Ayrat Nazarov

Ayrat Nazarov
Institute for Metals Superplasticity Problems of Russian Academy of Sciences | IMSPRAS

Dr. Sci.

About

154
Publications
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Introduction
Ayrat Nazarov currently works at Institute for Metals Superplasticity Problems of Russian Academy of Sciences. Ayrat does research in Materials Physics, Materials Science and Materials Engineering. Their current project is 'Ultrasonic treatment of ultrafine-grained materials processed by severe plastic deformation'. Ayrat Nazarov is also Deputy-Editor of research journal "Letters on Materials".

Publications

Publications (154)
Article
Joints of 0.5 mm thick sheets of commercially pure titanium have been processed by ultrasonic spot welding with the amplitude of vibrations 20 µm and welding time 2 and 3 seconds under the clamping force varied from 5 to 7 kN. It is shown that an increase in the clamping force and welding time results in an increase of the dimensions of defect-free...
Article
Full-text available
Solid state joints of samples of coarse-grained (CG) and ultrafine-grained (UFG) nickel have been obtained for the first time using spot ultrasonic welding (USW). The UFG structure in disk-shaped samples was processed by means of high-pressure torsion (HPT). On the basis of lap shear tests, the optimal values of the clamping force resulting in the...
Article
Microstructure and room temperature mechanical properties of α-titanium alloy Ti-5Al-0.5 V subjected to equal channel angular pressing (ECAP) and subsequent ultrasonic treatment (UST) have been studied. The ECAP was carried out at 600 °C by route Bc and the UST at the frequency of 20 kHz and amplitude of compression-tension stresses of 100 MPa for...
Article
For the first time, the relaxation of disordered dislocation arrays in a model 3×3 columnar polycrystal under ultrasonic action is studied using the discrete-dislocation approach. All grains contain three non-parallel slip systems located at an angle of 60° to each other. The non-equilibrium state of the grain boundaries is modeled using two finite...
Article
Full-text available
Solid state joints were obtained for the first time by ultrasonic welding (USW) of ultrafine-grained (UFG) thin disks of Ni processed by high pressure torsion (HPT). Samples of two types were studied: the ones for lap shear mechanical tests were prepared by joining two disks superimposed on each other under static loads of 4.5 and 6.0 kN, and the o...
Article
Full-text available
The results of the study on the microstructure and properties of solid state joints of titanium sheets obtained by ultrasonic welding (USW) with frequency 20 kHz and vibration amplitude 20 μm during 2 and 3 s under a 6 kN clamping force are presented. The thermo-mechanically affected zone is observed along the defect-free weld line (joint). It was...
Article
Full-text available
The results of studies on the development of instruments for ultrasonic welding (USW) of metals, which is the basic process for ultrasonic additive manufacturing, are presented. The influence of process parameters (static loading and welding time) on the microstructure and strength of joints produced by USW of commercially pure copper, nickel and t...
Article
Full-text available
Ultrasonic welding (USW) is one of the methods for producing solid-phase joints of thin metal sheets, which in the future can be used to obtain laminated composite materials, for additive manufacturing and renovation of metallic articles. The quality of joints depends on both the processing conditions and the properties of welded metals and alloys....
Article
Ultrasonic treatment of commercially pure ultrafine-grained Ti processed by high pressure torsion is performed. Measurements show no significant relaxation of the structure and no changes in both microhardness and microdeformation even at the maximum possible ultrasound amplitudes. Validation of the experimental observations is made with the help o...
Article
Full-text available
Effect of oscillating tension-compression stresses on a nonequilibrium grain boundary containing a disclination dipole in titanium is studied by means of molecular dynamics simulations. The system with nonequilibrium boundary was constructed by joining two bicrystals with tilt boundaries Ɵ = 36.87 ° and Ɵ = 28.07 °, thus the disclination dipole had...
Article
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Field electron emission from a copper based composite reinforced with carbon nanotubes (Cu-4 wt.% CNT) was studied. The composite samples were processed by mixing copper powders and carbon nanotubes (CNTs) in a ball mill followed by hot isostatic pressing. To obtain a more even distribution of CNTs, the samples were subjected to high pressure torsi...
