Phase Particles Research Articles

Structural characterization and luminescence characteristics of Dy3+ doped Sr9Y2W4O24 phosphor for application in white-LEDs

In this research, a series of Dy3+ ions doped Sr9Y2W4O24 (SYWO) phosphors was prepared for the application in white-LEDs and display devices. The structure, surface, and photo-luminescent (PL) behaviour of the samples were studied. X-ray diffraction (XRD) and Fourier Transform Infra-Red (FT-IR) spectroscopy indicated the formation of single phase particles with no contaminants with various vibrational bands present in the host lattice. The synthesised powders showed agglomeration with the average crystallite size to be in the range of 22–27 nm. The optical band gaps were estimated using diffuse reflectance spectral (DRS) data. The emission spectra of SYWO: xDy3+ (1.0, 2.0, 3.0, 4.0, & 5.0 mol%) have been obtained at different excitation wavelengths of 354, 367, and 391 nm. The SYWO phosphors emit intense blue and yellow colors at 491 nm (4F9/2 → 6H15/2), 576 nm (4F9/2 → 6H13/2) & 679 nm (4F9/2 → 6H11/2), respectively. Furthermore, from the CIE 1931 diagram, it is evident that the emission from these Dy3+ doped phosphors lies in the white region. The lifetime of excited Dy3+ ions decreased with increasing Dy3+ concentration as seen in the luminescence decay graphs. Finally, to determine the phosphor's luminescence thermal stability, temperature dependent photoluminescence (TD-PL) was recorded and the activation energy calculated from this study was found to be 0.231 eV. In the light of aforementioned results, we can conclude that Dy3+ doped Sr9Y2W4O24 phosphors could be used in construction of w-LEDs or as white-emitting luminescent materials in various photonic devices and other photonic applications.

Electrochemical and statistical study of Nickel ion assessment in daily children intake samples relying on magnesium aluminate spinel nanoparticles

Lately, children's daily consumption of some products, such as cereals and candies, has been rising, which provides a compelling rationale for determining any metallic substances that may be present. Monitoring the concentration of certain metals, like nickel, in these products is necessary due to medical issues in humans when consumed regularly. So, in this work, a novel and highly selective carbon paste as a Ni(II) ion-selective sensor was prepared and investigated using ceramic magnesium aluminum spinel nanoparticles as the ionophore and tritolyl phosphate (TOCP) as a plasticizer. A modified co-precipitation method was used to synthesize the spinel nanoparticles. X-ray diffraction, scanning electron microscope with EDAX, transmission electron microscope, and BET surface area were used to determine the phase composition, microstructure, pores size, particle size, and surface area of the synthesized nanoparticles. The spinel nanoparticle was found to have a nano crystallite size with a cubic crystal system, a particle size ranging from 17.2 to 51.52 nm, mesoporous nature (average pore size = 8.72 nm), and a large surface area (61.75 m2/g). The composition ratio of graphite carbon as a base: TOCP as binder: spinal as ionophore was 67.3:30.0:2.7 (wt%) based on potentiometric detections over concentrations from 5.0 × 10−8 to 1.0 × 10−2 mol L−1 with LOD of 5.0 × 10−8 mol L−1. A measurement of 29.22 ± 0.12 mV decade−1 over pH 2.0–7.0 was made for the Nernstian slope. This sensor demonstrated good repeatability over nine weeks and a rapid response of 8 s. A good selectivity was shown for Ni(II) ions across many interferents, tri-, di-, and monovalent cations. The Ni(II) content in spiked real samples, including cocaine, sweets, coca, chocolate, carbonated drinks, cereals, and packages, were measured. The results obtained indicated no significant difference between the proposed potentiometric method and the officially reported ICP method according to the F- and t-test data. In addition to utilizing ANOVA statistical analysis, validation procedures have been implemented, and the results exceed the ICP-MS methodology.

