Multiphase Layer Research Articles

HfB2-SiC ceramics fabricated by reactive melt infiltration and its long-term oxidation behavior at 1650°C

High-density HfB2-SiC ceramics were prepared by reactive melt infiltration (RMI) at a relatively low temperature (1500°C). The ceramics had the open porosity of 0.5 % and the uniform distribution of constituent phases. The long-term oxidation behavior of HfB2-SiC ceramics in air was investigated at 1650°C. After oxidation for 100 h, the weight gain rates of ceramics varied within the range of 1.30–2.26 %. The oxidation products included SiO2, HfO2, and HfSiO4 phases, among which the HfSiO4 compound possessed the higher stability resulting from the reaction between the HfO2 and SiO2 phases. The samples all exhibited the typical feature of layered scale structure after HfB2-SiC oxidation, which was composed of the outermost SiO2 glass layer with the uneven thickness, followed by a relatively porous oxide layer containing white HfO2 and slight HfSiO4, below it was the unoxidized HfB2-SiC. The presence of this multiphase glass layer endowed the samples with excellent oxidation resistance.

Li-Si alloy pre-lithiated silicon suboxide anode constructing a stable multiphase lithium silicate layer promoting Ion-transfer kinetics

Enhancing the initial Coulombic efficiency (ICE) and cycling stability of silicon suboxide (SiOx) anode is crucial for promoting its commercialization and practical implementation. Herein, we propose an economical and effective method for constructing pre-lithiated core–shell SiOx anodes with high ICE and stable interface during cycling. The lithium silicon alloy (Li13Si4) is used to react with SiOx in advance, allowing for improved ICE of SiOx without compromising its reversible specific capacity. The pre-lithiated surface layer contains uniform multiphase lithium silicates (L2SiO3, Li4SiO4, and Li2Si2O5) in the nanoscale. This multiphase lithium silicate layer exhibits mechanical robustness against variation of micro-stress, which can act as a buffer layer to relieve volume variation. In addition, analysis of dynamic electrochemical impedance spectroscopy (dEIS) and distribution of relaxation time (DRT) confirm that the multiphase lithium silicate layer enhances Li-ion diffusion kinetics and contributed to constructing stable SEI. As a result, the optimal L10-850 anode shows a high ICE of 85.3 %, together with a high specific capacity of 1771.5mAh mg−1. This work gives a perspective strategy to modify SiOx anodes by constructing a pre-lithiated surface layer with practical application potentials.

Preparation and ablation behavior analysis of non-equimolar Cf/(Hf1/2Zr1/3Ti1/6)C composites under oxyacetylene flame with different heat fluxes

In this study, the synthesis of Cf/(Hf1/2Zr1/3Ti1/6)C non-equimolar middle-entropy composites was reported through precursor infiltration and pyrolysis processing for the first time. The pyrolysis process of the (Hf1/2Zr1/3Ti1/6)C precursor was examined by XRD, while the resultant ceramic was characterized by SEM, EDS, and TEM. The results showed that precursor-derived (Hf1/2Zr1/3Ti1/6)C powders were characterized by single-phase and uniformly distributed elements from microscale to nanoscale. The Cf/(Hf1/2Zr1/3Ti1/6)C composites exhibited a density of 2.741 g/cm3 and a porosity of 11.49 vol%. The various elements were uniformly distributed throughout the material. It also demonstrated outstanding mechanical properties, with a flexural strength of 219.34 MPa and a modulus of 24.82 GPa. At the heat flux of 3 MW/m2, the oxides after ablation were inadequate to fully envelop the substrate. When the heat flux increased to 4 MW/m2, a dense Hf-Zr-Ti-O multiphase oxide layer was formed on the surface of the sample, providing the internal Cf/(Hf1/2Zr1/3Ti1/6)C composites against further ablation. At the heat flux of 5 MW/m2, (Hf, Zr)TiO4 was severely consumed. Our research expands the application scope of non-equimolar middle-entropy composites in the domain of ultra-high temperature ablation resistance.

