Evolution Of Properties Research Articles

Evolution of static and dynamic magnetic properties of Re/Co/Pt and Pt/Co/Re trilayers with enhanced Dzyaloshinskii-Moriya interaction

The influence of Re layer insertion either at the bottom or top interface of epitaxially grown Pt/Co/Pt heterostructures on their static and dynamic magnetic properties is discussed in terms of their crystalline structure. Magnetic properties were studied as a function of both Re and Co layer thicknesses (dRe and dCo, respectively) in the matrix-like samples with a double-wedge structure, in which the layer thickness gradients were oriented orthogonally. The comprehensive investigations of the changes in coercivity, perpendicular magnetic anisotropy, spin reorientation transition, interfacial Dzyaloshinskii-Moriya interaction (iDMI) and spin wave damping are reported. Two different magnetic phases depending on the Co layer thickness with volume anisotropies (determined without demagnetization term) of KV∼0.25 (low) and KV∼0.75 MJ/m3 (high) were observed. The relation between these phases depends on the stack sequence and thickness of Re inserted layer. For dRe = 0.2 ÷ 0.7 nm deposited as the bottom interface, dCo induced transition at dtr ∼ 2 nm from low to high volume anisotropy phases was observed. Low and high volume anisotropy phases are associated to Co fcc and hcp structural phases. The insertion of half atomic layer of Re had no influence on surface anisotropy but significantly enhanced iDMI above 1 pJ/m and reduced spin wave damping.

Chemical and Structural Evolution of Rb2-2xK2xTi2O5 Layered Titanates When Exposed to Ambient Air.

In this report, we combine thermogravimetric analysis, X-ray diffraction, and infrared spectroscopy to investigate the chemical and structural evolution upon exposure of alkali titanates Rb2Ti2O5 and K2Ti2O5 and mixed compound Rb2-2xK2xTi2O5, for which 0 ≤ x ≤ 1, to the ambient atmosphere. We show that a complete solid solution exists between the potassium and rubidium end-members and that mixed compounds exhibit an intermediate behavior. When exposed to the ambient atmosphere, all compounds degrade, with the progressive formation of first hydrates and then bicarbonates and a much quicker degradation of the rubidium titanate than of the potassium titanate. On the contrary, we show that upon hydration in the absence of CO2, the crystal structure of K2Ti2O5 is more quickly impacted than that of Rb2Ti2O5. These observations should be useful for understanding the evolution of the functional properties of M2Ti2O5 alkali titanates upon aging in the ambient atmosphere, as well as for the optimization of their hydration-dependent properties.

Wire arc additive manufacturing NiTi/Nb bionic laminated heterogeneous structure: Microsturcture evolution and mechanical properties

In the aerospace industry and the medical field, there is a demand for materials that combine the functional properties of NiTi with the excellent ductility of Nb. However, creating high-strength interfaces between these two materials has been difficult due to their inherent differences in physical and chemical properties. In this study, a laminated heterogeneous structure (LHS) combining NiTi and Nb was prepared using wire arc additive manufacturing (WAAM) with different layer thickness ratios. The resulting microstructure of the NiTi/Nb LHS components consisted of a large amount of NiTi and β-Nb eutectic structures. This was due to the metallurgical bonding between the NiTi and Nb layers. The NiTi/Nb LHS components exhibited excellent compressive strength, measuring at 2607.6 ± 31 MPa. Additionally, the interface strength of the NiTi/Nb LHS component was remarkable, showing an ultimate tensile strength of 789.3 ± 8 MPa. The enhanced strength of the NiTi/Nb LHS component can be attributed to the gradient microstructure of the NiTi layer, which promoted heterogeneous plastic deformation generation. Furthermore, this study unveiled the relationship between the formation mechanism of the heterogeneous eutectic microstructure and the strength-ductility synergistic mechanism. As a result, this study provides an innovative approach for additive manufacturing in the strengthening of laminated multi-material interfaces.

