Grain size reduction of copper subjected to repetitive uniaxial compression combined with accumulative fold

This paper reports a novel method of repetitive uniaxial compressioncombined with accumulative fold for preparing bulk submicron- tonanocrystalline copper starting with a coarse grained counterpart.Grain size reduction and microstrain variations of the high puritycopper samples after different passes of compression and fold areinvestigated by scanning electron microscope and x-ray diffraction(XRD), respectively. Our results show that the average grain size ofsamples decreases from about 830nm to 127nm as the number ofcompression passes increases to 30. Microstrain in the compressedsample is found to increase for the first 20 passes, but to decrease atthe last 10 passes. The variations of compressive yield strength andthe shift of XRD peaks to larger diffraction angles are observed inthe squeezed sample. Our experimental results demonstrate that therepetitive uniaxial compression combined with accumulative fold isan effective method to prepare bulk nanocrystalline metallicmaterials, in particular for soft metals such as Cu, Al and Pb.