High-entropy Layer Research Articles

On the Response of Massive Main Sequence Stars to Mass Accretion and Outflow at High Rates

Abstract With a one-dimensional stellar evolution model, we find that massive main sequence stars can accrete mass at very high mass accretion rates without expanding much if they lose a significant fraction of this mass from their outer layers simultaneously with mass accretion. We assume the accretion process is via an accretion disk that launches powerful jets from its inner zones. These jets remove the outer high-entropy layers of the mass-accreting star. This process operates in a negative feedback cycle, as the jets remove more envelope mass when the star expands. With the one-dimensional model, we mimic the mass removal by jets by alternating mass addition and mass removal phases. For the simulated models of 30M ⊙ and 60M ⊙, the star does not expand much if we remove more than about half of the added mass in not-too-short episodes. This holds even if we deposit the energy the jets do not carry into the envelope. As the star does not expand much, its gravitational potential well stays deep, and the jets are energetic. These results are relevant to bright transient events of binary systems powered by accretion and the launching of jets, e.g., intermediate luminosity optical transients, including some luminous red novae, the grazing envelope evolution, and the 1837–1856 Great Eruption of Eta Carinae.

Hollow-structured and nano-flower shaped high entropy layer double hydroxide for superiority specific capacitance and rate capability of supercapacitor

High entropy hydroxide as electrode materials has been widely studied in the field of supercapacitors, but due to the limited active site and poor conductivity, it usually shows poor specific capacity and magnification performance, which seriously limit its development in the field of supercapacitors. In this work, a hollow-structured and nano-flower shaped high entropy layer double hydroxide was synthesized by the double template method combined with nano-etching to achieve superiority specific capacitance and rate capability of supercapacitor. The experimental and theoretical results indicate that the specific capacitance of this novel electrode material is as high as 1820.1 F·g−1. In particular, after the current density was increased by 40 times, the specific capacitance can reach 1140.2 F·g−1, and its electrochemical performance is higher than most of high entropy electrode materials reported so far. More importantly, the S-HE-LDH//AC HSC was constructed with the material as the electrode. It has an energy density of 74.2 Wh·kg−1 at 475 W·kg−1 power density. After 5000 cycles, the specific capacitance of the HSC device can still maintain 90.8 % of its initial value. These results indicate that the electrochemical properties of LDHs can be effectively improved by the combination of microstructure adjustment and electronic structure optimization.

A high-entropy cathode for sodium-ion batteries: Cu/Zn-doping O3-Type Ni/Fe/Mn layer oxides

The O3 layered oxides have been extensively investigated as cathode materials for sodium-ion batteries due to their remarkable theoretical capacity. However, the large radius of Na+ lead to complex phase transitions and tortuous diffusion channels during extraction/insertion, which ultimately restricts the Na+ diffusion kinetics and cyclic stability. In this study, we report a Zn and Cu co-doping strategy to the high entropy layer oxide Na [Ni0·2Fe0·2Mn0·4Cu0·15Zn0.05]O2 (HEO-CuZn) using the sol-gel method to prepare the oxides. Here, Zn is used to stabilize the structure of layer between the transition metal and O atoms, which slows down the adverse phase transition. In the fabricated sample, the element Cu provides additional capacity and inhibits excessive oxidation. The prepared HEO-CuZn used as cathode for Na+ ion battery exhibits better electrochemical performance, delivering a high specific capacity of 148 mA h g−1, and 84 % capacity retention after 100 cycles, which is attributed to the expanded Na+ transfer channels, reduced activation energy and interface side reactions, thus enhancing the Na+ diffusion kinetics. Meanwhile, the high entropy strategy stabilizes the overall structure by reducing the John-Teller distortion and suppressing the Na+/vacancy order, and effectively avoids adverse phase transitions such as O′3 and P′3. This study provides a new insight for the advance of the next generation high specific energy sodium-ion battery.

The propagation behavior of reaction wave for Ni/Al clad particle composites under shock loading.

Prior studies indicate that the reaction wave can propagate from the impact surface, but the possibility and the influencing factors of the reaction wave formation are still unclear. This work investigates the propagation behavior of the shock-induced reaction wave for Ni/Al clad particle composites with varying stoichiometry (from 0.5 to 0.75 of the Ni mole fraction) through molecular dynamics simulations. It is found that the solid-state reaction processes with or without wave propagation strongly depend on the conjunction of stoichiometry and shock intensity. Within the cases of wave propagation, the calculated propagation velocity (in the range of 135-170m/s) increases linearly or exponentially with the Ni mole fraction. Furthermore, the thermodynamic criteria for the reaction wave formation, including Al melting at the collision surface and higher temperature gradient, are established by analysis of the shock-induced high-entropy layer. In addition, microstructural characterization reveals the intrinsic mechanisms of the propagation of the reaction wave and the formation of additional reaction wave, namely, the dissolution of Ni into Al and the coalescence of reaction zones. Apart from the propagation behavior, the initial stoichiometry influences the crystallization-dissolution of B2-NiAl during reaction processes, notably through an exponential growth relationship between maximum crystallinity and the Ni mole fraction. These findings may provide a physical basis for improving traditional reaction rate models to break through phenomenological understanding.

