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The mechanical properties of two types of laminated Cu/Nb composites (with layer thicknesses in the range of 10–12 mm and 10–18 nm, respectively) are investigated in the temperature range of 773–1073 K. The possibility of the manifestation of grain boundary and interfacial sliding along the internal interfaces of the studied materials is examined.

We have developed a new method for manipulating nanotopology and chemical composition of titanium surfaces by a scanning femtosecond laser beam with an asymmetrical spatial fluence distribution. Using of a common Gaussian laser beam leads to formation of combined nano- and micro-scale surface topologies owing to superimposition of different laser beam parts during the surface scanning. In contrast, beam shaping results in presumable surface structuring at specific laser fluences yielding in “clean” surface structures. In a simple case, cutting of a half beam perpendicular to the scanning direction enables to eliminate surface nanotopology, leaving less oxidized, cleaner and smoother microspikes, just by changing the scanning direction. Optimal experimental conditions were revealed to obtain in air the topologically and chemically different surface structures using the asymmetrical femtosecond laser beam and the opposite scanning directions.

The elastoplastic properties (elastic modulus, amplitude-independent damping ratio, microplastic flow stress) of a Ti-26Nb-7Mo-12Zr titanium β alloy are determined using an acoustic resonance method. The effect of the strain during thermomechanical treatment on the structural features of the micro-crystalline alloy and, hence, its elastoplastic properties is analyzed.

The results of an experimental investigation of the effect of mechanical-thermal treatment of submicrocrystalline and coarse-grained titanium on the deformation behavior in the stage of microplastic deformation at room and elevated temperatures are reported. The structural factors giving rise to the flowstress changes in the stage of microplastic deformation as a result of mechanical-thermal treatment are discussed. The general tendencies and special features of the effect of annealing and testing temperatures on the deformation behavior and flow stress in the first and second stages of microplastic deformation of submicrocrystalline and coarse-grained titanium subjected to large plastic deformation at 295 K are clarified.

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 thermomechanical stability of nanostructured (NS) commercially pure titanium is studied in the temperature range of 20–600°C using the method of dynamic mechanical analysis. It has been found that the maxima observed in the temperature dependence of the loss angle tangent (t = 350–600°C for the analyzed cyclic loading frequencies of 0.33–10 Hz) are of relaxation nature. The measured activation energies of microplastic deformation are close to the corresponding literary data on the experimental activation energies of the grain-boundary sliding under the studied conditions. The thermomechanical stability of NS VT1-0 titanium for medical application has been experimentally estimated up to 1.2 × 106 cycles of loading with cantilever bending at t = 100°C, which is substantially higher than the operating temperature (t = 37°C).

Explored was combustion synthesis in the Ni-Al-W system with special emphasis on structural features of the process. Using SHS in the 1500–1700°C temperature range, we observed the diffusion-induced processes at the interface between synthesized NiAl and W particles resulting in the formation of W2Ni and W-Ni intermetallics.

The structure and short-time strength of Nb-Al alloys of two compositions prepared by powder metallurgy are studied. The mechanical alloying of niobium with aluminum in a planetary ball mill in air is shown to result in simultaneous alloying of niobium with oxygen. During subsequent vacuum high-temperature sintering, disperse particles of a complex oxide, whose tentative composition is (AlNb)2O3, form in the alloy structure. The short-time strength at 1250°C of the prepared alloys exceeds that of nickel-aluminum superalloys.

The calculation of the choice of a new low modulus titanium β alloy was described. The investigations of the structure and properties (mechanical, tribological and corrosive) of low modulus titanium β alloy Ti–26Nb–7Mo–12Zr after mechanical–thermal processing were carried out. An analysis of the results of experimental research showed that the formation of homogeneous fine grained structure by sheet rolling with subsequent annealing before quenching leads to decreased elastic modulus, increased plasticity and wear resistance. Therefore, new titanium β alloy designed in the present study, Ti–26Nb–7Mo–12Zr, is expected to have good properties as biomaterial.

We studied the influence of the characteristics of oxide porous coatings on osteogenesis and integration of new bone tissue and titanium implant surface in the ectopic osteogenesis test. Implants with coating with pore size 2-20 μ exhibit better osteogenic and osteoconductive characteristics than implants with homogenous surface and smooth relief (pore size 0.5-5.0 μ). Physical characteristics of the surface of the material along with chemical composition of the coating are essential for the formation of bone tissue and its integration with the implant.

