Study of short duration heat treatments of an in situ copper-sheathedMgB2 wire

Abstract

The powder-in-tube technique has been used to fabricate Cu-sheathed magnesium diboride(MgB2) wiresusing an in situ reaction method. The effects of high heating rate, short duration heat treatments ofMgB2/Cu wires were studied by means of optical and scanning electron microscopy, x-ray diffraction, resistivity,ρ(T), andsusceptibility, χ′(T), measurements. The transport critical currents,Ic(B), of the wires were measured using both direct current in a constant field andpulse field–pulse current methods. Usage of high heating rates allows theprocesses of interest to occur in conditions closer to isothermal, which permitsthe influences of heat treatment time and temperature to be more readilydistinguished. The results show that the microstructure and properties of theMgB2/Cu wires are strongly dependent on the heat treatment temperature butquite insensitive to the reaction time: a short heat treatment for 5 min at700 °C was sufficient for obtaining the highest critical current achieved in this work.