Transition Layer Research Articles

Synergistic Enhancement of 7075 Aluminum Alloy Composites via High Entropy Alloy Particle Integration: Microstructural and Mechanical Insights

This study investigates the impact of high-entropy alloy (HEA) particle reinforcement on the microstructure, mechanical properties, and performance of 7075 aluminum matrix composites (AMCs). Utilizing spark plasma sintering (SPS), composites with varying HEA particle concentrations were synthesized to assess their effects comprehensively. The results indicate that increasing HEA content significantly enhances the density and hardness of the composites. Specifically, a 20 wt% HEA reinforcement achieved a high hardness of 61 HRB and a density of 3.21 g/cm³. The compressive strength initially increased with HEA content but then decreased as it ranged from 5 wt% to 20 wt%. Optimal mechanical properties, including a compressive strength of 680 MPa and a fracture elongation of 33%, were observed at 10 wt% HEA. Wear testing further demonstrated the advantages of HEA reinforcement, with a substantial reduction in wear rate from 9.97±1.1×10⁻⁴ to 2.06±0.1×10⁻⁴ mm³/N·m at 10 wt% HEA. Additional analyses using energy-dispersive X-ray spectroscopy (EDX) and nanoindentation identified an aluminum-rich transition layer at the HEA-aluminum interface, formed due to aluminum diffusion. This transition layer likely enhances interfacial wettability and bonding, contributing to the improved performance of the composite.

A study on influence of sintering temperature, diameter and volume fraction of metal hollow spheres on the mechanical properties of metal hollow spheres composites

The structural parameters (the sintering temperature, diameter, and volume fraction of the hollow spheres) have a considerable influence on the mechanical properties of metal hollow sphere composites (MHSCs). Hence, the influence laws of the structural parameters on the mechanical properties of MHSCs possess certain research significance. To obtain these laws, MHSCs with different structural parameters were fabricated using a pressure casting method. Subsequently, the density of the MHSCs was determined through the direct measurement method. Meanwhile, X-ray diffraction and scanning electron microscopy were employed to conduct in-depth analyses of the phase composition and microstructure of the MHSCs. Additionally, the compression performance of the MHSCs was measured with the assistance of a universal mechanical testing machine. The analysis of the microstructure and phase composition results revealed that MHSCs consisted of γ-Fe, Al, Si, Fe₂Al₇Si, Fe₂Al₄Si, and Al₈Si₆Mg₃Fe phases, with the transition layer composed of the Fe₂Al₇Si phase. The results of the compression performance indicated that the compression performance of MHSCs increased with the rise of the sintering temperature and decreased with the increase of the volume fraction. However, as the diameter of MHS increased, the yield strength of MHSCs declined while the deformation strength of MHSCs increased. When the diameter of the MHSs was 2.55mm and the volume fraction was 40%, the compression performance of the MHSCs reached its optimum. At that point, the yield strength was 113.65±3.37 Mpa, and the average deformation strength was 81.26±5.45 Mpa.

Enhanced strength and ductility of boron nitride nanosheet reinforced cu composites through constructing an interfacial three-dimensional structure

To address the poor wettability and weak interface bonding between boron nitride nanosheet (BNNS) and Cu, BNNS/CuTi composites were prepared through matrix microalloying by adding 1 wt% Ti. Solid-state interfacial reactions resulted in the formation of TiN transition layers and TiB whiskers (TiBw), collectively constructed a BNNS-(TiN&TiB)-Cu interfacial three-dimensional structure (I-3DS). The coherent I-3DS significantly reduced the interfacial energy, improved the interfacial stability, and achieved a favorable combination of strength and ductility in BNNS/CuTi composites. The 0.1 wt% BNNS/CuTi composite achieved an ultimate tensile strength (UTS) of 485 MPa, representing increases of 114 % and 62 % over pure Cu and 0.1 wt% BNNS/Cu composite, respectively. The interlocking structure formed by I-3DS and Cu doubled the theoretical interface shear strength limit and improved load transfer efficiency. This study offered new insights into the innovative design of high-performance Cu matrix composites (CMCs) by constructing I-3DS.

