I.V. Alexandrov (*), A.A. Dubravina (*), H.S. Kim(**)
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(*) Institute of Physics of Advanced Materials, Ufa State Aviation Technical University,
K. Marksa 12, 450000 Ufa, Russia
(**) Department of Metallurgical Engineering and RASOM, Chungnam National University, Yusong, Taejon, 305-764, Korea
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Severe plastic deformation (SPD) can be successfully applied to fabricate ultrafine-grained bulk nanostructured materials [1]. Nevertheless, the microstructure evolution and development of nanostructures during severe plastic deformation are still a subject for ongoing investigations.
In the present report TEM (an average grain size, diffraction patterns) and X-ray (an average coherently scattering domain size and its log-normal distribution, elastic microdistortions, dislocation density, crystallographic texture) results as well as results of the microhardness measurements in pure Cu, subjected to SPD via high pressure torsion (HPT) are presented. The features of microstructure evolution are discussed on the bases of the detailed investigations ranging from very small strains to very high ones (with true strains up till more than 10 ) enabling development of nanostructures.
The obtained results revealed the 3-stage microstructure evolution during HPT. In the first stage (up to 0.2 revolutions) the microstructure is of a cellular type with a high density of dislocations. The increase in a number of revolutions up to 0.4-0.5 (the second stage) resulted in the recovery, indicating to appearance of subgrain structure, increase in coherently scattering domain size, decrease in elastic microdistortions and dislocation density. In the third stage (from 1 to 5 revolutions) the grain nanostructure is developed along with some decrease in the coherently scattering domain size, increase in the elastic microdistortions and dislocation density. Considerable changes in the crystallographic texture were revealed as well. The obtained results of the structural investigations are in a good agreement with results of the microhardness measurements exhibiting similar 3-stage behaviour.
The three dimensional finite element analysis of microstructure evolution and plastic deformation behaviour of pure Cu during HPT has been fulfilled.
The obtained experimental results and results of computer modeling shed more light on the problem of the nanostructure development at SPD by HPT.

1. R.Z. Valiev, R.K. Islamgaliev, I.V. Alexandrov. Bulk Nanostructured Materials From Severe Plastic Deformation, Progress in Materials Science, 45 (2000), 103-189.

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1. A change in dislocation density during equal-channel angular pressing of Cu: experiment and simulation.
2. Analysis of homogeneity of texture formation processes under high pressure torsion
3. Analysis of Deformation Behavior of Cu Processed by High Pressure Torsion
4. X-RAY ANALYSIS OF HIGH PRESSURE TORSION INDUCED NANOSTRUCTURES IN TI AND NI
5. A physical criterion for the grain subdivision during severe plastic deformation
6. X-ray Analysis of Cu Subjected to SPD
7. Experimental studies and modeling of SPD materials