Deformation and activation volumes of cryomilled ultrafine-grained aluminum

The deformation behavior of cryomilled UFG C.P. Al and Al 5083 has been investigated. Deformation patterns on the surfaces of tensile samples indicate that deformation in uniaxial tension is localized in these materials. The activation volumes calculated from strain rate jump tests performed at room temperature and 422 K are relatively low in value and invariant with strain, suggesting that dislocation-dislocation interactions within the grain interiors do not take place. Strain rate sensitivities calculated from the strain rate jump tests are also low, indicating that grain boundary sliding does not contribute to the tensile deformation of this material. The activation volumes and strain rate sensitivities support the notion that in both alloys grain boundaries act as sources and sinks for dislocations that contribute to plastic deformation. This is consistent with numerous TEM images of deformed UFG materials which show either no or very limited dislocation activity within the grain interiors following deformation. These features are also consistent with the elastic nearly perfectly plastic stress-strain behavior exhibited by UFG materials. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.