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In this paper, we present an interatomic potential predicting thermal properties of phases of titanium in their temperature range of stability at zero pressure. The potential was developed within the approach proposed by A.G. Lipnitskii and V.N. Saveliev for atomic systems with metallic and covalent types of bonds, which exactly describes three-particle interactions. The parameters of the potential were optimized to the database of results of density-functional calculations and known experimental data for hexagonal close-packed phase of Ti. The developed potential correctly describe ω -Ti as the ground state at zero temperature. Prediction of the point-defect energies, stacking fault energies, surface energies, specific heat, and thermal expansion is in reasonable agreement with the experimental and density-functional data. This indicates the transferability of the potential to describe phases of titanium in a wide range of temperatures. Melting point of β -Ti predicted using the developed potential is in excellent agreement with the experimental value. For the developed potential the lowest temperature of the mechanical stability of the β phase equals to 1156 K, at which the spontaneous transition to the α phase occurs. The volume of the transformation from β to α phase is correctly predicted by the developed potential in agreement with the experimental value. MD simulations in combination with Gibbs-Helmholtz integration show that the α phase is mechanically and thermodynamically stable at any temperature up to melting temperature of the β -Ti. The constructed potential can be applied for modeling the β phase at its range of mechanical stability as well as α phase at temperatures up to melting point of the β -Ti.

The development of low-swelling radiation-resistant alloys is vital for the creation of reliable fusion reactors. In this article, we revisit the long-standing problem of very low radiation swelling in V-Ti-Cr alloys by means of DFT calculations. In particular, we study double and triple interactions of point defects such as solutes, vacancies and self-interstitial atoms in bcc V. According to our results titanium atom and vacancy are strongly attracted and in addition to pairs form highly stable triple Ti-Vacancy-Ti complexes, which are absent in the case of chromium. By using an analytic model of void growth and using calculated binding energies of point defect complexes in bcc vanadium we obtain three orders of magnitude reduction of swelling rate due to the formation of Ti-Vacancy-Ti complexes, which allows to explain experimental observations. Finally, we explain the causes of the strong attraction between titanium and vacancy using geometry and electronic structure analysis.

Titanium additions suppress the radiation swelling in vanadium alloys, but the mechanism of the suppression is debatable. It is claimed that interactions of Ti atoms with vacancies in vanadium are crucial in the suppression. In this paper we study clustering of excess vacancies in pure V and V-4Ti by molecular dynamics simulations at 700 K based on our interatomic potentials constructed earlier for the Ti-V system. For pure V the process results in the formation of a Frank sessile dislocation while the clustering in V-4Ti ends with the formation of the Ti-vacancies complexes with a specific structure. This allows us to discuss a possible mechanism of the swelling reduction in V caused by Ti alloying.

The peculiarities of interfacial boundary diffusion where the boundary goes between nonmiscible metals with body-centered cubic (BCC) and face-centered cubic (FCC) lattices have been studied taking, as a case in point, the Cu/Nb system, and using the molecular dynamics method. The diffusion atomic displacements were shown to occur mainly near the mismatch dislocations and their intersections. The diffusion of the high-melting component was found to be characterized by high anisotropy with the predominant atomic displacement along the dense-packed direction in the interfacial boundary plane being common to FCC and BCC lattices with the Kurdyumov–Sachs mutual orientation.

New interatomic potentials for Mo and binary systems V-Nb, V-Mo, Nb-Mo, Nb-W and Mo-W are constructed taking into account the angular dependencies of interatomic interactions. Together with the potentials constructed earlier in the same approach, a complete set of potentials for modeling alloys of the V-Nb-Mo-W system at any component concentrations is obtained. A tendency to narrow the range of values of the calculated enthalpy of formation and the volume of formation in equiatomic alloys of the V-Nb-Mo-W system with an increase in the number of components was found. Deviations from the Vegard’s rule in the volume of formation of these alloys are shifted to the negative range of values when the number of components is more than two.

This paper presents the development of methods for the theoretical study of diffusion processes in solid solutions based on molecular dynamics (MD), taking into account the effects of ordering. The influence of concentration and temperature on the features of diffusion characteristics in substitution alloys is studied using the example of solid solutions V50W50 and V90W10. Modeling has shown that the V-W ordering is associated with the separation of plates enriched with tungsten in the planes (100). Vanadium atoms are more mobile and the difference in diffusion coefficients decreases with the equalization of component concentrations and temperature increases.

