On the Strain Rate Sensitive Characteristics of Nanocrystalline Aluminum Alloys

For structural applications, ductility is essential along with high strength in nanocrystalline (nc) materials. In general, ductility is controlled by strain hardening and strain rate sensitivity. In conventional materials which are coarse grained, the deformation is mainly dislocation based and accumulation of these dislocations results in work hardening. The deformation mechanisms that are operative in nc materials are distinct and the strain hardening ability is limited in nc materials. Strain rate sensitivity (SRS) and activation volume are the two key parameters which govern the underlying deformation mechanisms in nc materials. Higher SRS value could be an indication of better ductility levels. In general, nanocrystalline single phase fcc metals showed increased SRS, where as bcc metals showed decreased SRS. The addition of second phase effects the overall SRS of the nano composite/alloy. Since producing nc materials in bulk quantities is a challenge, nanoindentation, which can be performed on smaller sized samples, is an useful technique to study SRS and activation volume. Strain rate sensitive characteristics of Al and its alloys are reviewed in this paper. Our earlier work as well as the available literature data on these alloys showed that the nature and structure of the second phase dispersions greatly influence the SRS.