The effect of thermomechanical treatment regimes on microstructure and mechanical properties of V–Me(Cr,W)–Zr–C alloys

The regularities of the formation of a heterophase structure in dispersion-strengthened vanadium V–Me(Cr, W)–Zr–C alloys are studied as a function of the regimes of their thermomechanical treatment. The regimes of treatment providing a substantial increase in the dispersity and homogeneity of spatial distribution of ZrC particles, temperature of recrystallization, and high-temperature (at T = 800°C) short-time strength are found in comparison to conventional treatment regimes.     

Thermal Stability of Microstructure and Mechanical Properties of V–Me(Cr,W)–Zr Alloys as a Function of Heat Treatment Modes

Russian Physics Journal - Using the methods of scanning and transmission electron microscopy, a study is performed of the influence of high-temperature annealing on the parameters of...     

Evolution of phase,texture, microstructure and magnetic properties of Fe–Cr–Co–Mo–Ti permanent magnets

Magnetic phase evolution, crystallographic texture, microstructure and magnetic properties of Fe–28Cr–15Co–3.5Mo–1.8Ti alloy have been investigated by X-ray diffractometry, scanning transmission electron microscopy and magnetometry techniques as a function of processing conditions. Heat treatment conditions for obtaining optimum textural, microstructural and magnetic properties have been established by the experimentations. The Goss {110}〈001〉 and cube type {001}〈010〉 textures have been developed in an optimal treated Fe–28Cr–15Co–3.5Mo–1.8Ti magnets. The coercive force in Fe–28Cr–15Co–3.5Mo–1.8Ti magnets depends critically on the shape anisotropy of rod-like Fe Co Ti-rich α₁ particles and remanence on the alignment and elongation of α₁ particles parallel to applied magnetic field 〈100〉 directions. The optimum magnetic properties obtained in Fe–28Cr–15Co–3.5Mo–1.8Ti alloy are intrinsic coercive force, _iH_c, of 78.8 kA/m (990 Oe), remanence, B_r of 1.12 T (11.2 kG) and energy product, (BH)_max of 52.5 kJ/m³ (6.5 MGOe). The development of Fe–28Cr–15Co–3.5Mo–1.8Ti magnets as well as characterization of texture, microstructural and magnetic properties in the current study would be helpful in designing the new Fe–Cr–Co–Mo based magnets suitable for scientific and technological applications.     

Calculation and analysis of vibrational spectra of adenine–thymine,guanine–cytosine,and adenine–uracil complementary pairs in the condensed state

We have calculated the frequencies of the normal vibrations of the complementary nucleic acid base pairs adenine–thymine, guanine–cytosine, adenine–uracil, corresponding to the Watson–Crick structure, and the adenine–uracil pair, corresponding to the Hoogsteen structure, in condensed states and we interpret the spectra. We determine the contributions of hydrogen bonds to the vibrational modes of the complementary pairs. We have analyzed the nature of the relative displacements of the nucleic acid bases as integral molecular units along the hydrogen bonds. We show the role of hydrogen bonds in tautomeric interconversions of complementary nucleic acid base pairs. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 84–92, January–February, 2009.     

Structure,thermal behavior,and chemical durability of lead–calcium–phosphate glasses

ABSTRACT

Structure and physical properties of 25CaO–xPbO–(75–x)P₂O₅ (0≤x≤35) glasses are investigated in this paper. Substitution of PbO for P₂O₅ in the binary 25CaO–75P₂O₅ glass was found to increase the density and to decrease the molar volume. Fourier transform infrared (FTIR) and Raman spectroscopies show the evolution of the phosphate skeleton when the PbO content increases: Q³ to Q² species (0<x≤25) and Q² phosphate network (x = 25) to short phosphate groups (x > 25) such as (P₄O₁₃^6?) (x = 35). The glass transition temperature first decreases with x, then increases for x values larger than 10%. The evolution of the glass transition temperatures is interpreted from the structural data: the minimum point observed in T_g is attributed to the transition of the ultraphosphate network from the network containing the modifying cations at isolated sites to a network with modifier sub-structure sharing terminal oxygens. At higher PbO content, the large increase in T_g is due to the reticulation of the phosphate network by PbO₄ groups.     

Franck–Condon Factors and r‐Centroids for the B–, C–, F–, and G–X Band Systems of YF Molecule

The Franck–Condon factors and r‐centroids, which are very closely related to relative transition probabilities, have been evaluated by a more reliable numerical integration procedure for the B¹π–X¹Σ⁺, C¹Σ⁺–X¹Σ⁺, F¹Σ⁺–X¹Σ⁺, and G¹π–X¹Σ⁺ band systems of the YF molecule, using suitable potentials.     