Article
Full-text available
This work presents the results of a study of the mechanical properties of a titanium alloy Ti-5Al processed by equal channel angular pressing (ECAP) and ultrasonic treatment (UST). The UST was carried out at a frequency of 20 kHz with an amplitude of oscillating tension-compression stresses of 100 MPa. It was shown that the alloy subjected to UST e...
Article
Full-text available
Ultrasonic consolidation of commercially pure copper plates with coarse-grained and ultrafine grained structures was carried out. Copper plates in both states were joined by ultrasonic welding using the same route. Consolidated samples were studied in a cross section parallel to the oscillation direction. The compressive strain value and the joint...
Article
Improving the superplasticity characteristics of alloys widely used in industry, such as titanium alloy Ti-6Al-4V, is an important practical problem. Processing by the methods of severe plastic deformation can reduce the temperature of superplasticity. However, the material exhibits high flow stresses. In this work we studied the effect of prelimin...
Article
Commercially pure coarse-grained nickel was studied. On the electrically polished surface of four samples an area 1 × 1 mm² in size was marked by a special indenter and studied by EBSD analysis. All the samples were subjected to ultrasonic treatment (UST) with stress amplitudes of 20–80 MPa. The marked area was studied after that. In all the sample...
Book
his book combines the perspectives of materials science of Superplasticity, on the one hand, and those of design and mechanics, on the other, in order to provide a holistic view of materials, design, mechanics and performance which will lead to useful solutions of societal benefits, in addition to providing great intellectual challenges. After cons...
Article
Full-text available
A short review on the results of research and development on superplasticity of alloys and related processes such as grain refinement, solid state bonding carried out at the Institute for Metals Superplasticity of the Russian Academy of Sciences (IMSP RAS) is given. One of the most important contributions of IMSP RAS to the fundamentals of superpla...
Article
Full-text available
Commercially pure nickel was processed by equal-channel angular pressing (ECAP) and subjected to ultrasonic treatment (UST) with a stress amplitude of 100 MPa. The microstructure, microhardness and mechanical properties of the deformed and sonicated samples were studied. It was shown that the UST affected the microstructure of ECAP nickel. A refine...
Article
Full-text available
Grain boundaries (GBs) in bulk nanostructured materials processed by severe plastic deformation (SPD) have a nonequilibrium structure caused by extrinsic grain boundary dislocations (EGBDs) absorbed during deformation. Under external influences (annealing or cyclic straining) these GBs relax towards equilibrium resulting in a release of the excess...
Article
Computer simulation was used to study the relaxation of disordered systems of dislocations in the stress field of nonequilibrium grain boundaries upon ultrasonic treatment (UST). The effect of ultrasound is simulated by an oscillatory shear stress applied to the crystal. Edge dislocations in a model grain with three nonparallel slip systems located...
Article
Atomic structure of columnar nickel nanocrystals with [1 1 2] column axis having nonequilibrium grain boundaries (GBs) containing extrinsic grain boundary dislocations (EGBDs) and its evolution under oscillating stresses are studied by molecular dynamics method. Energy of GBs as a function of the degree of nonequilibrium is evaluated. It is found t...
Article
Full-text available
Bulk nanostructured, or ultrafine-grained (UFG) metals and alloys produced by severe plastic deformation (SPD) methods have grain boundaries (GBs), which are in a specific, non-equilibrium state associated with extrinsic grain boundary dislocations (EGBDs) introduced into the boundaries during deformation. In the present review, the origin of this...
Article
Full-text available
Effect of ultrasonic treatment (UST) with an amplitude of oscillating tension-compression stresses 100 MPa on the characteristics of superplastic deformation of Ti-6Al-4V alloy with an ultrafine grained (UFG) structure processed by equal-channel angular pressing (ECAP) is studied. During tensile tests at 600°C with initial strain rates in the inter...
Article
Atomistic simulations of the structure, energy and relaxation under the action of high frequency cyclic straining are carried out for columnar nickel nanocrystals with [112] column axis, the grain boundaries (GBs) of which are in a nonequilibrium state caused by the presence of extrinsic grain boundary dislocations (EGBDs). A special method of intr...
