Ultrafine-grained (UGF) metals having the grain size less than one micrometer fabricated by severe plastic deformation (SPD) processes have several times higher strength compared with the coarse grained metals having the grain size more than several tens micrometers. It had been qualitatively said that UFG have high dislocation density in addition to the high density of grain boundary since the SPD processes are the plastic deformation process. Although there are reports about dislocation density evaluated by different techniques, the report about the comparison of techniques which can provide dislocation density using a unique UFG sample is rare. In the present study, UFG Cu was fabricated by accumulative roll bonding process which is one of the SPD processes. The microstructure characterization, especially the evaluation of dislocation density, was performed using scanning / transmission electron microscopy (S/TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and electrical resistivity. As a result, the dislocation density of UFG-Cu increases after first ARB cycle, and then, the values stay almost constant with increasing ARB cycle number. Although we use the different techniques, the evaluated values of dislocation density are within an order of magnitude, which is between the middle of 1014 m-2 and the beginning of 1015 m-2.
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