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Murzinova M.A.,RAS Institute for Metals Superplasticity Problems
Letters on Materials | Year: 2017

Most of titanium alloys contain two phases at temperatures of processing and exploitation: α-phase with HCP lattice and β-phase with BCC lattice. Stability of two-phase structure and thermodynamics of β/α transformation, which occurs in a wide range of temperatures, considerably depend on the specific energy of interphase boundaries, and, consequently, on their structure. Basing on the literature data, four schemes of “planar” semicoherent interfaces, in which mismatches in interatomic distances are accommodated by two or three sets of edge misfit dislocations, were plotted. Such types of conjugation are observed on side and end interfaces of lamellas in titanium alloys. The procedure developed by J. H. van der Merwe and G. J. Shiflet was used for estimation of specific energy of interphase boundaries in Ti-6Al-4V alloy. Effect of temperature and content of alloying elements on lattice parameters and elastic properties of the α-and β-phases in Ti-6Al-4V alloy was taken into account for calculations. This approach allowed one to estimate the change in the energy of interphase boundaries in the alloy in temperature interval 600-975°C, where diffusion β/α transformation and enrichment of β-phase by vanadium are observed. It was shown that the energy of interphase boundaries in Ti-6Al-4V alloy decreased by 1.3-1.5 times with increasing temperature from 600 to 975°C at all examined types of conjugation. Depending on the structure the energy of interphase boundaries can vary from 0.201 to 0.337 J/m2 at 975°C and from 0.298 to 0.429 J/m2 at 600°C. © 2017, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.


Khadeeva L.Z.,RAS Institute for Metals Superplasticity Problems | Dmitriev S.V.,RAS Institute for Metals Superplasticity Problems
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Molecular-dynamics method is used to study the influence of mass ratio of anions and cations on the phonon spectrum of the crystal with NaCl structure and on the conditions of existence and properties of gap discrete breathers (DBs). We show that DBs can be easily excited when the mass ratio of light to heavy components is less than 0.2 and the gap in the phonon spectrum is sufficiently wide. Nonexistence of DBs for larger mass ratios is explained through the excitation of the harmonic with the frequency equal to half of the main DB frequency that interacts with phonons below the gap. For the mass ratio equal to 0.1 we could find at least three types of stable DBs that differ by the number of atoms with the largest amplitude and by polarization of oscillations. A zone-boundary phonon mode with sufficiently large amplitude was found to be modulationally unstable. Dynamics of such mode lead to spontaneous localization of energy in the form of large-amplitude DBs according to the anti-Fermi-Pasta-Ulam mechanism. © 2010 The American Physical Society.


Baimova J.A.,Nanyang Technological University | Dmitriev S.V.,RAS Institute for Metals Superplasticity Problems | Zhou K.,Nanyang Technological University | Savin A.V.,RAS Semenov Institute of Chemical Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Molecular dynamics simulations based on many-body interatomic potentials are conducted to investigate the formation of unidirectional ripples in zigzag and armchair graphene nanoribbons with clamped edges under in-plane uniform strain. The ripple formation is found to be a result of buckling under in-plane membrane forces having compressive and tensile principle components. This study demonstrates that the amplitude and orientation of the unidirectional ripples can be controlled by a change in the components of the applied strain. The ripple wavelength is practically independent of the applied strain but increases with the increasing nanoribbon width. In the study of the temperature effect on strain-induced ripples it was found that with increase in temperature the degree of fluctuation of ripples increases. Ripples with larger formation energy are less affected by thermal fluctuations. © 2012 American Physical Society.


Utyashev F.Z.,RAS Institute for Metals Superplasticity Problems
Materials Science Forum | Year: 2011

Nanostructured (NS) metallic materials can exhibit high strength at room temperature and superplastic properties at elevated temperatures. This enables to enhance their technological and structural properties, when producing various parts from them. For producing NS materials by severe plastic deformation (SPD), the development of effective SPD techniques for practical use is an urgent task. It is shown that solution of such a task should take into account strain compatibility on the macro-, meso- and micro-levels. Not only shear but also rotational deformation mode should be considered. Properties of NS materials and possibilities of their structural applications are considered from this point of view.


Zherebtsov S.,Belgorod State University | Murzinova M.,RAS Institute for Metals Superplasticity Problems | Salishchev G.,Belgorod State University | Semiatin S.L.,Air Force Research Lab
Acta Materialia | Year: 2011

The spheroidization behavior of an α colony microstructure in Ti-6Al-4V alloy during warm working and subsequent annealing at 600 and 800 °C was established. The principal features of microstructure evolution were found to be temperature dependent. At 800 °C transformation of the lamellar microstrucuture into a globular one was associated primarily with the classical boundary splitting mechanism followed by further spheroidization of α particles by means of termination migration. For thick α lamellae, however, new grains were formed due to continuous dynamic recrystallization during deformation, but spheroidization per se was limited. A decrease in temperature to 600 °C resulted in increased shear strains, lower diffusivity, and a decrease in the volume fraction of the β phase. Consequently, the thin β interlayers transformed relatively quickly into separate particles while α became the matrix phase. Evolution of the α phase during deformation/annealing at 600 °C was associated with continuous dynamic recrystallization with only limited dynamic or static spheroidization. Static spheroidization kinetics during annealing following warm working were explained in the context of approximate models of boundary splitting and termination migration. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Sukhorukov A.A.,Australian National University | Dmitriev S.V.,RAS Institute for Metals Superplasticity Problems | Suchkov S.V.,RAS Institute for Metals Superplasticity Problems | Kivshar Y.S.,Australian National University
Optics Letters | Year: 2012

We demonstrate that light propagation in waveguide arrays that include PT -symmetric structures can exhibit strongly nonlocal sensitivity to topology of the array at fixed other parameters. We consider an array composed of lossless waveguides, that includes a pair of PT -symmetric waveguides with balanced gain and loss, and reveal that PT -symmetry breaking thresholds are different for planar and circular array configurations. These results demonstrate that PT -symmetric structures can offer new regimes for optical beam shaping compared to conservative structures. © 2012 Optical Society of America.