Research on the oxidation process of micro-boron below the melting point temperature

The ignition and combustion characteristics of boron and the energy release rate of boron-based fuel are closely related to the surface oxide layer of boron. To understand the oxidation process of boron below its melting point, the slow oxidation process of boron under different temperature and humidity storage conditions and the fast oxidation process under high-temperature conditions were investigated. The results indicate that the surface oxide layer mainly comprises boron (B), boron suboxides (BxOy), and boron trioxide (B2O3). When the degree of oxidation is low, BxOy and B are the main components. After deep oxidation, BxOy almost disappeared. The thickness and composition of the surface oxide layer vary with changes in environmental temperature, humidity, and aging time. The effect of temperature increase on the growth rate of the oxide layer thickness is significantly greater than that of moisture. With the prolongation of boron aging treatment time, the onset, end, and maximum weight gain rate temperatures of the boron thermal oxidation process all slightly decrease. As the ambient temperature increases, the formation of the oxide layer transitions from a unidirectional diffusion mechanism of oxygen into the interior of boron particles to a bidirectional diffusion mechanism of molten oxide and oxygen.

Polar Molecule Intercalation to Weaken P2─S Bonding in MnPS3 Toward Ultrahigh-Capacity Sodium Storage.

Layered transition metal trithiophosphates (TMPS3, TM = Mn, Fe, Co, etc.) with high theoretical capacity (>1300 mAh g-1) are potential anode materials for sodium-ion batteries (SIBs). However, the strong bonding between P2 dimers and S atoms in TMPS3 hinders the efficient alloying reaction between P2 dimers and Na+, resulting in practical capacities much lower than theoretical values. Herein, a polar molecule diisopropylamine (DIPA) is intercalated into MnPS3 for the first time to improve the sodium storage performance effectively. Theoretical calculations show that the electron transfer between DIPA and MnPS3 induces more delocalized S p states and weaker P─S bonds, significantly enhancing the electrochemical activity and sodiation/desodiation reaction kinetics. Moreover, the expanded interlayer spacing from 6.48 to 10.75 Å enables faster Na+ diffusion and more active sites for Na+ adsorption. As expected, the DIPA-MnPS3 exhibits an ultrahigh capacity of 1,023 mAh g-1 at 0.2 A g-1 and excellent cycling performance (≈100% capacity retention after 4200 cycles at 10 A g-1), far outperforming those metal thiophosphates anodes reported for SIBs. Interestingly, in situ and ex situ characterizations reveal a quasi-topological intercalation mechanism of DIPA-MnPS3. This work provides a novel strategy for the design of high-performance anode materials for SIBs.

Similarities between Directed Percolation and Boundary Layer Transition on a Flat Plate

Similarities between Directed Percolation and Boundary Layer Transition on a Flat Plate

Dynamic large-eddy simulation of hypersonic transition delay over broadband wall impedance

Three-dimensional numerical simulations of hypersonic boundary layer transition delay due to porosity representative of carbon-fibre-reinforced carbon-matrix ceramics (C/C) were carried out on a 7 $^{\circ {}}$ half-angle cone for unit Reynolds numbers $Re_m=2.43 \times 10^6$ – $6.40\times 10^6\ \text {m}^{-1}$ , at the free-stream Mach number $M_\infty =7.4$ , for both sharp and 2.5 mm nose tip radii. A broadband time-domain impedance boundary condition was used to model the acoustic effects of the porous surface on the flow field. A quasi-spectral sub-filter-scale dynamic closure was adopted to stabilize the computations upon turbulent breakdown under extreme cooling conditions, with wall-to-adiabatic temperature ratio of $T_{w}/ T_{ad} \simeq 0.08 $ , while accurately recovering the growth rates of the unstable modes present in the early transition stages. Good agreement is observed with the reference experimental data, both in terms of the predicted extent of the transition delay and the measured second-mode frequency spectrum. The latter is strongly modulated by the formation of near-wall low-temperature three-dimensional streaks. Pressure disturbances concentrate in corridors of locally thickened boundary layer, with frequencies lower than what predicted by linear theory. Here, trapped wavetrains are formed, which can persist long into the turbulent region. Finally, it is shown that the presence of a porous wall simply shifts the onset of turbulence downstream, without affecting its structure.