Interaction between dynamic recrystallization and phase transformation of Ti-43Al-4Nb-1Mo-0.2B alloy during hot deformation

The β solidified γ-TiAl alloy holds important application value in the aerospace industry, while its complex phase compositions and geometric structures pose challenges to its microstructure control during the thermal-mechanical process. The microstructure evolution of Ti-43Al-4Nb-1Mo-0.2B alloy at 1200 °C/0.01 s−1 was investigated to clarify the coupling role of dynamic recrystallization (DRX) and phase transformation. The results revealed that the rate of DRX in α2+γ lamellar colonies was comparatively slower than that in βo+γ mixed structure, instead being accompanied by intense lamellar kinking and rotation. The initiation and development rates of DRX in α2, βo, and γ phases decreased sequentially. The asynchronous DRX of the various geometric structures and phase compositions resulted in the uneven deformed microstructure, and the dynamic softening induced by lamellar kinking and rotation was replaced by strengthened DRX as strain increased. Additionally, the blocky α2 phase and the terminals of α2 lamellae were the preferential DRX sites owing to the abundant activated slip systems. The α2→βo transformation within lamellar colonies facilitated DRX and fragment of α2 lamellae, while the α2→γ transformation promoted the decomposition of α2 lamellae and DRX of γ lamellae. Moreover, the varied βo+γ mixed structures underwent complicated evolution: (1) The γ→βo transformation occurred at boundaries of lamellar colonies, followed by simultaneous DRX of γ lamellar terminals and neighboring βo phase; (2) DRX occurred earlier within the band-like βo phase, with the delayed DRX in enclosed γ phase; (3) DRX within the βo synapses and neighboring γ phase was accelerated owing to generation of elastic stress field; (4) Dispersed βo particles triggered particle stimulated nucleation (PSN) of γ phase. Eventually, atomic diffusion along crystal defects in βo and γ phases caused fracture of band-like βo phase and formation of massive βo particles, impeding grain boundary migration and hindering DRXed grain growth of γ phase.

Particle pinning during grain growth—A new analytical model for predicting the mean limiting grain size but also grain size heterogeneity in a 2D polycrystalline context

This study proposes a new analytical model for grain boundary pinning by second phase particles in two-dimensional polycrystals. This approach not only considers how particles impede grain growth, but also elucidates their role in preventing grain disappearance, thereby leading to stabilised microstructures characterised by heterogeneous grain size distribution comprising a mixture of small and large grains. By quantifying the number of particles intercepted by grain boundaries during grain growth or shrinkage, we are able to calculate the respective sizes and fractions of large and small grains. Furthermore, we identify ranges of particle surface fractions and particle sizes that maximise the heterogeneity in grain size. Additionally, we demonstrate the significant influence of initial grain size on the limiting grain size in pinned microstructures. Our analytical model’s results are compared with those obtained from full-field level-set simulations conducted in this study and from phase-field calculations reported in the literature, revealing very good agreement. Finally, the differences between the proposed model and existing ones in the literature are discussed.

Strengthening mechanism of sub-nano Ni3P and Cu3P phases particles on the Pb–Sn bronze alloy

The influence of the sub-nano Ni3P and Cu3P phases on the microstructure, mechanical properties, and strengthening mechanism of Cu–20Pb–5Sn-xP (x = 0,0.05,0.1,0.3,0.5) alloy were discussed under the addition of P to obtain a new Pb–Sn bronze alloy applying for bimetallic cylinder block. The results showed that the tensile strength and hardness of the Pb–Sn bronze alloy increase with the P contents, while the elongation increased first and then decreased. The main strengthen mechanism was that sub-nano Ni3P and Cu3P phases dispersed in the matrix, hindering the movement of dislocations during deformation. Additionally, the grain refinement also contributed to the improvement of mechanical properties. The Ni3P phase is easier to form than the Cu3P phase. And it is easier to combine with the matrix and more stable. The Ni3P and Cu3P phases were studied by using different characterization techniques, such as OM, SEM, EDS, XRD, TEM and First-principles, Phase diagram calculation method. When P is added to the alloy, the Ni3P phase first appears in the alloy, and when the P content increases to more than 0.3 wt%, the Cu3P phase begins to appear. This is because the Ni3P phase is easier to form than the Cu3P phase and is more stable. Only after part of P reacts with Ni dissolved in copper to form Ni3P, the remaining P and Cu can form Cu3P.

