Dislocation structure and crystallite size in severely deformed copper by X-ray peak profile analysis

Copper specimens were severely deformed by equal channel angular pressing (ECAP) up to eight passes. The microstructure was studied by X-ray diffraction peak profile analysis as a function of strain (ɛ). It was found that the crystallite size is reduced to a few tens of nanometers already at ɛ = 0.7 and it does not change significantly during further deformation. At the same time, the dislocation density increases gradually up to ɛ = 4. The dipole character of the dislocation structure becomes stronger with increasing strain. The thermal stability of the microstructure is examined by differential scanning calorimetry (DSC). The temperature of the DSC peak related to the recovery of the microstructure decreases with increasing strain. At the beginning of the heat release, a bimodal grain structure develops indicated by a special double-peak shape of the diffraction line profiles.