Microstructure evolution and tribological properties over a wide temperature range of Ni-based composite coatings with Ti3AlC2 addition

Ni60A alloy powders doped with varying concentrations (0, 10 wt% and 20 wt%) of Ti3AlC2 MAX phase were coated on S31008 NiCr stainless steel substrate using atmosphere plasma spraying technique in this work. Comparative investigation was conducted to examine the effects of Ti3AlC2 additions on the microstructure evolution, microhardness, and wide temperature range (room temperature to 800 oC) tribological performance of the composite coatings. The findings demonstrated that the composite coatings were composed of γ-Ni, intermetallic hard metal borides, Ti3AlC2 and TiC phases, without any noticeable oxide phases. The 20 wt% Ti3AlC2 additions to the Ni60A alloy coating exhibited minimum imperfections in microstructure with a porosity drop of 65.8 %, and the highest microhardness which was enhanced by 64 % to 924 HV0.515. After introducing of Ti3AlC2, the coefficient of friction decreased and appeared to distinguish itself by remaining minimal and stable at low-medium temperatures compared with an increase of more than 70 % at high temperatures. Ni60A-10 wt% Ti3AlC2 coating resulted in the lowest friction coefficient of approximately 0.45 from room temperature to 400 oC and it peaked to 0.78 at 800 oC, reducing by 19.6 % and 6 % compared to non-composite coating, respectively. The wear resistance of the composite coating was considerably improved with the increment of Ti3AlC2, and the coating with 20 wt% Ti3AlC2 showed the most significant reduction in wear rate: 18.5 % at room temperature, 45.2 % at 200 oC, 37.2 % at 400 oC, 60 % at 600 oC, 90.8 % at 800 oC. The lubricate layered Ti3AlC2 phases and the tribo-oxide film predominate composed of derivative NiO, Cr2O3 Al2O3 and TiO2 played a critical role in antifriction and wear resistance. The wear mechanisms were accordingly conducted as abrasion and adhesion wear at low-medium temperature and transferred into tribo-oxidation wear at elevated temperature.

Microstructure Evolution and Tensile Properties of Medium Manganese Steel Heat Treated by Two-Step Annealing

In this paper, the nucleation and growth of austenite are controlled through a two-step annealing process to achieve multi-scale distribution and content increase of retained austenite in low manganese series medium-Mn steel. Combining SEM, EBSD, AES, and other experimental equipment, the evolution rules of the microstructure, properties, and element distribution behavior of the test steel during the annealing process are studied. Compared with one-step annealing, the two-step annealing significantly broadens the size distribution range of retained austenite. In the first step, after annealing at a higher intercritical temperature (760 °C), the ferrite and the M/A island are obtained, completing the initial partition of Mn and the refinement of microstructures. During the second step of annealing (720 °C), the primary Mn-rich martensite region provides higher nucleation driving force and finer dispersed nucleation sites, promoting the nucleation and growth of reverse transformation austenite. At the same time, the metastable-retained austenite formed after the first step of annealing continues to grow through interface movement. Furthermore, a high proportion (23.4%) of retained austenite with multi-scale distribution is formed in the final microstructure, and the product of strength and elongation increased from 21.8 GPa·% by the one-step annealing process to 30.1 GPa·%.

The evolution of structural characteristics and redox properties of humin during the composting of sludge and corn straw.

Humins (HMs), the insoluble faction of humic substances (HSs), play a pivotal role in the bioremediation of pollutants by acting as electron shuttles that modulate the interactions between microorganisms and pollutants. This crucial function is intricately linked to their structural composition and electron transfer capabilities. However, the dynamics of the electron transfer capacity (ETC) of HM extracted during the composting process and its determinants have yet to be fully elucidated. This study undertakes a comprehensive analysis of the ETC of HM derived from composting, employing electrochemical techniques alongside spectroscopic methods and elemental analysis to explore the influencing factors, including the electron accepting capacity (EAC), electron donating capacity (EDC), and electron reversible rate (ERR). Our findings reveal substantial variations in the EAC and EDC of HM throughout the composting process, with EAC values ranging from 133.03-220.98 μmol e- gC-1 and EDC values from 111.17-229.33 μmol e- gC-1. Notably, the composting process enhances the ERR and EDC of HM while diminishing their EAC. This shift is accompanied by an augmented presence of aromatic structures, polar functional groups, quinones, and nitrogen - and sulfur-containing moieties, thereby boosting the HM's EDC. Conversely, the reduction in EAC is associated with a decline in lignin carbon content and the abundance of oxygen-containing moieties, as well as the diminishment of visible fulvic-like and protein-like substances within HM. Importantly, humic-like substances and nitrogen-containing moieties within HM demonstrated the capacity for repeated electron transfer, underscoring their significance in the context of environmental remediation.

