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Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.

In a high-temperature alloy of the Ni – Co – Cr – W – Ti system grade VZh171, using X-ray spectral analysis, scanning and transmission electron microscopy, the composition of the particles of the hardening phase — nitrides after internal nitriding and subsequent heat treatment was studied. It was found that the particles differ on it chemical composition: the main constituent element, titanium or chromium, is proportionally replaced by other alloy components. The nitride compositions near the surface and in the center of the sample differ in the titanium to chromium ratio. After annealing, this difference is smaller, and the chromium content also decreases. It was found that the nitrides formed during nitriding are compounds in which the main forming element, titanium or chromium, is proportionally replaced by other alloy components. The nitride compositions near the surface and in the center of the sample differ in the titanium to chromium ratio. After annealing, this difference is smaller, and the chromium content also decreases.

The characteristic features of a change in the structure of samples of submicrocrystalline (SMC) technically pure titanium of VT1-0 brand after long-term annealing in a wide temperature range of 150–700°C with a duration of 0.5 to 1008 h, as well as after action by nanosecond laser pulses, are studied by transmission electron microscopy. It is found that the microstructure of the material under study remains stable during annealing for 1 h in the temperature range 150–400°C. Long-term (more than 1000 h) low-temperature annealing in the temperature range 150–190°C also does not lead to a significant change in the size of the structural elements. The action of nanosecond laser irradiation leads to additional grinding of the original SMC structure in the surface layers of the material to a depth of about 1 μm.

An analysis of the influence of thermomechanical treatment (TMT) (rolling to a strain degree of 50%, annealing at a temperatures of 600–1200°C, 1 h) on the microstructure and phase composition of a VZh171 alloy in the initial state and after its bulk nitriding is performed. It is shown that nitriding leads to an increase in the thermal stability of the alloy microstructure. While a primary recrystallization and formation of finegrained structure occurs in an non-nitrided alloy quite intensively at the temperature above 1000°C, the process of collective recrystallization does not gain any significant development in the nitrided alloy even at an annealing temperature of 1200°C, and the microstructure remains ultrafine-grained (grain size 5–10 μm). The mechanical properties of the nitrided and non-nitrided alloy are investigated. It is established that nitriding has no significant effect on the alloy strength at room temperature. In the tests at 800°C, the maximum strength and the minimum plasticity are demonstrated by the nitrided alloy after rolling and subsequent annealing at 600°C. The optimum ratio of the ultimate tensile strength (480 MPa) to plasticity (elongation to fracture 23%) is observed in the nitrided alloy after TMT and annealing at 800°C.

An Erratum to this paper has been published: https://doi.org/10.1134/S002136402235003X

The influence of high-power beams of carbon ions (the ion energy is 250 keV; the pulse duration is ~100 ns; the current density in the pulse is 150–200 A/cm2; the surface energy density of a single pulse is j ~ 3 J/cm2 under the irradiation of the samples of the VT1-0 titanium alloy and j ~ 1 J/cm2 for the treatment of the samples of the VT6 titanium alloy; and the number of pulses is 1, 5, 10, and 50) on the surface topography and structure-phase state of the subsurface layer of submicrocrystalline titanium alloys VT1-0 and VT6 is studied. The sample surface before irradiation is preliminarily mechanically grinded and polished. It is shown that surface defects are formed on the alloy surface after irradiation. These are craters of various shapes and geometry with diameter from fractions of micrometer to 80–100 μm. Herewith, the grain structure in the subsurface layer becomes more uniform in size and degree of grain equiaxity. A rather homogeneous structure is characteristic of the state of the VT1-0 titanium alloy; the average grain size is ~0.31 μm, while that one the VT6 alloy is ~0.9 μm. The grain growth in the transverse direction to 0.54 μm is observed after one irradiation pulse in the subsurface layer of the VT1-0 alloy (at j ~ 3 J/cm2), while the grain size for the VT6 alloy (j ~ 1 J/cm2) decreases to ~0.54 μm. The average grain size in the subsurface layer after 50 pulses reaches ~2.2 μm for the VT1-0 alloy and ~1.6 μm for the VT6 alloy. It should be noted that a rather homogeneous grain structure with equiaxial grains is formed for both alloys already after the effect of one pulse of the high-power ion beam.