Microstructure and anti-ablation of laser cladding Ti-Zr-B-C coating on TC11 titanium alloy

To enhance the service life and application range of titanium alloys in the aerospace sector, Ti-Zr-B-C coatings with varying B4C contents (0–30 wt%) on TC11 titanium alloy was fabricated by laser cladding. The microstructure and anti-ablation were investigated in the present work. The results show that the whisker-like TiB phases and granular TiC and ZrC phases were observed in the coatings due to the in-situ reactions. With increasing the content of B4C, the number of reinforcing phases in the coating increased and distributed uniformly, resulting in the improvement of the microhardness up to 803.8HV. Furthermore, due to the formation of TiO2-ZrO2-B2O3 dense multiphase oxide layer on the surface during the ablation process, the coating with 20 wt% B4C exhibited the best anti-ablation at 1400ºC, the mass ablation rate (MAR) and linear ablation rate (LAR) were −2.62 mg/s and 3.67μm/s, respectively, which were just 62.8 % and 50.07 % in comparison with the substrate. This is mainly attributed to the formation of TiO2-ZrO2-B2O3 layer is beneficial to reduce the infiltration of O2 and the evaporation of liquid B2O3, leading to the excellent anti-ablation.

Combustion of ammonium dinitramide based solid propellant with PBT as energetic binders

AbstractFocusing on a new kind of solid propellants, which takes the ammonium dinitramide (ADN) as the high‐energetic oxidant, and 3,3‐bis(azidomethyl)oxetane and tetrahydrofuran copolymers (PBT) as the high‐energetic fuel binder, the burning rates and the theoretical performance of the propellant were measured under different ADN contents, ADN sizes and pressures. The burning rates increased from 7.9 mm/s to 117.4 mm/s and 49.1 mm/s to 74.2 mm/s when the pressure increased from 0.1 MPa to 10 MPa and from 12 MPa to 20 MPa separately, with a singularity in the pressure dependence of the burning rate at around 10 MPa. In terms of the effect of the ADN content, under the experiment pressures from 0.5 MPa to 5.0 MPa, the burning rates of the propellant were promoted by the increase of the oxidizer loading in a range of 50 wt% to 75 wt%, with a transition from a kinetically‐controlled reaction to a diffusion‐controlled one. Within the condition scope of this study, no obvious effect of the ADN sizes on the propellant combustion properties was observed. This could be attributed to the solid‐liquid mixed multiphase layer and the binder which served as a heat sink for the smaller ADN particles.

HfSi2-HfB2-SiC coating prepared at low temperature to protect SiC-coated C/C composites against oxidation at 1473–1973 K

To improve the oxidation resistance of carbon/carbon (C/C) composites in 1473–1973 K, a HfSi2-HfB2-SiC coating was prepared on the surface of SiC-coated C/C composites by a combined method of slurry dipping and oxidation sintering at low temperature (below 1473 K). The Hf-Si-O multiphase layer generated by the oxidation of the coating acted as oxygen barriers at 1473–1973 K in air. The in-situ formed HfSiO4 particles enhanced the thermal stability of the SiO2 glass, terminated propagation of the crack, and relieved CTE mismatch between the inner and outer coating. Besides, B2O3 filled pores in the early stage of oxidation and then SiO2 took the place of the B2O3 as a new filler with the increase time of oxidation. As a result, the coating can protect C/C composites for 516 h at 1473 K, 744 h at 1773 K, and 64 h at 1973 K with a mass gain of 0.63 wt%, 1.41 wt% and −1.91 wt%, respectively.

Effect of mullite content on microstructure and ablation behavior of mullite modified C/C-SiC-HfC composites

Mullite modified C/C-SiC-HfC composites were prepared via precursor infiltration and pyrolysis (PIP). The effects of mullite modification with different contents on the composition, microstructure, and ablation behavior of the composites were investigated. Results showed that inadequate and excessive mullite limited the improvement of the ablation resistance. At 8.88 wt% mullite, the composites exhibited relatively good ablation resistance with mass and linear ablation rates of 0.44 mg/s·cm2 and 6.39 µm/s. The addition of moderate mullite content promoted the formation of a dense Hf-Si-O multiphase oxide layer on the ablated surface without causing an excessive increase in surface temperature.

