V. V. Slezov

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.

Decomposition kinetics of a solid solution with the formation of a new phase of complex stoichiometric composition

The evolution of a metastable solid solution containing impurities of different sorts is investigated at the nucleation and transient stages upon precipitation of new-phase particles of a stoichiometric composition. The flux of new-phase particles in the size space, their maximum number, and the size distribution are determined.

Kinetics of first-order phase transitions in a solid solution

Abstract A wide variety of characteristics during the stage of nucleation of a single atom phase in a solid solution is obtained under steady-state external conditions for a broad range of sizes. These include, flux in the space of sizes, number of new phase particles and their distribution function. A technique is put forward to account for the influence of the elastic field, formed in the vicinity of the nucleated phase particles and interaction of the solute components in a solid solution on the kinetics of the phase transitions. The proposed theory is extended to phase transitions when the nucleated new phase has the complex stoichiometric composition.

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.

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.

Nucleation kinetics of a solid phase in supercooled melts or liquids under heat-insulating conditions (The Initial Stage)

The initial stage of decomposition of a supercooled melt or a viscous liquid under heat-insulating conditions has been considered in terms of the method of virtual media. The heat removal from the interface is taken as the controlling process in the vicinity of a growing nucleus. In addition to the quasi-steady-state equations (which already became standard) for the nucleation rate and the distribution function of subcritical particles of a new phase, an estimating equation has been derived for the time required to reach steady-state values of these characteristics. Numerical evaluations have been performed for nickel. It has been demonstrated that the chosen model of the controlling process is valid only under the condition of weak heat removal. Attention has been drawn to the difference between the “diffusion” and “thermal” processes of nucleation.

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.

Kinetics of nucleation of the solid phase in supercooled solutions or liquids under heat-insulating conditions: Intensive nucleation stage

The kinetics of decomposition of a supercooled melt or a viscous fluid under heat-insulating conditions during intensive nucleation has been investigated. Particles of a new phase have been studied, whose size is larger than the critical value, and for which the times are longer than the settling time of the classical quasi-steady state, which is characteristic of subcritical nuclei. The heat removal from the phase boundary is assumed to be the key process in the vicinity of a growing particle. The estimates of the duration of the stage of intensive nucleation, the maximum number of nucleated particles, and their average “size” have been obtained. Numerical simulations have been performed for nickel.

Adaptive photodetectors for vibration monitoring

We report on simple high-sensitivity interferometric technique of detecting vibrations and present characteristics of laser vibrometer using GaAs, CdTe and CdZnTe adaptive photodetectors based on the effect of the non-steady-state photoelectromotive force. It enables efficient direct conversion of high-frequency phase modulation of speckle-like optical wave reflected from the vibrating object into an output electrical signal with concomitant setting of optimal operation point of the interferometer and suppression of amplitude laser noise. The results of measurements of semiconductor materials parameters of CdTe and CdZnTe are presented. The experiments are carried out for diffusion regime of signal excitation at light wavelength &lgr;=1.15 &mgr;m. The sign, conductivity and diffusion length are estimated from the dependencies of the signal on the temporal and spatial frequencies. Preliminary studies at 1.06 &mgr;m showed that it is possible to detect ultrasonic vibrations with the amplitude of 0.2 Å with a signal power of 20 mW and a bandwidth of 15.5 MHz. This optical phase-to-electrical signal converter is not sensible to ambient vibrations, thermal drift, amplitude laser noise and is therefore appropriated for industrial applications.

Method of virtual media in the theory of first-order phase transitions

The method of deriving a set of equations describing the first-order phase transitions under different conditions has been proposed. A set of equations is obtained for a medium in which a decrease in the pressure leads to the formation of bubbles filled with a dissolved gas.