Lyashenko Y. Influence of diffusion processes on the evolution of phase distribution in the contact zones of the binary and ternary metallic systems

This thesis is devoted to the theoretical description and modeling of the peculiarities of the solid state reactions and interdiffusion in binary and ternary metallic systems on the basis of the general thermodynamic principles. Approaches to the self-consistent construction of the phase diagrams and evaluation of the diffusion interaction in the ternary systems with two-phase regions were developed. The criteria of the suppression/growth of the phases were obtained for the cases, when in the final diffusion zone some phases either completely suppressed, either their growth could be decelerated by the addition of the third component in the binary system. The problems of low-temperature diffusion phase transitions, namely discontinuous precipitation, phase formation at diffusion-induced boundary migration, segregation effects on the moving phase boundaries were considered on the basis of the developed approaches. The evolutionary equations which allows unambiguously calculate the thickness of the lamellas and the velocity of motion of the phase transition front were considered. The description of such kind of problems was performed on the basis of the developed approach for solution of the following equations: 1) of diffusion mass-transport; 2) of entropy flux balance; 3) of maximum of entropy production. The investigation methodology of the samples with specific shape (T-shape samples) was developed for the purpose of diffusion coefficient evaluation in the ternary multiphase systems.