Article
Relaxation of disordered dislocation structures under ultrasonic influence in a two-dimensional square-shaped grain is investigated using the discrete-dislocation approach. The model grain contains three non-parallel glide systems inclined at an angle of 60° to each other. Non-equilibrium grain boundary state is modeled by means of a mesodefect loc...
Article
Changes in the structure of coarse-grained nickel due to ultrasonic treatment (UST) are studied. For this purpose, commercially pure nickel was annealed at a temperature of 1300 °C for 1 h to obtain a coarse-grained structure with a low dislocation density. On the electrolytically polished surface of the sample, a 2 × 2 mm² sized area was marked an...
Article
Full-text available
Results of in situ transmission electron microscopic studies of annealing-induced evolution of grain boundary misorientations in ultrafine-grained aluminum alloy Al-4%Cu-0.5%Zr (wt.%) processed by high pressure torsion are presented. An experimental procedure based on the single reflection technique was applied for the measurements of orientations...
Article
Full-text available
A method for the construction of initial atomic models of nanocrystals with extrinsic grain boundary dislocations (EGBDs) in grain boundaries (GBs) for molecular dynamics (MD) simulations is developed. The method is realized for f.c.c. nanocrystals with columnar grains having common crystallographic axis [112] parallel to the column axis and thus d...
Article
Atomic structure of nonequilibrium [112] tilt grain boundaries in nickel containing disclination dipoles is studied by means of molecular dynamics simulations. Initial systems for simulations are constructed by joining together pieces of two bicrystals one of which contains a symmetric tilt GB S=11 / 62.96° and the other a GB S=105 / 57.12°, or S=1...
Chapter
Environmental superplasticity is demonstrated in polycrystalline materials that experience an anisotropic dimensional change in specific environment conditions [1].
Chapter
Like conventional alloys, usually brittle intermetallic alloys (TiAl, Ti3Al, Ni3Al etc.) in a fine-grained condition under a certain temperature-strain rate intervals display superplastic behavior [994–1003]. Phenomenological features like high elongation, low flow stress, high strain-rate sensitivity index and deformation mechanisms were found to...
Chapter
Structural superplasticity in relatively higher melting temperature materials such as Titanium alloys, Steels and Ni based alloys is discussed in this chapter.
Chapter
Scientific investigations on Superplasticity started with the works of Bengough [494], the scientists at the old Kaiser Wilhelm Institute in Berlin and Pearson [28], all from the early years of the twentieth century.
Chapter
Theories of superplasticity are reviewed in this chapter in the following order. (a) Theories of structural superplasticity, (b) Theories of environmental/transformation superplasticity. The theories proposed from the former Soviet Union during 1945–1962 are often referred to as the early theories and those propounded since the mid-1960s are known...
Chapter
The “superplasticity-like” behavior of geological materials, i.e. minerals, combinations of minerals, spinels, rocks etc., polycrystalline ice, amorphous materials (bulk metallic glasses) and some exotic materials like hydroxyapatite and CNT is discussed in this chapter.
Chapter
A majority of superplastic alloys require suitable thermo-mechanical processing to develop a microstructure conducive to superplastic deformation [11,13,14]. Several processing routes, including severe plastic deformation techniques, result in ultrafine grained (UFG) and nano-structured (NS) materials. Friction-stir processing (FSP) is one of the w...
Article
Evolution of disordered dislocation structures under ultrasonic influence is studied in a model two-dimensional grain within the discrete-dislocation approach. Non-equilibrium grain boundary state is mimicked by a mesodefect located at the corners of the grain, stress field of which is described by that of a wedge junction disclination quadrupole....
Article
Commercially pure nickel was processed by high pressure torsion (HPT) and subjected to ultrasonic treatment (UST) with different amplitudes of compression-tension stresses in the zone of stress antinode of a standing wave. It was found that microstructure parameters such as the dislocation density, low- and high-angle grain boundary fractions, micr...
Article
Using numerical computer simulation, the behavior of disordered dislocation systems under the action of monochromatic standing sound wave has been investigated in the grain of the model two-dimensional polycrystal containing nonequilibrium grain boundaries. It has been found that the presence of grain boundaries markedly affects the behavior of dis...
