Published online by Cambridge University Press: 03 March 2011
A fiber-reinforced in situ metal matrix composite (MMC) consisting of copper (Cu) and 20 mass% niobium (Nb) was produced by large strain cold rolling. The rolled MMC revealed a very high strength combined with good electrical conductivity. The microstructure of single Nb filaments was investigated employing transmission electron microscopy (TFM). In heavily rolled specimens (∊max = 99.4%) randomly arranged dislocations as well as dislocation cells were observed. Furthermore, structurally less-ordered areas were discovered, the size of which frequently extended over the entire filament width. The shrinkage of these zones during heating was directly observed in the TEM. The impact of such structurally less-ordered areas on the strength was assessed. The discovery of the degradation of structural regularity in the Nb filaments of heavily cold-worked Cu-20 wt. % Nb shows that the underlying microstructural mechanisms responsible for the high strengths observed are far from being understood and that the strain-hardening models for Cu-based in situ composites currently discussed do not yet account for all relevant microstructural features.