We examine the dynamics of a binary mixture in a cubic cell subjected to a temperature differential and oscillatory forcing. The Soret effect, which is negative in the present study, provides a ...coupling mechanism by which a temperature gradient establishes a concentration gradient in a mixture. We present the results of experiments that were performed on the International Space Station (ISS) and compare the observations with the results of direct numerical simulations. The evolution of temperature and concentration fields is investigated by optical digital interferometry. One advantage of the experimental technique is the observation of the fields along two perpendicular directions of the cell, allowing us to restore the three-dimensional field. Experimental evidence disproves speculations that the ISS microgravity environment always affects diffusion-controlled processes. Furthermore, we demonstrate that imposed vibrations with constant frequency and amplitude create slow mean flows and that they do influence the diffusion kinetics. The perturbation of the diffusive fields scales as the square of the vibrational velocity. In addition to calculations of the full three-dimensional Navier–Stokes equations, a two-time-scale computational methodology is used for situations in which the forcing period is very small compared to the natural time scales of the problem. The simulations show excellent agreement with experimental observations.
In the present study, the effect of nitrogen alloying on hydrogen embrittlement in FeMnNiCoCr high-entropy alloys was investigated. In tension, hydrogen-free nitrogen-alloyed FeMnNiCoCrN alloy (0.37 ...wt.% N) demonstrated higher strength, strain hardening, and elongation-to-failure than the interstitial-free FeMnNiCoCr Cantor alloy. Despite the different tensile properties, both alloys fractured via a ductile dimple micromechanism. After hydrogen charging, the nitrogen-alloyed material demonstrated lower strain hardening and higher sensitivity to hydrogen-assisted embrittlement than the interstitial-free alloy. Both alloys featured a stable austenitic structure and similar grain size, yet, the nitrogen-alloyed FeMnNiCoCr alloy was more susceptible to hydrogen embrittlement. Although, the overall degradation effects appear similar, there are pronounced differences in mechanical behavior and hydrogen transport upon hydrogen charging when the high-entropy alloys are compared to conventional austenitic stainless steels, and the experiments reveales that nitrogen alloying enhances hydrogen diffusivity in the Cantor alloy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Stainless steel/NiCr joint was produced by electron beam additive manufacturing.•NiCr-alloy addition stabilizes austenitic structure in EBAM-produced CrNi steel.•Stainless steel/NiCr ...double-wire EBAM allows to produce stable austenitic structure.
The gradient material “stainless steel/NiCr alloy” has been designed using the additive manufacturing method – double wire-feed electron-beam melting. The effect of gradual addition of Ni-based alloy on phase transformation and microstructure in additively-fabricated “stainless steel/NiCr alloy” joint has been revealed. Despite the abrupt change in wire composition during the fabrication of the joint, the wide transition zone is formed between two parts of the additively-manufactured billet: γ-austenitic matrix and dendritic δ-ferrite in steel part gradually passing into Fe-based austenite, then into Ni-based austenite, and, finally, into γ-(Ni,Cr) austenite with cellular-shape dendrites in NiCr part. The steel-based transition zone of the as-built joint possesses pure austenitic structure stabilized by nickel in comparison with two-phase dendritic microstructure typical for additively-manufactured CrNi stainless steel. The increased microhardness (2.3–2.4 GPa) corresponds to stable austenitic steel structure of the joint.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We study the influence of different grain size (density of grain boundaries) on the way of phase transformations in the surface layers of 316 L-type austenitic stainless steel under ion-plasma ...treatment. Using thermomechanical treatments, we fabricated a series of specimens possessing a single-phase austenitic structure, close density of the defects of the crystal lattice and different grain sizes (fine-grained with d ≈ 3–6 μm and coarse-grained with d ≈ 55 μm). These specimens were subjected to ion-plasma surface treatment at 550 ± 10 °C in N2+C2H2+Ar gases mixture to provoke a precipitation hardening. Although fine-grained and coarse-grained specimens possess similar penetration depth of interstitial atoms (N, C) under ion-plasma treatment (≈40–48 μm), the distribution of interstitials and phase composition are different in them. After ion-plasma treatment, specimens with low density of grain boundaries (coarse-grained structure) maintain a high level of N, C atoms in the solid solution of austenite (a = 0.3653–0.3674 nm) with a strip-like arrangement of Fe4(N,C) particles within grains, while precipitation of Cr(N,C) phase is suppressed. For these specimens, tensile diagrams have the extended linear stages typical of nitrogen-bearing austenitic steels, and the loss of ductility assisted with ion-plasma treatment is the smallest among studied specimens. Ion-plasma treated specimens with high density of grain boundaries (fine-grained structure) are prone to a decomposition of Fe-γN,C phase with the formation of grain-boundary and intragranular Cr(N,C) and Fe-α phases and partial preservation of a solid-solution strengthening of austenite (a = 0.3597–0.3622 nm). Precipitation hardening is more characteristic of these specimens and their flow curves are parabolic. The complex fracture mode of the specimens subjected to ion-plasma treatment is caused by the surface solid-solution strengthening and precipitation hardening. In the surface-hardened region (where the concentrations of N, C atoms are the highest), brittle quasi-cleavage fracture occurs due to the presence of Fe-based and Cr-based precipitates and austenite oversaturated with interstitials.
