Recent publications show that high strain rates influenced on the microstructure refinement similarly to large deformations. The strong tendency to microbands formation is observed in both cases. It was found that the width of microbands is very sensitive to the changes of deformation parameters. Especially, it has been observed that in the severely deformed materials the width of microbands is reduced to nanometric dimensions leading to the formation of nanometric microstructures.

In the process of hydrostatic extrusions, which has been used in this work for deformation of cooper, large plastic strain is substituted by high strain rates exceeding 3.84*102. In all investigated samples the numerous microbands were found in the microstructure. The intensive intersections of microbands were observed. The width of microbands was noticed from 20 nm to about 400 nm. It means that locally, in the areas of microbands, the width of microbands achieved dimensions typical of the nanometric materials. A special feature was also the appearance of large areas of subgrains with the average dimension of about 200 nm. These areas were identified as the dynamically or post- dynamically recrystalized.

The large misorientations were found between the microbands and the surrounding materials. The appearance of large misorientations between the microbands and the surrounding material results in formation of high misorientation boundaries, which contribute to the microstructural and mechanical changes. The mechanism of creation of high misorientation in the microbands areas is probably different to the one operating during the process of dynamic recrystalization.

The results indicate the possibility of obtaining nanometric structure at lower deformations but higher strain rates.