Simultaneous enhancement of mechanical and ablation properties of C/C composites modified by (Hf-Ta-Zr)C solid solution ceramics

In order to improve the mechanical and ablative resistance of C/C composites, (Hf-Ta-Zr)C single-phase solid solution ceramics were introduced into C/C composites by polymer infiltration and pyrolysis (PIP) to fabricate (Hf-Ta-Zr)C modified C/C composites (HTZ). Their mechanical property and ablation resistance were studied. The results showed that HTZ achieved simultaneous enhancement of mechanical property and ablative resistance. Their flexural strength and modulus could reach 219.34 MPa and 24.82 GPa, respectively. In addition, the mass and linear ablation rate of HTZ were 0.379 mg/s and 0.667 µm/s, respectively after the 90 s oxyacetylene ablation. A dense Hf-Ta-Zr-O multiphase oxide layer was formed on the surface of the HTZ during ablation process, which protected the interior modified C/C composites from ablation. Our work expands a rational design of modified C/C composites and broaden the application of solid solution ceramic in the field of ultra-high temperature ablation resistance for carbon or ceramic-based composites.

Thickness determination of multiphase layer via combined Rietveld and Grazing Incidence X-ray diffraction approach

Plates of Maraging-300 steel with a chemically grown layer on the surface were prepared by heat treatment in superheated steam at different times. The grown coating on the martensitic substrate was characterized in terms of thickness, compositional and structural information by means of optical and scanning electron microscopies and by Grazing Incidence X-ray Diffraction (GIXRD). The results showed the presence of the hematite, magnetite, and austenite crystalline phases in two different sublayers composing the entire reacted layer: an austenite sublayer over the maraging substrate, and an oxide sublayer at the top, right above the austenite layer, composed of interspersed hematite and magnetite. Quantitative Phase Analysis by the Rietveld method under GIXRD was used to obtain the thicknesses of multiphase chemically reacted layers. The methodology and mathematical formalism are described. The comparison with estimated values from optical and scanning electron microscopy have shown a good agreement between the imaging and diffraction techniques, suggesting that the reacted layer increases progressively with the heat treatment time.

An extraordinary-performance gradient nanostructured Hadfield manganese steel containing multi-phase nanocrystalline-amorphous core-shell surface layer by laser surface processing

• Gradient nanostructured layer on austenitic Hadfield manganese steel was fabricated by laser surface remelting technique. • Gradient refinement transits from dislocations activities and twinning in sub-region to three kinds of martensitic transformations, and finally a multi-phase nanocrystalline-amorphous core-shell structural surface. • The multi-phase nanocrystalline-amorphous core-shell structural surface with average grain size of ∼ 8 nm is obtained. • The core-shell structural surface exhibits tensile strength of ∼ 1.6 GPa, micro-pillar compressive strength of ∼ 4 GPa at a strain of ∼ 8% and nanoindentation hardness of ∼ 7.7 GPa. • Dislocation activities are kept inside extremely refined nanograins in the multi-phase nanocrystalline-amorphous core-shell structural surface. Reducing grain size (i.e. increasing fraction of grain boundaries) could effectively strengthen nanograined metals but inevitably sacrifices the ductility and possibly causes strengthening-softening transition below a critical grain size. In this work, a facile laser surface remelting-based technique was employed and optimized to fabricate a ∼600 μm-thick heterogeneous gradient nanostructured layer on austenitic Hadfield manganese steel, in which the average grain size is gradually decreased from ∼200 μm in the matrix to only ∼8 nm in the nanocrystalline-amorphous core-shell topmost surface. Atomic-scale microstructural characterizations dissected the gradient refinement processes along the gradient direction, i.e. transiting from the dislocations activities and twinning in sub-region to three kinds of martensitic transformations, and finally a multi-phase nanocrystalline-amorphous core-shell structural surface. Mechanical tests (e.g. nanoindentation, bulk-specimen tensile, and micro-pillar compression) were conducted along the gradient direction. It confirms a tensile strength of ∼1055 MPa and ductility of ∼10.5% in the laser-processed specimen. Particularly, the core-shell structural surface maintains ultra-strong (tensile strength of ∼1.6 GPa, micro-pillar compressive strength of ∼4 GPa at a strain of ∼8% and nanoindentation hardness of ∼7.7 GPa) to overcome the potential strengthening-softening transition. Such significant strengthening effects are ascribed to the strength-ductility synergetic effects-induced extra work hardening ability in gradient nanostructure and the well-maintained dislocation activities inside extremely refined nanograins in the multi-phase nanocrystalline-amorphous core-shell structural surface, which are evidenced by atomic-scale observations and theoretical analysis. This study provides a unique hetero-nanostructure through a facile laser-related technique for extraordinary mechanical performance.