Comparative studies of peculiarities of the formation, thermal stability of the structure, and mechanical properties of heat-resistant alloys based on iron and nickel and fabricated using additive technologies (ATs) by laser metal deposition and selective laser melting are performed. It is established that a cellular structure is formed in alloys fabricated by the laser metal deposition and small pores up to 200 nm in size are present. The structure of alloys fabricated by selective laser melting contains elements with a globular and lamellar morphology and incompletely melted regions, as well as large pores on the order of 5 μm in size. The possibility of manifestation of the nanophase hardening effect due to the presence of nanodimensional particles of chromium silicides is shown. A comparative analysis of mechanical properties of materials under study is performed. It is shown that iron-based alloys possess higher strength and lower ductility when compared with nickel alloys. All studied samples fabricated by selective laser melting have higher strength characteristics when compared with alloys fabricated by laser metal deposition. Short-term annealing at 900–1000°C for 1 h noticeably decreases both strength and plasticity in tensile and compression tests at room and elevated temperatures. Alloys based on iron and nickel fabricated by laser metal deposition and subjected to compression tests at t = 900°C have similar strength characteristics. In contrast with iron-based alloys, additional annealing of the nickel-based AT alloy almost does not decrease its strength characteristics.

The comparative study covers the features of formation, thermal stability of structure and mechanical properties of heatresistant Ni and Fe based alloys obtained using additive technologies (AT) by direct metal laser sintering, selective laser melting. It is found that alloys obtained by direct metal laser sintering have a cellular structure formed with small pores up to 200 nm in size, in contrast to alloys obtained by selective laser melting having elements with a globular and lamellar morphology and not completely melted areas as well as large pores about 5 μm in size. The study reveals a possible effect of nanophase hardening due to the presence of nanosized particles of chromium silicides in the material. A comparative analysis of the mechanical properties of studied materials is carried out. It is shown that the iron-based alloys have higher strength and lower ductility compared to nickel alloys. All studied samples obtained by selective laser melting demonstrate higher strength characteristics in comparison with alloys obtained by laser metal deposition. As a result of short-term annealing at a temperature of 900–1000 °C for 1 h leads to a significant reduction in the plasticity and strength of iron-based AT alloys during tensile and compression tests at room and elevated temperatures. During compression tests at t = 900 °C, iron-and nickel-based alloys obtained by laser metal deposition have similar strength characteristics. Unlike iron-based alloys, additional annealing of nickel-based AT alloys has virtually no impact on its strength properties.

An overview of our original studies and the results reported in the literature on the investigation of variations in structure, phase composition, mechanical and other properties of metallic materials under external impacts is made, including their high-pressure processing by large (severe) plastic and megaplastic deformation, explosion loading, and irradiation with ultra-short laser pulses.

The grain structure of M1 copper subjected to equal-channel angular pressing (ECAP) and subsequent annealing at 593K for 1 h is studied by means of transmission electron microscopy and scanning electron microscopy with the diffraction of backscattered electrons. An increase in grain size and the formation of special boundaries (Σ3 twins both coherent and incoherent) are observed, along with the migration of high-energy Σ3 twins and common grain boundaries, the splitting of Σ9 special boundaries into Σ3 twins, and the splitting of common grain boundaries into Σ9 and Σ3 special boundaries. The local transformation of common grain boundaries into special boundaries also occurs. Particles of the Cu2O phase are present on the migrating Σ3 twins and common grain boundaries.

The effect of the pulsed soft X-ray flux on the topography of surface the VТ 1-0 titanium alloy has been studied. The radiation energy density on the surface of the sample is ~10 J/cm2 for one pulse. It is found that a corrugated topography is formed on the surface of titanium as a result of melting followed by freezing: a cellular- or mesh-type topography is formed after one X-ray pulse, the mesh-type topography becomes more sharply defined after two pulses, and the surface of titanium is melted and the mesh structure is almost invisible after three pulses. Crater-like defects are not found, but small cracks are formed on the surface of titanium after melting caused by pulsed X-ray exposure followed by fast cooling of the molten metal.