Sol-Gel Production of Unmodified and Lanthanum-Modified BiFeO3 Nanomaterials and Photoelectrochemical Studies of Hydrogen Evolution

We provide a simple sol-gel method for synthesising LaxBi1-xFeO3 (x=0.00, 0.10). Greater control over the BiFeO3 particle shape and phase purity is possible with this manufacturing technique.X-ray diffraction, scanning electron microscopy, and UV-visible spectroscopy were used, respectively, to assess the crystallographic analysis, particle shape, and optical qualities of the material. The X-ray diffraction method proved the production of a pure phase of BiFeO3.The synthesised materials shown good photocatalytic activity when exposed to UV-visible light. We discovered that doped materials had better photocatalytic activity of producing hydrogen than virgin materials. We have also recorded the amount of hydrogen production by inverted burette technique.

Unexpected contributions by carbonates and organic matter in a silicate-dominated tropical catchment: An isotope approach

The understanding of global carbon has rarely extended to small-scale tropical river basins. To address these uncertainties, this study aims to investigate the importance of rock weathering and organic matter turnover in the carbon cycle in a terrain dominated by crystalline silicate rocks. The geochemical composition of the dissolved and particulate carbon phases (DIC, DOC and POC) and their stable carbon isotopes were studied in the Deduru Oya River in Sri Lanka. Dissolved inorganic carbon (DIC) was the most dominant carbon phase and its contribution to the total carbon pool varied between 67 and 89 %. Furthermore, the δ13CDIC values in the river varied between −1.1 and −16.5 ‰. The lithological characteristics and molar ratios between Ca2+, Mg2+ and HCO3− indicated rock weathering mainly by CO2 and carbonic acid. The δ13CDIC values for groundwater input were −15.9 ‰, while for carbonate weathering, mainly due to fertiliser input, they reached a value of −12.7 ‰. This input was fed into an isotope mass balance to determine the relative contributions. However, the isotope mass balance was only plausible after correcting for the effects on δ13CDIC caused by degassing and photosynthesis. Our study demonstrated that carbonate weathering and organic matter turnover are essential components of the river carbon cycle even in a silicate dominated catchment. They can represent up to 60 % of the DIC pool. Combined with the higher organic matter turnover and high pCO2 in the river water, it can be suggested that the Deduru Oya River acts as a net source of CO2 in the atmosphere. Our study shows that CO2 degassing and in-stream photosynthesis in tropical river systems need to be considered along with chemical weathering to account for carbon transport and turnover in tropical rivers.

Temporal dynamics of contaminants in an estuarine system affected by acid mine drainage discharges

The estuary of Huelva is constituted by the common mouth of the Odiel and Tinto rivers, which are extreme cases of acid mine drainage contamination due to the Iberian Pyrite Belt, the world's largest sulfide mineral province. The drained acidic waters are subjected to seawater mixing and thus, to dilution and precipitation processes that drive the load of contaminants entering the oceanic environment. This research reports the distribution of major metal(loid)s present in the highly acidic waters across the entire Tinto and Odiel estuarine systems as they are subjected to acid mine drainage neutralization, until reaching the ocean. The datasets presented are divided in low- and high-flow periods, corresponding to dry/warm and wet/cold seasons, respectively. Iron and Al were almost entirely removed from solution with pH increase at both periods due to their precipitation as schwertmannite and basaluminite, respectively. These mineral phases also, controlled the behavior of As, Cu and Pb, which were removed from solution, with >90 % of their concentration ending up in the particulate phase due to sorption processes. However, at pH >7, As returned entirely to the dissolved phase at both sampled seasons because of desorption, similarly to Cu at the low-flow period. On the other hand, concentrations of Zn, Cd, Mn, Co and Ni in solution decreased only by dilution with seawater, with null partitioning to any sorption processes during estuarine mixing until reaching the Atlantic Ocean.