•316 L steel with different grain size was modified with ion plasma treatment (IPT).•Phase composition of IPT-processed steel is grain size-dependent characteristic.•IPT-assisted Fe-γN,C and intragranular Fe4(N,C) prevail in coarse-grained specimens.•Fe-γN,C + Cr(N,C)+Fe-α microstructure is peculiar for fine-grained steel after IPT.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Coenzyme Q10 is a key component of the mitochondrial respiratory chain and a fat-soluble endogenous antioxidant performing many vital functions in the human body. Many researchers studied the plasma ...concentrations of ubiquinol, ubiquinone, total CoQ10 and the redox state (ubiquinol/ubiquinone ratio) of CoQ10 in healthy volunteers. However, these parameters in the plasma of patients with chronic heart failure (CHF) remain almost uninvestigated.
The aim of this case-control study was to investigate the effect of atorvastatin, amlodipine and ethoxidol on endogenous plasma concentrations of ubiquinol, ubiquinone, total CoQ10 and its redox state in patients with CHF.
The study included 62 patients with CHF divided into four groups depending on the prescribed therapy. For the quantitative determination of ubiquinol, ubiquinone, and total CoQ10 in the plasma of patients, HPLCMS/ MS was used.
It was established that the endogenous plasma concentration of total CoQ10 in patients with CHF is significantly lower than in healthy volunteers, and the ratio of reduced and oxidized forms of CoQ10 is shifted towards ubiquinone. It was a statistically significant effect of drugs with different physicochemical structures and pharmacological action on the plasma concentrations of ubiquinol, ubiquinone and total CoQ10: atorvastatin administration led to a decrease in the concentration of ubiquinol (-33.3Δ%), and total CoQ10 (-15Δ%), administration of amlodipine contributed to an increase in the levels of ubiquinol (+27.7Δ%) and total CoQ10 (+18.2Δ%), and the administration of ethoxidol caused an increase in the concentration of ubiquinol (+25Δ%), ubiquinone (+17.7Δ%) and total CoQ10 (+20.2Δ%).
Amlodipine is able to neutralize the negative effect of atorvastin on the redox balance of CoQ10 in patients with CHF. An additional prescription of the antioxidant ethoxidol to standard therapy for patients with CHF was substantiated. Determination of the redox state of CoQ10 in plasma can be used to diagnose and assess the degree of oxidative stress in patients with cardiovascular diseases, as well as to assess the efficacy and safety of ongoing pharmacotherapy.
Small particles transported by a fluid medium do not necessarily have to follow the flow. We show that for a wide class of time-periodic incompressible flows inertial particles have a tendency to ...spontaneously align in one-dimensional dynamic coherent structures. This effect may take place for particles so small that often they would be expected to behave as passive tracers and be used in PIV measurement technique. We link the particle tendency to form one-dimensional structures to the nonlinear phenomenon of phase locking. We propose that this general mechanism is, in particular, responsible for the enigmatic formation of the "particle accumulation structures" discovered experimentally in thermocapillary flows more than a decade ago and unexplained until now.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A straightforward approach for the construction of the new class of conjugated pyrans based on enamination of 2-methyl-4-pyrones with DMF-DMA was developed. 2-(2-(Dimethylamino)vinyl)-4-pyrones are ...highly reactive substrates that undergo 1,6-conjugate addition/elimination or 1,3-dipolar cycloaddition/elimination followed by substitution of the dimethylamino group without ring opening. This strategy includes selective transformations leading to conjugated and isoxazolyl-substituted 4-pyrone structures. The photophysical properties of the prepared 4-pyrones were determined in view of further design of novel merocyanine fluorophores. A solvatochromism was found for enamino-substituted 4-pyrones accompanied by a strong increase in fluorescence intensity in alcohols. The prepared conjugated structures demonstrated valuable photophysical properties, such as a large Stokes shift (up to 204 nm) and a good quantum yield (up to 28%).