Tungsten, as the most refractory metal, is applied in fusion reactor in parts subjected to high temperatures and strong neutron irradiation. These factors lead to intense diffusion processes causing degradation of the material. Experimental investigations under such conditions are usually highly complicated and cannot provide a comprehensive understanding of the occurring phenomena. Therefore, their combination with theoretical approaches is required. One of the most robust approaches to simulate diffusion processes is molecular dynamics simulations based on classical interatomic potentials. It allows modeling relatively large samples consisting of several grains, grain boundaries, dislocations, and other types of defects for a reasonable computational time. The reliable simulations of the diffusion process require interatomic potentials satisfying the following criteria: prediction of melting point and thermal expansion as close as possible to the experimental values because the diffusion coefficient strongly depends on the homologous temperature and size factor. In the present paper, we present the new interatomic potential for tungsten, developed within the N-body approach, which reproduces the experimental value of melting temperature (3695 K) and thermal expansion at temperatures up to a melting point. The calculated diffusion coefficient demonstrates adequate agreement with experimental results. The constructed potential is applicable for simulation of processes involving diffusion, one of which is the irradiation damage.

This paper describes the optimal modes of initiation of self-propagating hightemperature synthesis with the help of an electron beam on the example of a Ti–Al–C powder mixture. A pulsed electron beam with a particle energy of tens of kiloelectronvolts and a duration of hundreds of microseconds is used. Morphology, structure, and elemental composition of formed products in the form of Ti3AlC2 and TiC are studied.

Effect of femtosecond laser processing on mechanical properties of plates made of submicrocrystalline VT1-0 titanium alloy is studied using active deformation and fatigue testing involving cantilever bending.

Effect of the pulsed soft X-ray fluxes (PSXF) on the surface topography of metals (Mg and Cu) has been investigated. Soft pulse X-ray irradiation (energy quanta of 0.1-1.0 keV) were carried out on a high-current MIG generator. The sample of magnesium was located at a distance of 10 cm from the X-ray source. Since the distance to the sample significantly exceeded the size of the X-ray beam, it can be assumed that the density of the X-ray radiation flow to the magnesium sample was uniform. The duration of the radiation pulse was 100 ns, and the radiation energy density in the pulse varied from 13 to 19 J/cm2. As a result of melting under the action of PSXF of the near-surface layer of metals and subsequent solidification, a wavy relief is formed on their surface. Defects in the form of craters, which usually occur after the impact of a powerful pulsed ion flow on metals, were not detected.

This article considers the results of the study of the titanium VT1-0 surface degradation (Grade-4 equivalent) for recrystallized- and ultrafine-grained states after fatigue testing. Comparative analysis of peculiarities of the titanium samples degradation was performed after coating formation by Micro-Arc Oxidation. It was found, that the coating formed by Micro-Arc Oxidation shows different degradation behaviors for recrystallized and ultrafine-grained states

—Regularities of the formation of ultrafine-grained (UFG) and submicrocrystalline (SMC) structures in new nickel-free low-modulus Ti–Nb–Mo–Zr titanium β alloys under the action of plastic deformation have been studied. Temperature–time ranges of the development of dynamic recrystallization processes under the simultaneous action of temperature and plastic deformation are determined. A type-II recrystallization diagram of the Ti–28Nb–8Mo–12Zr alloy is constructed and analyzed. It is shown using scanning electron microscopy and the electron backscatter diffraction method that the UFG structure with an average grain size of no more than 7 μm and high fraction of high-angle grain boundaries is formed in the investigated alloys as a result of longitudinal rolling, followed by annealing for quenching. It is found that the formation of the UFG structure leads to a significant increase in the strength and plastic characteristics of these alloys. The regularities of the formation of UFG and SMC structures in titanium β alloys Ti–28Nb–8Mo–12Zr and industrial VT30 under the action of plastic deformation by the helical rolling method are studied. It is shown that the helical rolling of the VT30 alloy leads to the formation of the homogeneous UFG state as opposed to the Ti–28Nb–8Mo–12Zr alloy, where this method causes structure softening with micropores and microcracks formed in the central region. It is possible to form a nanostructured state with an average grain size of about 100 nm in Ti–Nb–Mo–Zr titanium β alloys using the high-pressure torsion method.

The behavior of elastic (Young’s modulus) and microplastic properties of titanium depending on the initial structure and subsequent severe plastic deformation that transforms the material (concerning the grain size) into the submicrocrystalline structural state has been studied. It has been shown that, to a great extent, different initial structures of the metal predetermine its elastic properties after deformation.

