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Papers by Valentin Gavriljuk

Exploratory Materials Science Research, 2020

METALLOFIZIKA I NOVEISHIE TEKHNOLOGII, 2019

Mobility of hydrogen atoms in the β-phase of titanium alloys doped with iron is studied by means ... more Mobility of hydrogen atoms in the β-phase of titanium alloys doped with iron is studied by means of mechanical spectroscopy. As shown, the hydrogen dissolution in the β-phase results in appearance of the Snoek-like relaxation at temperatures about 80 K. The ab initio atomic calculations are used to analyse atomic complexes responsible for the relaxation. The results suggest an affinity of hydrogen atom to iron in titanium and a responsible of s-H complexes (s-substitutional atom) with the symmetry lower than the cubic one for Snoek-like relaxation. The obtained activation energy of hydrogen migration in the β-phase assumes that such phase could serve as a pathway of hydrogen to the α-phase where the hydride could form.

Hydrogen in Engineering Metallic Materials

Material Science & Engineering International Journal, 2017

A mechanism for a similar effect of hydrogen and surface-active elements, surfactants, on the str... more A mechanism for a similar effect of hydrogen and surface-active elements, surfactants, on the structure and properties of metals is discussed based on studies of austenitic steels and using the ab initio calculations and experimental measurements of the electron structure, mechanical spectroscopy and tension tests. The similarity is originated from the local enhancement of the metallic character of interatomic bonds. The obtained results are interpreted within the frame of the electron approach to the hydrogen-enhanced localized plasticity phenomenon, HELP, in hydrogen embrittlement. The surfactants increase the density of electron states at the Fermi level and, correspondingly, the concentration of free electrons. As a response, a local decrease of the shear modulus resulted in the initiation of dislocation sources, decrease of the line tension of dislocations and distance between their assembles is expected, which facilitates the opening and propagation of cracks and mechanical degradation. The comparison with the adsorption-induced dislocation emission hypothesis, AIDE, for hydrogen and liquid metal embrittlements is carried out.

Scripta Materialia, 2017

Comments to the paper "in situ observations of silver-decoration evolution under hydrogen permeat... more Comments to the paper "in situ observations of silver-decoration evolution under hydrogen permeation: Effects of grain boundary misorientation on hydrogen flux in pure iron", the authors: M.

Materials Science Forum, 2007

Interstitials N, C and H in steels are compared in terms of their effect on the electronic struct... more Interstitials N, C and H in steels are compared in terms of their effect on the electronic structure and stacking fault energy, atomic distribution, phase transformations and precipitation, mobility of dislocations, mechanisms of deformation, strengthening and fracture. It is shown that the observed similarities and differences are essentially controlled by the decrease of the electron state density at the Fermi level of the iron due to carbon and its increase due to nitrogen and hydrogen. The increase in the concentration of vacancies with increasing content of interstitials and its possible role in mechanical properties are considered. The nature of nitrogen- and hydrogenincreased localized plasticity of austenitic steels is discussed and some consequences for their fracture are analyzed.

Materials Science Forum, 1999

ABSTRACT

Scripta Materialia, 2001

Relevant mechanisms of cementite dissolution due to cold work of pearlitic steel are discussed ba... more Relevant mechanisms of cementite dissolution due to cold work of pearlitic steel are discussed based on experimental data obtained using M ossbauer spectroscopy and internal friction. It is concluded that a strong interaction between carbon atoms and dislocations at the interface is the most probable reason for decomposition of the cementite lamellae.

Scripta Materialia, 2003

Internal friction (IF) was measured in two non-stoichiometric Ni 2 MnGa alloys. Several IF peaks ... more Internal friction (IF) was measured in two non-stoichiometric Ni 2 MnGa alloys. Several IF peaks attributed to some restructuring of the martensitic lattice were observed below M s. From the strain dependence of IF, the activation enthalpy for movement of twin boundaries between martensitic domains was estimated to be equal to 0.02-0.04 eV.

