Strength and ductility of heavily drawn bundled Cu-Nb filamentary microcomposite wires with various Nb contents

The strength and ductility of heavily drawn bundled Cu-Nb filamentary microcomposite was examined as a function of Nb content. In order to predict the variation of the yield strength (YS) with Nb content, the interfilamentary spacing was calculated as a function of Nb content based on the assumption that Nb filaments are distributed regularly along the sides of a triangular unit cell in the transverse section. The yield stress can be described as the sum of the substructure strengthening component due to elongated grains, subgrains and/or cells, the phase boundary strengthening term associated with the Hall-Petch type interaction between dislocations and phase boundaries, and the precipitate strengthening component. The contributions from phase boundary strengthening, σPB (Cu-Nb), and precipitate strengthening, σppt, increase with increasing Nb content. However, the contribution from substructure strengthening, σsub (Cu-Nb), decreases with increasing Nb content since more grain or subgrain boundaries are absorbed at Cu/Nb phase boundaries with increasing Nb content. The good agreement between the prediction and the experimental data suggests that the increase of the strength in Cu-Nb filamentary microcomposite with increasing Nb content results mostly from an increasing volume fraction of Nb filaments, which act as barriers to plastic flow.