The Ti–C system is poorly studied at low carbon concentrations (

Results obtained from a comparison study on the deformation behavior of submicrocrystalline and coarsegrained titanium in the temperature interval 295–773 K are presented. The microplastic strain mechanisms underlying a change in the deformation behavior of submicrocrystalline titanium in the melting temperature interval 0.35–0.40 Т m and a reduction in the strain hardening effect due to formation of submicrocrystalline structure of the material are examined. A multiscale model for development of microplastic deformation in submicrocrystalline metals and alloys is offered.

The change of the structural and phase composition of the austenitic steel 12Cr18Ni10Ti is studied after nitriding in the plasma of a non-self-sustained low-pressure arc discharge at different temperatures. It is shown that, as a result of ion nitriding, it is possible to increase the microhardness and wear resistance of the investigated steel. The basic parameters of the nitriding process (temperature and composition of the gas mixture) that make it possible to improve the mechanical properties without significant changes in magnetic characteristics are selected.

The article presents the results of an investigation into the influence of the composition of a plasma-forming gas (N2, Ar, He) on nitriding of VT1-0 grade titanium (0.25%-Fe; 0.1%-Si; 0.2%-O) and commercial 40X steel (0.4%-C; 1.0%-Cr) in the plasma of a non-self-maintained glow discharge with a large hollow cathode. It is shown that the efficiency of nitriding of 40X steel weakly depends on the composition of the plasma-forming gas mixture, whereas nitriding of VT1-0 titanium in a helium-nitrogen mixture leads to a noticeable increase in the microhardness of the specimen’s surface in comparison with nitriding in an argon-nitrogen gas mixture.

Methods of intensive plastic deformation such as equal-channel angular pressing and versatile forging (abcpressing) [1–3] have been used most widely for the formation of the submicrocrystalline structure in titanium. However, in these methods, intensive plastic deformation is performed generally at a temperature above 0.3 Tm (Tm is the melting temperature of titanium), and the mean size of the elements of the grain-subgrain structure exceeds 300 nm. To reduce the size of the elements of the grain-subgrain structure after intensive plastic deformation, titanium was subjected to a special thermomechanical treatment including plastic deformation by cold rolling with annealing till recrystallization. However, the experimental data obtained are still insufficient to elucidate the mechanisms of hardening of submicrocrystalline titanium by thermomechanical treatment. Since a texture is changing during rolling, there are reasons to assume that the hardening effect of thermomechanical treatment can differ for deformation by tension, compression, bending, and torsion. In this work the effect of thermomechanical treatment of submicrocrystalline titanium on its deformation behavior and elastoplastic properties under tension at a rate of 3·10 s is investigated. The object of investigation was submicrocrystalline α-titanium VT1–0 of the following chemical composition: 0.18% Fe, 0.12% O, 0.07% C, 0.04% N, and 0.01% H (in weight %). The submicrocrystalline structure was formed by warm deep plastic deformation with a stepwise decrease of the temperature from 773 to 673 K. This submicrocrystalline structure was characterized by highand low-angle grain boundaries with relative fraction of the high-angle boundaries more than 50% and mean size of the elements of the grain-subgrain structure of 350 nm. The dislocation density inside the grains reached 2·10 cm, and the grain boundaries were imperfect [4]. Multiple rolling of titanium with submicrocrystalline structure to a total deformation degree of 40% at room temperature virtually had no effect on the size of elements of the grain-subgrain structure, but led to an increase in the dislocation density in grains and in the degree of nonequilibrity of the boundaries. At the same time, when the degree of deformation increased up to 80%, the mean size of elements of the grain-subgrain structure greatly reduced (up to 150 nm) with simultaneous increase in the fraction of high-angle boundaries (approximately up to 90%), the degree of nonequilibrity of the boundaries, the internal stresses, and the dislocation density inside the grains. The elements of the grain-subgrain structure are elongated along the rolling direction [5]. Figure 1 shows the flow curves of coarse-grained (mean grain size of 10 μm) and submicrocrystalline titanium under tension at a rate of 3·10 s at room temperature. They were calculated assuming uniform plastic deformation over the entire working length of the sample, i.e., without accounting for macrolocalization of plastic deformation before failure of the sample. It follows from this figure that in the transition from the coarse-grained structure to the submicrocrystalline structure formed during intensive plastic deformation the form of the flow curves is retained in

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.

