Cold rolling of bulk nanocrystalline copper

By means of the electrodeposition technique, a bulk nanocrystalline (nc) co pper sample was prepared with a high purity and a high density. The nc Cu s ample was found to exhibit extreme extensibility under rolling at room temp erature [Science, 287 (2000) 1463]. In this paper, the microstructure evolu tion of the nc Cu during the cold-rolling process was examined by means of X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) an d differential scanning calorimetry (DSC). It was found in the initial stag e of cold rolling that the microstrain and grain boundary energy increase s ubstantially, while the crystallite size remains unchanged during the whole process. When the degree of deformation exceeds 1000%, the microstrain and the.-rain boundary energy tend to saturated values, implying that this def ormation process is dominated by grain boundary activity rather than lattic e dislocation. This phenomenon agrees well with the observed mechanical beh avior of the nc Cu sample. (C) 2001 Acta Materialia Inc. Published by Elsev ier Science Ltd. All rights reserved.