Khadeeva L.Z.,RAS Institute for Metals Superplasticity Problems | Dmitriev S.V.,RAS Institute for Metals Superplasticity Problems
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Crystals having a gap in a phonon spectrum can support so-called gap discrete breathers (DBs), i.e., nonlinear localized vibrational modes existing in perfect crystals and having frequencies within the gap. In our recent work, for a two-dimensional crystal with stoichiometry A3B, we have demonstrated that if the atomic weight of the components is related as M A MB, then there is a wide gap in the phonon spectrum and the gap DBs can be easily excited. The situation is opposite if the above condition is not satisfied. In the present work the gap DBs are studied at thermal equilibrium, whereas in the previous study the temperature was zero. We demonstrate that in the crystal supporting DBs, in contrast to the opposite case, the lifetime of high-energy light atoms grows with temperature. The possible role of gap DBs in the thermally activated formation of vacancy and interstitial atom pairs (Frenkel pairs) was studied. We have measured the time needed for the appearance of a Frenkel pair as a function of temperature for the crystals supporting and not supporting DBs. A minor difference in waiting time of Frenkel pair nucleation was found in these two cases. We argue that, for the model and its parameters considered in the present work, the main mechanism of thermally activated Frenkel pair formation is the cooperative motion of atoms rather than the excitation of DBs. © 2011 American Physical Society.


Patent
RAS Institute for Metals Superplasticity Problems, Open Joint Stock Company Aviadvigatel and Joint Stock Company UFA Engine Industrial Association | Date: 2016-10-19

The invention relates to metal forming using diffusion welding and superplastic forming. Stop-off material is preliminarily applied in a predetermined screen pattern to areas where surfaces of skin and core preforms come into contact. Skin preforms are provided with a groove, and core preform is provided with a slot for mounting at least one tube. A stack is sealed along edges with the exception of where at least one tube is to be mounted. A tube is mounted to be connected to a collector zone, and oxygen and binder of the stop-off material are removed from cavities in the stack. The stack is fully sealed, heated, and the preforms are diffusion-welded in predetermined areas, also along an entrance edge, an exit edge and a peripheral edge. An integral structural preform is given an airfoil shape and subjected to superplastic forming by supplying working fluid into cavities between the skin and core preforms through also at least one tube. The collector zone is disposed on the side of the stack, which corresponds to the peripheral edge of the blade. For mounting one or more tubes for supplying working fluid at superplastic forming, the groove in the skin preforms and the slot in the core preform are provided at a distance from the outer boundary of the entrance edge or exit edge less than L/3, where L is the length of the blade chord along the peripheral edge. It is thus possible to eliminate risk of defects during blade forming without compromising performance characteristics of the blade and increase in labor intensity of producing same.


Patent
RAS Institute for Metals Superplasticity Problems | Date: 2010-09-08

The invention relates to the electronic engineering and, more specifically, to the fields thereof where the physical phenomenon of electron, or ion-electron, or cold emission is used, and concerns a cold cathode and a method for fabricating the same. Provided is a method for fabricating a cold cathode, according to which a cathode workpiece of a metal or alloy is subjected to severe plastic deformation to transform an initial structure of the workpiece into a fragmented structure comprising fragments of nanometric size or into a mixed structure comprising grains and fragments of nanometric size, characterized in that, after the severe plastic deformation, the cathode workpiece is subjected to a low-temperature annealing for transforming at least part of said fragments into grains of nanometric size at a temperature not lower than the operating temperature T_(oper) of the cathode. The invention is an improvement of the method for fabricating a cold cathode using severe plastic deformation and allows to further enhance efficiency of the cathode via a reduction in the electronic work function value.


Patent
Open Joint Stock Company Aviadvigatel and RAS Institute for Metals Superplasticity Problems | Date: 2011-09-28

A method for manufacturing a hollow fan blade of a titanium alloy, said blade consisting of skins and a filler forming stiffeners, comprises the step of working skin workpieces with a preformed blade root portion, during which working on surfaces of the skin workpieces, areas to be bonded to a filler workpiece are shaped in the form of projections with a surface flat in a cross-section, and areas to be not bonded to the filler workpiece are shaped in the form of recesses, respectively, wherein at least a part of a surface of recesses opposite to projections in a stack assembled for diffusion welding is made flat in a cross-section, and also comprises the steps of: applying a bond preventing coating onto surfaces of workpiece areas to be not bonded; assembling the skin and filler workpieces into a stack; diffusion welding the skin and filler workpieces; forming stiffeners by superplastic forming, the method further comprises the step of providing the skin and filler workpieces with an aerodynamic profile by applying a deforming load thereto, including forming a pressure face and a suction face of the blade and twisting its airfoil. The method is characterized in that said projections and recesses are made on the surfaces of the skin workpieces prior to providing them with the aerodynamic profile, while the step of providing the workpieces with the aerodynamic profile is performed after diffusion welding. The method is particularly applicable to aircraft engine building.

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