The problem of reliability of the prediction of alloy properties, which can be established from the results of atomistic simulations, is one of the factors constraining the integration of computer modeling into effective technologies for the development of new materials. The solution of this problem requires further development of methods for constructing interatomic potentials to improve the reliability of theoretical predictions, including the properties of materials at moderate and high temperatures. In this paper a new method for constructing interatomic potentials in binary systems is proposed. The method uses CALPHAD and experimental data on the formation enthalpies and lattice parameters, including characteristics at moderate and high temperatures. The new method is tested on the example of solid solutions of V-W system. The constructed V-W potentials predict the formation enthalpies and lattice parameters in good agreement with the known CALPHAD data at 2000 K and the results of experimental studies at 300 K, respectively. The new method can be applied to specify the interactions between atoms in multicomponent systems.The problem of reliability of the prediction of alloy properties, which can be established from the results of atomistic simulations, is one of the factors constraining the integration of computer modeling into effective technologies for the development of new materials. The solution of this problem requires further development of methods for constructing interatomic potentials to improve the reliability of theoretical predictions, including the properties of materials at moderate and high temperatures. In this paper a new method for constructing interatomic potentials in binary systems is proposed. The method uses CALPHAD and experimental data on the formation enthalpies and lattice parameters, including characteristics at moderate and high temperatures. The new method is tested on the example of solid solutions of V-W system. The constructed V-W potentials predict the formation enthalpies and lattice parameters in good agreement with the known CALPHAD data at 2000 K and the results of experimental studi...

Modeling of high-speed deformation of α-Ti at a pressure of 20 GPa and a temperature of 700 K simulating the conditions of high-energy effects is carried out. The mechanisms of plastic deformation, including sliding along prismatic planes and the α-ω transition, are established. A feature of the deformation process of titanium in the considered conditions, which leads to the formation of disperse inclusions of the α-phase in the ω-phase matrix, is revealed.

A model of high-angle general-type grain boundaries is developed and grain-boundary diffusion of niobium in a Nb–Cu system is investigated using the method of molecular dynamics. The results of predictions of the effect of a copper impurity on grain-boundary self-diffusion of niobium are compared with the experimental data on diffusion annealing of multi-layered composites containing Cu/Nb boundaries. Recrystallization of polycrystalline niobium is investigated under the conditions of grain-boundary diffusion of copper.

The results of theoretical and experimental studies of the mechanisms of diffusion-controlled processes in nanostructured metals and alloys available in the literature and obtained by the authors are discussed. The molecular dynamic method was used in the context of a modified embedded-atom method was used to investigate the process of collective recrystallization of nanocrystalline titanium. An analytical description of the recrystallization kinetics has been proposed which takes into account the contributions of triple joints to the thermodynamic driving force. Methods of transmission, including high-resolution, electron microscopy were used to examine the kinetics of collective recrystallization in nanostructured titanium VT1-0. The temperature dependence and values of the activation energy for collective recrystallization have been determined. Problems of practical implementation of nanostructured unalloyed titanium in medicine are discussed.

Suggested methods describe the process of self-diffusion along grain boundaries and triple junctions in polycrystals without using geometric models of the grain boundaries structure. The calculation method introduced diffusion characteristics along grain boundaries derived from the results of molecular dynamic simulations of nanocrystalline materials. The diffusion experiments were imposed to establish relationship between introduced diffusion characteristics and the diffusion parameters along grain boundaries and triple junctions of the Fisher’s grain boundary diffusion model. By the example of copper for the first time the characteristics of self-diffusion along grain boundaries of nanocrystalline materials and coarse grained analog defined in the same temperature range was compared for the first time. It was found that values of the self-diffusion characteristics along grain boundaries in high purity nanocrystalline and polycrystalline copper are equal at the same temperatures.

The evolution of atomic structure of the interphase boundary for composites from immiscible Cu/Nb elements is studied by the molecular dynamics method. It is established that the planar interphase boundary is stable at temperatures up to 1200 K. Atomic dissolution of elements is not revealed in the entire examined temperature interval, and the components are mixed on the interphase boundary of finite curvature in the form of clusters and nanolamellas; moreover, the amorphous state is not formed in the process of migration of the interphase boundary.

Investigations of the features of the diffusion along grain boundaries and of the diffusion-controlled processes in submicroscopic and nanocrystalline materials produced by methods of intense plastic deformation are reviewed. To determine the parameters of the diffusion along grain boundaries and triple junctions in metals, which are independent of the results of processing of diffusion experiments based on diffusion models, results of a molecular dynamic investigation of the diffusion in nanocrystalline copper considered as an example are presented. Comparison of the features of grain boundary diffusion in submicroscopic and nanocrystalline materials produced by various methods is performed.

