Development of high-strength and high-conductivity conductor materials for pulsed high-field magnets at Dresden

Abstract

The work at the IFW Dresden is focused on the development of microcomposite Cu–Ag alloys and steel–copper macrocomposites with high-nitrogen steel and pearlitic steel jackets, respectively. In Cu–Ag alloys the investigation of continuously cast rods with different starting diameters suggests that the cooling rate during solidification determining the dendrite arm spacing has a minor influence on the development of the strength compared to the cooling velocity after solidification which determines the extent of the Ag-supersaturation in the Cu solid solution. Maximum strength at minimum drawing strain demands (i) a sufficient volume fraction of eutectic in order to suppress discontinuous precipitation (absence of grain boundaries) and (ii) a sufficiently rapid cooling after solidification in order to prevent pre-precipitation. With a continuously cast starting rod of 12 mm diameter a maximum tensile strength of 1.3 GPa was obtained after a drawing strain of only η=4.3. Steel–copper macrocomposites were fabricated by the ‘rod-in-tube’ technology. The experiments with austenitic high-nitrogen steels were performed with two alloys. With the commercial alloy Nicrofer 3033 a strength level of 1.2 GPa has been achieved with a 52 vol% Cu composite at a drawing strain of η=2.3. A composite with pearlitic C60-steel (0.6 wt% C) and 56 vol% Cu showed a tensile strength of 1.53 GPa after a final patenting at a diameter of 14.7 mm and a drawing strain of η=4.