High-entropy layer assisting quasi-zero-strain cathodes for P2-Na2/3Ni1/3Mn2/3O2

Layered transition metal oxides have attracted much attention for high-energy density sodium ion batteries. However, most P2-type layered oxides undergo a large volume change when they are charged at a deep desodiated state, accompanied by inevitable anisotropic stress, leading to poor structural stability and terrible ion transfer. In this work, a high entropy (HE) material with a robust structure and fast ion transportation was decorated on P2-Na2/3Ni1/3Mn2/3O2 (NM) layered oxides. The unique characteristics of HE shells with similar lattice constants could effectively depress particle crack and exfoliation through buffering severe lattice strains, thus leading to enhanced cycling stability and kinetic properties of the HE-NM electrode. In situ x-ray diffraction analysis confirms that the volume expansion of NM could be prominently restrained both under thermal treatments and electrochemical after HE decoration. The modified cathode exhibits a volume change as low as 0.5%. The findings highlight the significance and superiority of the HE coating layer and provide insight for the rational design of high-performance sodium-ion batteries.

Fabrication of FexCoCrAlNi medium and high entropy layers on a carbon steel through TIG cladding

FexCoCrAlNi medium and high entropy layers were fabricated on a carbon steel using multilayer TIG cladding. The Fe content of the deposited layers decreased by moving away from the substrate due to the dilution effect. FexCoCrAlNi (with x>1) medium entropy alloys (MEAs) with a major Fe-rich BCC and minor Fe–Al–Ni-rich FCC phases developed in the inner parts of the fabricated layers. No intermetallic compounds appeared in MEAs. Microstructural assessments revealed that a FeCoCrAlNi high entropy alloy (HEA) containing Al–Ni-rich BCC and Fe–Cr-rich FCC crystal structures was achieved in the upper part of the deposited layers. It was found that Fe–Cr and Al–Ni pairs had contradictory effects on stabilizing crystal structure in MEAs and HEA. The Al–Ni pair was FCC-phase stabilizer in MEA while it was responsible for the formation of BCC phase in HEA. The microhardness of the deposited layers increased successively to reach 430 HV in the HEA due to the solid solution strengthening and formation of BCC phase with high-entropy characteristics.

Formation of High-Entropy Multilayer Compositions with a Hierarchical Structure

The authors carried out complex studies of a composite multilayer high-entropy coating obtained by HVOF in a protective atmosphere. They also investigated metallophysical properties of the coating (using electron microscopy and X-ray diffraction analysis) in order to obtain new information on its composition, mechanical properties, and phase composition. Functional properties of the high-entropy layer were also determined. The effect of mechanical activation of powders on the structural-phase state and quality of the layered coating has also been studied. On the basis of complex metallophysical studies, they investigated the formation of a structure in a composite multilayer high-entropy coating after HVOF in a protective atmosphere and subsequent thermomechanical treatment. Calorimetric tests of the functional high-entropy layer were carried out to reveal the exo effect corresponding to the manifestation of phase transformation. The mechanical properties of steel with a multilayer composite coating have been determined.

Study of the structure and properties of a high-entropy ceramic composite material

The article describes the technology development of layered surface compositions, including a high-entropy layer of a material with high-temperature memory effect of TiNiZrHfCoCu and a high-temperature ceramic layer based on zirconium dioxide ZrO2 stabilized by Y2O3. The authors also studied the structure, functional and mechanical properties of the abovementioned compositions. The proposed technology was implemented on a patented multifunctional technological complex for the formation of composite layered materials on the surface of steel products in a single technological cycle. On the basis of complex X-ray diffraction and electron microscopic studies, the structural parameters of the constituent layers of the surface composition were determined with subsequent thermal and thermomechanical treatment. The tests for ‘friction-wear’ and mechanical multi-cycle fatigue of the constituent layers of the surface composition showed a decrease in wear intensity and an increase in cyclic durability compared to the steel base. The comparison of wear intensity and cyclic durability of the surface-modified layers of the layered composition TiNiZrHfCoCu-ZrO2(Y2O3) with the composite materials obtained and studied by the authors earlier allowed the recommendation of the surface composition ‘high-entropy alloy TiNiZrHfCoCu-high-temperature ceramics’ for products of various purposes.

