Theory of formation of second-phase particles as a result of diffusive saturation of solid solutions

A complete system of canonical equations, which describes the precipitation of new-phase particles as a result of diffusive saturation, is formulated. An asymptotic solution of this system of equations with respect to time is obtained in the general form. The volume of the precipitated new phase and the motion of the boundary of a two-phase region at a given point in the crystal is found for sufficiently large times to be independent of the nucleation mechanism and of the mechanism of mass to the particles of the precipitated phase.     

Evolution of a microstructure of materials under irradiation

The evolution of a microstructure of metals (or alloys) under irradiation resulting in swelling of the material is considered for the case with the formation of Frenkel pairs. A closed system of equations describing the evolution of the microstructure of the material exposed to irradiation is obtained, and relationships for the swelling rate are derived. It is shown that the swelling rate varies linearly with time for a stationary source of point defects (the number of Frenkel pairs per lattice site). An expression for the swelling rate is deduced for a radiation source operating in a more realistic pulsed mode.     

Phase competition in late stages of diffusive decomposition

The late stages of diffusive decomposition of a supersaturated solid solution into phases consisting of multicomponent stoichiometric compounds with a common element are investigated. It is shown that a competition is possible between phases for the common component, as a result of which only one of these phases survives. Fiz. Tverd. Tela (St. Petersburg) 40, 655–657 (April 1998)     

Theory of diffusive decomposition of supersaturated multicomponent systems

A closed system of equations, which describes the evolution of supersaturated multicomponent solutions, is obtained. A general solution of these equations is determined in the late stage of decomposition, which is determined by nonlinear diffusive interaction of macrodefects.The algebraic equations, which determine the coexistent phases, are obtained.The size of distribution function for particles is determined for each phase. The boundaries of the coexistent phases are defined.     

Theory of diffusive decomposition of supersaturated solid solution under the condition of simultaneous operation of several mass-transfer mechanisms

The kinetics of diffusive decomposition of a supersaturated solid solution under the condition of simultaneous operation of several mass-transfer mechanisms are developed. It is shown that the expressions for the growth rate of the precipitate and for the size distribution function have one peak. The location of these peaks, which slowly changes with time, can be considered a slowly changing parameter.     

Kinetics of the phase separation of a low-viscosity liquid supersaturated with gas at the intermediate and later stages

The separation kinetics of a low-viscosity liquid supersaturated with gas is studied. It is shown that the number of bubbles per unit volume at the intermediate stage of the process remains virtually constant, whereas the amount of the gas per unit volume of the solution significantly decreases, almost attaining the equilibrium value. At the later stage, small subcritical bubbles disappear due to gas transfer to large supercritical bubbles; as a result, the number of bubbles in the virtually equilibrium (as to the dissolved gas) liquid decreases. For all the stages, the kinetics of the changes in the bubble distribution function and in the amount of gas per unit volume of the solution is determined.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 94–105.Original Russian Text Copyright © 2005 by Slezov, Abyzov, Slezova.     

Kinetics of impurity segregation at grain boundaries in polycrystals. II. Concentrated solution

The isothermal impurity segregation from a finite-size grain into an intergrain boundary region or at an external free surface is investigated when the impurity concentration in the boundary region is not small. Simple algebraic equations are obtained that describe the impurity concentration for the case of several competing and interacting impurities. The process of segregation of two impurities is discussed in detail, and it is shown that the concentration of one of them can have a maximum as a function of time. Fiz. Tverd. Tela (St. Petersburg) 40, 251–253 (February 1998)     

Phase transitions in condensed media at a finite rate of formation of a metastable state

The influence of the finite rate of formation of a metastable state on the kinetics of the first-order phase transition is analyzed. The conditions determined by the thermodynamic parameters and the cooling rate of the system under consideration are derived. Under these conditions, the formation of the metastable state can be treated either as an instantaneous process, when nucleation occurs at the end of the cooling stage, or as a slow process, when intensive nucleation of a new phase proceeds within the cooling stage. An equation describing the time and temperature that correspond to intensive nucleation of new-phase particles is obtained. The nucleation stage of the new phase takes place in the immediate vicinity of the temperature determined from this equation. All the other parameters, which determine the kinetics of the initial and transient stages of the phase transition, are calculated with respect to this temperature. As an example, all the relationships for a weak solid solution are presented.     

Theory of gas porosity produced as a result of diffusive decomposition of multicomponent systems

A complete set of equations, which describe the kinetics of formation of gas porosity, is derived. The large and small pores are defined and analyzed. The methods of solution for an arbitrary number of impurity atoms are given for the limiting cases of large and small pores. The filling of pores with a molecular gas containing matrix atoms is analyzed in detail. The obtained results are compared with the experimental data.     

Gas bubbles in viscous liquids and melts

The basic set of equations and boundary conditions for viscous liquids and melts with gas has been derived. The flux of bubbles in the space of sizes, distribution of bubbles with respect to size, number of bubbles in the unit volume, and swelling of the system of viscous gas with liquid have been found. The initial and intermediate stages of the diffusion decomposition of the metastable system of viscous liquid with gas are considered.