Features of high-speed sintering of WC–Co nanopowders with various contents of excess carbon (colloidal graphite) were studied. Powders were obtained in a process that included plasma-chemical and ...low-temperature syntheses and a chemical-metallurgical method of applying ultrathin cobalt layers by precipitation from a solution of salts. Powder materials were consolidated by high-speed spark plasma sintering. It was found that an increase in the concentration of free carbon (colloidal graphite) has the greatest effect on the shrinkage and the sintering rate at the stage of intense shrinkage of WC–Co nanopowders. It was revealed that the process of nanopowder compaction at the intense shrinkage stage is determined by the intensity of the plastic flow and the intensity of diffusion along the boundaries of cobalt grains. It was shown that the mechanism of plastic deformation of the cobalt-based γ phase corresponds to the Coble diffusion creep. It was found that an increase in carbon content lowers the activation energy at the stage of intense shrinkage and does not significantly affect the activation energy at stage III of sintering, where the shrinkage intensity is observed to decrease. It was shown that a decrease in the sintering activation energy is due to a decrease in the tungsten concentration in the γ phase.
The strength and the plasticity properties of sheet high-strength austenitic–martensitic VNS9-Sh TRIP steel (23Kh15N5AM3-Sh) are studied as functions of the tempering temperature in the range ...125–600°C. A nonmonotonic decease in the strength and the plasticity properties of the steel has been detected when the tempering temperature increases, and they increase in the range 300–450°C. The influence of aging processes, the precipitation of carbide, and the phase transformations in tempering on the mechanical properties of austenitic–martensitic corrosion-resistant steel is discussed.
The mechanism of high-temperature creep deformation during compression tests of ceramic tungsten carbide samples with different particle size has been studied. Tungsten carbide samples with high ...relative density (96.1–99.2%) were fabricated by the method of high-speed spark plasma sintering (SPS) from nano-, submicron, and micron powders of α-WC. Creep tests were carried out in two modes: isothermal holding at different temperatures (1300–1375°C) at a specified compression, which enabled one to evaluate the creep activation energy, and tests by the method of “compression jumps” at a temperature of 1325°C, which enabled one to estimate the value of the coefficient
n
in the equation of power creep. It was shown that the creep activation energy in ultrafine-grained (UFG) tungsten carbide with a grain size of ~0.15 μm sintered from plasma chemical nanopowders was ~31
kT
m
. This value was 1.5–2 times higher that the creep activation energy in fine-grained tungsten carbide samples produced by the SPS method from submicron (~0.8 μm) and micron (~3 μm) industrial powders. It was determined that the value of the coefficient
n
varied from 2.4 to 3.1, which corresponds to the case of the movement of lattice dislocations in the field of uniformly spaced point obstacles. It was assumed that one of the reasons for the increase of the creep activation energy during testing of UFG tungsten carbide samples was the increased volume fraction of particles of lower carbide W
2
C formed during high-speed sintering of plasma chemical nanopowders α-WC with an increased concentration of adsorbed oxygen.
The properties of austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) sheet TRIP steel during static and cyclic loading are studied. The specific features of the mechanical behavior of the steel during ...static tension that are related to shearing, twinning, and martensite formation processes are detected. The static stress–strain curve of the steel has a developed microyield stage, a long yield plateau, and a serrated stage of strain hardening (Portevin–Le Chatelier effect). The shear mechanisms at the initial stages of cyclic deformation and fatigue crack propagation mechanisms are investigated.