Numerical modeling of heat transfer behavior for two-phase flow in a nozzle considering phase change

The heat transfer and phase change of alumina particles in the gas-particle flow of the nozzle plays an important role in solid rocket motors (SRM) due to the coupling between the heat transfer and two-phase flow. However, it lacks precise modeling of the heat transfer behaviors of condensed particles in the nozzle, especially the phase change effect. In this article, we determine that the Drake model has the highest accuracy in calculating the convective heat flux between two phases, and propose a correlation to obtain radiative heat flux between the particle and walls. Then, a one-dimensional two-phase non-equilibrium model is established to consider the effects of heat transfer and solidification of particles on the two-phase flow in the nozzle. The results show that considering the phase change of particle improves the outlet thrust of the nozzle, but such increment decreases with the gas inlet temperature. When the supercooling phenomenon is considered, the nozzle thrust is reduced by 1.14% compared with that considering no supercooling. As the particle size increases, the outlet temperature of the particle phase rises and can even surpass the solidification temperature of particles and the velocity of the particle phase decreases significantly.

Enhanced mechanical properties of TZM alloy via doping Y2O3 along with creating heterogeneous grain structures

The further application exploration of TZM alloys have been hindered by the limited strength especially at high temperatures. Herein, we propose a strategy to enhance the mechanical properties of TZM alloys by introducing heterostructures through Y2O3 doping combined with rotary forging (RF). The particle stimulated nucleation (PSN) mechanism promotes fine grains (FGs) nucleate close to the micron-sized second phase particles. The mechanical properties of Y2O3-TZM (YTZM) alloy are improved through the synergistic strengthening influence of back stress strengthening and second phase strengthening. The ultimate tensile strength (UTS) of YTZM at room temperature and 1000 °C is 820 MPa and 433 MPa, respectively, which are about 15% and 51% higher than that of TZM. In addition, the FCC-oxides generated by adding Y2O3 can trigger twinning, stacking faults, and 9R structures during high-temperature deformation, and the long-period stacked ordered phase (LPSO) nucleates at the stacking faults and twin boundaries through the 9R structures, which is more conducive to alleviate the stress concentration at the oxide/matrix interface and improve the dislocation blocking ability. The present strategy provides a paradigm for the development of high-performance TZM alloys through creating heterostructures.

Microstructures and compositions of nano-precipitates and reverted austenite in custom 455 stainless steel in over-aged condition studied by transmission electron microscopy and atom probe tomography

The microstructures and nano-scale precipitate phases of Custom 455 stainless steel quenched from 850 °C and over-aged at 480 °C for 256 h have been studied in a quantitative way by using transmission electron microscopy and atom probe tomography. The results show that plate reverted austenite is formed between the martensite laths. In the reverted austenite, a rod-shaped Ni3Ti phase particle of about 40 nm long is precipitated at the interphase interface between martensite and reverted austenite, with an adjacent Cu-rich precipitate with a size of ∼20 nm. In the martensite, spherical G-phase particles with a diameter of about 8.0 ± 1.6 nm are precipitated adjacent to the Cu-rich precipitates with a size of about 10.0 ± 2.0 nm. These Cu-rich precipitates in the martensite are much smaller than those in the reverted austenite, but have a ten times higher number density than that in the latter. The orientation relationships between the martensitic matrix, reverted austenite, Ni3Ti phase, G-phase and Cu-rich precipitates are: (01−1)M//(1−11)γ//(0004)η//(02−2)G//(111)Cu,[111] M //[011]γ//[2−1−10]η//[111]G//[11−2]Cu.

Concentrations of potentially endocrine disrupting chemicals in car cabin air and dust – Effect of temperature and ventilation

Materials in car cabins contain performance-enhancing semi-volatile organic compounds (SVOCs). As these SVOCs are not chemically bound to the materials, they can emit from the materials at slow rates to the surrounding, causing human exposure. This study aimed at increasing the understanding on abundance of SVOCs in car cabins by studying 18 potential endocrine disrupting chemicals in car cabin air (gas phase and airborne particles) and dust. We also studied how levels of these chemicals varied by temperature inside the car cabin along with ventilation settings, relevant to human exposure. A positive correlation was observed between temperature and SVOC concentration in both the gas and the particle phase, where average gas phase levels at 80 °C were a factor of 18–16,000 higher than average levels at 25 °C, while average particle phase levels were a factor of 4.6–40,000 higher for the studied substances. This study also showed that levels were below the limit of detection for several SVOCs during realistic driving conditions, i.e., with the ventilation activated. To limit human exposure to SVOCs in car cabins, it is recommended to ventilate a warm car before entering and have the ventilation on during driving, as both temperature and ventilation have a significant impact on SVOC levels.