Multiple Strategies to Build High-Performance Spherical Na-Ion Layered Oxide Cathodes.

The development prospect of layered transition metal oxides in sodium-ion batteries is excellent, but there are some problems, such as poor cycle stability and a complex phase transition. The spherical NaNi0.25Fe0.15Mn0.3Ti0.1Sn0.05Co0.05Li0.1O2 (SP-HEO) has been developed to address the challenges faced by O3-type layered oxide in sodium-ion batteries. The SP-HEO material is synthesized by piling and high entropy. The multiple strategies combine to enhance the electrochemical performance and air stability. The SP-HEO demonstrated a specific discharge capacity of 150.1 mA h g-1 at 0.1 C and 100.4 mA h g-1 at 7 C. Ex situ XRD analysis confirmed that the SP-HEO effectively retards complex phase transitions. This study not only introduces a high-entropy design for high tap density spherical storage materials but also dispels industry concerns regarding the performance of sodium ion layered oxide cathode materials.

Determination of Optical and Structural Parameters of Thin Films with Differently Rough Boundaries

The optical characterization of non-absorbing, homogeneous, isotropic polymer-like thin films with correlated, differently rough boundaries is essential in optimizing their performance in various applications. A central aim of this study is to derive the general formulae necessary for the characterization of such films. The applicability of this theory is illustrated through the characterization of a polymer-like thin film deposited by plasma-enhanced chemical vapor deposition onto a silicon substrate with a randomly rough surface, focusing on the analysis of its rough boundaries over a wide range of spatial frequencies. The method is based on processing experimental data obtained using variable-angle spectroscopic ellipsometry and spectroscopic reflectometry. The transition layer is considered at the lower boundary of the polymer-like thin film. The spectral dependencies of the optical constants of the polymer-like thin film and the transition layer are determined using the Campi–Coriasso dispersion model. The reflectance data are processed using a combination of Rayleigh–Rice theory and scalar diffraction theory in the near-infrared and visible spectral ranges, while scalar diffraction theory is used for the processing of reflectance data within the ultraviolet range. Rayleigh–Rice theory alone is sufficient for the processing of the ellipsometric data across the entire spectral range. We accurately determine the thicknesses of the polymer-like thin film and the transition layer, as well as the roughness parameters of both boundaries, with the root mean square (rms) values cross-validated using atomic force microscopy. Notably, the rms values derived from optical measurements and atomic force microscopy show excellent agreement. These findings confirm the reliability of the optical method for the detailed characterization of thin films with differently rough boundaries, supporting the applicability of the proposed method in high-precision film analysis.

From weak- to strong-coupling superconductivity in the AlB2-type solid solution SrGa1−xAlxGe with honeycomb layers

We report on the structure and the superconducting properties of 9-electron 111 compounds with honeycomb layers, namely SrGaGe, SrAlGe, and the SrGa1-xAlxGe solid solution. By means of single-crystal x-ray diffraction we show that, on one hand, SrGaGe crystallizes into the centrosymmetricP6/mmmspace group (a= 4.2555(2) Å,c= 4.7288(2) Å) with statistical disorder in the [GaGe]62-honeycomb layers. On the other hand, we confirm that SrAlGe crystallizes in a non-centrosymmetric space group, namelyP6¯m2(a= 4.2942(1) Å,c= 4.7200(2) Å) with fully ordered [AlGe]62-honeycomb layers. By using magnetization and specific heat measurements, we show that the superconducting properties of SrGaGe and SrAlGe differ significantly from each other. SrGaGe is a superconductor with a critical temperature ofTc= 2.6 K falling into the weak coupling limit, while SrAlGe has aTc= 6.7 K and can be classified in the strong coupling limit. By realizing the SrGa1-xAlxGe solid solution, we were able to investigate the transition between the different crystal structures as well as the evolution of the electronic properties. We show that the transition from the weak-to strong-coupling superconductivity in this system is likely associated with the disorder-to-order transition of the honeycomb layer, along with the loss of the inversion center in the crystal structure.

