X-ray peak profile analysis of crystallite size distribution and dislocation type and density evolution in nano-structured Cu obtained by deformation at liquid nitrogen temperature

X-ray peak profile analysis was employed to determine the crystallite size distribution and the evolution of dislocation type and density in pure Cu deformed by rolling at liquid nitrogen temperature for the following rolling reduction levels: 67, 74, 87, and 97%. The results show that as the deformation level increases, the variance and the median of the crystallite size distribution decreases. It was also found that the dislocation density decreases in the first segment of the deformation, and increases slightly after reaching a minimum. This can be explained by the fact that the mobility of the dislocations was limited by the low deformation temperature. In order to reduce the strain energy, the dislocations reorganize themselves into dislocation cell structure, which leads to the reduction of the X-ray coherent domain length. Furthermore, it was established that full dislocations dominate the deformation process at lower deformation levels, when the median of the crystallite size distribution is greater then 50 nm. At higher deformation levels and smaller crystallite size, the fraction of partial dislocations become significant, while the overall dislocation density increases slightly and the population of the full dislocation decreases. It is concluded that the increase in dislocation density is due to the emission of a new generation of partial dislocations, which become the leading deformation mechanism.