A study of the parameters of the high-temperature background of internal friction of a dispersed-hardened polycrystalline CrNi29Co28WMoTi alloy has been carried out. It is established that the transition of the investigated alloy from an elastic to a viscoelastic state occurs when the temperature limit Tcr = 791 K is reached in at least two stages. The first stage determines the migration of point defects of the crystal structure along the grain boundaries at low deformation in the low-temperature region, which corresponds to the diffusion activation energy of 0,51 eV. The second stage determines the separation and movement of dislocations from the impurity atoms, as well as the appearance of grain boundary sliding in the high-temperature region. This requires an activation energy of 0,86 eV. The relative decrease in the shear modulus in the temperature range 300 – 890 K was ≈ 0,15. To determine the temperature boundary of the Tcr, a formula is proposed that allows calculating the temperature of the Tcr based on data on the activation parameters of the high-temperature background of internal friction. In addition, a general thermodynamic condition for the transition of a material from an elastic to a viscoelastic state corresponding to high-temperature deformation mechanisms is formulated. It is shown that the temperature boundary that determines the beginning of the transition of a material from an elastic to a viscoelastic state can be used to diagnose the heat-resistant properties of nitrided alloys as an additional criterion.

The possibility of synthesis of a tungsten–copper pseudo-alloy by the infiltration method in the highly exothermic reaction of combustion of silicon in nitrogen as a heating source has been studied. Under the action of heat released during combustion, the porous tungsten frame was impregnated with molten copper. The pseudo-alloys with a relative density of 0.9 was synthesized.

An alloy of the Cr – Ta – W system containing a tungsten-doped intermetallic Laves phase Cr2Ta (C15) and bcc phases of chromium and tantalum has been studied. The structural-phase state of the alloy was studied by scanning and transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. The concentrations of alloying elements in the above phases of the alloy have been determined.

The effect has been studied of treatment with nanosecond laser pulses on the fatigue resistance of plate samples of recrystallized (grain size of the order of 2-3 μm) commercially pure titanium (grade VT1-0) under cyclic tensile loading. The results of investigations by scanning and transmission electron microscopy of the subsurface layer microstructure of the alloy under study after exposure to nanosecond laser irradiation and subsequent fatigue tests are presented. Keywords: titanium, surface, pulsed nanosecond laser irradiation, shock-wave action, fatigue properties.

Heat-resistant materials used, for example, in aircraft parts, are exposed to high temperatures and are heated under the impact of variable external forces. At a certain point in time, the material that first experienced a small deformation ceases to be simply elastic and graduates into a viscoelastic state. Microyield thus developed in the material, subsequently leads to the creep. We present the results of studying the microyield in a heat-resistant polycrystalline alloy VZhl71 of the Ni - Co - Cr system. A high-temperature background of the internal friction was studied by mechanical spectroscopy. It is shown that the transition of the alloy from an elastic to a viscoelastic state proceeds in two stages and is accompanied by microyield resulted from the dislocation movement. The first and second activation energies of the high-temperatureinternal friction background are determined for the state of the material under consideration. An expression for calculating the transition temperature is derived. The results obtained can be used in the study of the states of heat-resistant, high-temperature and structured materials, as well as amorphous metals and alloys.

Modification of titanium microstructure after propagation of a melting shock wave (SW) generated by a femtosecond laser pulse is investigated experimentally and analyzed using hydrodynamic and atomistic simulations. Scanning and transmission electron microscopy with analysis of microdiffraction is used to determine the microstructure of modified subsurface layers of titanium. We found that two layers are modified beneath the surface. A top surface polycrystalline layer of nanoscale grains is formed from shock-molten material via rapid crystallization. In a deeper subsurface layer, where the shock-induced melting changes into plastic deformation due to attenuation of SW, the grain structure of solid is considerably affected, which results in a grain size distribution differing from that in the intact titanium. Molecular dynamics simulation of single-crystal titanium reveals that the SW front continues to melt even after its temperature drops below the melting curve Tm(P). The enormous shear stress of ∼12 GPa generated in a narrow SW front leads to free slip of atomic planes, collapse of the crystal lattice, and formation of a supercooled metastable melt. Such melt crystallizes in an unloading tail of SW. The mechanical melting ceases after drop in the shear stress giving rise to the shock-induced plastic deformation. The last process triggers a long-term rearrangement of atomic structures in solid. The overall depth of modified layers is limited by SW attenuation to the Hugoniot elastic limit and can reach several micrometers. The obtained results reveal the basic physical mechanisms of surface hardening of metals by ultrashort laser pulses.