Materials Science and Engineering: A, 2006

The effects of C, N and H in the iron-based alloys are studied in terms of the electronic and cry... more The effects of C, N and H in the iron-based alloys are studied in terms of the electronic and crystal structure, atomic distribution, phase transformations, crystal lattice defects and some peculiarities of mechanical behavior. Similarities and differences in thermodynamic behavior, structure and properties are derived from the theoretical and experimental findings showing that carbon assists the covalent character of interatomic bonds, whereas nitrogen and hydrogen increase the concentration of conduction electrons.

Materials Science and Engineering: A, 2003

The available experimental data and hypotheses concerning cementite decomposition during the cold... more The available experimental data and hypotheses concerning cementite decomposition during the cold work of pearlitic steels are reviewed. The results of studies performed using thermomagnetic analysis, Mössbauer spectroscopy, internal friction and APFIM are used to discuss the mechanism governing cementite decomposition. The following features of this phenomenon seem to be important: (i) the fraction of the decomposed cementite increases with the refining of the initial pearlitic structure, i.e. with the increase of the ferrite–cementite interfacial area; (ii) the decomposition effect saturates as strain increases; (iii) carbon–dislocation interaction in ferrite and MeC bonding in cementite have a strong influence on cementite decomposition. The conclusion is made that cementite decomposition is controlled by the transfer of carbon atoms from cementite to dislocations accumulated near the interface during deformation. This is because the binding enthalpy between carbon atoms and dislocations in ferrite exceeds the solution heat of cementite. Some relevant effects of cementite decomposition in practice are discussed.

International Journal of Hydrogen Energy, 2001

Cohesive properties and electronic structures of face-centered (FCC) and hexagonal close-packed (... more Cohesive properties and electronic structures of face-centered (FCC) and hexagonal close-packed (HCP) phases of CrNiFe2Hx (x = 0; 2; 4) alloys have been studied using ab initio linear mu n-tin orbital method (LMTO). The cohesion energy of these crystalline phases has been calculated as a function of the Wigner-Seitz radius. The results of the electronic structure calculations were used to determine relative stability of di erent structures. The predicted structure and calculated equilibrium lattice constants are in good agreement with the experimental data. The nature of FCC → HCP transformation in CrNiFe2 alloy during hydrogen charging is found to be due to the weakening of interatomic bond.

Journal de Physique IV (Proceedings), 2003

Similarities and differences in the structure of carbon and nitrogen austenites and martensites a... more Similarities and differences in the structure of carbon and nitrogen austenites and martensites are reviewed. It is shown that different atomic distribution of interstitial and substitutional solute atoms (tendencies towards clustering in carbon austenite and short range atomic ordering in nitrogen austenite) stems from the preferential localisation of electrons on the atomic sites by carbon and increase in the concentration of free électrons by nitrogen. Increased stability of nitrogen austenitic steels in relation to sensitisation treatments and martensitic transformation is attributed to the nitrogen-assisted short range atomic ordering. A more homogeneous distribution of interstitial and substitutional solutes is inherited by martensite, which results in delayed precipitation during tempering, the lower rate of coarsening in nitrides as compared to carbides and improved mechanical properties of nitrogen martensitic steels.

$Research paper thumbnail of Neutron-diffraction study of martensitic transformation in austenitic stainless steel under low-cycling tensile-compressive loading$

Applied Physics A: Materials Science & Processing, 2002

Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiom... more Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiometric Heusler-type Ni 2:16 Mn 0:78 Ga 1:06 single crystal (conduction electron-to-atom ratio = 7.56). The splitting of a cubic (020) peak on a reciprocal lattice c Ã-plane was traced with decreasing temperature from 400 to 37 K. It was found that an orthorhombic structure (a > b > c) appears slightly below the transformation temperature as a metastable transient precursor structure before the formation of a final stable tetragonal structure (a ¼ b < c). The modes of deformation from cubic to orthorhombic are (i) simple shrinking and elongation of two cubic axes or (ii) a shuffling-like deformation along the cubic h110i direction on one of the cubic planes. The mode of deformation from orthorhombic to tetragonal is a shuffling-like deformation along the orthorhombic h110i direction on the orthorhombic c-plane. Both shuffling-like deformations originate from tilting deformations that preserve the common h111i direction.