Revealing the Universal Pressure‐Driven Behavior of Hybrid Halide Perovskites and Unique Optical Modifiability in Extremely Soft 2D Tin‐Based System

AbstractAs promising photovoltaic materials, halide perovskites display large structural modifiability specific to their organic‐inorganic hybrid lattices, thus providing key to unlock many enhanced and novel physical properties. In particular, hybrid perovskites exhibit extraordinary functional responses to mechanical stimulation due to their soft lattices. However, a general pattern describing the evolution of perovskite properties under pressure is missing, rendering such research without theoretical guidance and further the optimization of optoelectronic performance. Here, a framework delineating the pressure‐dependent evolutions of lattice structure, bandgap, and photoluminescence (PL) across four distinct regions in all perovskites assuming 3D and 2D structures is unveiled, accrediting long‐range disorderness to be the common origin of bandgap blueshift, PL annihilation, and structural amorphization. Using such developed model as an instructional guideline, an optical bandgap and luminescent evolutions in quasi‐2D tin(II) iodide perovskites are revealed, where (C4H9NH3)2(CH3NH3)Sn2I7 (C4H9NH3+: butylammonium; CH3NH3+: methylammonium) is found to be the softest perovskite (bulk modulus ≈4.8 GPa) known so far. By meticulously choosing appropriate peak pressure ≈4 GPa, (C4H9NH3)2(CH3NH3)Sn2I7 shows irreversible defect healing (carrier lifetime prolongation from 7 to 22 ns) and permanent PL enhancement upon decompression to ambient condition, signifying practicality of the pressure‐driven behaviors unveiled in this work.

Effect of evanescent wave on vector vortex beams on higher-order Poincaré sphere

Abstract Based on the vector angular spectrum representation, the contributions of the propagating and evanescent waves to the vector vortex Laguerre–Gaussian beams on the higher-order Poincaré sphere are investigated in the nonparaxial regime. The evolution properties of the propagating and evanescent waves are closely related to the topological charge, the radial order, the ellipticity angle, and the waist width. The influences of the evanescent waves on the intensity, the spin and orbital angular momenta of the vector vortex beams are discussed in detail.

Quasars as standard candles

A sample of quasars has been recently assembled to investigate the non-linear relation between their monochromatic luminosities at 2500 Å and 2 keV and to exploit quasars as a new class of ‘standardized candles’. The use of this technique for cosmological purposes relies on the non-evolution with redshift of the UV-optical spectral properties of quasars, as well as on the absence of possible contaminants such as dust extinction and host galaxy contribution. We address these possible issues by analysing the spectral properties of our cosmological quasar sample. We produced composite spectra in different bins of redshift and accretion parameters (black hole mass, bolometric luminosity), to investigate any possible evolution of the spectral properties of the continuum of the composites with these parameters. We found a remarkable similarity amongst the various stacked spectra. Apart from the well known evolution of the emission lines with luminosity (i.e. the Baldwin effect) and black hole mass (i.e. the virial relation), the overall shape of the continuum, produced by the accretion disc, does not show any statistically significant trend with black-hole mass (MBH), bolometric luminosity (Lbol), or redshift (z). The composite spectrum of our quasar sample is consistent with negligible levels of both intrinsic reddening (with a colour excess E(B − V)≲0.01) and host galaxy emission (less than 10%) in the optical. We tested whether unaccounted dust extinction could explain the discrepancy between our cosmographic fit of the Hubble–Lemaître diagram and the concordance ΛCDM model. The average colour excess required to solve the tension should increase with redshift up to unphysically high values (E(B − V)≃0.1 at z > 3) that would imply that the intrinsic emission of quasars is much bluer and more luminous than ever reported in observed spectra. The similarity of quasar spectra across the parameter space excludes a significant evolution of the average continuum properties with any of the explored parameters, confirming the reliability of our sample for cosmological applications. Lastly, dust reddening cannot account for the observed tension between the Hubble–Lemaître diagram of quasars and the ΛCDM model.