The present article investigates the effect of graphite powder layers on the titanium surface layer during the treatment by the laser-induced plasma-assisted ablation method. Previous research mainly focuses on studying the effect of laser action on the quality of glass plate processing, rather than observing the changes in the substrate morphology caused by the treatment. Varying laser radiation parameters allowed obtaining the arrays of structures and determining the diagram of hardness values depending on the parameters of laser exposure. The method of laser treatment to increase the hardness of the surface layer under a graphite powder layer in contact with a dielectric transparent layer has been proposed and tested; the method has demonstrated a tenfold increase in the hardness of the surface layer. The results can be used in the improvement of cutting tools performance and applied in mechanical engineering or metalworking.

The microstructure and phase composition of a nickel -based heat -resistant alloy samples doped with Cr, Co, Ti, W and Mo (alloy VZh171) in the nitrided state were studied using methods of autoemission high -resolution scanning electron microscopy. The change in the particle sizes of titanium nitrides during isothermal annealing at a temperature of 1300 degrees C for 1.5, 2 and 3 hours was studied. It is shown that the evolution of particle sizes under the studied conditions corresponds to the Lifshitz-Slezov-Wagner model of diffusive coalescence of particles.

The effect of creep on changes in the structure of samples of recrystallized microcrystalline aluminum in the fracture region and at some distance from it is studied. Transmission and scanning electron microscopy have been used to study the features of the formation of a globular ultrafine-grained structure in the region of destruction with a minimum manifestation of crystallographic texture, as well as the presence of micro- and nanoporosity.

The change in porosity during isothermal vacuum annealing of the pseudo alloy W – 18 wt. % Cu obtained by powder metallurgy methods in the temperature range of 800 – 1200 °C and the resistance to oxidation under the action of high-temperature plasma of the outer surface of a hybrid laboratory structure, consisting of two composite elements made of dissimilar materials: graphite and alloy W – 18 wt. % Cu. The process of evolution of the microstructure controlled by diffusion along the internal interfaces (grain and subgrain boundaries) of copper atoms from copper particles located on these surfaces in the near-surface layers of the sample has been studied.

In modern dentistry, dental implants are widely used to replace lost teeth. However, the placement of an implant may not be possible due to bone atrophy. One of the most popular ways to restore jawbone after atrophy is the use of barrier membranes. This paper proposes a method to design and create improved barrier membranes using neural networks and laser technology. The method allows to obtain personalized titanium membrane with laser-induced antibacterial coating. At the first step, the membrane is designed based on CT scan of the patient using 3D modeling software and convolutional neural network U-net which allows us to reduce modeling time. The second step is to create membrane by micromilling from titanium block. Finally, we create antibacterial membrane surface under laser oxidation and UV-activation of singlet oxygen production on the surface.

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.

By means of the X-ray microspectral analysis and scanning and transmission electron microscopy, we investigate the composition of hardening phase particles—nitrides—after internal nitriding and subsequent heat treatment in the Ni–Co–Cr–W–Ti system of grade VZh171. The particles differ significantly in chemical composition: the main forming element—titanium or chromium—is proportionally replaced by the other alloy components. The nitride compositions at the surface and in the center of the sample differ in the element ratio. After annealing in vacuum, the content of chromium, tungsten, and cobalt in nitrides decreases, also less becomes the difference in the precipitate composition in the surface and the central layers of the sample; this phenomenon can be used to improve the alloy properties.

