Papers by Author: Anna Dubravina

Abstract: The evolution of strength characteristics and the microstructure of copper subjected to high pressure torsion (HPT) are studied under variation of strain and hydrostatic pressure. Measurements of Multiple X-ray Bragg Profile Analysis (MXPA) yield microstructural parameters like dislocation density and arrangement, as well as crystallite (domain) size and distribution, and long-range internal stresses. TEM investigations are carried out to analyse the structural elements and to compare them with the results of MXPA. The strength behaviour is studied by microhardness measurements. The investigations are performed within wide ranges of resolved shear strains 􀁊 = 1 to 400 and of applied pressures p = 0.8 to 8 GPa. The onset of the deformation stages IV and V is strongly affected by the hydrostatic pressure i.e. shifted to higher values of stress and strain with increasing pressure. The experimental results indicate the occurrence of recovery effects, which seem to be of static as well as of dynamic nature, and to be responsible for extended ductility in SPD materials.

Abstract: In the present work the processes of crystallographic texture formation during severe plastic deformation (SPD), which has been carried out in the conditions of high imposed pressures (up to 6 GPa) and extremely large cumulative deformation degree (e up to 1÷100 and more) in pure metals, are investigated. It is shown that the processes of nanostructure formation as a result of SPD are accompanied not only by known processes such as a fragmentation, extension of misorientation angles, character modification of dislocation density, but also by the formation of deformation textures. The deformation textures, having been formed as a result of SPD are analyzed for the examples of FCC Cu, BCC W and HPC Ti, depending on a cumulative deformation degree and SPD scheme. The obtained crystallographic texture data are used for the analysis of the nanostructured state formation regularities.