Gatsenko O. Evolution of hierarchical defect structures and phase composition in the unsteady conditions of deformation of fcc metal materials

The dissertation is devoted to the analysis of the mechanism and the dynamics of relaxation and synergetic structure formation during plastic deformation of fcc metals and multiphase aluminum-based alloys. The quantitative characteristics of the structure were determined by statistical analysis of the transmission electron microscopy data. The methods of computer simulation with application of GRID technologies were used for large-scale computing of deformation formation with application of the molecular dynamics method. The calculations were made on the basis of the cluster IMP NASU. The experimental and computational results obtained by MD simulations are important and relevant from theoretical and practical point of view. On the basis of statistical analysis of the TEM-images of deformed and destroyed 2024-T3 alloy samples and comparison with the results of the TEM investigation of structure formation by rolling the polycrystalline nickel samples shows that the softening of the material during deformation and fracture is caused by the evolution of recrystallization processes. The analysis of the kinetics of recrystallization shown that the possible mechanism of the growth of recrystallization nuclei, i.e. micrograins formed by crystallization of the amorphous structure of the hydrodynamic flow channels (HC), is their merging. Ignoring the fact that micrograins have different crystallographic orientation, in the area of the micrograins boundaries some processes can occur, which are similar to those occurring in the deformed crystalline material far from the balance and they can lead to the formation of the HC. The liquid-like structure of boundary layers makes it easier to turn the neighboring micrograins in the right direction and provides the single orientation of the area of their accumulation, which lead to further evolution of the recrystallization process. The important issue of aviation 2024-T3 alloy is realted with a search of machining, which can contribute to an increase of its fatigue life. Until recently, experimental researches of various authors were ambiguous and did not solve this issue. It was shown for the first time in the thesis on the basis of the statistical analysis of the phase composition of 2024-T3 alloy after various machining conditions, that the fatigue life increases after preliminary deformation with impulse load. It is the result of the formation of the optimal concentration of the strengthening phase particles. In the alloy, which is fractured during fatigue loading, the total concentration of particles is substantially smaller than in the alloy, which is fractured under static or dynamic tension. From the fundamental point of view, the issue of formation HC remains to be unresolved. The molecular dynamics (MD) simulations with application of GRID technologies and the interatomic interaction potentials by embedded atom method (EAM) - allowed for the first time to show the possibility of formation of atom-vacancy states in dislocation-free fcc nanocrystals that may be considered as the nucleus of HC