Assessment of validity of local neoclassical transport theory for studies of electric-field root-transitions in the W7-X stellarator

Abstract The neoclassical ambipolarity condition governing the radial electric field in stellarators can have several solutions, and sudden transitions (in radius) between these can then take place. The radial position and structure of such a transition cannot be determined from local transport theory, and instead a non-rigorous model based on a diffusion equation for the electric field is usually employed for this purpose [1]. We compare global (full plasma volume) drift-kinetic simulations of neoclassical transport in the Wendelstein 7-X stellarator with this model and find significant discrepancies. The position r0 of the transition is not predicted correctly by the diffusion model, but the radial structure of the transition layer is in reasonable agreement if the diffusion coefficient is chosen appropriately. In particular, it should depend on the plasma temperature in the same way as the plateau-regime coefficient of neoclassical transport theory or the gyro-Bohm diffusion coefficient. In the small-gyroradius limit, the prediction of r0 by the diffusion model simplifies to the so-called Maxwell construction [2, 3]. However, this property also emerges from a wide range of other mathematical models in the appropriate limit. The basic assumption underlying these models is that the diffusion, or generalisations thereof, is independent of the radial electric field, which is however unlikely to be the case in practice. Presumably this fact explains the discrepancy between the diffusion model and the drift-kinetic simulations. Finally, it is found that global simulations replicate the phenomenon of spontaneous root transitions driven by variations in the electron-to-ion temperature ratio, as predicted by local theory in the small-gyroradius limit.

Transition of the thermal boundary layer and plume over an isothermal section-triangular roof: an experimental study

The development of thermal boundary layers and plume near a section-triangular roof under different isothermal heating conditions has been the focus of numerous numerical studies. However, flow transition in this type of flow has never been observed experimentally. Here, phase-shifting interferometry and thermistor measurements are employed to experimentally observe and quantify the flow transitions in a buoyancy-driven flow over an isothermal section-triangular roof. Visualisation of temperature contours is conducted across a wide range of Rayleigh numbers from laminar at 103 to chaotic state at 4 × 106. Power spectral density of the temperature measurements reveals the type of bifurcations developing as the Rayleigh number is increased. This flow transition is characterised as a complex bifurcation route with the presence of two fundamental frequencies, a low and a high frequency. We found that the thermal stratification in the environment plays a significant role in the flow transition. The spatial development of flow is also quantitatively and qualitatively described. In addition to clarifying flow transition in experiments, the work demonstrates the implementation of phase-shifting interferometry and punctual temperature measurements for characterisation of near-field flow over a heated surface.

Thermal stress concentration points and stress mutations in nano-multilayer film structures

In the multilayer film-substrate system, thermal stress concentration and stress mutations cause film buckling, delamination and cracking, leading to device failure. In this paper, we investigated a multilayer film system composed of a substrate and three film layers. The thermal stress distribution inside the structure was calculated by the finite element method, revealing significant thermal stress differences between the layers. This is mainly due to the mismatch of the coefficient of thermal expansion between materials. Different materials respond differently to changes in external temperature, leading to compression between layers. There are obvious thermal stress concentration points at the corners of the base layer and the transition layer, which is due to the sudden change of the shape at the geometric section of the structure, resulting in a sudden increase in local stress. To address this issue, we chamfered the substrate and added an intermediate layer between the substrate and the transition layer to assess whether these modifications could reduce or eliminate the thermal stress concentration points and extend the service life of the multilayer structure. The results indicate that chamfering and adding the intermediate layer effectively reduce stress discontinuities and mitigate thermal stress concentration points, thereby improving interlayer bonding strength.

