Characterization of the strength and microstructure of heavily cold worked Cu-Nb composites

The mechanical properties and microstructures have been evaluated for heavily cold worked wires of Cu-12% Nb and Cu-20% Nb composites. The strength of these composites increases dramatically with increasing deformation up to a true strain of 11.9, the maximum investigated. This continued strengthening is a consequence of deformation-induced microstructural changes in both Cu and Nb. During deformation the Nb precipitates adopt a filamentary morphology, and both the size and spacings of these filaments decrease. The microstructural evolution in the Cu matrix involves a deformation-recovery-recrystallization cycle, which allows further deformation and the concurrent refinement of the Nb. Strengthening in these composites appears to arise from the Nb filaments which act as planar barriers to plastic flow between the two phases. The strength of these composites is dependent on the spacing of the Nb filaments in accord with a Hall-Petch relationship. Furthermore, it was found that due to the deformation, induced recovery and recrystallization processes, the strengthening is not in accord with models based on the development of very large dislocation densities (10/sup 13/ cm/sup -2/)