Study of short duration heat treatments of an in situ copper-sheathed MgB2 wire

The powder-in-tube technique has been used to fabricate Cu-sheathed magnesium diboride (MgB2) wires using an in situ reaction method. The effects of high heating rate, short duration heat treatments of MgB2/Cu wires were studied by means of optical and scanning electron microscopy, x-ray diffraction, resistivity, ρ(T), and susceptibility, χ'(T), measurements. The transport critical currents, Ic(B), of the wires were measured using both direct current in a constant field and pulse field-pulse current methods. Usage of high heating rates allows the processes of interest to occur in conditions closer to isothermal, which permits the influences of heat treatment time and temperature to be more readily distinguished. The results show that the microstructure and properties of the MgB2/Cu wires are strongly dependent on the heat treatment temperature but quite insensitive to the reaction time: a short heat treatment for 5 min at 700 0C was sufficient for obtaining the highest critical current achieved in this work.