Electrochemical corrosion behavior,Vickers microhardness,and microstructure of Co–Cr and Ni–Cr dental alloys

Electrochemical corrosion behaviors, Vickers microhardness, microstructure, and electrical properties of Magnum H50 (Co=64.5%, Cr=29%, Mo=6.5% ) and Nikkeli–Kromi–Polttosekoitus (Ni=65.2%, Cr=22.5%, Mo=9.5%, X=2.8% Nb, Si, Fe, and Mn) dental alloys have been investigated. The corrosion potential for the Co_64.5Cr₂₉Mo_6.5 alloy in HCl was higher than that of the Ni_65.2Cr_22.5Mo_9.5X_2.8 alloy. The corrosion rate with 0.5 M HCl for the Ni_65.2Cr_22.5Mo_9.5X_2.8 alloy was measured as being high and the corrosion resistance as being small as compared with the values for the Co_64.5Cr₂₉Mo_6.5 alloy. Vickers hardness of the Co_64.5Cr₂₉Mo_6.5 alloy was higher than that of the Ni_65.2Cr_22.5Mo_9.5X_2.8 alloy. Also Vickers hardness values of the used alloys were decreased by increasing indentation load. The thermal conductivity and minimum shear stress values of the used alloys are calculated.     

First principle simulations of the surface diffusion of Si and Me adatoms on the Si(111)3×3-Me surface,Me= Al,Ga, In,Pb

The intriguing but yet still unexplained experimental results of Hibino and Ogino [Phys. Rev. B 54, 5763 (1996); Surf. Sci. 328, L547 (1995)], who have observed single defect movement on an Me induced Si(111)$\sqrt{3}\times \sqrt{3}$ surface, have been revived and theoretically analysed. Using Nudged Elastic Band (NEB) optimization, the minimal energy path for an Si adatom moving on the ideal and vacancy defected surfaces has been obtained and the most probable mechanism of the vacancy mediated single defect diffusion has been established. This mechanism is shown to be responsible for the experimentally observed Si adatom movement and predicts a far easier movement of the Me adatom on vacancy defected Me induced Si(111)$\sqrt{3}\times \sqrt{3}$ surfaces.     

Surface tension and density of liquid Bi–Pb,Bi–Sn and Bi–Pb–Sn eutectic alloys

Surface tension and density measurement of liquid Bi₅₆Pb₄₄, Bi₄₃Sn₅₇ and Bi₄₆Pb₂₉Sn₂₅ eutectic alloys was carried out by using the large drop method over the temperature range of 380–750 K. The regular solution model has been used in conjunction with Butler's equation to calculate the surface tension of binary and ternary alloys of the Bi–Pb–Sn system, while the surface tension of ternary alloys has also been predicted by using geometric models. The new experimental results were compared with the calculated values of the surface tension as well as with the data available in the literature.     

Limits of Gaudin Algebras,Quantization of Bending Flows,Jucys–Murphy Elements and Gelfand–Tsetlin Bases

Gaudin algebras form a family of maximal commutative subalgebras in the tensor product of n copies of the universal enveloping algebra \({U(\mathfrak {g})}\) of a semisimple Lie algebra \({\mathfrak {g}}\). This family is parameterized by collections of pairwise distinct complex numbers z ₁, . . . , z _n . We obtain some new commutative subalgebras in \({U(\mathfrak {g})^{\otimes n}}\) as limit cases of Gaudin subalgebras. These commutative subalgebras turn to be related to the Hamiltonians of bending flows and to the Gelfand–Tsetlin bases. We use this to prove the simplicity of spectrum in the Gaudin model for some new cases.     

W-algebras and the equivalence of bihamiltonian,Drinfeld–Sokolov and Dirac reductions

We prove that the classical $W$-algebra associated to a nilpotent orbit in a simple Lie-algebra can be constructed by preforming bihamiltonian, Drinfeld–Sokolov or Dirac reductions. We conclude that the classical $W$-algebra depends only on the nilpotent orbit but not on the choice of a good grading or an isotropic subspace. In addition, using this result we prove again that the transverse Poisson structure to a nilpotent orbit is polynomial and we better clarify the relation between classical and finite $W$-algebras.     

Evolution of the atomic order and valence state of rare-earth atoms and uranium in a new carbon-metal composite—diphthalocyanine pyrolysate C64H32N16 Me (Me = Y,La, Ce,Eu, and U)

The structure of a metal-carbon composite formed by the pyrolysis of diphthalocyanine of some rare-earth elements (Y, La, Ce, Eu) and uranium in the temperature range T _ann = 800–1700°C has been investigated for the first time by the methods of X-ray diffraction analysis and X-ray line shift. It has been shown that, in the general case, the studied pyrolysates consist of three phases. One phase corresponds to the structure of graphite. The second phase corresponds to nitrides, carbides, and oxides of basic metal elements with a crystallite size ranging from 5 to 100 nm. The third phase is amorphous or consisting of crystallites with a size of ～1 nm. It has been found that all the basic elements (Y, La, Ce, Eu, U) and incorporated iodine atoms in the third phase are in a chemically bound state. The previously unobserved electronic configurations have been revealed for europium. The possibility of including not only atoms of elements forming diphthalocyanine but also other elements (for example, iodine) in the composite structure is of interest, in particular, for the creation of a thermally, chemically, and radiation resistant metal-carbon matrix for the radioactive waste storage.     