Soil pore dynamics and infiltration characteristics as affected by cultivation duration for Mollisol in northeast China

Elucidating the effects of long-term cultivation on pore structure and infiltration characteristics is essential for understanding soil degradation mechanism and improving cropland sustainability. In this study, we evaluated a number of indicators regarding soil properties, pore structure, and water infiltration during long-term cultivation and the relationship of basic properties and pore structure with soil infiltration in northeast Mollisol region of China. The studied cropland involved four cultivation durations (20, 40, 60, and 100 years) and one forest (FR) as the control. X-ray computed tomography (CT) and mini disk infiltrometer were applied to assess the effects of long-term cultivation on soil pore structure and infiltration characteristics at soil depths of 0–100 cm. The pore properties including soil porosity (TP), pore number (PN), pore size distribution, mean shape factor (MSF), fractal dimension (FA), anisotropy (DA), and Euler number (EN), and infiltration properties including mean (IR), initial (IIR), stable infiltration rate (SIR), and saturated hydraulic conductivity (Ks) were planned to be measured in this study. The results showed that soil organic carbon (SOC) in cropland was significantly lower than that in FR, while bulk density (BD) and mean weight diameter (MWD) exhibited an opposite trend. Long-term cultivation altered the soil pore size and shape distribution, and decreased the macroporosity (>500 μm) and elongated porosity, which suggested that long-term cultivation results in a simpler pore network. FR took a longer time to reach a stable state in infiltration curve over time, while cropland had lower IR, IIR, SIR and Ks, indicating negative effects of cultivation on water infiltration. > 500 μm porosity and elongated porosity were positively correlated with infiltration characteristics (P<0.01). The infiltration parameters were mainly affected by soil pore properties (MSF, PN, and DA) and basic properties (SOC, MWD, and BD), highlighting the importance of pore morphology in the infiltration process. Our results provide new insights into the evolution of soil structure and properties and explanations for water infiltration dynamics under long-term cultivation from the microscale.

Evolution of tooth surface morphology and tribological properties of helical gears during mixed lubrication sliding wear

In mixed lubrication, the interplay of lubricant flows, solid asperity contact, and material wear between tooth surfaces creates complex and unpredictable contact states on tooth surface. To comprehensively understand the interaction between the lubrication and wear characteristics of the rough tooth surfaces of helical gears, this study established a mixed lubrication sliding wear calculation model for helical gears based on the mixed elastohydrodynamic lubrication model and Archard’s model. Specifically, the study aimed to examine the effects of surface topography features on average film thickness, contact area ratio, and accumulated wear at the meshing point. The findings demonstrated that the texture and power spectral density distributions of a non-Gaussian reconstructed surface closely resembled those of the actual ground surface. Furthermore, for non-Gaussian rough surfaces, a larger wavelength ratio enhanced microwedge motion, which increased film thickness and reduced wear. Additionally, a negatively skewed surface demonstrated better lubrication performance compared to both positively skewed and Gaussian surfaces. This improved performance is evident in the smaller contact area ratio and lower accumulated wear value of the negatively skewed surface.

Deciphering the evolution of electronic and magnetic properties in alkali doped nickel oxide: An In-silico approach

In this study, we employed the DFT+U method to systematically explore the electronic, and magnetic properties of nickel oxide doped with alkali metal atoms (Li, Na, K). The Hubbard potential-U was judiciously applied to all doped compound resulting from alkali doping, and were found to exhibited half-metallic properties. A noteworthy observation was the half-metallic band gap in the spin-down channel, which exhibited a linear variation with the increasing value of the Hubbard potential. Furthermore, the total magnetic moment was discernible in the supercells, with all supercells demonstrating 100% spin polarization at the Fermi level. Consequently, the findings from this study hold significant potential for applications in spintronics, thereby paving the way for future research in this domain.