An LSTM-enhanced surrogate model to simulate the dynamics of particle-laden fluid systems

The numerical treatment of fluid–particle systems is a very challenging problem because of the complex coupling phenomena occurring between the two phases. Although an accurate mathematical modelling is available to address this kind of applications, the computational cost of the numerical simulations is very expensive. The use of the most modern high performance computing infrastructures could help to mitigate such an issue but not completely to fix it. In this work we develop a non intrusive data-driven reduced order model (ROM) for Computational Fluid Dynamics (CFD) - Discrete Element Method (DEM) simulations. The ROM is built using the proper orthogonal decomposition (POD) for the computation of the reduced basis space and the Long Short-Term Memory (LSTM) network for the computation of the reduced coefficients. We are interested to deal both with system identification and prediction. The most relevant novelties rely on (i) a filtering procedure of the full order snapshots to reduce the dimensionality of the reduced problem and (ii) a preliminary treatment of the particle phase. The accuracy of our ROM approach is assessed against the classic Goldschmidt fluidized bed benchmark problem. Finally, we also provide some insights about the efficiency of our ROM approach.

Sustainable microwave processing and surface characterization of powdered tungsten reinforced copper metal matrix (Cu-Wx) castings

The present work focuses on in-situ melting and casting of powdered copper metal matrix composites using a microwave hybrid heating approach. The composites of copper metal matrix are developed in such a way that the conductivity is least affected and related mechanical properties like flexural strength, tensile strength and hardness can be improved. Present work reports the processing and characterization of tungsten (W) powder reinforcement copper metal composites with weight percentages of W varied from 1%, 3% and 5%. The complete mechanism of interactions of Cu-Wx (x = 1%, 3% and 5% weight of copper powder) based composite powders with microwave heating is explained. The processed composite castings are characterized metallurgically through metallurgical microscope, SEM/EDS and XRD analysis; which reveals even dispersion of W particles in Cu matrix phase with some agglomerations. Some intermetallic formations are observed due to intense heating characteristics of microwaves. Further, mechanical and electrical characterizations of developed castings are carried out through Vicker's microhardness testing and electrical conductivity tests respectively. Addition of reinforced particles in metal matrix leads to an increase in microhardness on the expense of conductivity of composite. The 5% W addition led to 1.5 times increase in microhardness and 18.25% increase in resistivity. The mechanical testing revealed that the 5% W reinforced casting led to ∼22% higher ultimate tensile stress in comparison to pure copper casting. However, there was a significant decrease in ductility of metal matrix composites.

Laboratory study on the characteristics of fresh and aged PM1 emitted from typical forest vegetation combustion in Southwest China

The frequency and intensity of forest fires are amplified by climate change. Substantial quantities of PM1 emitted from forest fires can undergo gradual atmospheric dispersion and long-range transport, thus impacting air quality far from the source. However, the chemical composition and physical properties of PM emitted from forest fires and its changes during atmospheric transport remain uncertain. In this study, the evolution of organic carbon (OC), elemental carbon (EC), water-soluble ions, and water-soluble metals in the particulate phase of smoke emitted from the typical forest vegetation combustion in Southwest China before and after photo-oxidation was investigated in the laboratory. Two aging periods of 5 and 9 days were selected. The OC and TC mass concentrations tended to decrease after 9-days aged compared to fresh emissions. OP, OC2, and OC3 in PM1 are expected to be potential indicators of fresh smoke, while OC3 and OC4 may serve as suitable markers for identifying aged carbon sources from the typical forest vegetation combustion in Southwest China. K+ exhibited the highest abundant water-soluble ion in fresh PM1, whereas NO3− became the most abundant water-soluble ion in aged PM1. NH4NO3 emerged as the primary secondary inorganic aerosol emitted from typical forest vegetation combustion in Southwest China. Notably, a 5-day aging period proved insufficient for the complete formation of the secondary inorganic aerosols NH4NO3 and (NH4)2SO4. After aging, the mass concentration of the water-soluble metal Ni in PM1 from typical forest vegetation combustion in Southwest China decreased, while the mean mass concentrations of all other water-soluble metals increased in varying degrees. These findings provide valuable data support and theoretical guidance for studying the atmospheric evolution of forest fire aerosols, as well as contribute to policy formulation and management of atmospheric environment safety and human health.