Regulation of Interface Compatibility and Performance in Soft Magnetic Composites with Inorganic Insulation Layers by FePO4 Intermediate Transition Layer

In the fabrication of soft magnetic composites, the lattice mismatch between the inorganic insulation layer and the iron matrix often leads to the formation of cracks during the molding process, which significantly impairs the operational performance of the materials. Consequently, it is imperative to develop novel strategies for inorganic insulation coatings that offer high electrical resistivity and thermal stability and are less susceptible to cracking during formation. This paper presents a new structure for soft magnetic composites that incorporates FePO4 as an intermediate transition layer between the iron-based soft magnetic particles and the inorganic ceramic insulation layer. This configuration is designed to provide insulation coatings with superior voltage and thermal resistance, as well as high electrical resistivity. The research details the processes forming the FePO4 intermediate transition layer and the SiO2 insulation layer on the iron powder surface, along with their interaction mechanisms. An analysis comparing the scenarios with and without the FePO4 intermediate transition layer shows its beneficial impact on the magnetic properties and mechanical strength of the soft magnetic composites. Further investigations reveal that at a phosphoric acid concentration of 1 wt.%, the FePO4 layer significantly enhances the interface compatibility between the Fe powder matrix and the SiO2 insulation layer. Under these conditions, the Fe@ FePO4/SiO2 soft magnetic composites demonstrate outstanding overall performance: the saturation magnetization stands at 215.60 emu/g, effective permeability at 83.2, resistivity at 57.42 Ω·m, power loss at 375.0 kW/m3 under 30 mT/100 kHz, and radial compressive strength at 15.95 Kgf. These findings offer novel insights and practical approaches for advancing inorganic insulation coating strategies and provide vital scientific support for further enhancing the magnetic and mechanical properties of soft magnetic composites.

Impact of axial strain on linear, transitional and self-similar turbulent mixing layers

Impact of axial strain on linear, transitional and self-similar turbulent mixing layers

Progress and Perspective of High‐Entropy Strategy Applied in Layered Transition Metal Oxide Cathode Materials for High‐Energy and Long Cycle Life Sodium‐Ion Batteries

AbstractLayered transition metal oxide (LTMO) cathode materials of sodium‐ion batteries (SIBs) have shown great potential in large‐scale energy storage applications owing to their distinctive periodic layered structure and 2D ion diffusion channels. However, several challenges have hindered their widespread application, including phase transition complexities, interface instability, and susceptibility to air exposure. Fortunately, an impactful solution has emerged in the form of a high‐entropy doping strategy employed in energy storage research. Through the implementation of high‐entropy doping, LTMOs can overcome the aforementioned limitations, thereby elevating LTMO materials to a highly competitive and attractive option for next‐generation cathodes of SIBs. Thus, a comprehensive overview of the origins, definition, and characteristics of high‐entropy doping is provided. Additionally, the challenges associated with LTMOs in SIBs are explored, and discussed various modification methods to address these challenges. This review places significant emphasis on conducting a thorough analysis of the research advancements about high‐entropy LTMOs utilized in SIBs. Furthermore, a meticulous assessment of the future development trajectory is undertaken, heralding valuable research insights for the design and synthesis of advanced energy storage materials.

The Interfacial Reaction Traits of (Al63Cu25Fe12) 99Ce1 Quasicrystal-Enhanced Aluminum Matrix Composites Produced by Means of Hot Pressing

This study fabricated (Al63Cu25Fe12)99Ce1 quasicrystal-enhanced aluminum matrix composites using the hot-pressing method to investigate their interfacial reaction traits. Microstructure analysis revealed that at 490 °C for 30 min of hot-pressing, the interface between the matrix and reinforcement was clear and intact. Chemical diffusion between the I-phase and aluminum matrix during sintering led to the formation of Al7Cu2Fe, AlFe, and AlCu phases, which, with their uniform and fine distribution, significantly enhanced the alloy’s overall properties. Regarding compactness, it first increased and then decreased with different holding times, reaching a maximum of about 98.89% at 490 °C for 30 min. Mechanical property analysis showed that compressive strength initially rose and then fell with increasing sintering temperature. After 30 min at 490 °C, the reinforcement particles and matrix were tightly combined and evenly distributed, with a maximum compressive strength of around 790 MPa. Additionally, the diffusion dynamics of the transition layer were simulated. The reaction rate of the reaction layer increased with hot-pressing temperature and decreased with holding time. Selecting a lower temperature and appropriate holding time can control the reaction layer thickness to obtain composites with excellent properties. This research innovatively contributes to the preparation and property study of such composites, providing a basis for their further application.