A Triple-Step Asynchronous Federated Learning Mechanism for Client Activation, Interaction Optimization, and Aggregation Enhancement

Federated Learning in asynchronous mode (AFL) is attracting much attention from both industry and academia to build intelligent cores for various Internet of Things (IoT) systems and services by harnessing sensitive data and idle computing resources dispersed at massive IoT devices in a privacy-preserving and interaction-unblocking manner. Since AFL is still in its infancy, it encounters three challenges that need to be resolved jointly, namely: 1) how to rationally utilize AFL clients, whose local data grow gradually, to avoid overlearning issues; 2) how to properly manage the client-server interaction with both communication cost reduced and model performance improved; and finally, 3) how to effectively and efficiently aggregate heterogeneous parameters received at the server to build a global model. To fill the gap, this article proposes a triple-step asynchronous federated learning mechanism (TrisaFed), which can: 1) activate clients with rich information according to an informative client activating strategy (ICA); 2) optimize the client–server interaction by a multiphase layer updating strategy (MLU); and 3) enhance the model aggregation function by a temporal weight fading strategy (TWF), and an informative weight enhancing strategy (IWE). Moreover, based on four standard data sets, TrisaFed is evaluated. As shown by the result, compared with four state-of-the-art baselines, TrisaFed can not only dramatically reduce the communication cost by over 80% but also can significantly improve the learning performance in terms of model accuracy and training speed by over 8% and 70%, respectively.

High temperature oxidation behavior and mechanism of SiC-TaB2 composites

In order to improve the oxidation resistance of SiC in its ceramic matrix composites (CMCs), monolithic SiC ceramics doped with various proportions of TaB2 were prepared, isothermal and non-isothermal oxidation was investigated in detail as well. It was found that even a small proportion addition of TaB2 can effectively alleviate the intense oxidation of SiC between 1200 ºC to 1600 ºC, i.e., an oxidation degree of SiC can be reduced by 37% in the case with 10 wt% TaB2 under non-isothermal oxidation from room temperature to 1600 ºC. The oxidation resistance mechanism was also studied via analyzing the composition and microstructure of the formed oxide layer, it was found that the transformation of Ta2O5 in the multiphase oxide layer from grainy to flaky shape at about 1500 ºC plays the most important role in the excellent high temperature oxidation resistance of composites.

Improvement in microstructure and mechanical properties of laser welded steel/aluminum alloy lap joints using high-entropy alloy interlayer

This study focused on the effect of a high-entropy alloy (HEA) interlayer on the improvement of microstructure and mechanical properties of steel/Al alloy lap joints by laser welding. The FeCoCrNiCu HEA improved metallurgical reaction by restricting the formation of Fe–Al intermetallic compounds (IMCs) at the interface. Results showed that in the steel on Al alloy lap joint without an interlayer, the discontinuous multi-phase IMCs layer mainly consisted of three types of IMCs, Fe-rich β-FeAl phases, and Al-rich θ-Fe4Al13 + η-Fe2Al5 phases. With the addition of a HEA interlayer, owing to the sluggish diffusion effect in the fusion zone (FZ), the diffusion of Fe atoms from FZ to the IMCs layer was significantly controlled, which limited the generation of IMCs at the FZ/Al alloy interface. The IMCs layer was only composed of single-phase β-FeAl with the absence of highly brittle Al-rich IMCs and the thickness of IMCs layer was reduced from 85 μm to 30 μm, resulting in the enhancement of toughness of the joint. Additionally, the improvement of mechanical properties of the joint, including microhardness and tensile shear strength was consistence with the reduction of brittleness of IMCs at the interface.