Investigations of disperse nonmetallic inclusions in unalloyed alpha titanium VT1-0 have been performed by using transmission electron (including scanning and high-resolution) microscopy. Characteristic electron energy losses spectroscopy has shown that these inclusions are titanium carbide particles. It has been revealed that the disperse carbides are formed in the titanium hcp matrix as a phase based on the fcc sublattice of titanium atoms. The inclusion–matrix orientation relationship corresponds to the well-known Kurdyumov–Sachs and Nishiyama–Wassermann relationships $ {\left[ {2\overline {11} 0} \right]_{{\upalpha }}}\parallel {\left[ {011} \right]_{{\updelta }}}{\text{ and }}{\left( {000\overline 1 } \right)_{{\upalpha }}}\parallel {\left( {1\overline 1 1} \right)_{{\updelta }}} $ .

Quasi-periodic nano- and microstructures have been formed on silicon surface using IR ( l » 744 nm) and UV ( l » 248 nm) femtosecond laser pulses. The influence of the incident laser fluence and the number of pulses on the structured surface topology has been investigated. The silicon nanostructuring thresholds have been determined for the above-mentioned wavelengths. Modulation of the surface relief at the doubled spatial frequency is revealed and explained qualitatively. The periods of the nanostructures formed on the silicon surface under IR and UV femtosecond laser pulses are comparatively analysed and discussed.

One-dimensional quasi-periodic nanogratings with spacings in the range from 160 to 600 nm are written on a dry or wet titanium surface exposed to linearly polarized femtosecond IR and UV laser pulses with different surface energy densities. The topological properties of the obtained surface nanostructures are studied by scanning electron microscopy. Despite the observation of many harmonics of the one-dimensional surface relief in its Fourier spectra, a weak decreasing dependence of the first-harmonic wavenumber (nanograting spacing) on the laser fluence is found. Studies of the instantaneous optical characteristics of the material during laser irradiation by measuring the reflection of laser pump pulses and their simulation based on the Drude model taking into account the dominant interband absorption allowed us to estimate the length of the excited surface electromagnetic (plasmon-polariton) wave for different excitation conditions. This wavelength is quantitatively consistent with the corresponding nanograting spacings of the first harmonic of the relief of the dry and wet titanium surfaces. It is shown that the dependence of the first-harmonic nanograting spacing on the laser fluence is determined by a change in the instantaneous optical characteristics of the material and the saturation of the interband absorption along with the increasing role of intraband transitions. Three new methods are proposed for writing separate subwave surface nanogratings or their sets by femtosecond laser pulses using the near-threshold nanostructuring, the forced adjustment of the optical characteristics of the material or selecting the spectral range of laser radiation, and also by selecting an adjacent dielectric.

The structure and mechanical properties of nanostructured titanium VT1-0 derived using an ingenious method which combines helical and longitudinal rolling are studied in comparison with the properties of commercial titanium alloys VT6 and VT16, as well as VT1-0 in a coarse-grained state. The mechanical properties of these materials are studied using quasi-static tensile and torsion tests (including finished products, i.e., implants for osteosynthesis), as well as fatigue tests. It is shown that the use of the developed method of severe plastic deformation is an efficient mode for the formation of a high-strength nanostructured state in titanium VT1-0, which exhibits sensitivity to stress concentrators under cyclic loading that is characteristic of titanium alloys and an extremely high reserve of torsional plasticity.

The effect of an infrared pulse laser with femtosecond radiation (λ = 744 nm, τ ≈ 120 fs, E ≤ 8 mJ) on the surface of Ti of commercially purity in the submicrocrystalline state is investigated using scanning electron microscopy (SEM). Laser irradiation leads to the formation of a surface nanorelief consisting of alternating projections (bars) and hollows (grooves). After surface treatment under a water layer, cube-shaped particles are formed on Ti surface; they are composed of many tightly contiguous rectangular plates.