Article
Commercially pure nickel was processed by equal channel angular pressing (ECAP) through route Bc for 12 passes to obtain an ultrafine grained (UFG) microstructure and further subjected to an ultrasonic treatment (UST) which introduced a maximum amplitude equivalent to anormal stresses of 100 MPa in a steady state regime. It was observed that the mi...
Article
Effect of ultrasonic treatment (UST) on the microstructure and microhardness of ultrafine grained nickel processed by high pressure torsion (HPT) was studied. With this aim, samples after HPT were subjected to oscillating compression-tension stresses with amplitudes 15, 30, 45, 60 and 90 MPa in the zone of strain antinode of an ultrasonic instrumen...
Article
The effect of ultrasonic vibrations on the structure of nonequilibrium symmetric [112] tilt grain boundaries (GBs) in nickel containing dipoles of wedge disclinations is studied by means of molecular dynamics simulations. As an example, symmetrical Σ = 15 / 78.46° tilt boundary is considered. It is shown that above some critical amplitude of the ap...
Article
The dynamics of the motion of various dislocation tripoles under the effect of a monochromatic standing sound wave has been studied using numerical modeling. Stable configurations of the tripoles that are in drift motion have been found and mutual transitions between these configurations have been investigated. The dependence of the velocity of dri...
Article
Numerical simulations of dynamics of different stable dislocation tripoles under influence of monochromatic standing sound wave were performed. The basic conditions necessary for the drift and mutual rearrangements between dislocation structures were investigated. The dependence of the drift velocity of the dislocation tripoles as a function of the...
Article
Full-text available
Composites with a copper matrix, reinforced by carbon nanotubes, have been produced by the multistage method including functionalization of carbon nanotubes, their dissolution, mixing with a copper powder, preliminary warm isostatic compaction, and severe plastic deformation by torsion. The microstructure and microhardness of composites containing...
Data
Full-text available
Composites with a copper matrix, reinforced by carbon nanotubes, have been produced by the multistage method including functionalization of carbon nanotubes, their dissolution, mixing with a copper powder, preliminary warm isostatic compaction, and severe plastic deformation by torsion. The microstructure and microhardness of composites containing...
Article
Full-text available
Research of microstructure, X-ray diffraction and microhardness metall-matrix composites reinforced with carbon nanotubes (CNT) obtained by severe plastic deformation were carried out. As starting materials for the preparation of composites multi-walled CNT and powders of copper and aluminium were used. Composites in the form of discs with a diamet...
Article
Using equal-channel angular pressing as an example, the effect of metal-flow kinematics under condition of severe plastic deformation of metals on the value of strain and features of structural changes is considered. The role of shear and rotational strain in the formation of ultrafine-grained structures is shown and the contribution into the total...
Article
The effect of ultrasonic treatment (UST) on the microstructure and mechanical properties of bulk nanostructured nickel processed by equal-channel angular pressing (ECAP) is studied in the range of stress amplitudes between 0 and 100 MPa. It is shown that UST results in a considerable simultaneous increase of the ultimate strength and ductility of t...
Article
Scientific bases of a technology for superplastic roll forming of axially symmetric parts of gas turbine engines that are made of heat-resistant alloys are described. It is shown that a formed microcrystal structure allows their deformation under conditions of superplasticity, thereby providing changes in physical and mechanical and processing prop...
Article
A model of the relaxation of the nonequilibrium structure of grain boundaries in bulk nanomaterials, which are produced by deformation methods, under an ultrasonic wave effect is proposed. Changes in the microstructure and the mechanical properties of nanostructured nickel produced by torsion under quasi-hydrostatic pressure and equal-channel angul...
Article
Impact strength tests of nickel samples exposed to equal-channel angular pressing (ECAP) were carried out. The influence of annealing and ultrasonic treatment with stress amplitudes of 20, 50 and 100 MPa on the impact fracture of ultrafine grained nickel processed by ECAP was shown.
Article
Full-text available
Classical molecular dynamics with the AIREBO potential is used to investigate the effect of two types of the Stone-Thrower-Wales (STW) defects in an infinite graphene sheet on structural stability of graphene. The borders of the structural stability of graphene in the two-dimensional space of the strain components () are found for the two types of...