Mechanical stability under prolonged loading and thermostability under annealing have been studied for nano- and microcrystalline titanium obtained by different methods of intense plastic deformation. The effect of nanoporosity and the fraction of high angle boundaries formed due to intense plastic deformation has been revealed and analyzed. It has been established that, depending on the loading or the annealing temperature, thermomechanical stability of titanium can be affected, apart from the above structural characteristics, by either twin grain boundaries or titanium-carbide disperse particles.

The paper presents the experimental results on thermomechanical stability of the structure and the evolution of microstructure of the type ВТ1-0 nanostructured titanium. The cyclic tests are performed within the temperature range of 30–350°С.

By subjecting technical grade titanium to irradiation with femtosecond laser pulses with high energy density, we create a microporous nanocrystalline oxide layer with a thickness of ∼50 μm on its surface. The structure and phase composition of the modified surface layers are studied using X-ray diffraction and high-resolution scanning and transmission electron microscopies.

The topography of surface layers of 12Cr18Ni10Ti (AISI 321) steel after pulsed high-power Cn+ ion beams irradiation was investigated by scanning electron microscopy. A thin foil was prepared from the cross section of a crater with the use of a focused ion beam in the column of a two-beam electron-ion microscope. The microstructure and chemical composition of the crater were studied by transmission electron microscopy. It is shown that the near-surface layer (~2 μm in depth) of the crater is represented by an area of columnar grains elongated in the direction of the surface. Under the layer of columnar grains, the region with equiaxial submicrocrystalline grains is situated.

We have experimentally studied the structure and phase variations in polycrystalline titanium stimulated by stepwise shock compression at pressures up to 40 GPa with subsequent unloading. The experiments were performed on samples of commercial titanium (VT1-0 grade) in a broad range of initial grain sizes (0.2–50 μm). The phenomenon of grain refinement and phase composition variation in titanium under stepwise shock-wave action has been studied by transmission and scanning electron microscopy techniques. Specific features of these changes are discussed.

The topography and structure of near surface layers of submicrocrystalline austenite steel 12Kh18N10T after pulsed irradiation with C+ and H+ ions were investigated. Ion beam irradiation resulting in modification of the near surface layer and formation of a structure close to an equiaxed ultrafine grain structure with a high fraction of high-angle boundaries were shown.

The publication describes the study of durability in tensile creep of VT1-0 commercial titanium in its two states-coarse-grained and ultrafine-grained. It is shown that the best temperature for log-term testing is 350°C. At this temperature, the ultrafine-grained titanium structure remains stable both during free annealing and durability testing. The obtained data enable retrieving the difference in fracture initiation energies for titanium in its coarse-grained and ultrafine-grained states.

In the present work for the first time copper icosahedral microparticles in form of truncated icosahedrons were grown. They have 5-fold axis and appearance are similar with fullerene C60. Their shape, faceting, surface morphology and unique structure were investigated. The main idea of the work was to describe transformation during the process of growth of fullerene-like copper microparticles, which have non-equilibrium heterogeneous structure, to perfect icosahedron. The perfect icosahedrons have 5-fold axis; however, they have more equilibrium crystal state. Results of electron microscopic studies of icosahedral particles are described. The obtained copper microparticles can be used as effective and low-cost low temperature catalysts.

The recrystallization kinetics in submicrocrystalline titanium (Grade 4) have been studied in a wide temperature range by transmission and scanning electron microscopy. We have assessed kinetic laws, evaluated the activation energy for the recrystallization process, and examined the mechanism of the process in different temperature ranges.

A Co–Cr–Mo alloy was produced by centrifugal SHS and its fine structure, elemental maps, defect structure, and orientation relationships between the constituent phases were characterized by highresolution TEM.

A Co–Cr–Mo alloy with homogenous ultrafine-grained structure prepared by combined use of metallothermic SHS and subsequent thermomechanical treatment (TMT) was characterized by SEM and XRD and the processing conditions were optimized.

Quantitative methods have been developed to estimate the anisotropy of the strength properties and to determine the phase composition of Mg-Al alloys. The efficiency of the methods is confirmed for MA5 alloy subjected to severe plastic deformation. It is shown that the Taylor factors calculated for basal slip averaged over all orientations of a polycrystalline aggregate with allowance for texture can be used for a quantitative estimation of the contribution of the texture of semifinished magnesium alloy products to the anisotropy of their strength properties. A technique of determining the composition of a solid solution and the intermetallic phase Al12Mg17 content is developed using the measurement of the lattice parameters of the solid solution and the known dependence of these lattice parameters on the composition.