High- and low-entropy layers in solids behind shock and ramp compression waves

Non-uniform temperature fields are analyzed, which arise in the problems of formation of the steady shock wave at impact and ramp loading of metals, exit of the steady shock wave to the free surface, and the shock wave passing through the interface between two different materials. Theoretical analysis and computations show that high-entropy (with the temperature increase) and low-entropy (with the temperature decrease) layers arise near the interfaces in the above problems of shock and ramp loading. The impact produces the high-entropy layer; while the ramp loading can result in the both high- and low-entropy layers. At the shock wave passing through the interface, the high-entropy layer is formed in the lower-impedance material and the low-entropy—in the higher-impedance one. The formation of high-entropy layer at impact is supported by molecular-dynamics simulations in addition to continuum modeling. The high- and low-entropy layers should be taken into account in simulations of shock-wave processes in thin targets or in other cases where surface effects are important.

SURFACE LAYER HIGH-ENTROPY STRUCTURE AND ANTI-CORROSION PERFORMANCE OF AERO-ALUMINUM ALLOY INDUCED BY LASER SHOCK PROCESSING

7075 aluminum alloy is an ultra-high strength alloy containing Al, Zn, Mg, Cu and Cr elements,and is widely used in the aviation industry, but it has severe intergranular corrosion characteristics. The high-entropy alloys are composed of more than five major metallic elements and possess excellent corrosion resistance.When laser shock, featuring ultra high energy as well as the thermodynamic and kinetic loading characteristics farfrom-equilibrium states, acts on the surface of alloys with multiple elements, high-entropy alloy surface layer with specific properties may be obtained. In this work, surface modification of 7075-T76 aluminum alloy by laser shock was investigated. The microstructure, formation cause of the amorphous/nano- crystalline composite high- entropy alloy surface layer obtained by laser shock, hardness and corrosion resistance of the laser were analyzed by means of SEM and TEM. The results show that the adiabatic shear thermal effect induced by super high energy, ultra-fast process of laser shock causes surface alloy system to occur entropy increase effect and partitioning. The high mixing entropy contributes to the randomization increase of the alloy system. Thus, the elements in the system spontaneously self- organize in accordance with the law of Boltzmann. The dynamical formation of the nano- crystalline grains coordinates the thermodynamic equilibrium during the process. The strain- hardened layer is composed of amorphous microstructure and nanocrystalline grains, and the total depth of it reaches up to about 100 μm. After 1time laser shock,the depth of the surface high entropy layer is about 20 μm, of which the diameter of the nanocrystalline grains is 6~8 nm. After 3 times laser shock, the thickness of the layer can increase to more than 40 μm, and the diameter of the nanocrystalline grains is 2~3 nm. Meanwhile, the intense ultra high strain-rate induced by the laser shock makes precipitates deform, producing parallelly distribution of deformation twins in order to balance the laser energy. After repeated laser shocks, the hardness of the amorphous/nanocrystalline layer gradually closes to that of the matrix of the alloy because of the disappearing of the support of grain boundaries to the strength, the dislocation strengthening effect in nano-crystalline grains, and the coherent relationship between precipitates and matrix. Due to that the amorphous microstructure can prevent galvanic effect around precipitates, and nano-crystalline has good chemical stability, the nano-crystalline/amorphous composite high-entropy layer on surface of 7075-T76 aluminum alloy induced by laser shock can significantly improve the corrosion resistance, and effectively block the intergranular corrosion of the alloy.

Two-Dimensional Shock-Wave/Boundary-Layer Interaction in the Presence of Entropy Layer

Results of experimental and numerical study of gas flow and heat transfer in the region of interference of the impinging oblique shock wave with the near-wall flow on sharp and blunt plates are presented. The study is performed for the freestream Mach numbers from 5 to 10 and Reynolds numbers from to corresponding to the laminar and turbulent undisturbed boundary layers. The plate bluntness, location of the impinging shock, and the shock strength are varied. It is shown that the plate bluntness significantly reduces the heat transfer in the interference region due to the increase of separation-zone size and the reduction of gas density in the high-entropy layer. As the plate bluntness increases the heat transfer decays to a certain threshold value of the bluntness radius. The bluntness effect on the heat transfer increases and the bluntness threshold value decreases with the freestream Mach number.