Stacking of charge-density waves in 2H−NbSe2 bilayers

We employ electronic-structure calculations to investigate the charge-density waves and periodic lattice distortions in bilayer 2H−NbSe2. We demonstrate that the vertical stacking can give rise to a variety of patterns that may lower the symmetry of the charge-density waves exhibited separately by the two composing 1H−NbSe2 monolayers. The general tendency to a spontaneous symmetry breaking observed in the ground state and the first excited states is shown to originate from a non-negligible interlayer coupling. Simulated images for scanning tunneling microscopy as well as geometric structure factors show signatures of the different stacking orders. This may not only be useful to reinterpret past experiments on surfaces and thin films, but it may also be exploited to devise ad hoc experiments for the investigation of the stacking order in 2H−NbSe2. We anticipate that our analysis not only applies to the 2H−NbSe2, but is also relevant for thin films and bulk, whose smallest centrosymmetric component is indeed the bilayer. Finally, our results illustrate clearly that the vertical stacking is not only important for 1T structures, as exemplified by the metal-to-insulator transition observed in 1T−TaS2, but seems to be a general feature of metallic layered transition metal dichalcogenides as well. Published by the American Physical Society 2024

A mathematical model for wind-generated particle–fluid flow fields with an application to the helicopter cloud problem

We develop a model for the interaction of a fluid flowing above an otherwise static particle bed, with generally the particles being entrained or detrained into the fluid from the upper surface of the particle bed, and thereby forming a fully two phase fluidized cloud above the particle bed. The flow in this large-scale fluidized region is treated as a two-phase flow, whilst the key processes of entrainment and detrainment from the particle bed are treated by examining the local dynamical force balances on the particles in a thin transition layer at the interface between the fully fluidized region and the static particle bed. This detailed consideration leads to the formation of an additional macroscopic boundary condition at this interface, which closes the two-phase flow problem in the bulk fluidized region above. We then introduce an elementary model of the well-known helicopter brownout problem, and use the theory developed in the first part of the paper to fully analyse this model, both analytically and numerically.

Parasitic taxa are key to the vertical stratification and community variation of pelagic ciliates from the surface to the abyssopelagic zone.

An increase in upper-ocean thermal stratification is being observed worldwide due to global warming. However, how ocean stratification affects the vertical profile of plankton communities remains unclear. Understanding this is crucial for assessing the broader implications of ocean stratification. Pelagic ciliates cover multiple functional groups, and thus can serve as a model for studying the vertical distribution and functional strategies of plankton in stratified oceans. We hypothesize that pelagic ciliate communities exhibit vertical stratification caused by shifts in functional strategies, from free-living groups in the photic zone to parasitic groups in deeper waters. 306 samples from the surface to the abyssopelagic zone were collected from 31 stations in the western Pacific and analyzed with environmental DNA (the V4 region of 18S rDNA) metabarcoding of pelagic ciliates. We found a distinct vertical stratification of the entire ciliate communities, with a boundary at a depth of 200m. Significant distance-decay patterns were found in the photic layers of 5m to the deep chlorophyll maximum and in the 2,000m, 3000m and bottom layers, while no significant pattern occurred in the mesopelagic layers of 200m - 1,000m. Below 200m, parasitic Oligohymenophorea and Colpodea became more prevalent. A linear model showed that parasitic taxa were the main groups causing community variation along the water column. With increasing depth below 200m, the ASV and sequence proportions of parasitic taxa increased. Statistical analyses indicated that water temperature shaped the photic communities, while parasitic taxa had a significant influence on the aphotic communities below 200m. This study provides new insights into oceanic vertical distribution, connectivity and stratification from a biological perspective. The observed shift of functional strategies from free-living to parasitic groups at a 200m transition layer improves our understanding of ocean ecosystems in the context of global warming.