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Korznikova E.A.,RAS Institute for Metals Superplasticity Problems | Dmitriev S.V.,Saint Petersburg State Polytechnic University
JETP Letters | Year: 2014

The formation of wrinkles in thin membranes is a widespread phenomenon. In particular, wrinkles can appear in graphene, which is the thinnest natural membrane, and affect its properties. A region where wrinkles with different wavelengths are linked is called wrinklon. Conditions of the fixing of an elastically deformed graphene sheet dictate a certain wavelength of wrinkles near the fixed edge. Wrinkles with a longer wavelength become more energetically favorable with an increase in the distance from the edge. As a result, wrinklons appear and reduce the potential energy of the system by uniting wrinkles into larger wrinkles with an increase in the distance from the edge. The possibility of implementing various equilibrium configurations of wrinklons at given plane strains in graphene has been demonstrated by the molecular quasistatic method. The distributions of the energy and elastic strain components in wrinklons with various configurations for nanoribbons with different widths have been calculated. © 2014, Pleiades Publishing, Inc.

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.

Korznikova E.A.,RAS Institute for Metals Superplasticity Problems | Dmitriev S.V.,Saint Petersburg State Polytechnic University
Journal of Physics D: Applied Physics | Year: 2014

Graphene is a two-dimensional, one-atom thick carbon nano-polymorph with a unique combination of physical and mechanical properties promising for many applications. Compressive in-plane stresses can result in the formation of wrinkles in a graphene sheet. Elastic strain and wrinkles are often used to control various physical properties of graphene. Wrinklon is a transition zone where two or more wrinkles merge into one. In this study, by means of molecular dynamics simulations, the potential energy density and amplitude of unidirectional wrinkles in suspended graphene are calculated as the functions of their wavelength for a given in-plane strain. Overdamped motion of wrinklons along graphene nanoribbons of different widths is studied. The shape and potential energy of wrinklons as well as elastic strain in the vicinity of wrinklons are calculated. The results of the present study should lead to a better understanding of suspended graphene devices and the effect of wrinkle dynamics on the electronic properties of graphene. © 2014 IOP Publishing Ltd.

Mukhtarov S.,RAS Institute for Metals Superplasticity Problems
Materials Science Forum | Year: 2010

The present paper deals with the review of earlier studies and original investigation of microcrystalline (MC) and nanostructured (NS) nickel based INCONEL® alloy 718 processed by severe plastic deformation (SPD) via multiple isothermal forging (MIF). The alloy with a mean grain size of 1 μm - 80 nm has been studied in terms of its thermal stability, superplastic and mechanical properties. It was established that the NS state with the 80 nm grain size can be considered as thermally stable up to the temperature 600°C (0.56Tm). The increase of annealing temperature beyond 600°C causes static recrystallization. Investigations of mechanical properties at room temperature have shown that the decrease of a mean grain size provides the enhancement of strength and reduction of plasticity. Thus, the alloy with a grain size of 80 nm has shown the ultimate strength - 1920 MPa and ductility - 4.8%. Mechanical properties of the NS state of the alloy after annealing are discussed. It has been established that alloy 718 with a grain size of 80 nm displays superplasticity at 600°C and a strain rate of 1.5×10 -4s-1 The values of relative elongation and strain rate sensitivity coefficient m are 350% and 0.37, respectively. © (2010) Trans Tech Publications.

Konkova T.,RAS Institute for Metals Superplasticity Problems | Mironov S.,Tohoku University | Korznikov A.,RAS Institute for Metals Superplasticity Problems | Semiatin S.L.,Air Force Research Lab
Acta Materialia | Year: 2010

A high-resolution electron backscatter diffraction technique was applied to quantify grain-structure development and texture evolution during/after cryogenic rolling of pure copper. Microstructure evolution was found to be a complex process involving mainly geometrical effects associated with strain and discontinuous recrystallization but also including limited twinning and grain subdivision. Recrystallization was deduced to be static in nature and probably occurred during static storage of the material at room temperature after cryogenic rolling. The texture contained a pronounced {1 1 0}〈1 1 2〉 brass component; this observation was interpreted in terms of the suppression of cross-slip at cryogenic temperatures. In general, cryogenic rolling was found to be ineffective for the formation of a nanocrystalline structure in pure copper. © 2010 Acta Materialia Inc. Published by Elsevier Ltd.

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