Grain-boundary stresses in copper for 60 symmetrical tilt grain boundaries with different orientations of the grain-boundary plane and tilt axis have been calculated by the molecular-statics method with the use of embedded-atom-method potentials of interatomic interaction. It has been established that the grain-boundary stresses are negative for grain boundaries with small excess volumes and increase approximately linearly with a buildup of the excess volume. It has been shown that the increase in grain-boundary stresses is connected with a decrease in the average coordination number of atoms, whereas pairs of closely spaced atoms in the grain-boundary core cause a negative contribution to grain-boundary stresses.

An analysis of manifestation of the effect of acceleration of creep in polycrystalline metals and alloys in the presence of grain-boundary diffusion fluxes of an impurity from an external medium (coating) is performed. The influence of the softened (due to impurity diffusion fluxes) layer thickness on the creep character in molybdenum is discussed for the case of its diffusion contact with nickel. An analysis of the effects of the regime of impurity grainboundary diffusion on the value of strain-rate sensitivity and on the behavior of grain-boundary migration as a function of external stress is made. Using submicrocrystalline nickel as an example, the influence of grainboundary state on properties of metallic materials in submicrocrystalline state is investigated. Direct measurements, theoretical calculations and indirect estimations of the differences in grain-boundary diffusion coefficients in coarse- and ultrafine-grained states are performed. The role of dispersion hardening in stabilizing the submicrocrystalline structure and improving the creep resistance is addressed, including the case where the grain-boundary fluxes of impurity atoms are forced from an external medium.

We present a self-consistent calculation of the electronic structure for the (1 1 0) surface of equiatomic XTi (X=Fe, Co, and Ni) alloys in the B2 (CsCl) structure. The results were obtained using the film linearized augmented-plane-wave method. We have analyzed the change of the local density of states, the valence electronic charge distribution and the calculated work function in the series FeTi, NiTi, and CoTi alloys. It has been found that the bond ionicity at the surface is enhanced and the work function is reduced from FeTi to NiTi. The trend to surface segregation and chemical activity for the (1 1 0) surface of the studied alloys is discussed.

This paper presents the ternary interaction of N, H, and vacancy point defects and the nitrogen trapping ability of aluminum vacancies induced by hydrogen by means of DFT methods employed in VASP (Vienna Ab initio Simulation Package) and Abinit packages. The obtained vacancy formation energy of 0.65 eV is close to experimental values. Although the N–vacancy complex is unstable with the negative binding energy of −0.51 eV, the stability of H–vacancy–N is proved by the positive binding energy of 0.59 eV and the appearance of the orbital hybridization in the density of state (DOS) of atoms connecting to this complex. Moreover, Al vacancies can trap more than 4 N atoms, which prevents the formation of aluminum nitride and subsequently affects not only the hardness of the Al surface but also many practical applications of AlN coating.

The mesorelief of the surface of plastically deformed specimens is characterized by a correlation function. It makes it possible to determine the fractal dimension Dc and the correlation length ΔL from surface images of the studied specimens obtained under light and scanning electron microscopes. It is shown that two modes of behavior of the correlation function can be distinguished for specimens of iron silicide and austenitic steel broken in the process of active stretching. In one mode Dc and ΔL characterize the mesorelief of the surface at scale levels less than the grain size (Dc1, ΔL1) and in the other they describe it at scale levels on the order of several grains (Dc2, ΔL2). The behavior of Dc1, ΔL1, Dc2, and ΔL2 is studied as a function of the distance from the head to the breakage place for specimens of iron silicide and as a function of the degree of plastic deformation for specimens of corrosion-resistant steel. The characteristics increase stage-by-stage with increase in the degree of plastic deformation until the specimen fails.

A molecular-dynamic study of nucleation of structural defects in materials with an initially perfect crystal lattice by thermal fluctuations under high strain rates is performed. It is shown that thermal fluctuations can generate structural defects. There exists some threshold value of strain at which abrupt growth of regions with local structural changes is observed.

We have calculated the binding energy using the inserted atom method for divacancies for a large number of surfaces of aluminum, nickel, copper, palladium, silver, platinum, and gold, and also in the near-surface layers. A correlation was found between the binding energies at the high-index and low-index surfaces. The transition of the calculated quantities to bulk values was tracted while successively moving the defects into the depth of the near-surface layer of the material.

The energies for migration of vacancies and adatoms and the adatom formation energy at surfaces with low indices have been calculated for aluminum, nickel, copper, palladium, silver, platinum, and gold using the inserted atom method. We have found the self-diffusion activation energies for the jumpwise diffusion mechanism with participation of both types of surface point defect.

The vacancy formation energy is calculated using the inserted atom method for faces with high and low indices and in the near-surface atomic layers of aluminum, nickel, copper, palladium, silver, platinum, and gold. The transition of the calculated quantities to the bulk quantities is traced for successive insertion of a defect deeper into the near-surface layer of the material. The relaxation contribution to the energetics is revealed for each type of surface. A correlation is seen between the energies of formation at surfaces with high and low indices.