Effects of multistage thermomechanical treatment on the microstructure and properties of Cu–Ni–Co–Si–Mg alloy strip by HCCM horizontal continuous casting

Multistage thermomechanical treatment experiments were conducted on Cu–Ni–Co–Si–Mg alloy strip prepared by the Heating Cooling Combined Mold (HCCM) horizontal continuous casting-cold rolling process. Effects of various heat treatments on the microstructure, mechanical properties, and electrical conductivity of the alloy were studied. The strengthening mechanisms and factors influencing the performance of each process has been analyzed. The tensile strength, yield strength, and electrical conductivity of Cu–Ni–Co–Si–Mg alloy can reach 894 MPa, 855 MPa, and 47.1 %IACS after a third-stage of thermomechanical treatment (TTMT). The cold rolling in first-stage of thermomechanical treatment (FTMT) not only caused work hardening of the alloy but also promoted the precipitation of solute atoms and the growth of second phase particles, limiting the increase in strength. Second-stage of thermomechanical treatment (STMT) effectively hindered the excessive growth of second phase particles in FTMT but shortened recrystallization process. The superior performance of Cu–Ni–Co–Si–Mg alloy after TTMT was attributed to dispersive precipitation of Ni, Co, and Si elements as (Ni, Co) 2Si phases in the copper matrix, strengthening the interaction between the precipitates and dislocations. A short process of HCCM horizontal continuous casting-cold rolling-thermomechanical treatment was developed to produce a high strength and highly electrically conductive Cu–Ni–Co–Si alloy strip used in lead frames.

Efficient point-based simulation of four-way coupled particles in turbulence at high number density.

In many natural and industrial applications, turbulent flows encompass some form of dispersed particles. Although this type of multiphase turbulent flow is omnipresent, its numerical modeling has proven to be a remarkably challenging problem. Models that fully resolve the particle phase are computationally very expensive, strongly limiting the number of particles that can be considered in practice. This warrants the need for efficient reduced order modeling of the complex system of particles in turbulence that can handle high number densities of particles. Here we present an efficient method for point-based simulation of particles in turbulence that are four-way coupled. In contrast with traditional one-way coupled simulations, where only the effect of the fluid phase on the particle phase is modeled, this method additionally captures the back-reaction of the particle phase on the fluid phase, as well as the interactions between particles themselves. We focus on the most challenging case of very light particles or bubbles, which show strong clustering in the high-vorticity regions of the fluid. This strong clustering poses numerical difficulties which are systematically treated in our work. Our method is valid in the limit of small particles with respect to the Kolmogorov scales of the flow and is able to handle very large number densities of particles. This methods paves the way for comprehensive studies of the collective effect of small particles in fluid turbulence for a multitude of applications.

Solvethermal synthesis and thermochromic properties of CaF2@VO2-based core-shell structure composites

Vanadium oxide (VO2)-based core-shell structures exhibit unique properties due to their reversible metal–insulator transition (MIT). As a result, numerous applications on the device level have been reported in the literature. However, since VO2 are multivalent compounds, the controllable preparation of VO2 core-shell-based particles is quite challenging. Along these lines, in this work, to overcome these limitations, the growth mechanism of VO2 shells on spherical substrates was systematically investigated. More specifically, the CaF2@VO2 core-shell microspheres were fabricated successfully by applying the solvent/hydrothermal-calcination method for the first time, while the phase evolution and morphological characteristics of the preparation process were studied in detail. From the obtained results, it was demonstrated that the composite particle's morphology and phase structure strongly depend on the activator, solvent, annealing atmosphere, and the annealing temperature. In addition, the infrared transmittance of the prepared CaF2@VO2(M) coating exhibited a decrease of 34.08 % during the metal–semiconductor phase transition in the 4–12 μm wavelength. Compared with the VO2 coatings and the uncoated CaF2/VO2 coatings, the transmittance conversion performance (ΔT) of the CaF2@VO2(M) coating was also increased by 22.62 % and 21.22 %, respectively.

Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

Particle image velocimetry was employed to investigate the impact of convergent–divergent riblets on turbulent boundary layers in both clear water and liquid–solid two-phase flow fields containing 155 μm polystyrene particles. The turbulence statistics such as turbulence intensity and Reynolds stress were investigated. The spatial topology of spanwise vortex head and the development and evolution process of hairpin vortices were explored from Euler and Lagrange perspectives, respectively. Additionally, the particle distribution, concentration, and dispersion within the turbulent boundary layer were statistically analyzed. The results indicated that the boundary layer thickness, friction resistance, integrated turbulence intensity, and Reynolds stress were significantly lower on divergent riblet walls compared to convergent riblet walls. Notably, divergent riblets with a yaw angle of 30° exhibited the best drag reduction effect in both single-phase and two-phase flow fields. The addition of particles resulted in an increase in boundary layer thickness but effectively reduced turbulent fluctuations in the logarithmic region, enhancing drag reduction. This extended the drag reduction range of divergent riblets to a yaw angle of 45°, increasing the maximum drag reduction rate to 26.18%. Through spatial multi-scale local average structure function and finite-time Lyapunov exponent field analysis, it was found that the 30° divergent riblet wall significantly inhibited the development of vortex structures and reduced momentum exchange within the boundary layer. Conversely, the 30° convergent riblet wall had the opposite effect, while the particle phase inhibited the development of all wall turbulent structures. Analysis of particle concentration variations within different regions of the turbulent boundary layer revealed that as the normal height of the boundary layer increased, particle concentration gradually increased, and particle dispersion decreased accordingly. The analysis further showed that particle dispersion was mainly influenced by flow structures, whereas concentration was significantly affected by turbulence intensity. These findings elucidate the effect of the flow field on the particle phase and provide insights into the interaction mechanism between the flow field and particles.

Friction stir welding of as-cast and pre-aged Al–Si–Zn–Mg–Fe alloy: Microstructure, mechanical and corrosion properties

Al–Si–Zn–Mg–Fe alloy in as-cast and artificially aged (T6) conditions was friction stir-welded with a traveling speed of 200 mm/min and a rotation speed of 800 rpm. Their microstructure, mechanical and corrosion properties were investigated. α-Al, Si, Mg2Si, MgZn2 and Fe-rich phase were detected in the as-cast and pre-aged Al–Si–Zn–Mg–Fe before and after FSW. The secondary phases in pre-aged Al–Si–Zn–Mg–Fe after FSW are slightly more than those in the as-cast Al–Si–Zn–Mg–Fe after FSW. For the pre-aged Al–Si–Zn–Mg–Fe after FSW, the grains are refined and the dislocation density decreases. Hardness of the pre-aged Al–Si–Zn–Mg–Fe is higher than that of the as-cast one, whereas the hardness of weld nugget zones (NZs) of the both FSWed Al–Si–Zn–Mg–Fe joints is lower than their base materials, and the strength coefficients of both FSWed joints of the as-cast and pre-aged Al–Si–Zn–Mg–Fe are 0.82 and 0.9 respectively. The ultimate tensile strength (UTS) and yield strength (YS) of the pre-aged Al–Si–Zn–Mg–Fe after FSW (UTS = 208.86 MPa and YS = 156.72 MPa) is about 35% higher than that of as-cast Al–Si–Zn–Mg–Fe after FSW (UTS = 159.4 MPa and YS = 112.06 MPa) mainly due to the smaller grain size and more precipitates in the former. The corrosion resistance (CR) of the FSWed joint of the pre-aged Al–Si–Zn–Mg–Fe is the highest, owing to the most refined grain size, highest HAGBs, lowest KAM, increase in the close-packed {111} (α-Al) texture, dispersed particles of secondary phases, followed by the pre-aged Al–Si–Zn–Mg–Fe and then the FSWed joint of the as-cast Al–Si–Zn–Mg–Fe, and the as-cast one is the lowest.