Investigation of the structural-phase state and its role in the formation of heat-resistance properties of 12% chromium steel

Results of investigations into the structural-phase state of éK-181 ferritic-martensitic low-activate steel after thermal treatment including quenching, intermediate tempering, and subsequent long tempering under loading at temperatures of 923 and 973 K are presented. The influence of the defect substructure of the ferrite matrix, phase composition, and character of the secondary dispersed phase distribution in the volume of the material on the heat-resistant steel properties is examined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 36–42, November, 2007.     

Change in elemental composition and structural-phase transformations in molybdenum with the high-dose implantation of metal ions

A study is made of features of structural-phase transformations that occur in molybdenum during the high-dose implantation of metal ions in a vacuum ∼2·10⁻⁴ torr. It is established that ion-stimulated interaction of the surface of the target with elements in the residual gases plays an important role in the modification of the microstructure of the ion-alloyed layer under these conditions. It is shown that such interaction leads to the formation of thin continuous layers of a carbide phase in the surface layer. The continuous layers are in highly nonequilibrium structural-phase states. Experimental data is used as a basis for discussion of the mechanism of this interaction as a function of implantation conditions. V. D. Kuznetsov Siberian Physico-Technical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 65–74, September, 1996.     

Optical properties of GaAs films deposited via pulsed ion ablation

Optical reflectance and absorbance of gallium arsenide films formed on polycrystalline corundum, quartz glass, and copper foil are investigated in the energy interval of 1.1–6.2 eV. The films have been deposited from ablation plasma induced by a high-power ion beam. The exponential and interband absorbance spectra of the material of films are determined by defects in the GaAs crystalline lattice and the intricate composition of the material with predominance of nanocrystalline inclusions in the amorphous phase. Films deposited on polycor at the plasma flame center with the use of a low-resistance target have optimal properties for application in devices of optoelectronics and solar power engineering. Thermal vacuum treatment at 300–850 K modifies the optical properties of films owing to annealing of defects and changing of the structural-phase composition of a material.     

Relationship between the electronic properties of the interface and the interphase interactions in NbN-GaAs heterostructures

Peculiarities of contact formation in the system NbN-GaAs upon a change in the structural-phase state of the deposited metal are investigated. It is shown that the role of the chemical factor in the processes of contact formation decreases as the degree of structural perfection of the NbN alloy increases. The causes of the corresponding changes in the electronic structure of the interface as a result of the phase transition NbN-Nb₄N₃ are discussed. The Auger spectrum and current-voltage and capacitance-voltage characteristics of NbN-GaAs surface-barrier structures are measured before and after annealing in vacuum at T=850 °C for 10 s. Zh. Tekh. Fiz. 68, 63–66 (January 1998)     

Study of metal-supported carbon matrix as a high-capacity anode for Li-ion battery

Tin–graphite composite with 20 wt. % metal content as well as its structural and electrochemical characteristics are presented. Synthetic graphite—super flake type—was used as object for the modification experiment. Chemical reduction was applied for the loading process, which was carried out under inert argon atmosphere. Composite with specific morphology and improved electrochemical behavior was prepared. The obtained material shows higher discharge capacity as well as increased initial charge–discharge coulomb efficiency, compared with the unmodified one. The supporting metal morphology, the type of graphite, and the preparation process taken together generally affect the improvement of the electrochemical performance. This work was presented at the 11th Euro Conference on Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007.     

Interaction of lithium-titanium ceramics with air during sintering

Interaction of lithium-titanium polycrystalline ferrites with ambient air during their sintering is investigated using the methods of electroconductivity and thermal gravimetry within the temperature interval T = 600–1300 K. It is found out that the temperatures exceeding T = 1100 K correspond to effective course of reducing reactions in this material, which results in the formation of an oxygen-deficient ceramic structure in the stage of isothermal tempering (T = 1280 K). It is shown that in the final cooling stage the process of exchange of the ferrite ceramics with the ambient atmosphere exhibits a pronounced oxidative character. The role of these redox processes in the formation of the oxygen non-stoichiometry of the sintered specimen and the depth of its distribution are analyzed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 35–40, February, 2007.     

The influence of gamma irradiation on structural-phase transformations in hardened structural steel

Based on structure investigations, a comprehensive effect of irradiation by gamma quanta on the structural steel hardened to martensitic steel (multi-component alloy in a highly non-equilibrium structural-phase state due to martensitic transformations occurring in it during hardening) is reported. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 74–83, April, 2008.     