The structure and phase composition of a VKNA-25 alloy based on the Ni3Al intermetallic compound, produced by directional solidification, and alloyed with rare-earth metals are studied in the following two states: after annealing at 1100°C and after creep at 1100°C.

One-dimensional periodic nanostructures have been produced on the surface of an aluminum specimen using femtosecond laser pulses at wavelengths of 744 and 248 nm. The nanostructurization of the specimen has been conducted in water and in air in the preablation regime. We investigate the dependence that the surface topology has on the parameters of laser radiation (wavelength, fluence, and number of pulses), as well as on the medium in contact with the specimen surface. A calculation of the optical characteristics of aluminum as they depend on the electron temperature is performed that is good at describing the dependence that the reflection of the p-polarized infrared femtosecond pulses of pumping has on the fluence. Using these optical characteristics of the photoexcited aluminum within the interferential model, periods of the aluminum surface nanogratings are estimated which are in good agreement with the periods measured experimentally.

Gradual evolution of self-induced silicon surface topology from one-dimensional ridge-like to two-dimensional spike-like nanogratings and then to isotropic sets of micro-columns was observed by evenly increasing IR and UV femtosecond laser irradiation dose. This topological evolution exhibits clear indications of consequent melting and vaporization processes being set up during the prolonged laser irradiation. Monotonously decreasing cumulative IR and UV femtosecond laser-nanostructuring thresholds may indicate an increase of optical absorbance of the laser-nanostructured silicon surfaces versus the increasing laser dose, consistent with the consequent onset of the abovementioned thermal modification processes.

The main approaches to the formation of modern functional materials for medical implants, including the principles of material choice on the criteria of their biochemical and biomechanical compatibility and their technological effectiveness, are represented in this review. Titanium alloys are considered the most prospective and extended materials for implants in traumatology, orthopedics, and stomatology. The trend over the last decade has been to exclude alloying components that may cause local allergic reactions on living tissues or general toxic effects on an organism from the structure of titanium alloys. One compromise to preserve high biochemical compatibility with the necessary increase in the mechanical properties of titanium alloys is based on the formation of submicrocrystalline (SMC) or nanostructured (NS) states in commercially pure titanium. The prospect of using SMC and NS titanium as a material for manufacturing implants is proven. An analysis of the results of experimental and theoretical research of the diffusion features on intergranular areas is carried out, and the role of diffusion-controlled processes in the formation of a microstructure of metals and alloys, as well as the microstructured state, is discussed. The efficiency of computer simulation on an atomic level in establishing the dependence of diffusion characteristics on intergranular areas from the average grain size and the structural state of internal boundaries of section is proven. A short description of simulation and semi-industrial methods of the formation of SMC and NS states in metals and alloys by means of severe plastic deformation—which are known as materials related to the “top-down approach,” assuming the initial structure is crushed to nanosized components—is presented. Special attention is given to the recent developed of low-cost and high-efficiency technological schemes for the mass production of nanostructured titanium alloys for medical purposes, including radial-shift and screw rollings, along with a combination of traditional methods of mechanical-thermal processing, which make it possible to receive an assortment of the titanium and its alloys necessary for the mass production of medical implants and tools.

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.

The relative energies of possible phases in a Ti-C system in the hcp-lattice of titanium are calculated. A probability of formation of a more energetically favorable structure is shown than that of NaCl, which is well-known from the phase diagram of Ti-C. The results of calculations of lattice parameters, elasticity moduli, and charge density distribution in the predicted phase are presented. The relationship between the atomic structure peculiarities and the chemical bonding type in this phase is discussed.

Regularities and mechanisms of the creep of submicrocrystalline copper and Cu-1.1 vol % Al2O3 dispersion-hardened powder composite in a temperature range of (0.2–0.35) Tm Cu have been investigated. The role that the grain-boundary state and dispersion-hardening material with Al2O3 nanosized (10–40 nm) particles plays in the development of plastic deformation during creep is analyzed.

