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Kvashnin A.G.,Moscow Institute of Physics and Technology | Sorokin P.B.,National University of Science and Technology "MISIS"
Journal of Physical Chemistry Letters | Year: 2014

We investigate the properties of potentially the stiffest quasi-2-D films with lonsdaleite structure. Using a combination of ab initio and empirical potential approaches, we analyze the elastic properties of lonsdaleite films in both elastic and inelastic regimes and compare them with graphene and diamond films. We review possible fabrication methods of lonsdaleite films using the pure nanoscale "bottom-up" paradigm: by connecting carbon layers in multilayered graphene. We propose the realization of this method in two ways: by applying direct pressure and by using the recently proposed chemically induced phase transition. For both cases, we construct the phase diagrams depending on temperature, pressure, and film thickness. Finally, we consider the electronic properties of lonsdaleite films and establish the nonlinear dependence of the band gap on the films' thicknesses and their lower effective masses in comparison with bulk crystal. © 2014 American Chemical Society. Source

Golovin I.S.,National University of Science and Technology "MISIS"
Physics of Metals and Metallography | Year: 2013

Linear anelastic effects in binary and ternary alloys of iron with 13 and 17 at % Ga, 12 at % Ge, and 4-8 at % Al (Fe-13Ga, Fe-17Ga, Fe-12Ge, Fe-8Al-3Ga, Fe-8Al-4Ge, and Fe-4Al-8Ge) have been investigated. In all of these alloys, thermally activated effects of linear anelasticity have been found and identified that are caused by point defects in interstitial (Snoek-type relaxation) and substitutional (Zener relaxation) solid solutions, as well as by dislocations (Hasiguti effect), and by grain boundaries. The effects of the alloy composition on the activation parameters of the above-mentioned relaxation mechanisms have been determined. In addition, frequency-independent effects related to processes of structural rearrangement, such as ordering and disordering of the alloys have been revealed due to the specific features in the curves of the temperature dependences of internal friction for almost all compositions. © Pleiades Publishing, Ltd., 2013. Source

Golovin I.S.,National University of Science and Technology "MISIS"
Materials and Design | Year: 2015

Frequency, amplitude, and temperature dependent effects of anelasticity in Fe-Ga and Fe-Ga-Al alloys are studied by mechanical spectroscopy techniques using forced bending and torsion subresonance vibrations (f from 0.001 to 200Hz, ε from 10-6 to 10-2, T from 0 to 600°C). The structure and the properties of the studied alloys are characterized by scanning electron microscopy and magnetic force microscopy. Main regularities of amplitude dependent damping are attributed to magnetomechanical damping, which is very sensitive to the structural state of alloys, their composition, magnetostriction, and testing method. Two maximal damping peaks at about 18% and 27%Ga correspond to similar maxima of magnetostriction against %Ga. Both temperature dependent thermally activated relaxation effects and anelastic effects due to phase transitions are discussed in terms of alloys structures. Thermally activated internal friction peaks are ascribed to different atomic mechanisms. A phase transition from bcc originated structures (A2 and D03) to an fcc ordered structure (L12) is accompanied by a transient anelastic effect typical for a shear diffusionless transition. © 2015 Elsevier Ltd. Source

Zhevnenko S.N.,National University of Science and Technology "MISIS"
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

The surface energies of Cu-Co solid solutions in hydrogen atmosphere were measured. The measurements were performed on pure copper and copper alloys containing 0.45, 0.7, 1.4, 2.25, 2.50, and 2.8 at. pct Co and 4.1 at. pct Co for the temperature range 1245 K to 1349 K (972 C to 1076 C). The experiments were conducted using the zero creep method for 18 mcm foils. The modified method allowed "in situ" determining of the surface energy. It was shown that the surface energy increases as the concentration increases up to 1.4 at. pct Co and then decreases. Such extreme behavior was obtained by the direct method for the first time in a solid metallic system. © 2013 The Minerals, Metals & Materials Society and ASM International. Source

Khovaylo V.,National University of Science and Technology "MISIS"
Journal of Alloys and Compounds | Year: 2013

Critical analysis available in the literature experimental results on magnetocaloric effect in ferromagnetic shape memory alloys Ni-Mn-X (X = Ga, In, Sn, Sb) is given. Based on a model developed by Pecharsky et al. [22], it is shown that the isothermal magnetic field-induced entropy change in the Ni-Mn-X alloys should not greatly exceed 30 J/kg K. Considering thermodynamics of temperature- and magnetic field-induced martensitic transformations, it is demonstrated that a contribution of the structural subsystem to the magnetocaloric effect in the Ni-Mn-X alloys studied so far is irreversible in magnetic fields below 5 T. This makes ferromagnetic shape memory alloys an inconvenient system for the practical application in modern magnetic refrigeration technology. © 2012 Elsevier B.V. All rights reserved. Source

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