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The influence of the orientation of Ti–Al interphase boundary on the intensity of mutual diffusion, as well as the influence of its deformation of Ti at temperatures above the melting temperature of Al, were studied by the method of molecular dynamics. Zope and Mishin EAM potentials were used to describe interatomic interactions in the Ti–Al system. Three orientations of the boundary relative to the hcp Ti crystal were considered: , , and . It was found that the orientation of the interfacial boundary affects the intensity of diffusion in the Ti phase: Al atoms diffused more intensively into the titanium lattice at the orientation and less intensively at the and orientations. This influence of the orientation of the interphase boundary is associated with the probability of detachment of the Ti atom from the crystal–liquid interface and is determined by the difference in the energies of the Ti atoms in the aluminum phase and those built into the boundary of the crystalline phase. At the initial stage of mutual diffusion, the boundary between the crystal and liquid metal was observed to shift from the very interface between Ti and Al by two or three atomic planes into the aluminum phase—a thin layer of aluminum near the boundary remained in the crystalline state, repeating the crystal lattice of titanium. This is due to the fact that the Ti–Al bonds at the boundary are much stronger than the interatomic bonds in liquid aluminum. When studying the effect of elastic deformation on the intensity of mutual diffusion, it was found that, in almost all cases, the intensity of diffusion increases with tension and decreases with compression, which is associated with a corresponding change in the free volume, which largely affects the diffusion mobility of atoms. [ABSTRACT FROM AUTHOR]

The process of diffusion mixing at the aluminum-silicon interface in the case of two, four, seven, and ten atomic aluminum monolayers on the silicon (111) surface has been studied. The investigations were performed by the molecular dynamics simulations method using Large-scale Atomic/Molecular Massively Parallel Simulator package. Concentration and density profiles at the phase interface were analyzed to investigate the kinetics of mixing. The formation of a transient diffusion layer at the boundary of the liquid and crystalline phases is established. The melting of the phase interface was explained in the framework of the theory of contact melting. It is shown that diffusion mixing, which precedes contact melting, occurs at the level of atomic blocks (clusters), i.e. we can talk about the island nature of contact melting at the initial stage. The diffusion process was analyzed based on the theory of free volume in liquids. [ABSTRACT FROM AUTHOR]

Tracer self-diffusion of Co in a compositionally complex AlCoCrFeNiTi 0.2 alloy is measured using the radiotracer technique. The complex multi-phase microstructure (a mixture of BCC, B2, σ, and FCC phases in dependence of the processing conditions) is carefully analyzed to quantify the measured concentration-depth profiles in terms of volume and short-circuit diffusion contributions. The analysis allowed to determine the volume diffusion coefficients in the B2 phase and those along the high-angle B2/B2 grain boundaries (GBs). The absence of any "sluggishness" of diffusion in this alloy is unambiguously verified, both for volume and GB diffusion contributions. [Display omitted] [ABSTRACT FROM AUTHOR]

Atomistic computer simulations are applied to investigate the atomic structure, thermal stability, and diffusion processes in Al–Si interphase boundaries as a prototype of metal–ceramic interfaces in composite materials. Some of the most stable orientation relationships between the phases found in this work were previously observed in epitaxy experiments. A non-equilibrium interface can transform to a more stable state by a mechanism that we call interface-induced recrystallization. Diffusion of both Al and Si atoms in stable Al–Si interfaces is surprisingly slow compared with diffusion of both elements in Al grain boundaries but can be accelerated in the presence of interface disconnections. A qualitative explanation of the sluggish interphase boundary diffusion is proposed. Atomic mechanisms of interphase boundary diffusion are similar to those in metallic grain boundaries and are dominated by correlated atomic rearrangements in the form of strings and rings of collectively moving atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

A consistent thermodynamic description of the process of stationary eutectic solidification at low supercoolings is presented. To find the relation between the parameters that characterize this process, a new approach has been used that is based on obtaining an expression for the rate of the free-energy change by two different methods. This has made it possible to obtain a new relationship between the parameters of the arising structure. The first method is based on the consideration of the free-energy change that is due to the dissipative process of separative diffusion, which occurs in the bulk of the liquid phase. The second method involves the consideration of the balance of changes in the free energy far from the solidification front. Based on various extremum principles, analytical expressions for the rate of solidification and for the parameters of the arising eutectic structure have been derived. Rodlike and lamellar structures, which are observed most often in experiments, have been considered. It has been shown that conditions for the appearance of a particular structure are governed by the minimum values of the surface energy of the interfaces between the solid phases and by the 'decomposition structure factor,' which is introduced in this work. [ABSTRACT FROM AUTHOR]

Conditions of equilibrium at the interface between the solid and liquid phases in the course of directional solidification of a two-component melt and the rate of the decrease in the free energy of such a system in the case where diffusion in the solid phase can be neglected have been investigated. Using the previously suggested new boundary conditions for the diffusion equation, analytical expressions have been obtained for the shifts of the values of the concentrations in the liquid and solid phases at their interface, as well as for the solidification temperature as compared to the initial equilibrium values corresponding to a zero growth rate. It is shown that the magnitudes of these shifts are directly proportional to the solidification rate and are inversely proportional to the coefficients that describe the transport of atoms of various sorts through the interface. Using the above-mentioned boundary conditions, we have found an expression for the rate of the decrease in the free energy of the system under consideration and have shown that it can be divided into two parts, one of which is determined by the processes at the interface between the phases and the other is controlled by diffusion processes that occur inside the volume of the phases. The results are compared with those obtained in terms of a different approach, which is based on the determination of the balance between the changes in the free energy in the solid and liquid phases far from the solidification front. It is shown that both approaches yield similar results, so that in some cases they can be used as mutually complementary. [ABSTRACT FROM AUTHOR]

The rate of a free-energy decrease upon the motion of a planar interface between two phases of a binary solid solution has been studied. A general expression for this rate in such a system has been obtained; it has been shown that the expression can be divided into two parts, one of which is determined by the processes at the interface and the other, by diffusion processes occurring inside the bulk of the phases. For the case of dilute solutions, analytical expressions have been obtained for each of the terms with the use of characteristic times that describe the processes of atomic transitions through the interface. Numerical calculations of the time dependence of both terms have been performed; in the limiting cases of long and short times, the corresponding expressions were found explicitly. [ABSTRACT FROM AUTHOR]