One-dimensional quasiperiodic structures whose period is much smaller than the wavelength of exciting radiation have been obtained on a titanium surface under the multipulse action of linearly polarized femtosecond laser radiation with various surface energy densities. As the radiation energy density increases, the one-dimensional surface nanorelief oriented perpendicularly to the radiation polarization evolves from quasiperiodic ablation nanogrooves to regular lattices with subwave periods (100–400 nm). In contrast to the preceding works for various metals, the period of lattices for titanium decreases with increasing energy density. The formation of the indicated surface nanostructures is explained by the interference of the electric fields of incident laser radiation and a surface electromagnetic wave excited by this radiation, because the length of the surface electromagnetic wave for titanium with significant interband absorption decreases with an increase in the electron excitation of the material.

Characteristics of diffusion transformations in a multi-layer composite of a Cu–Ti system, which was produced by high-temperature diffusion welding followed by rolling at room temperature, are reported. It is shown that phase-formation at the layer boundaries in this system at the temperature below 823 K is determined by diffusion along the inner surfaces of these boundaries; while above this temperature it is controlled by bulk diffusion.

Based on the study of grain-boundary internal friction, it has been demonstrated that the temperatures of onset and intensive development of true grain-boundary sliding (grain-boundary microsliding) as well as the activation energy of this process in submicrocrystalline and nanocrystalline metals and alloys with imperfect grain boundaries relative to coarse-grained ones with perfect grain boundaries decrease. For all grain structures studied the activation energy of grain-boundary internal friction is found to exceed the respective one for grain-boundary diffusion but to be lower than the activation energy of bulk diffusion. The diffusion-controlled mechanism of true grain-boundary sliding is validated.

Mechanisms of plastic deformation have been studied in detail in the process of isothermal loading at room temperature in a high-purity shape-memory alloy of composition Ti49.4Ni50.6. The alloy was studied in two initial states: usual coarse-grained (with an average grain size of 20–30 μm) and submicrocrystalline (with an average grain size of 0.2–0.3 μm). It has been shown that during tensile tests there occurs a mechanically induced martensitic transformation in the alloy at stresses corresponding to stages I, II, and III in the tensile curve and then elastic and plastic deformation of B19′ martensite is observed at stages IV, V, and VI, respectively. Optical metallography in situ and electron microscopy have been used to study microstructural features and mechanisms of plastic deformation of the alloy up to its failure.

This work presents the results of studies of the Ti49.4Ni50.6 alloy of enhanced purity with shapememory effects in an ordinary coarse-grained state with an average grain size of 20–30 μm or in a submicrocrystalline state with an average grain size of 0.2–0.3 μm. In this alloy the initial structure, phase composition, martensitic transformations, mechanical properties, and character of fracture have been investigated in a wide temperature range. It has been shown that upon cooling and mechanical tests at room temperature, the alloy exhibits highly reversible thermoelastic martensitic transformations. It has been established that the alloy exhibits high values of the strength and plastic properties and strain-hardening coefficients.

The hardening mechanisms are studied in the cast high-temperature next-generation materials that are based on the intermetallic compound Ni3Al and are low alloyed with refractory (W, Re, Mo, Cr) and reaction- and surface-active (REM, Ti, etc.) metals. The interaction of the main impurities (C, O, Si, S) with three characteristic representatives of the REM group (namely, Y, La, Ce), which can be used for alloying, is analyzed. The reported data on the behavior of some REMs in the alloys based on nickel monoaluminide NiAl are considered. The effect of the REMs on the phase compositions of real multicomponent semicommercial Ni3Al-based VKNA alloys produced by directional solidification is investigated, and the excess phases precipitating upon alloying are revealed. Alloying with refractory metals and REMs is shown to lead to the formation of nanophases that stabilize the dendritic or single-crystal structure of VKNA-type cast alloys and strengthen the interface boundaries in them.

The structural state of the γ′ and γ phases of modern superalloys is considered in detail. A classification of the scale effects in the γ′ phase morphology is proposed.

The effect of nonuniform size distribution of grain-subgrain structure elements on the mechanical properties of an alloy Ti-6Al-4V in a submicrocrystalline state produced by multiple pressing is investigated. The presence of a small number of coarse grains in the grain size distribution is shown to decrease the yield and ultimate strength at room temperature and the degree of fracture strain under superplastic flow conditions.

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.