Interaction between an Inclined Shock and Boundary and High-Entropy Layers on a Flat Plate

The flow structure and heat exchange in the zone of interference between an inclined shock and the surface of a flat plate are investigated experimentally and theoretically as functions of many parameters, the interference being studied in both the presence and the absence of bluntness of the leading edge. The experiments were carried out at Mach numbers M = 6, 8, and 10 and the Reynolds numbers Re L , calculated using the plate length L = 120 mm and the free-stream parameters, varied over the range from 0.24 ⋅ 106 to 1.31 ⋅ 106. The bluntness radius of the leading edge of the plate, the intensity of the impinging shock, and its location with respect to the leading edge were varied. The numerical simulation was carried out by solving the complete two-dimensional Navier-Stokes equations and averaged Reynolds equations using the q-ω turbulence model. The laminar boundary layer became turbulent inside the separation zone induced by the shock. It is shown that the plate bluntness significantly reduces the heat exchange intensity in the interference zone, this effect intensifying with increase in the Mach number.

Effect of a high-entropy layer on heat transfer in the region of the incidence of an oblique shock wave on a blunted-plate surface

Effect of a high-entropy layer on heat transfer in the region of the incidence of an oblique shock wave on a blunted-plate surface

A Blunt-Nosed Thin Body in Hypersonic Flow

An inverse problem is posed to simulate the influence of the nose bluntness on the hypersonic inviscid steady flow field around a slender two-dimensional section. In this formulation a bow shock is given in advance whereas the body contour comes at the end of analysis being identified with a particular streamline. An equation for the shock shape involves two terms in the form of different powers of the distance measured along the direction of oncoming stream. The leading term derives from a classical similar solution for the strong viscous/inviscid interaction regime; a correction to it models bluntness effects at large distances downstream. Matched asymptotic expansions are used to solve the problem within the hypersonic small- disturbance theory. In the outer region bounded by the shock, two sets of ordinary differential equations control the pressure, density, and velocity distributions. The second-order approximation admits of an explicit integral obtainable from a consideration of the finite drag exerted on the blunted nose of a section. The use of the momentum conservation law allows us to predict the power of the exponent of the correction term entering the shock equation. The asymptotic behavior of both first- and second-order approximations is established and employed for providing conditions for a solution in the inner region occupied by a high-entropy layer. Governing equations here are solved, explicitly determining a dependence of the body shape on the correction in the shock representation. A thorough analysis of the Newtonian approach reveals certain limitations inherent in this sim- plified treatment of steady hypersonic flows.

Method of mean-mass parameters for a three-dimensional boundary layer in a flow with vorticity

When a gas flows with hypersonic velocity over a slender blunt body, the bow shock induces large entropy gradients and vorticity near the wall in the disturbed flow region (in the high-entropy layer) [1]. The boundary layer on the body develops in an essentially inhomogeneous inviscid flow, so that it is necessary to take into account the difference between the values of the gas parameters on the outer edge of the boundary layer and their values on the wall in the inviscid flow. This vortex interaction is usually accompanied by a growth in the frictional stress and heat flux at the wall [2, 3]. In three-dimensional flows in which the spreading of the gas on the windward sections of the body causes the high-entropy layer to become narrower, the vortex interaction can be expected to be particularly important. The first investigations in this direction [4–6] studied the attachment lines of a three-dimensional boundary layer. The method proposed in the present paper for calculating the heat transfer generalizes the approach realized in [5] for the attachment lines and makes it possible to take into account this effect on the complete surface of a blunt body for three-dimensional laminar, transition, or turbulent flow regime in the boundary layer.

Influence of vorticity on the heat transfer to blunt bodies in hypersonic flight

When blunt bodies are in hypersonic flight, a high-entropy layer of gas with nonzero vorticity is formed near their surface. The transverse gradients of the entropy, density, and gas velocity in the layer are high, which makes it necessary to take into account its absorption by the boundary layer of finite thickness δ. This vortex interaction is usually accompanied by an increase in the heat flux q and the frictional stress τ on the wall compared with their values as calculated in accordance with the classical scheme of a thin boundary layer, when the parameters on the outer edge of the boundary layer are set equal to the inviscid parameters on the body. This effect has been investigated on the side surface of slender (with angle θ ≪ 1 to the undisturbed flow) blunt bodies in a hypersonic stream [1–3]. It is shown in the present paper that the effect can have a stronger and even qualitative influence on the flow over blunt bodies with θ ∼ 1 if the radius of curvature Rs of the detached shock wave on the axis is small compared with the midsection radius R of the body. It is shown that the distributions of the heat fluxes with allowance for the vorticity of the inviscid shock layer are similar in the case of slightly blunt (r0/R → 0) cones with half-angles θ less than a critical θ*.