We present the calculations of vibrational states on the Al(110), Cu(110), Ag(110) and Pd(110) surfaces. The surface phonon frequencies and polarizations are calculated using embedded atoms potentials. For all surfaces of interest a surface state at the \ gG point, characterized by shear vertical displacements of atoms of the two upper layers is obtained. It is in contradiction to earlier calculations and experimental study for the Al(110) surface and in good agreement with experimental measurements for the Cu(110), Ag(110) and Pd(110) surfaces. It is shown that vibrational spectra of these surfaces are like to each other. On the whole, obtained results are in good agreement with available experimental data and first principles calculation results.

The spalling fracture in a copper crystallite with a specific intergrain boundary under pulsed loading is modeled numerically. It is found that the grain boundary changes the parameters of nonlinear waves generated by loading and significantly affects the character of the spalling fracture.

The process of pulse-train-induced cleavage fracture in a copper crystal with grain boundary was studied by methods of computer simulation. It is demonstrated that trains of isolated compression pulses induced in the material favor the tendency to fracture propagation along the grain boundary.

An attempt is made to estimate the fractal dimension of the lateral surface of a steel sample formed as a result of friction by analyzing an image obtained using a scanning electron microscope.

The electronic structure of the Ni3Al(001) surface is calculated using the self-consistent film linearized augmented- plane-wave method. As a result, surface states both above and below the Fermi level have been found. Practically, all the occupied surface states are generated by the atoms of nickel. There is only one occupied state at the M point localized at the surface atoms of aluminium. The states above the Fermi level are mainly localized at the Al atoms of the surface layer. There are states totally generated by the atoms of aluminium. Calculated work function exceeds the corresponding values for the Ni(001) and Al(001) surfaces.

A molecular dynamics method was used to study the interaction of isolated compression pulses with the (100) and (110) free surface in a copper monocrystallite. It is shown that this may be accompanied by cleavage fracture. Parameters of compression pulses which lead to cleavage processes are determined.

08 at metal surfaces is important for studying surface processes such as crystal growth or epitaxial growth of thin films on surfaces, catalysis, etc. Data of this kind are hard to obtain experimentally. Because it is necessary to include a large number of atoms in the calculations, and because of the low symmetry, conventional first-principles computations for systems with defects at a surface are technically difficult. In order to compute the characteristics in these cases, various semiempirical methods are used. One of them is the method used in this paper, i.e., the embedded atom method. However, in contrast to Refs. 1 and 2 in this paper we use the charge density of a free atom calculated in the local density approximation to construct the embedded atom function. The embedded atom method was developed for calculations of bulk properties of transition metals, but in recent times it has been used successfully to study many features of surfaces as well, including surface phonons, surface diffusion, reconstruction, determining the shape of adsorbed clusters, surface relaxation, etc. Along with papers that use this method for transition metals, attempts have been made to use it for nontransition metals as well, in particular for Al. Recently, the energetics of vacancies at metal surfaces have been studied theoretically. As a rule, the authors limit themselves to two to three materials. In this paper we calculate the energy characteristics of defects within the framework of a single approach for a wide range of metals: namely, Al and the six transition metals Ni, Cu, Pd, Ag, Pt and Au. We calculated energies of formation for vacancies located on the low-index surfaces ~111!, ~100! and ~110!. We also calculated energies for vacancies located in a nearsurface layer of material. This approach allows us to compare the values of energies of formation for a representative series of metals among themselves, and to follow how the values of energy of formation of vacancies change with depth into the bulk. In addition, we calculate the relaxation contributions to the energetics for each type of surface. Table I lists the energies of formation for vacancies in the bulk, along with the experimental quantities used to fit the interaction potentials. Table II lists the computed values of energies of formation for vacancies at surfaces, and also in near-surface atomic layers. In Table II we also list known results of other calculations. As is clear from this table, for all materials the energy of formation of a vacancy has its lowest value on the ~110! surface compared to other surfaces, and is roughly 20% of its bulk value. It is clear from these low values of energy of formation that even at relatively low temperatures we should observe copious vacancy formation

The achievements of electron theory in investigation of the electronic and atomic properties of metal surfaces are reviewed for simple metals. The local density functional approach is used to describe the electron-electron interaction. The results of first-principles calculations of true surface and resonance surface states, charge density distributions, work function, surface layer geometry and surface phonon frequencies are given. The influence of adsorbed layers on the surface electronic characteristics is investigated. The prospects of this method for studying metal surfaces in electric fields as well as for studying the metal-electrolyte interface are outlined.