Search Results (4,583)

Enhancing the strength and toughness of aluminum alloys using microstructure optimization remains a key challenge. In this study, an AA2024 aluminum alloy with a double-layer multi-gradient structure was fabricated using 50% constrained deformation and single-stage peak aging at 150 °C. Microstructural and compositional analysis was performed using SEM, XRD, and TEM to investigate grain structures, dislocation density, and the distribution of precipitated phases. The results revealed a heterogeneous microstructure with variations in grain size, dislocation gradient, and precipitation phases between the constrained and deformation layers. Mechanical testing demonstrated a 30.9% increase in yield strength, a 16.4% increase in tensile strength, and a 13.9% improvement in uniform elongation compared to the T6 temper. Corrosion tests showed enhanced resistance, with a shallower intergranular corrosion depth and higher self-corrosion potential. The improved mechanical properties were attributed to the dislocation gradient and heterogeneous precipitation phases, while the enhanced corrosion resistance resulted from the transformation of the S phase from a continuous grain boundary distribution to a discontinuous distribution along dislocations. This study provides a novel approach for optimizing the mechanical and corrosion properties of AA2024 aluminum alloy using microstructure design and precise thermal–mechanical treatment. Full article

Materials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromising their safety during cryogenic temperature service. This study investigates the quasi-static mechanical properties of a CoCr₀.₄NiSi₀.₃ medium-entropy alloy (MEA) at room temperature, −75 °C, and −150 °C. The deformation behavior and mechanisms responsible for strengthening and toughening at reduced cryogenic temperatures are analyzed, revealing that decreasing cryogenic temperature enhances the strength of the as-cast MEA. Specifically, both the yield strength (YS) and ultimate tensile strength (UTS) of the MEA increase significantly with decreasing temperature during cryogenic tensile testing. Under tensile testing at −150 °C, the YS reaches 617.5 MPa, the UTS is 1055.0 MPa, and the elongation to fracture remains approximately 21.0% at both −150 °C and −75 °C. After cryogenic temperature tensile deformation, the matrix exhibits a dispersed distribution of nanoscaled tetragonal and orthorhombic phases, a coherent hexagonal close-packed phase, L1₂ phase and layered long-period stacking ordered (LPSO) structures, which are rarely observed in the cryogenic deformation of metals and alloys. The metastable phase evolution path of this MEA at cryogenic temperatures is closely associated with the decomposition of perfect dislocations into a/6<112> Shockley partial dislocations and their subsequent evolution at reduced cryogenic temperatures. At −75 °C, the a/6<112> Shockley partial dislocation interacts with the L1₂ phase to form antiphase boundaries (APBs) approximately 3 nm thick. At −150 °C, two phase transition paths from stacking faults (SFs) to nanotwins and LPSO occur, leading to the formation of layered LPSO structures and deformation-induced nanotwins. The dispersion of these coherent nanophases and nanotwins induced by the reduced stacking fault energy under cryogenic temperatures is the key factor contributing to the excellent balance of strength and plasticity in the as-cast MEA, providing an important basis for research on the cryogenic mechanical properties of CoCrNi-based MEAs. Full article

Seismic wave propagation in complex terrains, especially in the presence of air layers, plays a crucial role in accurate subsurface imaging. However, the influence of different boundary conditions on seismic wave propagation characteristics has not been fully explored. This study employs the finite element method (FEM) to simulate and analyze seismic wavefields under different boundary conditions, including perfectly matched layer (PML), Neumann free boundary conditions, and air layer conditions. First, the finite element solution for the 2D frequency-domain acoustic wave equation is introduced, and the correctness of the algorithm is validated using a homogeneous model. Then, both horizontal and undulating terrain interfaces are designed to investigate the kinematic and dynamic characteristics of the wavefields under different boundary conditions. The results show that PML boundaries effectively absorb seismic waves, prevent reflections, and ensure stable wave propagation, making them an ideal choice for simulating open boundaries. In contrast, Neumann boundaries generate significant reflected waves, particularly in undulating terrains, complicating the wavefield characteristics. Introducing an air layer alters the dynamics of the wavefield, leading to energy leakage and multi-path effects, which are more consistent with real-world seismic-geophysical models. Finally, the computational results using the Overthrust model under different boundary conditions further demonstrate that different boundary conditions significantly affect wavefield morphology. It is essential to select appropriate boundary conditions based on the specific simulation requirements, and boundary conditions with an air layer are most consistent with real seismic geological models. This study provides new insights into the role of boundary conditions in seismic numerical simulations and offers theoretical guidance for improving the accuracy of wavefield simulations in realistic geological scenarios. Full article