Variables (order parameters) that are related to plastic deformation sites and complement the local densities of grain-boundary defects are separated out in a bicrystal being deformed under creep. By solving an evolutionary equation for the order parameters, it is shown that the nonuniformity and periodicity of spontaneous grain-boundary slippage in bicrystals and an increase in the grain-boundary strain rate under the conditions of boundary-lattice dislocation interaction may be attributed to the occurrence of local nonequilibrium regions (autosolitons).

Results of investigations into the structural-phase state of EK-181 ferritic-martensitic low-activate steel after thermal treatment including quenching, intermediate tempering, and subsequent long tempering under loading at temperatures of 923 and 973 K are presented. The influence of the defect substructure of the ferrite matrix, phase composition, and character of the secondary dispersed phase distribution in the volume of the material on the heat-resistant steel properties is examined.

Methods of scanning and transmission electron microscopy are used to perform a comparative analysis of the structur evolution of ultrafine-grained molybdenum subjected to nickel-free annealing and to diffusion annealing accompanied by nickel penetration from the surface into the bulk of Mo(Ni) specimens. The kinetics of nickel diffusion-induced recrystallization of ultrafine-grained molybdenum in the temperature interval 1123–1223 K is investigated and the recrystallization activation energy is determined. Plausible reasons for a decrease in the nickel diffusion-induced recrystallization temperature of ultrafine-grained molybdenum as compared to its fine-grained cousin are discussed. The nickel diffusivity in ultrafine-grained molybdenum along grain boundaries is estimated on the basis of the results obtained.

The special features of the evolution of the structural and phase states of a Ti-6Al-4V alloy in forming submicrocrystalline structure with the use of temporary hydrogen treatment are studied by electron microscopy and x-ray diffraction analysis. Plastic deformation in the α + β two-phase region at 1023 K is found to initiate a complete β → α transformation in a Ti-6Al-4V-H alloy to form an α phase with lattice parameters different from those of the equilibrium α phase. Isothermal annealing at a dehydrogenation temperature of 873 K gives rise to α + β two-phase submicrocrystalline structure with a grain size of ∼ 0.3 µm. The use of nonequilibrium hydrogen release in the deformed Ti-6Al-4V-H alloy exposed to electron beams is shown to result in one-phase submicrocrystalline structure and grain refining. Possible reasons underlying the phase transformations in the alloy under study are discussed.

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.

The experimental and theoretical investigations of grain boundary diffusion processes have been performed using metals and alloys in nanostructured state produced by severe plastic deformation and the respective polycrystalline counterparts. The main features of diffusioncontrolled mechanisms of plastic deformation observed by the creep of nanostructured metals are considered. The use of severe plastic deformation treatment and of the effect of activation of diffusion-controlled processes for enhancing the properties of nanostructured steels and alloys designed for engineering and medical applications (nanostructured titanium-bioactive coating composite included) is described and examples are offered.

The effect of equal-channel angular pressing (ECAP) on the structure-phase state and superplasticity development was investigated using the 1421 Al-Mg-Li alloy. The physical reasons for the displacement of the temperature range of superplasticity to lower temperatures after ECAP by comparison with the initial state are considered. Possible reasons are discussed for the decrease in the activation energy of true grain boundary sliding in the alloy produced using ECAP by comparison with the initial condition.

The characteristic features of diffusion and diffusion controlled processes in polycrystalline metals and alloys with bcc and fcc crystal lattice during annealing and creep are examined. Consideration is given to the interrelated processes of diffusion, grain boundary sliding/migration, which determine plastic deformation development at specified conditions. The distinctive features of grain boundary diffusion of substitution impurity from coating are investigated for nanostructured metals and alloys and the respective coarse grain counterparts. The manifestations of low temperature and/or high strain rate superplasticity in nanostructured metals and alloys are considered.

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.

The temperature dependence of internal grain-boundary friction in coarse- and ultrafine-grained titanium is investigated. It is demonstrated that true grain-boundary slipping causes internal grain-boundary friction in ultrafine-grained titanium, as in coarse-grained metals. It is established that when going from the coarse-grained structure with perfect grain boundaries to ultrafine-grained structure with imperfect grain boundaries, the temperatures of the beginning and intense development of true grain-boundary slipping decrease together with the activation energy of this process. The diffusion mechanism of true grain-boundary slipping is justified for both structural states.