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.

The laws of formation of an ultrafine structure in an Mg–Al–Zn–Mn alloy (MA5 alloy) under severe plastic deformation have been studied during lengthwise section rolling at a strain e = 1.59. The deformation behavior and the physical factors of anisotropy of yield strength during compression tests in various directions with respect to axis of rolling are analyzed. The role of crystallographic texture and twinning processes in the generation of strength processes and the development of plastic deformation of the alloy is analyzed.

The effect of nanoporosity and the highly dispersed carbide particles that form during screw and lengthwise rolling of VT1-0 titanium on its mechanical and, partly, thermal stability characteristics is revealed and analyzed.

Surface topography, phase composition and compressive residual stresses were characterized in surface layers of α + β titanium alloys VT6 (Ti–6Al–4V) and VT16 (Ti–3Al–4.5V–5Mo) nanotextured by 744-nm, 120-fs-laser pulses. The relative content of β-phase, along with the residual compressive stresses, increases significantly in both these materials over the depth ~0.2 μ in the nanotextured surface layer comprised by nanograins and remains almost unchanged at higher depths of 1–2 μ in bulk. The laser-driven α → β phase transformation is related to the combined effect of ultrafast heating/cooling, strong (multi-GPa) shock waves, chemical segregation and nanograin formation induced during the ablative surface nanotexturing.

The first findings on the effect of propagation of localized deformation bands during torsion of nanostructured technically pure VT1-0 titanium are considered.

The literature contains many contradictory data about the most thermodynamically favorable structure of precipitates in α -Ti matrix of the hypoeutectoid Ti–Si alloys. In this work we applied our recently developed thermodynamic model to predict the structure of Ti–Si precipitates in α -Ti matrix of the Ti–Si alloy with total Si concentration of 0.7 wt.%. We considered all prominent Ti–Si phases such as Ti 3 Si , Ti 5 Si 3 , Ti 5 Si 4 , TiSi and two TiSi 2 phases and discovered that formation of the Ti 5 Si 3 phase is more favorable than that of the Ti 3 Si in contradiction with the known phase diagrams. Theoretical result was confirmed by experimental investigation of microstructure and phase composition of the model Ti–0.7Si alloy annealed at 873 K for 10 h. Indeed, the only observed phase has hexagonal Ti 5 Si 3 structure. To ensure the completeness of the results we calculated ab initio elastic constants for all considered Ti–Si phases.

The structure and the short-term high-temperature strength of Ni-18.7 at % Si (Nb-Nb3Si eutectic) alloys fabricated by vacuum electron-beam zone melting and induction melting in an argon atmosphere are studied. The structure of the samples prepared by vacuum electron-beam zone melting is characterized by the presence of primary Nb5Si3 intermetallic precipitates and the absence of its secondary precipitates. The structure of the samples prepared by induction melting in an argon atmosphere has two characteristic zones, namely, eutectic and eutectoid ones.

Two separate sets of microcones were observed on titanium surface under various ablative 248-nm femtosecond-laser exposures near rough spallation crater edges and in crater centers, respectively. “Heterogeneous” nucleation of microcones occurred on crater edge spikes above the corresponding cumulative spallation thresholds, with their gradual growth proceeding through redeposition of the ablated matter. In contrast, quasi-periodical central microcones emerged through a “homogeneous” nucleation process owing to ablative surface instability, with average cone volume increasing exponentially versus the shot number over the broad fluence range until its stabilization, and logarithmically versus laser fluence at the different shot numbers above the instability threshold fluence of about 30 mJ/cm2. The instability was assigned to a positive optical feedback, resulting from enhanced laser energy deposition and ablation within the inter-cone valleys, as previously suggested and demonstrated by our numerical modeling of near-surface electromagnetic intensity distribution.

An example of original studies of titanium alloys for medical applications is used to discuss methodical features of analysis of the structural-phase state of metal materials with usage of contemporary methods of analytical scanning and transmission (including high-resolution) electron microscopy. Methods of X-ray energy dispersion spectroscopy and spectroscopy of characteristic electron energy loss are described and discussed. The possibilities of these methods for local (nanometer range) measurement of concentrations of alloying elements, including light ones (carbon), are shown. An example of focused ionic beam for study of grain boundary gliding in nanostructured pure titanium at room temperature is considered.