Symmetry Reduction and Exact Solutions of the Euler–Lagrange–Born–Infeld,Multidimensional Monge–Ampere and Eikonal Equations

Abstract

Using the subgroup structure of the generalized Poincaré group P (1, 4), ansatzes which reduce the Euler–Lagrange–Born–Infeld, multidimensional Monge–Ampere and eikonal equations to differential equations with fewer independent variables have been constructed. Among these ansatzes there are ones which reduce the considered equations to linear ordinary differential equations. The corresponding symmetry reduction has been done. Using the solutions of the reduced equations, some classes of exact solutions of the investigated equation have been presented.     

Features of the structure and dynamics of Me1−x (NH4) x SCN (Me = K, Rb) mixed crystals

Neutron scattering is used to study the structure and dynamics of Me_{1 − x} (NH₄) _x SCN (Me = K, Rb) mixed crystals along the concentration section of 0.0 < x < 1.0 at room temperature 10 and 290 K. Phase transitions in Me_{1 − x} (NH₄) _x SCN mixed crystals are analyzed by neutron powder diffraction. The measured spectra of inelastic incoherent neutron scattering from mixed crystals in a concentration range of 0.0 < x < 1.0 at 10 are transformed into the generalized phonon density of states G(E) in the one-phonon incoherent approximation. Using G(E), we determine the changes in ammonium ion dynamics during phase transitions. Low energy resonance and local translational (two bands) and librational (two bands) modes are observed in the disordered rhombic phase at 10 K. The low energy resonance mode is not found in the ordered monoclinic phase at 10 K, though the local translational mode in the form of two bands and the local librational mode in the form of four bands are present there. The low energy resonance mode appears due to hybridization of the phonon spectrum of the host crystal with rotational tunneling modes of the split librational ground state of the impurity’s molecular ammonium ion.     

Ricci flow,Courant algebroids,and renormalization of Poisson–Lie T-duality

We use a generalized Ricci tensor, defined for generalized metrics in Courant algebroids, to show that Poisson–Lie T-duality is compatible with the 1-loop renormalization group flow.     

Thermal Stability of Structure and Properties of Gradient and Gradient-Layered Coatings of the Ti–Al–Si–Cu–N System

Russian Physics Journal - Using the methods of dark-field electron microscopy analysis, energy-dispersive X-ray microanalysis, hardness measurements and scratch testing, the variations of elemental...     

Analysis of the common characteristics of the Hartmann,Ronchi, and Shack–Hartmann tests

An overview of the settings of the planes for the filters and observed patterns in the Hartmann and Ronchi tests is presented. Also a new set of filters for both test were developed. In a similar way, it is easy to extend this analysis to the Shack–Hartmann test, and to propose a new Null Shack–Hartmann filter.     

Atomic structure of the Zr–He,Zr–vac,and Zr–vac–He systems: First-principles calculation

The ab initio investigations have been performed for the atomic structure of the Zr–He, Zr–vac, and Zr–vac–He systems with concentrations of helium atoms and vacancies (vac) of ~6 at %. A heliuminduced instability of the zirconia lattice has been revealed in the Zr–He system, which disappears with the formation of vacancies. The most preferred positions of impurities in the metal lattice have been determined. The energy of helium dissolution and the excess volume introduced by helium have been calculated. It has been established that the presence of helium in the Zr lattice leads to a significant decrease in the energy of vacancy formation.     

Influence of Chemical-Heat Treatment on Thermal Stability of Microstructure,Mechanical Properties and Fracture of V–Cr–Ta–Zr Alloy

Russian Physics Journal - A study of the features of structural-phase state, thermal stability, characteristics of mechanical properties and fracture behavior of V–Cr–Ta–Zr alloy...     

Synthesis,Characterization, and X-Band Permittivity Studies of Polypyrrole–Zirconium Composite

The zirconium dioxide-doped polypyrrole composites with different weight percentage were prepared by in situ polymerization methods. The prepared composites were subjected for characterization with different tools like Fourier transform infrared spectroscopy and scanning electron microscopy. The Fourier transform infrared spectroscopy spectra indicate a characteristic peaks which confirms the formation of composites. Scanning electron microscopy image indicates that the metal oxides are agglomerated with polypyrrole due to that the size of the composite particles increases to 7 µm. The real part of permittivity (?′) at X-band measurements of all samples first decrease and then increase in the higher frequency range. Meanwhile, the values of ?″ for polypyrrole–zirconia composites changes spontaneously due to the scattering of free charges explained by Kramers–Kronig relations. The reflection loss graph shows that the maximum reflection loss (RL) reaches up to ?54.6 dB at 10.8 GHz and the effective absorption bandwidth (RL ≤ ?10 dB) is 6.7 GHz.