Microstructural stability and strengthening mechanism of Cu-15Nb filamentary microcomposites: (II) Strengthening mechanism

摘要

In this study, the deformation and fracture behaviorof the Cu-Nb microcomposites fabricated by the bundling anddrawing process was investigated. The yield strength of a Cu-20%Nb microcomposite was predicted by modifying the model ofVerhoeven et al. It was assumed that the substructuralstrengthening in pure Cu and Nb phase fully contribute to the yieldstrength of Cu-Nb microcomposite, σCu-Nb at low draw strains(η<5.5). At high drawing strains (η>5.5) where the microstructuralscale of the Cu matrix is limited by Nb filaments, the contributionof the partial grain boundaries (connecting the edge of Nbfilaments) to the strength was assumed to be proportional to (λ/WNb)1/2. The good agreement between the yield stress predictedin this study and the experimental data at drawing strains between6 and 9.5 supports the suggestion of the present study that theeffectiveness of substructure strengthening of Cu and Nb inheavily deformed Cu-Nb microcomposites is much lower than thatexpected from the yield strength of heavily deformed Cu and Nb.The yield stress of the Cu-Nb microcomposite fabricated by thebundling and drawing process was found to be in good agreementwith the predicted yield stress of the present model. At drawingstrains above 10, Nb filaments reached a thickness ofapproximately 10 nm and thereafter further working resulted inrandom rupture of the filaments rather than continued plasticdeformation and thinning, which may result in the slower increaseof the strength than the predicted values with drawing strain.