Article
Fundamentals of the roll forming technology for disks of gas-turbine engines under super-plasticity conditions are stated. Because of deep underlying reasons of materials science, the technology provides a high process efficiency, equipment universality, the possibility of obtaining workpiece blanks with a high accuracy approaching that of the fina...
Article
Full-text available
The role of disclinations in the processing, microstructure and properties of bulk nanostructured materials is reviewed. Models of grain subdivision during severe plastic deformation (SPD) based on the disclination concept, a structural model of the bulk nanostructured materials processed by SPD are presented. The critical strength of triple juncti...
Article
We investigate the kinetics of grain rotation in a bicrystal with a tilt grain boundary by studying the relaxation of an edge dislocation wall in a discrete-dislocation approach. The boundary is infinitely extended in one direction and of finite size in the orthogonal one. The relaxation process is simulated numerically by solving the equations of...
Article
Principles of fabrication of ultrafine grained bulk and sheet materials for superplastic deformation by the methods of multiple isothermal forging and warm rolling are formulated. New data on superplastic behaviour of commercial alloys, on diffusion bonding of similar and dissimilar materials, and superplastic forming of titanium alloys are present...
Article
Full-text available
This paper investigates the morphology and in-plane thermal conductivity of hybrid graphene sheets (HGSs), which consist of un-hydrogenated and single-side or double-side hydrogenated strips, via molecular dynamics simulation. The study shows that the hydrogenation styles and hydrogen coverage significantly affect the morphology and thermal conduct...
Article
Full-text available
The method of molecular dynamics was used to investigate the effect of strengthening-phase particles on the process of plastic deformation in two-dimensional nanocrystalline material at given temperature, hydrostatic pressure, and the maximum shear stress. We consider the deformation of a single-phase nanocrystal (material 1); a nanocrystal with pa...
Article
Full-text available
Commercially pure (99.9%) copper was severe plastically deformed by equal-channel angular pressing (ECAP) following route-Bc in three different processing regimes in order to obtain ultrafine-grained (UFG) microstructures leading to improved mechanical properties. In regime-1, the billets were processed at room temperature up to eight passes. The b...
Article
Full-text available
A new method of microstructure design in axisymmetric gas turbine engine components made of superalloys is proposed. The method is based on obtaining three types of microstructures by means of superplastic roll forming: coarse-grained one with coherent nano-sized precipitates of the gamma'-phase, the second with ultrafine grains of both phases and...
Article
Full-text available
Qualitative comparison of the effect of ultrasonic treatment and annealing on the structural relaxation of a two-dimensional nanocrystalline material after severe plastic deformation has been performed by the molecular-dynamics method. The treatments of both types lead to a decrease in the dislocation density and to a more equilibrium state of grai...
Article
Full-text available
Effect of ultrasonic treatment on the microstructure, microhardness, and thermal stability of nickel subjected to high-pressure torsion (under a quasi-hydrostatic pressure of 6 GPa) has been studied. It has been demonstrated that ultrasound favors a considerable decrease in internal microstresses. It has been found that after an ultrasonic treatmen...
Article
The effect of ultrasonic treatment on the microstructure, microhardness and thermal stability of pure nickel after high pressure torsion (HPT) was studied. It was shown that the ultrasonic treatment reduces internal stresses induced by severe plastic deformation. The higher the intensity of ultrasound in the range studied, the stronger is this effe...
Article
Full-text available
The principles of fabricating nanostructured bulk and sheet materials by the methods of multiple isothermal forging and warm rolling are formulated. The first method, which is based on dynamic recrystallization, allows one to obtain bulk materials with a uniform nanostructure. The second method makes it possible to transform the latter into a sheet...
Article
On the basis of generalization of research results obtained at the Institute for Metals Superplasticity Problems, principles of fabrication of bulk ultrafine-grained and nanostructured materials by multiple isothermal forging are formulated Multiple isothermal forging is shown to be a universal high-performance deformation technique for the grain r...
Article
Full-text available
The gliding and annihilation of edge dislocations in a two-dimensional hexagonal lattice are investigated at different temperatures by the molecular dynamics method. The data obtained are used to determine the coefficients of the phenomenological equation of motion of dislocations that exhibit an inertia and experience retardation due to the intera...