The deposition of titanium oxides during titanium laser ablation in air has been experimentally and numerically investigated. A titanium sample was irradiated by nanosecond pulses from an Yb-fiber laser with a beam scanned across the sample surface for its texturing. As a result, the hierarchical structure was observed consisting of a microrelief formed by the laser ablation and a nanoporous coating formed by the reverse deposition from the laser induced plasma plume. The chemical and phase composition of the nanoporous coating, as well as the morphology and structure of the surface, were studied using scanning electron microscopy, atomic force microscopy, and X-ray microanalysis. It was found that the deposit consists mostly of porous TiO 2 with 26% porosity and inclusions of TiO, Ti 2 O 3 , and Ti 2 O 3 N. Optical emission spectroscopy was used to control the plasma composition and estimate the effective temperature of plasma plume. The chemical-hydrodynamic model of laser induced plasma was developed to get a deeper insight into the deposition process. The model predicts that condensed titanium oxides, formed in peripheral plasma zones, gradually accumulate on the surface during the plasma plume evolution. A satisfactory agreement between the experimental and calculated chemical composition of the plasma plume as well as between the experimental and calculated composition and thickness of the deposited film was demonstrated. This allows a cautious conclusion that the formation of condensed oxides in the plasma and their consequent deposition onto the ablation surface are among the key mechanisms of formation of porous surface films.

The effect of treatment with nanosecond laser pulses on the fatigue resistance of plate samples of recrystallized (grain size of the order of 2-3 µm) commercially pure titanium (grade VT1-0) under cyclic tensile loading is studied. The results of investigations by methods of scanning and transmission electron microscopy of the microstructure of the subsurface layer of the alloy under study after exposure to nanosecond laser irradiation and subsequent fatigue tests are presented.

The paper presents the measurement results of the internal friction high temperature background for the VZh171 refractory alloy before and after its nitridation. The obtained data are used to study mechanisms of the alloy transition from the elastic to viscoelastic state at elevated temperatures. The nitridation process leads to a rise of the transition temperature from 571 K (initial state) to 763 K (after nitridation). The activation energy of the internal friction high temperature background is 0.63±0.01 and 0.59±0.01 eV before and after the bulk nitridation, respectively. The activation energy of processes responsible for the formation of viscoelastic properties, is ≈2.52 and ≈2.36 eV before and after the bulk nitridation, respectively. These values correspond to the self-diffusion activation energy in nickel, the main component of the alloy matrix. The presence of the dispersed nitride phase in the matrix decreases the activation energy of viscoelastic processes by about 6

The results of measurements of the high-temperature internal friction background of the heat-resistant alloy VZh171 in the initial state and after volume nitriding presented. The obtained data used to study the regularities of the transition from the elastic to the viscoelastic state of the material at elevated temperatures. Nitriding the alloy leads to an increase in the transition temperature to the viscoelastic state from 571 K (initial state) to 763 K (after nitriding). The values of activation energy of the high-temperature internal friction background obtained: U f = 0.63 ± 0.01 eV for the alloy VZh171 in the initial state and U f = 0.59 ± 0.01 eV for the alloy after volume nitriding. The activation energies U 0 of the processes responsible for the formation of the viscoelastic properties of the substance are estimated: U 0 ≈ 2.52 eV for the alloy in the initial state, U 0 ≈ 2.36 eV for the nitrided alloy. The obtained values U 0 correspond to the self-diffusion activation energy in nickel, the main component of the alloy matrix. The appearance of dispersed nitride phases in the matrix leads to a decrease in the activation energy of viscoelasticity processes by about 6%. Possible reasons for the change in the transition temperature and the activation energy of the viscoelastic state at moderately high temperatures as a result of nitriding discussed.

Using the methods of Raman spectroscopy, optical metallography and scanning electron microscopy, combined with the measurements of tribological characteristics, special aspects of the formation of microrelief and variation of the structural-phase state of carbon coatings formed on the surface of AISI 321 heat-resistant steel by pulsed cathodic arc deposition followed by their irradiation with nanosecond laser pulses are studied.

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.