V. Yu. Dobretsov

Effects of the Interaction between Order Parameter and Concentration on the Kinetics of Antiphase Boundary Motion

The microscopic mean-field kinetic equation introduced previously is used to investigate the motion of an antiphase boundary (APB) after the quench of a disordered alloy below the ordering spinodal. A strong interaction between order and concentration fields in non-stoichiometric alloys results in a peculiar evolution of the structure of an APB and in unusual concentration, temperature and time dependence of the kinetic coefficients for its motion.

Effect of atomic binding on inelastic νe scattering

The energy spectra of electrons knocked out from atoms due to inelastic νe scattering are calculated within the electroweak minimal model, incorporating neutrino electromagnetic form factors. It is shown that these spectra differ significantly from the free scattering ones not only at incoming neutrino energies comparable with electron binding, but also at energies being an order of magnitude larger. For magnetic scattering, the cross sections on bound electrons are always less than on the free ones, and recoil electron spectra at low kinetic energies are naturally cut off. The role of these effects in the scattering of reactor νeis demonstrated.

The microscopical theory of homogeneous nucleation in alloys : I. General relations

The earlier-described generalized Gibbs distribution approach to the theoretical description of non-equilibrium alloys is used to develop the microscopical theory of homogeneous nucleation in metastable alloys. Some exact and approximate relations for the free energy of a non-uniform alloy depending on the local concentrations are presented. These relations are used to microscopically describe the alloy state with the critical embryo. This state is supposed to correspond to the saddle point of the generalized grand canonical potential in the -space, while the variations of the size and the position of the embryo correspond to certain fluctuative modes at this saddle point. These notions are used to derive the microscopical expressions for all of the parameters of the phenomenological theory of nucleation - in particular, for the nucleation barrier and the prefactor in the Zeldovich-Volmer equation for the nucleation rate.

The microscopical theory of homogeneous nucleation in alloys: II. Calculations of nucleation parameters for various alloy models

The earlier-described microscopical theory of homogeneous nucleation in alloys is used to calculate the nucleation rate and the critical embryo parameters for several alloy models. The results of the calculations provide both qualitative and quantitative information about the characteristics of nucleation in alloys and their variations with the supersaturation s, the temperature T, and the inter-atomic interaction range . Several approximations of various levels of sophistication are used to treat the composition fluctuation effects which are shown to be usually important for the thermodynamics of nucleation. With increasing supersaturation or temperature the nucleation barrier lowers and the embryo interface with the exterior phase gets more diffuse, in agreement with the results of previous treatments, but making allowance for the fluctuative effects provides significant quantitative refinements for the results. The limitations of the conventional theories of nucleation due to neglecting the interaction of different embryos are discussed, and their region of validity, depending on the parameters s, T, and , is estimated.

Stochastic description of phase separation near the spinodal curve in alloys

The earlier-developed statistical methods for nonequilibrium alloys are applied to stochastically describe phase separation near the spinodal curve. An important parameter of the theory is the size of local equilibrium regions, which is estimated using simulations for the different values of this parameter. The simulations based on this approach reveal significant changes in the type of evolution from nucleation to spinodal decomposition under variation of concentration and temperature across the spinodal curve. The scale of these changes seems to be mainly determined by the difference of the properly defined supersaturation parameters.

Kinetic Features of Non-Simplest Alloy Orderings: D03, L12,and L10 Orderings

The earlier-developed master equation approach is used to study kinetic features of alloy orderings with more than two types of ordered domains. We develop a kinetic cluster field method being a kinetic analogue of the known cluster variation method, and present a microscopical model for deformational interactions in concentrated alloys. The described methods are used for extensive simulations of various phase transformations involving D03, L12 and L10 orderings. The simulations reveal a number of interesting microstructural effects, many of them agreeing well with experimental observations.

Kinetics at Early Stages of Phase Transformations in Metallic Alloys

Problems of the theoretical description of nonequilibrium statistical systems are important for various areas of physics. For equilibrium systems, such a description is given by the Gibbs distribution and statistical thermodynamics, but for states far from equilibrium there are no analogous standard approaches available. The elaboration of suitable approaches is of particular interest for configurational alloy kinetics, the evolution of the atomic distribution in nonequilibrium alloys. The microstructure and macroscopic properties of such alloys, e.g. strength and plasticity, depend crucially on their thermal and mechanical history, for example, on the particular kinetic path of the phase transformation. A number of theoretical approaches have been proposed in that field, e.g.1–3. However, these approaches either treat the uniform alloy case1 which excludes from consideration most applications of interest, or use various unclear approximations, such as the extrapolation of the linear Onsager equation for weakly nonequilibrium states to the nonlinear region of states far from equilibrium2,3, which can result in significant errors4,5.

Kinetics At Early Stages of Phase Separation And Ordering in Alloys

Problems of structural evolution of nonequilibrium alloy states attract much attention. Theoretically, they are studied using either approximate kinetic equations1–6 (AKE) for the local concentration or mean occupation number c i =c(r i ,t) at lattice site i (say, for A-atoms in the binary A-B alloy), or direct simulation, e.g. Monte-Carlo methods7,8. AKE seem to be more transparent and universal than simulation methods, and many new qualitative results in this field1–4 were obtained using AKE. However, the currently used phenomenological forms of AKE3,4 are based on Onsager-type linear relations between time derivatives dc i /dt and thermodynamic driving forces ∂F/∂c j (where F is the free energy of an inhomogeneous alloy), which hold only for near-equilibrium states. Thus extrapolation of these relations to states far from equilibrium, such as those obtained by deep quenching, transient states at spinodal decomposition (SD), etc, can hardly be justified, while kinetic phenomena just in these states attract most interest3,4,9.