Semiempirical theory of the generation of discrete tones by a supersonic underexpanded jet flowing over an obstacle

i. G. G. Chernyi, Gas Flow with a High Supersonic Velocity [in Russian], Fizmatgiz, Moscow (1959). 2. Modern Problems of Gasdynamics [Russian translation], Mir, Moscow (1971). 3. O. S. Ryzhov and E. D. Terent'ev, "On the entropy layer in hypersonic flows containing compression shocks whose form is given by a power-law function," Prikl. Mat. Mekh., 34, No. 3 (1970). 4. O. S. Ryzhov and E. D. Terent'ev, "Theory of the high-entropy layer in hypersonic flows~' Zh. Vychisl. Mat. Mat. Fiz., Ii, No. 2 (1971). 5. V. G. Dulov, "Equations of three-dimensional steady gas flows in special dynamic variables," in: Proceedings of Second International Colloquium of the Gasdynamics of Detonation and Reactive Systems, Novosibirsk, 1969. Section of Numerical Methods in Gasdynamics [in Russian], Izd. Vychisl. Tsentr. Akad. Nauk SSSR, Moscow (1969). 6. J. D. Cole, Perturbation Methods in Applied Mathematics, Blaisdell, Waltham, Massachusetts (1968). 7. S. S. Grigoryan, "The Cauchy problem and the piston problem for one-dimensional unsteady gas motions (self-similar motions)," Prikl. Mat. Mekh., 22, No. 2 (1958). 8. V. P. Korobeinikov, "Problems of the theory of a point explosion in gases," in: Proceedings of the V. A. Steklov Moscow Mathematics institute [in Russian] (1973). 9. G.M. Fikhtengol'ts, A Course in Differential and Integral Calculation [in Russian], Vol. 2, Nauka, Moscow (1969). I0. V. V. Sychev, "Method of small perturbations in problems of flow over thin blunt bodies by a hypersonic gas stream," Zh. Prikl. Mekh. Tekh. Fiz., No. 6 (1962).

Theory of the high-entropy layer in hypersonic flows

WE consider the inverse problem of hypersonic flow with an infinitely great Mach number of the oncoming flow at a condensation jump differing little from the jump obtained by using the explosive analogy. By joining the external and internal asymptotic expansions it has been possible to construct the body and study the flow immediately adjacent to the body, namely the flow in the entropy layer. The very concept of the theory of the high-entropy layer formed when a hypersonic flow flows past blunt bodies, is due to the papers of Cheng [1], V. V. Sychev [2–4] and Yakyra [5]. Comprehensive reviews of the advances of this theory were made first by Mirels [6], and later by Guiraud, Vallee and Zolver [7], to whom are also due a whole series of original results. A thorough approach to the investigation of the flow in the entropy layer was made by Freeman [8]. It was developed in greater detail from the mathematical point of view in the paper by Hornung [9], who also compared the theoretical and experimental data [10]. An analysis recently undertaken by the authors [11, 12] led to simple qualitative results on the structure of the velocity field in the inverse problem where the form of the shock wave is defined by a power function of the coordinates. The questions discussed below are closely connected with those studied in papers [8–12]. Their solution is based on the assumption that the front shock differs little from the jump obtained by the use of the explosive analogy [13–17] to calculate the hypersonic flows. However, precisely this small difference makes it possible to construct streamlined bodies the contours of which deviate from the particle trajectories in the problem of a strong explosion [18–20] the more strongly, the further the points chosen for the comparison are situated from the nose. Both the equation of the contour of the streamlined body and also the equation of the particle trajectory in the explosion are expressed asymptotically in terms of power functions, but the exponents of these functions differ by a finite quantity.

Method of mass-average quantities for the boundary layer in an outer flow with transverse nonuniformity

An engineering method is proposed for calculating the friction and heat transfer through a boundary layer in which a nonuniform distribution of the velocity, total enthalpy, and static enthalpy is specified across the streamlines at the initial section x0. Such problems arise in the vortical interaction of the boundary layer with the high-entropy layer on slender blunt bodies, with sudden change of the boundary conditions for an already developed boundary layer (temperature jump, surface discontinuity), and in wake flow past a body, etc.

Boundary layer development in a gas flow with stagnation enthalpy varying across the streamlines

We consider a laminar boundary layer for which the stagnation enthalpy specified in the initial section is variable with height. Such problems arise, for example, for bodies located in the wake behind another body, for hypersonic flow past slender blunted bodies (as a result of the large transverse entropy gradients in the highentropy layer), for stepwise variation of the temperature of a surface on which there is an already developed boundary layer, for sudden expansion of the boundary layer as a result of its flow past a corner of the surface, etc.