheathed MgB₂ wires for AC and weight-critical applications

The peculiar features of magnesium diboride make it suitable for many potential applications. In the last four years of investigation of MgB ₂, the scientific community's research was mainly motivated by features such as low cost, compatibility with straightforward processing methods, relatively high critical temperature, and absence of weak links between grains. Other applications suggest the accentuation of other MgB₂ properties. In particular its very low mass density makes it attractive for space activities, where the cost per kilogram for orbiting is still a huge obstacle, e.g. the cost of transport to low Earth orbit can reach 15 k$ kg^-1. In order to promote the use of this compound for space activities, we tested titanium as a sheath material. Titanium is non-magnetic and its alloys are almost half the weight of steel but with yield stresses up to three times higher. We fabricated Ti-sheathed MgB₂ through the powder-in-tube process. These wires show similar results to those sheathed with Fe. At 4 K the critical current density J_c is well above 7 × 10⁵ A cm^-2. The interface between the superconducting intermetallic compound and the lightweight sheath does not show any evidence of reaction and diffusion up to 900 °C. An analysis was carried out using x-ray diffraction, scanning electron microscopy with an energy dispersive spectrometer, and electron microprobe analysis.