Balancing efficiency and accuracy is often challenging in the numerical solution of three-dimensional (3D) point source acoustic wave equations for layered media. To overcome this, an efficient solution method in the spatial-wavenumber domain is proposed, utilizing the Non-Uniform Fast Fourier Transform (NUFFT) to achieve arbitrary non-uniform sampling. By performing a two-dimensional (2D) Fourier transform on the 3D acoustic wave equation in the horizontal direction, the 3D equation is transformed into a one-dimensional (1D) space-wavenumber-domain ordinary differential equation, effectively simplifying significant 3D problems into one-dimensional problems and significantly reducing the demand for memory. The one-dimensional finite-element method is applied to solve the boundary value problem, resulting in a pentadiagonal system of equations. The Thomas algorithm then efficiently solves the system, yielding the layered wavefield distribution in the space-wavenumber domain. Finally, the wavefield distribution in the spatial domain is reconstructed through a 2D inverse Fourier transform. The correctness of the algorithm was verified by comparing it with the finite-element method. The analysis of the half-space model shows that this method can accurately calculate the wavefield distribution in the air layer considering the air layer while exhibiting high efficiency and computational stability in ultra-large-scale models. The three-layer medium model test further verified the adaptability and accuracy of the algorithm in calculating the distribution of acoustic waves in layered media. Through a sensitivity analysis, it is shown that the denser the mesh node partitioning, the higher the medium velocity, and the lower the point source frequency, the higher the accuracy of the algorithm. An algorithm efficiency analysis shows that this method has extremely low memory usage and high computational efficiency and can quickly solve large-scale models even on personal computers. Compared with traditional FEM, the algorithm has much higher advantages in terms of memory usage and efficiency. This method provides a new approach to the numerical solution of partial differential equations. It lays an essential foundation for background field calculation in the scattering seismic numerical simulation and full-waveform inversion of acoustic waves, with strong theoretical significance and practical application value. Full article

In this study, commercial Nd-Fe-B magnets were utilized as starting materials to investigate the impact of various Tb-containing diffusion sources on the magnetic properties. Tb, Tb₆₀Nd₅Al₃₀Ga₅, and Tb₆₅Pr₁₀Nd₅Al₅Cu₁₀Ga₅ were developed as diffusion sources. After grain boundary diffusion treatment, the magnetic parameters of the magnets were evaluated at 20 °C, 90 °C, and 140 °C. The composition, microstructure, and elemental distributions of the magnets before and after diffusion were examined. It was found that the inherent coercivity of the magnets showed a dramatic increment of 49.4% at 20 °C after diffusion with Tb-containing alloys. The benefits and drawbacks of the designed diffusion sources were thoroughly discussed. Magnets diffused with the Tb₆₅Pr₁₀Nd₅Al₅Cu₁₀Ga₅ source displayed the highest overall performance, generating a thin layer with a grid-like structure at the grain boundaries and a consistent shell structure of Tb around the main phase grains. This work offers a promising alternative in the optimization of Nd-Fe-B magnets. Full article

As the development of nuclear fusion depends on plasma-facing materials, new methods for improving the radiation resistance of tungsten are being created and tested. This paper presents the results of studying the structure, surface morphology, phase composition, and residual internal stresses in tungsten alloys modified by plasma flows and irradiated with helium ions with an energy of 40 keV and doses of (1–3) × 10¹⁷ cm⁻². It is shown that the effect of compression plasma flows on tungsten leads to the modification of its grain structure in the near-surface layer, forming dispersed cells of 220–320 nm in size due to high-speed crystallization. The results of measuring the lattice parameters and internal stresses in irradiated tungsten alloys showed that the near-surface layer accumulates radiation defects, creating internal stresses, the relaxation of which leads to local destruction of the surface. Preliminary plasma treatment creates an increased density of intergranular boundaries, which serve as sinks for radiation defects and increase the radiation resistance of tungsten alloys. Full article