The Effect of Boriding and Heat Treatment on the Structure and Properties of 100Cr6 Steel

The main aim of this case study is to present the changes caused by heat treatment on the structure and properties of 100Cr6 steel by annealing, hardening, and tempering in combination with previous chemical-heat treatment (CHT) by boriding. The boriding causes changes to the microstructure of the steel samples, which include a change in the morphology of the deposited cementite and a change in the volume of the chromium carbide particles. The cementite is transformed from its original granular form to a lamellar form. An increase in the proportion of chromium carbide particles in the sample occurs due to the higher affinity of chromium for carbon. This leads to precipitation of chromium carbides rather than carbides of iron. A multi-phase diffusion layer Fe2B-FeB with a thickness of 31 ± 2.8 µm is formed during boriding, with a typical tooth-like texture. Although the diffusion layer does not have the same toughness and resistance as the single-phase Fe2B diffusion layer, samples after boriding increase their resistance to tribological abrasion by 29 % compared to samples without this treatment. After quenching and tempering of the borided samples, a maximum tensile strength of Rm = 1779 MPa is measured. Compared to samples which are only quenched and subsequently tempered, this is an increase in tensile strength of about 59 %.

Структура и свойства высокоэнтропийного сплава, подвергнутого насыщению бором аддитивным методом

Using the electron-ion-plasma additive method, the HEA film formed on a substrate (AISI 304 steel) was saturated with boron by vacuum deposition from gas-metal plasma created by simultaneous independent vacuum arc discharge evaporation of the cathodes of selected elements in the plasma-assisted mode. Doping of HEAs with boron and oxygen atoms, as well as with substrate atoms has been revealed. It is shown that the multicycle modification of the HEA film is accompanied by the formation of a nanostructured multiphase layer with a thickness of 5-7 µm, containing inclusions of borides and oxides of the HEA chemical elements and the substrate. It has been established that the modification of the HEA film leads to a multiple (by 18 times) decrease in the wear parameter of the material.

On shear layer atomization within closed channels: Numerical simulations of a cough-replicating experiment

Aerosol generation during coughing and sneezing has gained major relevance due to the current COVID pandemic. The atomization involved in this process takes place in the complex context of the respiratory system and develops very rapidly. In order to get further insights on the early spray generation, we introduce a simplified model of physiological coughing or sneezing, in the form of a thin liquid layer subject to a rapid (30 m/s) air stream. The setup is simulated using the Volume-Of-Fluid method with octree mesh adaptation, the latter allowing grid sizes small enough to capture the Kolmogorov length scale. The results confirm the trend to an intermediate distribution between a Log-Normal and a Pareto distribution P(d)∝d−3.3 for the distribution of droplet sizes in agreement with a previous re-analysis of experimental results by one of the authors. The mechanism of atomization does not differ qualitatively from the multiphase mixing layer experiments and simulations. No mechanism for a bimodal distribution, also sometimes observed, is evidenced in these simulations.

Simulation of concentration of an admixture in the multiphase layer with random spherical inclusions

The diffusion of an admixture substance in a multiphase layer with randomly disposed spherical inclusions was investigated. The solution of the initial contact-boundary value problem is obtained in the form of the integral Neumann series. Computer simulation was performed based on the obtained calculation formula. Main regularities of the distributions of the averaged admixture concentration in the layer depending on the values of the diffusion coefficients, density and volume fractions of inclusions were established. The influence of the number of phases of the porous body on the diffusion processes in a multiphase layer with a uniform distribution of spherical inclusions was determined. The dependence of the increase of the averaged concentration function on the characteristic radii of spherical inclusions was analyzed, in particular, it is shown that the behavior of this function does not depend on the ratios of the reduced diffusion coefficients.

