Bulk nanocrystalline Cu-Nb composites produced by powder approach: Processing and characterization

Cu-Nb composites (10-20 wt%Nb) are promising conductors for microsecond range high-field pulsed magnets (inductors), owing to their stable high strength and conductivity. However, the superior performance of these composites is mainly achieved by means of severe plastic deformation of the alloy, e.g. by cold drawing, thereby yielding maximum strength and conductivity along the drawing direction. Here, bulk Cu-Nb composites were developed by processing two types of powders: the first one was obtained by ball milling of heavily drawn Cu-18 %Nb wire, and the second one by electrical co-explosion of Cu and Nb wires (25 wt%Nb). The bulk materials were produced by powder dynamic compaction and subsequent sintering at 650-850 degrees C, without the application of strain post-hardening. The sintered materials were examined by X-ray diffraction, scanning electron and optical microscopy. The annealing effect on the electrical conductivity and mechanical properties of the materials has been investigated. The bulk composites, obtained by sintering of compacted nanocrystalline powders at 780 f 30 degrees C for 1-3 hours, have shown a combination of an ultimate tensile strength of 900 f 40 MPa and a resistivity of 3.8 f 0.4 mu Ohm & sdot;cm. The crystallite size of the composite phases did not exceed 90 nm. High density of grain boundaries gives the main contribution to the strength and resistivity besides the dispersion and solid solution strengthening. Both of the developed materials have demonstrated a higher thermal stability, by 50-100 degrees C, in comparison to the wire due to in situ dispersion hardening by niobium-based nanoparticles formed during the sintering.