This work concerns the Taylor formula for the turbulence kinetic energy dissipation rate in the stable atmospheric boundary layer. The formula relates the turbulence kinetic energy dissipation rate to statistics at large scales, namely, the turbulence kinetic energy and the integral length scale. In parameterization schemes for atmospheric turbulence, it is usually assumed that the dissipation coefficient $C_{ϵ}$ in the Taylor formula is constant. However, a series of recent theoretical works and laboratory experiments showed that $C_{ϵ}$ depends on the local Reynolds number. We calculate turbulence statistics, including the dissipation rate, the standard deviation of fluctuating velocities and integral length scales, using observational data from the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition. We show that the dissipation coefficient $C_{ϵ}$ varies considerably and is a function of the Reynolds number, however, the functional form of this dependency in the stably stratified atmospheric boundary layer is different than in previous studies. Full article

Single-layered Ni/Ni₃N, inter-layered Ni/Ni₃N/Ni, and double-layered Ni/Ni₃N composite films were produced on an AZ31 magnesium alloy substrate through a magnetron sputtering technique, utilizing precise control over the N₂ flow’s modulation. An investigation was conducted to examine the phase composition, structural characteristics, tribological behavior, and corrosion resistance of the developed composite films. The experimental findings reveal that the composite film exhibits a stratified structure, wherein layers of Ni and Ni₃N are superimposed with distinct interlaminar boundaries, and the layers have a tight connection between them. Relative to the AZ31 magnesium alloy, the wear volume for the single-layered Ni/Ni₃N, inter-layered Ni/Ni₃N/Ni, and double-layered Ni/Ni₃N composite films was significantly reduced, exhibiting reductions of 68.1%, 80.4%, and 90.1%, respectively. The electrochemical corrosion current density was substantially reduced for the composite film deposition, with respective decrements of 89.5%, 91.4%, and 88.2%. The influence of Ni and Ni₃N on the wear and corrosion resistance of composite films varies with different laminated configurations, resulting in distinct levels of wear and corrosion resistance among the various films. Full article

This study investigates the scratch response of α-phase commercially pure titanium (cp-Ti) produced via wire arc directed energy deposition (WDED), focusing on the thermal history and directional effects. Progressive scratch tests (1–50 N) revealed heterogeneous wear properties between the top and bottom layers, with the top layer exhibiting higher material recovery (58 ± 5%) and wear volume (5.02 × 10⁻³ mm³) compared to the bottom layer (42 ± 5% recovery, 4.46 × 10⁻³ mm³), attributed to slower cooling rates and coarser grains enhancing ductility. The variation in the properties stems from the thermal gradient generated during WDED. Electron backscatter diffraction analysis showed higher kernel average misorientation (KAM) in the bottom layer (0.84° ± 0.49° vs. 0.51° ± 0.44°), affecting plasticity by reducing dislocation and twin boundary mobility. No significant differences were observed between longitudinal and transverse orientations, with coefficients of friction averaging 0.80 ± 0.12 and 0.79 ± 0.13, respectively. Abrasive wear dominated as the primary mechanism, accompanied by subsurface plastic deformation. These findings highlight the significant influence of WDED thermal history in governing scratch resistance and deformation behavior, providing valuable insights for optimizing cp-Ti components for high-performance applications. Full article