Synthesis,structure stability and magnetic properties of nanocrystalline Ag–Ni alloy

Silver–nickel alloy nanoparticles with an average size of 30–40 nm were synthesized by chemically reducing the mixture of silver and nickel salts using sodium borohydride. The structure and the magnetic properties of the alloy samples with different compositions were investigated. The phase stability of the material was analysed after annealing the sample in vacuum at various temperatures. The material exhibits single fcc phase which is stable up to 400 °C and Ni precipitation sets in when the sample is annealed to 500 °C. The thermal analysis using DSC was carried out to confirm the same. The alloy compositions are found to be in close correlation with the metal salt ratios in the precursors. The synthesized samples exhibit weak paramagnetic to ferromagnetic behaviour. The magnetic measurements reveal that by adjusting the precursor ratio, the Ni content in the material can be altered and hence its magnetic properties tailored to suit specific requirements. The formation of Ag–Ni alloy is confirmed by the observed Curie temperature from the magneto thermogram. Annealing the sample helps to produce significant enhancement in the magnetization of the material.     

Nature of the structural degradation of rail surfaces during operation

Patterns in the transformation of the structural and phase states and the defect substructure of rail surface layers up to 10 mm thick during long-term operation (gross transit tonnages of 500 and 1000 mln t) are found via optical, scanning, and transmission electron microscopy. According to the nature of the fracture and the degree of defectiveness, three layers can be distinguished: a surface layer, a transition layer, and the base metal. It is shown that the operation of steel rails is accompanied by full fractures in surface layers up to 15 μm thick with lamellar pearlite grains and the formation of ferrite–carbide mixtures with nanosized particles. The deformation of steel increases the densities of scalar and excess dislocations, the curvature–torsion values of the crystal lattice, and the amplitudes of internal stress fields. Structural elements that can act as stress concentrators are identified.     

The effect of electron irradiation on the optical properties of the natural armenian zeolite-clinoptilolite

Infrared (IR) absorption and luminescence in chemically and radiation-modified natural Armenian Zeolite (clinoptilolite) samples have been studied. The luminescence was studied in 390–450 nm and 620–710 nm wavelength bands, and the IR measurements were carried out in the 400–5400 cm⁻¹ range. It is shown that the luminescence intensity depends on the content of pure clinoptilolite in the samples and, probably on the distribution of “passive” luminescence centers over Si and Al sites that became “active” under radiation or chemical treatment. The samples of electron irradiated clinoptilolite have higher luminescence intensity than the chemically and thermally treated ones. A decrease in the intensity of IR absorption bands at 3550 cm⁻¹ and 3650 cm⁻¹ was found after irradiation.     

Features of the plastic deformation of steels with lamellar perlite structure

The evolution of the perlite structure in the course of plastic deformation of U8 and St70 steels has been studied. With increasing degree of cold working, the dislocation density increases near the interphase boundary in the ferrite interstices of perlite, which forms a dislocational “fringe”, which in turn forms a pseudocellular structure. Under thermal deformation conditions, a subgrain structure arises in the ferrite interstices of lamellar perlite. The most dangerous localized flow channels in which plasticity is exhausted for the first time and cracks appear, are the deformation bands. The narrower the deformation bands and the larger the value of the relative displacement of the subcolumn blocks adjacent to them, the more dangerous they are with regard to failure. The features revealed in the development of deformation and failure provides a basis for controlling steel treatment regimes in order to produce perlite with the optimum structural parameters. Novosibirsk State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–10, July, 1996.     

Structural-phase transformations in low-stability condensed state systems

The conditions of formation of low-stability condensed state systems, their behavior and structure are investigated. The objects under study are alloys and compounds undergoing structural-phase transitions of the second type or close to it. The low-stability (pre-transitional) state is treated here as the state of a system near its structural-phase transformations, in which its structure and properties exhibit anomalies. An attempt is made to interpret the system from the physical standpoint relying on a new insight into its state, in which the traditionally accepted phase-transition point is represented by a range of values of the parameter controlling the transition. The material state within this range of values is structurally weakly stable in terms of slight variations in the controlling parameter. It is shown that the thermodynamics of structural-phase transformations of the material in this transient state is significantly affected by the interaction of structure defects.     

Influence of a forming process and electric fields on the insulator-conductor transition in thin films of polyheteroarylenes

The results of experiments on initiation of the high-conductivity state of a metal/polymer/metal system by varying the boundary conditions with allowance for the possible influence of diffusion of the electrode material into the polymer film are presented. It is established that forming does not occur in poly(phthalidylidenebiphenylylene) and that the transition to the high-conductivity state can occur without an external source of electric voltage. Zh. Tekh. Fiz. 69, 85–87 (March 1999)     

Scientific basis for cold brittleness of structural BCC steels and their structural degradation at below zero temperatures