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•Low-temperature deformation-induced γ-α’ transformation was studied in 316L steel.•A 4-μm surface layer of nitrogen-expanded austenite was produced on 1.5 mm-thick specimens.•Thin surface layer of ...nitrogen-expanded austenite affects bulk phase transformation.•Surface nitriding suppresses inhomogeneity in deformation-induced γ-α’ transformation.
Deformation-induced γ-α’ phase transformation was studied in austenitic stainless 316L steel in low-temperature deformation regime (tension at 77 K). Before deformation, the surface of the steel specimens was saturated with nitrogen by ion-plasma nitriding at 673 K for 12 h. Thin 4-μm surface layer of nitrogen-expanded austenite (S-phase) does not influence mechanical properties but affects phase transformation in the bulk 1.5 mm-thick specimens. Surface nitriding effectively suppresses the inhomogeneity in deformation-induced martensite nucleation and formation of the α’-phase prior the macroscopic neck formation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In the present paper, the method of electron-beam additive manufacturing is used to produce specimens of vanadium-alloyed chromium-manganese steel with a high concentration of interstitial atoms (C + ...N = 1.9 wt %). Microstructure and mechanical properties of the specimens are analyzed against the specimens obtained by conventional metallurgy and thermal-mechanical treatments. It is experimentally shown that additive manufacturing and subsequent heat treatment do not affect the concentration of interstitial atoms in the steel specimens, do not change the mechanism of steel crystallization, and do not provide high-temperature ferrite formation. Regardless of the production method, specimens of vanadium-alloyed chromium-manganese steel with a high concentration of interstitial atoms have a heterophase structure composed of austenite and dispersed phases. In addition to vanadium and chromium carbonitrides, which are characteristic of the conventionally fabricated steel and do not dissolve during thermal-mechanical treatment, repeated heating and cooling during additive manufacturing cause the formation of plates of chromium and manganese carbonitrides within austenitic grains and globular intermetallides (Fe, Cr, Mn, and V) along grain boundaries. The high concentration of interstitial atoms promotes high solid-solution and precipitation hardening of additively manufactured specimens, resulting in a higher yield stress (σ
0.2
= 880 MPa) as compared to conventionally fabricated specimens (σ
0.2
= 840 MPa). At the same time, the presence of dispersed phases leads to premature fracture of the specimens, so that the additively manufactured steel, even after heat treatment, has low plasticity.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The paper presents the experimental data on the temperature dependence of mechanical properties and plastic flow behavior of cast alloys Fe
20
Cr
20
Mn
20
Ni
20
Co
20-
x
C
x
(
x
= 0, 1, 3, 5) in the ...temperature range from 77 to 297 K. In the as-cast state, high-entropy Cantor alloy Fe
20
Cr
20
Mn
20
Ni
20
Co
20
and multicomponent alloy Fe
20
Cr
20
Mn
20
Ni
20
Co
19
C
1
have an austenitic structure, while carbon doping results in solid solution strengthening of austenitic grains and carbide precipitation at the grain boundaries. The temperature dependence of the yield stress for the Fe
20
Cr
20
Mn
20
Ni
20
Co
19
C
1
alloy significantly exceeds the σ
0.2
(
T
) dependence for the Fe
20
Cr
20
Mn
20
Ni
20
Co
20
alloy. Carbon-assisted solid solution strengthening is accompanied by an increase in flow stress and strain hardening as well as by a decrease in low-temperature plasticity in the Fe
20
Cr
20
Mn
20
Ni
20
Co
19
C
1
specimens. Alloys Fe
20
Cr
20
Mn
20
Ni
20
Co
17
C
3
and Fe
20
Cr
20
Mn
20
Ni
20
Co
15
C
5
have a predominantly austenitic structure with coarse incoherent carbides. The heterophase Fe
20
Cr
20
Mn
20
Ni
20
Co
15
C
5
alloy is characterized by a decrease in yield stress σ
0.2
and its weaker dependence on the temperature as compared to single-phase alloys with lower solid solution strengthening. In addition, the stage of microplasticity is pronounced in stress-strain curves in the low-temperature deformation regime. Transmission and scanning electron microscopy of the Fe
20
Cr
20
Mn
20
Ni
20
Co
15
C
5
alloy reveals dislocation slip at this stage of deformation in austenitic regions between carbides. It is shown that the precipitation of coarse incoherent carbides in the austenitic matrix promotes macroscopically and microscopically inhomogeneous plastic flow of the heterophase 3 and 5 at % carbon alloys. Mechanical behavior of such heterophase multicomponent materials is caused by different elastic moduli of carbon austenite and carbides as well as by their different temperature dependences.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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