The article presents the results of a comparison of the wear resistance of coatings with a two-layer architecture (adhesion layer–wear-resistant layer) of Zr-ZrN, Zr-(Zr,Ti)N, Zr,Hf-(Zr,Hf)N, Zr,Nb-(Zr,Nb)N, Zr,Hf-(Ti,Zr,Hf)N, and Zr,Nb-(Ti,Zr,Nb)N coatings, deposited on a titanium alloy substrate. The wear resistance was studied using two different counterbodies: Al₂O₃ and steel. When in contact with the Al₂O₃ counterbodies, the best wear resistance was demonstrated by samples with Zr,Hf-(Zr,Hf)N and Zr,Nb-(Zr,Nb,Ti)N coatings. In tests conducted in contact with the steel counterbody, the best resistance was demonstrated by samples with Zr-ZrN and Zr,Hf-(Ti,Zr,Hf)N coatings. The wear resistance of samples with (Zr,Hf)N and (Zr,Nb,Ti)N coatings was 2.5–3.3 times higher than that of the uncoated sample. The Zr,Nb adhesion layer ensures better adhesion of the coating to the substrate. It was found that not only the adhesion strength of the adhesion layer to the substrate and coating is of significant importance but also the strength of the adhesion layer itself. The surface film of titanium oxide must be completely etched off to ensure maximum strength of the adhesive bond between the coating and the substrate. It has been established that the adhesion of the coating and the titanium substrate is also affected by the characteristics of the outer (wear-resistant) coating layer, which is the composition and structure of the wear-resistant coating layer. Delamination can occur both at the boundary of the adhesive layer with the substrate and at the boundary of the wear-resistant and adhesive layers of the coating depending on the strength of the adhesive bonds in the corresponding pair. It is necessary to ensure a good combination of properties both in the substrate–adhesion layer system and in the adhesion layer–wear-resistant layer system. Full article

To address the need for accurate classification of electrocardiogram (ECG) signals, we employ an interpretable KAN to classify arrhythmia diseases. Experimental evaluation of the MIT-BIH and PTB datasets demonstrates the significant superiority of the KAN in classifying arrhythmia diseases. Specifically, preprocessing steps such as sample balancing and variance sorting effectively optimized the feature distribution and significantly enhanced the model’s classification performance. In the MIT-BIH, the KAN achieved classification accuracy and precision rates of 99.08% and 99.07%, respectively. Similarly, on the PTB dataset, both metrics reached 99.11%. In addition, experimental results indicate that compared to the traditional multi-layer perceptron (MLP), the KAN demonstrates higher classification accuracy and better fitting stability and adaptability to complex data scenarios. Applying three clustering methods demonstrates that the features extracted by the KAN exhibit clearer cluster boundaries, thereby verifying its effectiveness in ECG signal classification. Additionally, convergence analysis reveals that the KAN’s training process exhibits a smooth and stable loss decline curve, confirming its robustness under complex data conditions. The findings of this study validate the applicability and superiority of the KAN in classifying ECG signals for arrhythmia and other diseases, offering a novel technical approach to the classification and diagnosis of arrhythmias. Finally, potential future research directions are discussed, including the KAN in early warning and rapid diagnosis of arrhythmias. This study establishes a theoretical foundation and practical basis for advancing interpretable networks in clinical applications. Full article

Near-surface ozone is a secondary pollutant, and its high concentrations pose significant risks to human and plant health. Based on an Extra Tree (ET) model, this study estimated near-surface ozone concentrations with the high spatiotemporal resolution based on Himawari-8 aerosol optical depth (AOD) data and meteorological variables from 1 January 2016 to 31 December 2020. The SHapley Additive exPlanation (SHAP) method was employed to evaluate the contribution of AOD and meteorological factors on ozone concentration. The results indicate that (1) the ET model achieves a sample-based cross-validation R² of 0.75–0.87 and an RMSE (μg/m³) of 17.96–20.30. The coefficient of determination (R²) values of the model in spring, summer, autumn, and winter are 0.81, 0.80, 0.87, and 0.75, respectively. (2) Higher temperature and boundary layer heights were found to positively contribute to ozone concentration, whereas higher relative humidity exerted a negative influence. (3) From 11:00 to 15:00 (Beijing time, UTC+08:00), ozone concentration increases gradually, with the highest occurring in the summer, followed by spring. This study has obtained high spatial and temporal resolution ozone concentration data, offering valuable insights for the development of fine-scale ozone pollution prevention and control strategies. Full article

