Ductility of ultrafine grained copper

In this letter, we address the effect of grain refinement on room-temperature ductility of copper. Recent experimental results have shown that this material, as well as a number of other single-phase metals that are ductile when coarse grained, lose their ductility with decreasing grain size in the submicrometer range. A recently developed model in which such materials are considered as effectively two-phase ones (with the grain boundaries treated as a linearly viscous second phase) was applied to analyze the stability of Cu against ductile necking. As a basis, Hart's stability analysis that accounts for strain-rate-sensitivity effects was used [E. W. Hart, Acta Metall. 15, 351 (1967)]. The results confirm the observed trend for reduction of room-temperature ductility with decreasing grain size. The model can be applied to predicting the grain-size dependence of ductility of other metallic materials as well. (C) 2001 American Institute of Physics.