Papers by Author: S.Yu. Mironov

Abstract: The paper considers the structure evolution during annealing of submicrocrystalline (SMC) titanium with a mean grain size of 0.2 µm, processed by severe plastic “abc” deformation. Electron microscopic studies have revealed that the microstructure of the SMC titanium is heterogeneous and of a mixed type. One can observe a high density of dislocations, grains, subgrains, elements of a banded structure and areas comprising coarse (up to 1-2µm) and fine (up to 0.1µm) grains. The grain boundary misorientation spectrum is presented by low angle and high angle boundaries of random and special types. Three stages of annealing of SMC titanium have been revealed. The second stage is connected with the intense SMC grain growth and the value of activation energy of grain growth at this stage is twice less than the value of activation energy of grain boundary diffusion in titanium. The latter is caused by acceleration of diffusion processes at SMC grain boundaries having an atom-disordered structure. The texture evolution with annealing temperature is characterized by weakening of predominantly basal texture in the as-received SMC state and strengthening of a prismatic component. The weakening of the basal component is connected with the growth of SMC grains first of all, as well as the increase of the volume fraction of special boundaries.

Abstract: The microstructure and texture evolutions in pure titanium during severe plastic deformation at T=400°C were investigated. Compressive deformation of prismatic samples was sequentially applied in three orthogonal directions up to 12 steps and a strain at each step of 40%. A radical microstructure refinement (from 20 to 0.2 µm) during strain has been found. The features of the deformation structure are a high level of internal stresses, high density of dislocations, a large number of deformation induced boundaries and the presence of twins. It is shown that during strain there is a significant change in disorientation angles and axes of individual high angle grain boundaries. At the same time the total set of high angle boundaries - Misorientation Distribution Function (MDF) and texture - does not change significantly with strain. The reasons for the change in disorientation angles and axes at new deformation-induced boundaries during plastic flow are discussed.

Abstract: Microstructure evolution in alpha-beta Ti-64 alloy samples with lamellar structure deformed to a height reduction of 70% at temperatures between 450 and 800°C has been investigated. The deformation led to a distinctly globularized structure of α- and β-phase in the whole temperature interval. The dependence of globular grain size on deformation temperature is of a linear character up to the temperature of warm deformation at which formation of an SMC structure takes place. Continuous recrystallization was observed in the α-and β-phases. Different types of defects responsible for splitting of α-lamellae such as low and high angle boundaries, shear bands and twins were found. An investigation of boundary misorientation spectra in the α-and β-phases deformed to different strains at 550 and 800°C was carried out. Typical boundary misorientation spectra for single phase metals with the same lattice were obtained. The boundary misorientation spectrum depends weakly on strain and deformation temperature. The results of this study show the importance of transformation of semi-coherent interphase boundaries to non-coherent ones for globularization of lamellar microstructures.