MnFe Prussian Blue Analogue Open Cages for Sodium-Ion Batteries: Simultaneous Evolution of Structure, Morphology, and Energy Storage Properties.

Prussian blue analogues (PBAs) exhibiting hollow morphologies have garnered considerable attention owing to their remarkable electrochemical properties. In this study, a one-pot strategy is proposed for the synthesis of MnFe PBA open cages. The materials are subsequently employed as cathode electrode in sodium-ion batteries (SIBs). The simultaneous evolution of structure, morphology, and performance during the synthesis process is investigated. The findings reveal substantial structural modifications as the reaction time is prolonged. The manganese content in the samples diminishes considerably, while the potassium content experiences an increase. This compositional variation is accompanied by a significant change in the spin state of the transition metal ions. These structural transformations trigger the occurrence of the Kirkendall effect and Oswald ripening, culminating in a profound alteration of the morphology of MnFe PBA. Moreover, the shifts in spin states give rise to distinct changes in their charge-discharge profiles and redox potentials. Furthermore, an exploration of the formation conditions of the samples and their variations before and after cycling is conducted. This study offers valuable insights into the intricate relationship between the structure, morphology, and electrochemical performance of MnFe PBA, paving the way for further optimizations in this promising class of materials for energy storage applications.

Physical properties and anisotropy of sandstone during freeze-thaw cycle under unidirectional constraint

To investigate the evolution of physical properties of sandstone under unidirectional constraint during freeze-thaw cycles, an experimental device was specifically designed. Unidirectional constraint freeze-thaw tests were performed on sandstone specimens. The study analyzed variations in the dry mass, saturated mass, and longitudinal wave velocity of the sandstone both before and after undergoing freeze-thaw cycles, as well as examining the evolution of resistivity throughout the process. Results revealed that an increase in the number of freeze-thaw cycles leads to a gradual increase in the saturated mass of sandstone, while its dry mass consistently decreases, irrespective of whether it is subjected to constraint or not. The change rates of both dry mass and saturated mass were found to be significantly lower under unidirectional constraint compared to that without constraint. With more freeze-thaw cycles, a decline in longitudinal wave velocity was noted. Under unconstrained conditions, no significant direction dependence in longitudinal wave velocity was detected. However, under unidirectional constraint, there was a smaller decrease in the longitudinal wave velocity along the direction of constraint compared to other directions. This indicates that constraint mitigates frost heave damage. In the temperature rise and maintenance stages, resistivity initially dropped, then increased prior to stabilizing at a constant value. Conversely, in temperature decrease and maintenance stages, resistivity first rose, then dipped before ultimately rising again. Temperature primarily influenced resistivity by affecting the ion movement velocity within pore water and the connectivity of the conductive network.

Soft X-ray emission from the classical nova AT 2018bej

Context. Classical novae are known to demonstrate a supersoft X-ray source (SSS) state following outbursts. This state is associated with residual thermonuclear burning on the white dwarf (WD) surface. During its all-sky survey (eRASS1), the eROSITA telescope on board the Spectrum-Roentgen-Gamma observatory discovered a bright new SSS, whose position is consistent with the known classical nova AT 2018bej in the Large Magellanic Cloud. There were two eROSITA spectra obtained during the eRASS1 and eRASS2 monitoring epochs and one XMM-Newton grating spectrum close to the eRASS1 epoch. Aims. We aim to describe the eROSITA and follow-up XMM-Newton spectra of AT 2018bej with our local thermodynamic equilibrium (LTE) atmosphere models. We focussed on the evolution of the hot WD properties between the eRASS1 and eRASS2 epochs, especially with respect to the change in carbon abundance. Methods. A grid of LTE model atmosphere spectra was calculated for different values of the effective temperature (from Teff = 525 to 700 kK in steps of 25 kK), surface gravity (six values), and chemical composition, assuming approximately equal hydrogen and helium number fractions, and five different values of carbon and nitrogen abundances. Results. Both eRASS1 and XMM 0.3–0.6 keV spectral analyses yield a temperature of the WD of Teff~ 600 kK and a WD radius of 8000–8700 km. A simultaneous fitting of the eROSITA spectra for two epochs (eRASS1 and eRASS2) with a common WD mass parameter demonstrates a decrease in Teff, accompanied by an increase in the WD radius and a decrease in the carbon abundance. However, these changes are marginal and remain within the errors. The derived WD mass is estimated to be 1.05–1.15 M⊙. Conclusions. We traced a minor evolution of the source on a half-year timescale accompanied by a decrease in the carbon abundance and concluded that LTE model atmospheres can be used to analyse the available X-ray spectra of classical novae during their SSS state.