Corrosion of Fe–B–Si alloys in liquid zinc

The influence of the Si content and corrosion temperature on the formation of the compact multiphase corrosion-product layer when Fe–B–Si alloys were corroded in liquid zinc, was studied. Si was enriched at the corrosion interface and dissolved in the corrosion product layer, thus, affecting the diffusion of Zn and Fe. The multiphase corrosion product layer composed of Fe–Zn compounds with residual Fe2B at the corrosion interface was formed. The Fe–Zn compounds are tightly occluded among the residual Fe2B phase, which can inhibit diffusion. The Fe–Zn compounds tend to dissolve at high temperatures. However, because the complete residual Fe2B skeleton structure was retained and a small number of compounds remained among the residual Fe2B skeletons, the inhibition of the multiphase corrosion product layer did not cease. When the Si content was 0.318 wt%, the corrosion product layer was the densest, and when the Si content was 0.196 wt%, the corrosion product layer had the weakest diffusion-inhibition effect.

Dynamics of a Solidifying Icy Satellite Shell

AbstractOcean worlds have been identified as high‐priority astrobiology targets due to the link between life and liquid water. Young surface terrain on many icy bodies indicates that they support active geophysical cycles that may facilitate ocean‐surface transport that could provide observables for upcoming missions. Accurately interpreting spacecraft observations requires constraining the relationship between ice shell characteristics and interior dynamics. On Earth, the composition, physical characteristics, and bioburden of ocean‐derived ices are related to their formation history and parent fluid composition. In such systems, the ice–ocean interface, which exists as a multiphase mushy layer, dictates the overlying ice’s properties and evolution. Inclusion of the physics governing these boundaries is a novel strategy in modeling planetary ices and thus far has been limited to 1D approaches. Here, we present results from 2D simulations of an archetypal ice–ocean world. We track the evolution of temperature, salinity, porosity, and brine velocity within a thickening ice shell enabling us to place improved constraints on ice–ocean world properties, including the composition of planetary ice shells, the thickness and hydraulic connectivity of ice–ocean interfaces, and heterogeneous dynamics/structures in the interfacial mushy layer. We show that stable eutectic horizons are likely a common feature of ice–ocean worlds and that ocean composition plays an important role in governing the structure and dynamics of the interface, including the formation of chemical gradient‐rich regions within the mushy layer. We discuss the geophysical and astrobiological implications of our results and highlight how they can be validated by instrument‐specific measurements.

Characterisation of the hydrospheres of TRAPPIST-1 planets

Context. Planetary mass and radius data suggest that low-mass exoplanets show a wide variety of densities. This includes sub-Neptunes, whose low densities can be explained with the presence of a volatile-rich layer. Water is one of the most abundant volatiles, which can be in the form of different phases depending on the planetary surface conditions. To constrain their composition and interior structure, models must be developed that accurately calculate the properties of water at its different phases. Aims. We present an interior structure model that includes a multiphase water layer with steam, supercritical, and condensed phases. We derive the constraints for planetary compositional parameters and their uncertainties, focusing on the multi-planetary system TRAPPIST-1, which presents both warm and temperate planets. Methods. We use a 1D steam atmosphere in radiative-convective equilibrium with an interior whose water layer is in supercritical phase self-consistently. For temperate surface conditions, we implement liquid and ice Ih to ice VII phases in the hydrosphere. We adopt a Markov chain Monte Carlo inversion scheme to derive the probability distributions of core and water compositional parameters. Results. We refine the composition of all planets and derive atmospheric parameters for planets ‘b’ and ‘c’. The latter would be in a post-runaway greenhouse state and could be extended enough to be probed by space missions such as JWST. Planets ‘d’ to ‘h’ present condensed ice phases, with maximum water mass fractions below 20%. Conclusions. The derived amounts of water for TRAPPIST-1 planets show a general increase with semi-major axis, with the exception of planet d. This deviation from the trend could be due to formation mechanisms, such as migration and an enrichment of water in the region where planet d formed, or an extended CO2-rich atmosphere.