Calcium–magnesium–alumina–silicate (CMAS), as an environmental deposit, deposits on engine components and causes serious damage to traditional thermal barrier coatings (TBCs) at high temperatures. The rare-earth silicate apatite dense reaction layer is regarded as a promising strategy to prevent TBCs from molten CMAS penetration and corrosion. The interactions between the Gd₂O₃ ceramic and CMAS are discussed at various temperatures and times in the study. The main reaction products are gadolinium silicate apatite (Ca₂Gd₈(SiO₄)₆O₂, Gd-apatite) and melilite phases. Within the first 15 min of interaction, a thin, continuous and dense reaction layer (DRL) consisting of Gd-apatite comes to form, and it thickens with increasing exposure temperature and time. The thickness of the DRL is ~0.8 μm after 15 min of the reaction at 1250 °C and it slowly increases to ~9.1 μm after a duration of 24 h at 1400 °C. This is attributed to CMAS infiltration along the grain boundaries of the Gd-apatite phases in the DRL. The growing rates of the Gd-apatite DRL decrease with reaction time and are significantly influenced by the temperature and the ability of the DRL to inhibit CMAS infiltration. Full article

This study achieved the successful creation of a 6061/M21/6061 composite sheet, with Cu powder incorporated in the middle, through a two-pass hot roll bonding process. The effect of Cu powder addition on interface microstructure evolution of Mg-Al composite plate during annealing was studied. The results show that the incorporation of copper powder significantly suppresses the formation of Mg-Al intermetallic compounds (IMCs) at the boundary of Al-Mg bonded plates. The IMCs’ thickness of composite plate Mg-Al interface absent Cu powder increased from 7.0 µm at 250 °C to 61.2 µm at 400 °C, showing a rapid growth trend. On the contrary, in the area with Cu powder of composite plate containing Cu powder, when the temperature ranges from 250 °C to 350 °C, the Mg-Al diffusion layer is thin and only varies between 1 µm and 3.2 µm and, even when the temperature rises to 400 °C, the diffusion layer is only 18.8 µm. At a constant temperature, the diffusion rate of IMCs in the Cu powder-containing region of the composite plate is significantly lower than that in the region without Cu powder. Upon the addition of Cu powder, Al₂Cu and Al_0.92Cu_1.08Mg phases are formed, which decrease the proportion of the brittle phases Al₃Mg₂ and Mg₁₇Al₁₂ at the composite plate interface, thereby effectively mitigating the diffusion of IMCs within the Mg-Al interface. This presents a novel concept for the investigation of enhanced interface bonding and the fabrication of Mg-Al composite plates. Full article

The accurate prediction of heat demand in retrofitted residential buildings is crucial for optimizing energy consumption, minimizing unnecessary losses, and ensuring the efficient operation of heating systems, thereby contributing to significant energy savings and sustainability. Within the framework of this article, the dependence of the energy consumption of a thermo-modernized building on a chosen set of climatic factors has been meticulously analyzed. Polynomial fitting functions were derived to describe these dependencies. Subsequent analyses focused on predicting heating demand using artificial neural networks (ANN) were adopted by incorporating a comprehensive set of climatic data such as outdoor temperature; humidity and enthalpy of outdoor air; wind speed, gusts, and direction; direct, diffuse, and total radiation; the amount of precipitation, the height of the boundary layer, and weather forecasts up to 6 h ahead. Two types of networks were analyzed: with and without temperature forecast. The study highlights the strong influence of outdoor air temperature and enthalpy on heating energy demand, effectively modeled by third-degree polynomial functions with R² values of 0.7443 and 0.6711. Insolation (0–800 W/m²) and wind speeds (0–40 km/h) significantly impact energy demand, while wind direction is statistically insignificant. ANN demonstrates high accuracy in predicting heat demand for retrofitted buildings, with R² values of 0.8967 (without temperature forecasts) and 0.8968 (with forecasts), indicating minimal performance gain from the forecasted data. Sensitivity analysis reveals outdoor temperature, solar radiation, and enthalpy of outdoor air as critical inputs. Full article