Effect of Y content on microstructure evolution and tensile properties of Mg-8Li-3Al-2Sn-xY alloys

Abstract The design of new ultra-light Mg-Li alloys have great significance in aerospace and other fields. In this paper, Sn and Y elements were simultaneously added into Mg-8Li-3Al (wt%) alloy and the effect of Y content on microstructure evolution and tensile properties of Mg-8Li-3Al-2Sn-xY (wt%) alloys was studied. The as-cast Mg-8Li-3Al-2Sn alloy is composed of α-Mg + β-Li duplex-phase matrix, fine MgLiAl2 phase and coarse fishbone-like Li2MgSn phase. As Y element is added, granular Al2Y phase is formed, and grain size of α-Mg phase decreases significantly with shape changing from well-developed coarse dendritic to equiaxed dendritic. After hot extrusion, α-Mg phase is elongated along the extrusion direction, and β-Li phase undergoes complete dynamic recrystallization and transforms into fine equiaxed grains. The addition of 0.5% Y improves the tensile properties of as-cast Mg-8Li-3Al-2Sn-0.5Y alloy. However, the tensile properties show a downward trend with further increase of Y content. Hot extrusion significantly enhances the tensile properties of Mg-8Li-3Al-2Sn-xY alloys. Similarly, strength reaches the highest when the Y content is 0.5% for extruded Mg-8Li-3Al-2Sn-xY alloys.

Evolution characteristic and mechanism of microstructure, hydraulic and mechanical behaviors of sandstone treated by acid-rock reaction: Application of in-situ leaching of uranium deposits

The main difficulty in understanding the effects of chemical-physical composite stimulation for low-permeability sandstone-type uranium deposits is clarifying the influence of acidification on pore response mechanism and permeability-mechanical properties evolution during loading-deformation-failure process. Therefore, the acid-rock reaction experiment was first performed, the multiple testing methods (X-ray Diffraction, thin-section identification, high-pressure mercury intrusion porosimetry, stress-seepage coupling experiment) were then conducted, the evolution laws and mechanisms of reservoir physical characteristics after acidification were finally clarified. Results show that after the acid-rock reaction, the contents of calcite, feldspar and kaolinite of samples are decreased and the quartz content is increased, the permeabilities of samples are all promoted, the peak strength, elastic modulus, and shear modulus of samples are reduced and the Poisson’s ratio is raised. The acid-rock reaction changes the energy storage performance and promotes the plasticization of samples. It is suggested to adopt a lower sulfuric acid concentration (2 g/L) and longer reaction time (>45 d) for the ISL of uranium deposits. This work has important theoretical and practical significance for an in-depth understanding of the enhanced mining of low-permeability sandstone-type uranium deposits.

