STRUCTURAL CHARACTERIZATION OF NANOSTRUCTURED MATERIALS PROCESSED BY SEVERE PLASTIC DEFORMATION

I.V. Alexandrov and R.Z. Valiev

Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, K.Marksa 12, 450000 Ufa, Russia

Keywords: nanostructured materials, plastic deformation

Recent studies showed that bulk samples of nanostructured pure metals and alloys processed by severe plastic deformation (SPD) posses attractive mechanical and physical properties. In a number of cases one can observe a change of usually insensitive constants where modulus of elasticity, Debye and Curie temperatures are present. Appearance of unusual properties in nanostructured materials are conditioned by formation of a specific defect structure due to severe plastic deformation process.

In the given research, which was devoted to studies of peculiarities of structure evolution during the SPD process and a detailed characterization of the formed nanostructured state, there were presented summarised results of the conducted TEM and X-ray investigations. It was shown that SPD leads to transformation of subgranular cellular structure, containing small angle misorientations among neighbouring elongated fragments, into equiaxed granular structure with high angle grain boundaries.

There were presented facts about the formed during the SPD process nanostructure, characterized by ultrafine grain size of 100-200 nm, a high level of internal microdistortions in a crystallite lattice, extrinsic grain boundary dislocations of high density (EGBDs) initiating long range fields of internal stresses and resulting in elevated values of the atomic displacements, and also lowered Debye temperature.

Based on the obtained results a structural model of nanostructured materials processed by SPD technique was developed.