The magnetic state of Y^sub 1 - x^Tb^sub x^Mn^sub 6^Sn^sub 6^ (with x <= 0.25) alloy is studied at different temperatures and magnetic fields by neutron diffraction. The alloy with x ^sub c^ = 0.22 ...exhibits an incommensurate-to-commensurate structure phase transition. The transition is accompanied by a decrease in the unit-cell volume. The weak dependence of the intensity of satellites on the x concentration and the monotonic displacement of their angular positions with increasing x allow us to conclude that the antiferromagnet arrow right ferrimagnet transition occurs through the uniform magnetic state. The incommensurate phase in YMn^sub 6^Sn^sub 6^ exhibits four satellites, which are observed in the low-angle range of X-ray diffraction pattern and demonstrate different behavior with changing temperature. At 293 K, the antiferromagnet arrow right ferromagnet transition in the Y^sub 1 -x^Tb^sub x^Mn^sub 6^Sn^sub 6^ compound can be induced by applied magnetic field, in particular, the field mu^sub 0^ H = 0.3 T induces the transition in Tb^sub 0.15^Y^sub 0.85^Mn^sub 6^Sn^sub 6^.PUBLICATION ABSTRACT
The magnetic state of Y.sub.1 - xTb.sub.xMn.sub.6Sn.sub.6 (with x ≤ 0.25) alloy is studied at different temperatures and magnetic fields by neutron diffraction. The alloy with x.sub.c = 0.22 exhibits ...an incommensurate-to-commensurate structure phase transition. The transition is accompanied by a decrease in the unit- cell volume. The weak dependence of the intensity of satellites on the x concentration and the monotonic displacement of their angular positions with increasing x allow us to conclude that the antiferromagnet → ferrimagnet transition occurs through the uniform magnetic state. The incommensurate phase in YMn.sub.6Sn.sub.6 exhibits four satellites, which are observed in the low-angle range of X-ray diffraction pattern and demonstrate different behavior with changing temperature. At 293 K, the antiferromagnet → ferromagnet transition in the Y.sub.1 - xTb.sub.xMn.sub.6Sn.sub.6 compound can be induced by applied magnetic field, in particular, the field μ.sub.0H = 0.3 T induces the transition in Tb.sub.0.15Y.sub.0.85Mn.sub.6Sn.sub.6. Keywords: magnetic phase transitions, neutron diffraction, intermetallic compounds DOI: 10.1134/S0031918X13070028
An improved method for calculating the minimum permissible electron beam welding (EBW) speed with continuous penetration is described. Calculations are carried out to construct nomograms for ...determining the welding speed in relation to the thickness of the welded joint and the width of the vapour-gas channel for 40Kh13 steel, 5V titanium alloy and D16 aluminium alloy. To confirm the efficiency of the proposed method, the results of experiments with EBW with continuous penetration at different welding speeds are presented.
Research on the use of high-magnesia fluxes in (160–400)-t oxygen converters reveals the influence of the smelting parameters, the composition of the metal and the slag, and the working temperature ...on the assimilation of MgO from the flux. Slag formation and the removal of sulfur and phosphorus are considered, as well as the influence of magnesia slags on lining wear in the converter.
A new class of slag-forming materials has been developed: magnesia fluxes with up to 90% MgO. Their mineralogical composition and physicomechanical properties are investigated. The solution of fluxes ...in synthetic and converter slag melts is studied as a function of their structural properties and chemical composition. A production technology for such fluxes has been developed and introduced.
Purpose:
to evaluate the diagnostic significance of magnetic resonance imaging in the differential diagnosis of ischemic heart damage and non-coronary myocardial diseases.
Materials and methods:
a ...retrospective analysis of medical documentation of 60 patients of cardiac departments of the Rostov Regional Clinical Hospital was conducted. Held a comparative analysis of the informativeness of the application of instrumental researchmethods (ECG, echocardiography, coronary angiography with leftventriculography and magnetic resonance imaging of the heart) among the patients with myocardial damage of different origins.
Results:
in patients with IHD, postinfarction cardiosclerosis, in most cases, the results of instrumental studies were diagnosed as having a diagnostic relationship. Conducted MRI of the heart was of decisive importance in the evaluation of the state of the myocardium after systemic thrombolysis or questionable ECG and EchoCG data and was also significant in the differential diagnosis of acute coronary syndrome and focal myocarditis. The results of MRI played an important role in determining the etiology of myocardial hypertrophy, in particular hypertrophic cardiomyopathy, and also helped in the case of differential diagnosis in the syndrome of cardiomegaly.
С
onclusions:
shown a high diagnostic value of magnetic resonance imaging with the use of contrast agents in the differential diagnosis of ischemic and noncoronary myocardial diseases.
PDF