Experiments and modeling of microstructural and mechanical behaviors of laser-welded Ni-based superalloy at high temperatures

The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts. The tensile properties and related microstructural evolutions such as the carbide precipitate and grain of a laser-welded Ni-based alloy were experimentally and numerically investigated at different temperatures (20, 300, 500, 800 °C). The results show that at room temperature, the strength of the Base Material (BM) was slightly smaller, with a difference of less than 1%, than the Welded Material (WM), which can be attributed to the more uniformly distributed needle-shaped carbide precipitates in the WM than those nonuniformly coarser spherical ones in the BM. While at 300 °C and 500 °C, the strength of WM decreased more obviously compared with that of BM due to the more apparent growth of grain: 13.52% loss in yield strength in WM alloys as compared with BM alloys at 300 °C, and 16.57% at 500 °C. At 800 °C, the strength of BM and WM both decreased to a similar level due to Dynamic Recrystallization (DRX). However, a much higher elongation was observed for the BM than WM (less than 50% of BM), which can be attributed to the enhanced dislocation accumulation capability of the large spherical carbides along grain boundaries on the fracture surface in BM. Furthermore, a unified model considering the welding effects on both microstructures (dislocation, carbides, and grain) and mechanical properties evolutions at different temperatures was developed and validated. Based on this model, the key temperature ranges (20–600 °C) where apparent weakening of strength and uniform plasticity occurs for welded structures were identified, providing a direct guidance for potential structure and process design.

3D LES numerical investigation of vertical vortex-induced vibrations of a 4:1 rectangular cylinder

The aerodynamic characteristics of rectangular cylinders provide valuable references for many engineering structures. Aiming to investigate the characteristics of vortex-induced vibration (VIV) of this kind of bluff section cylinder, the three-dimensional (3D) large-eddy simulations (LES) were conducted on the flow around an elastically mounted rectangular cylinder with an aspect ratio of 4. A novel method for creating 3D meshes was introduced and validated by comparing the aerodynamic parameters and vibration amplitudes with those of experimental data. The mechanism of VIV was then investigated by examining the evolution properties (including the mean and fluctuating pressure, predominant frequency, and spanwise correlation) of distributed pressure at various amplitude-dependent VIV stages. Additionally, the contributing/inhibiting effect of wind load acting on specific regions around the cylinder’s surface on VIV was clarified by investigating the energy input or output. The results show that the vibration amplitude affects both static and fluctuating pressures, with a significant variation in these pressures observed during the amplitude-ascent stage. The distributed aerodynamic force is mainly due to self-excited forces resulting from the cylinder vibration during amplitude-ascent stage, whereas both self-excited forces and forcing forces are prominent during the amplitude-descent stage. Notably, the spanwise correlation coefficient displays its minimum value at the peak amplitude, even lower than that in the non-lock-in region, with the highest value occurring at the onset of the amplitude-ascent stage. The energy analysis revealed that the wind loads acting on the upstream of the cylinder's surface tend to enhance VIV, while those acting downstream tend to inhibit it.

Revealing the evolution of microstructure and mechanical properties with deposition energy and shielding gas to achieve phase-balanced directed energy deposition of 2205 duplex stainless steel

Directed energy deposition-arc (DED-arc) manufactured duplex stainless steel (DSS) has shown great potential for use in marine propellers. However, challenges remain in achieving phase-balanced DSS deposits through the DED-arc process. To overcome this, we conducted a study that involved regulating the deposition energy and shielding gas with the use of ER2205 wire. The results show that the austenite content in DSS deposits increases with the increase of deposition energy, and the content in the Ar+2%N2-protected deposits is significantly higher than that of Ar+2%CO2-protected deposits. Ultimately, DSS deposits with balanced phase content (austenite content of ∼48.4 %) are obtained at a line energy of 600 J/mm for DED-arc under Ar+2%N2 protection. Unlike the N loss in Ar+2%CO2-protected samples, more nitrogen elements are introduced into the DSS samples by Ar+2%N2 shielding gas. Ar+2%N2-protected samples contain more austenite and exhibit a more homogeneous microstructure, which results in the solid solution strengthening and a significant reduction in the anisotropy of the tensile properties. Furthermore, a more systematic evolution of the microstructure and tensile properties of DSS deposits under the influence of deposition energy and shielding gas is revealed. This study preliminarily obtains the relationship between the DED-arc parameters, microstructure, and tensile properties of DED-arc-fabricated DSS, which will provide an important reference for tailoring microstructure and properties in additive-manufactured DSS.