The paper considers the physics of cold brittleness of structural bcc steels and methods of reducing the ductile-brittle fracture temperature. A complex study was performed to examine the degradation of structural phase state of pipe steel 09Mn2Si from the main gas pipeline of Yakutia after long-term (over 3 0 years) operation. Important regularities of degradation of pearlite colonies with carbide precipitation on ferrite grain boundaries were revealed. This phenomenon is associated with brittle fracture of gas pipelines. It is shown that the low-temperature kinetic processes in main pipelines which define the degradation of their structure and properties are related to interstitial athermal structural states in the zones of local crystal structure curvature. This is a fundamentally new, as yet unknown, mechanism. Pipe steels in warm rolling acquire a longitudinal textured band structure with alternating bands of initial ferrite grains and bands of fine grains with carbide precipitates formed during lamellar pearlite degradation. This type of structure allows for a shift of ductile-brittle transition temperature down to -80°C and ductility δ = 22% at this temperature. The production of high-curvature vortex structure in pipe steel surface layers results in a 3.5-fold increase in their service life.     

Effect of a magnetic field on the electroluminescence intensity of single-crystal ZnS

After exposure of single-crystal ZnS with microscopic twinning to magnetic fields of 1–10 T, the integral electroluminescence brightness is found to increase by several times. It is proposed that the magnetic field facilitates relaxation of a metastable state of the structural defects. Fiz. Tverd. Tela (St. Petersburg) 41, 1944–1947 (November 1999)     

Transition of expanded liquid iron to the nonmetallic state under supercritical pressure

A transition of expanded liquid iron to the nonmetallic state under high pressures (30–100 kbar) at high temperatures (of about 1 eV) is discovered. The result is obtained by direct measurement of the dependence of resistivity on the specific internal energy and volume. Measurements are taken in the specific volume range from the melting curve to values six times higher than the normal specific volume V ₀ in the solid state. It is shown that iron remains in the metallic state up to a relative volume of V/V ₀ = 3–4, at which the resistivity attains a value of about 3–4 μΩ m and becomes almost independent of temperature, while the conduction electron mean free path decreases to the atomic spacing. For V/V ₀ = 4–5, a transition to the nonmetallic state takes place, for which the temperature coefficient of resistance becomes negative and its absolute value becomes much higher than in the metallic state.     

First principles study of <Emphasis Type="Italic">p</Emphasis>-type doping in SiC nanowires: role of quantum effect

Using first principles density functional theory calculations, we investigated the X and X–N–X (X = Al and Ga) doped 3C–SiC nanowires grown along the [111] crystal direction with diameter of 1.00 and 1.33 nm. We found that the ionization energy of acceptor state is much larger in nanowires than that in the bulk SiC as a result of quantum confinement effect. Simulation results show that the reduced dimensionality in p-type SiC nanowires strongly reduces the capability of the materials to generate free carriers. It is also found that X–N–X (X = Al and Ga) complexes are energetically favored to form in the materials and have lower ionization energy than single doping. It is confirm that codoping is more suitable method for achieving low-resistivity semiconductors either in nano materials or bulk material.     

Investigation into the special features of the dielectric and polarization properties of lithiumtitanium ferrite ceramics

Loop-shaped dependences of the electric polarization on the electric field strength (the dielectric hysteresis) are registered for the first time for polycrystalline Li–Ti ferrite. Temperature evolution of the hysteresis loop parameters is investigated for ferrite samples. The results obtained can be interpreted from the viewpoint of the Maxwell–Wagner relaxation polarization or induced ferroelectric-like state in the electric ferrite subsystem.     

The influence of the initial structural state of armco iron on the ultrasonic treatment effect

Methods of diffraction electron microscopy have been used to examine the types of dislocation substructures formed in the surface layer of armco-iron specimens subjected to ultrasonic treatment. It is shown that banded or equiaxed ultrafine-grained structure can be generated in the material depending on its initial structural state. The special features of the plastic deformation and fracture of the ultrafine-grained surface layers of the specimens under uniaxial tension are described. The extent to which the mechanical properties of the examined material are improved by ultrasonic treatment has been found to depend on its initial state. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 74–82, January, 2009.     

Effect of the electric field on “incommensurate-commensurate” magnetic phase transitions in BiFeO3-type multiferroics

The specific features of the “incommensurate-commensurate” phase transitions induced by a magnetic field in multiferroics (materials with coexisting magnetic and electric ordering) are considered. These materials are ferroelectromagnets, for example, bismuth ferrite BiFeO₃ and BiFeO₃-based compounds, which have spatially modulated spin structures. It is shown that the interaction between the electric and magnetic subsystems of the multiferroic material can lead to an electric-field-induced shift of the critical magnetic field corresponding to the transition from a spatially modulated state to a homogeneous antiferromagnetic state. According to the theoretical estimates obtained for material parameters characteristic of the bismuth ferrite, this shift is of the order of 0.5 T in an electric field of 50 kV/cm. The phase diagrams are constructed in the “electric field-magnetic field” coordinates. The results of calculations performed in the harmonic incommensurate structure approximation are compared with the exact soliton solution.