Search Results (164)

This study investigates the synergistic effects of Cr–Zr and Mn–Zr additions on the microstructural evolution and mechanical properties of Al–6 wt.%Cu alloys. Alloys were designed with solute concentrations positioned below, near, and above their maximum solubility limits, and were evaluated under as-cast, T4, and T6 heat treatment conditions. Mechanical testing revealed distinct behavioral trends depending on the heat treatment: the T4 heat treatment condition generally exhibited superior hardness and yield strength, whereas the T6 heat treatment condition resulted in a slight reduction in hardness but facilitated a significant recovery in tensile strength and structural stability, particularly in alloys designed near the solubility limit. To elucidate the crystallographic origins of these mechanical variations, X-ray diffraction analysis was conducted to monitor changes in lattice parameters, dislocation density, and micro-strain. The results showed that T4 heat treatment induced lattice contraction and a decrease in dislocation density, suggesting that the high strength under T4 heat treatment conditions arises from lattice distortion caused by supersaturated solute atoms. Conversely, T6 aging led to lattice relaxation approaching that of pure aluminum, yet simultaneously triggered a re-accumulation of dislocation density and micro-strain due to the coherency strain fields surrounding precipitates, which effectively impede dislocation motion. Therefore, rather than proposing a single, definitive optimization condition, this study aims to secure foundational data regarding the correlation between these microstructural descriptors and mechanical behavior, providing a guideline for balancing the strengthening contributions in transition metal-modified Al–Cu alloys. Full article

In recent years, honeycomb sandwich structures have seen continuous development due to their excellent structural performance and design flexibility in heat dissipation. However, their complex heat transfer mechanisms and diverse modes of thermal exchange necessitate research on the air flow behavior and temperature distribution characteristics of micro-channels and lattice pores. This study investigates the internal flow field within a ventilated honeycomb sandwich structure through numerical simulation. The spatial flow characteristics and temperature distribution are analyzed, with a focus on the effects of turbulent kinetic energy, heat flux distribution on the heated surface, and varying pressure drop conditions on the thermal performance. The results indicate that the micro-channels inside the honeycomb core lead to a strong correlation between temperature distribution, flow velocity, and turbulence intensity. Regions with higher flow velocity and turbulent kinetic energy exhibit lower temperatures, confirming the critical role of flow motion in heat transfer. Heat flux analysis further verifies that heat is primarily removed by airflow, with superior heat exchange occurring inside the honeycomb cells compared to the solid regions. The intensive mixing induced by highly turbulent flow within the small cells enhances contact with the solid surface, thereby improving heat conduction from the solid to the flow. Moreover, as the inlet pressure increases, the overall temperature gradually decreases but exhibits a saturation trend. This indicates that beyond a certain pressure level, further increasing the inlet pressure yields diminishing returns in heat dissipation enhancement. Full article

The influence of M site substitution in MCr₂O₄ nanoceramics on their properties is examined in this research. This study is an attempt to correlate the structural, morphological, and optical properties of M-site-modified chromites. The MCr₂O₄ nanoceramics-CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ were synthesized using a wet chemical sol–gel auto-combustion method, and all three samples were annealed for 4 h at 900 °C. X-ray diffraction analysis showed that the XRD patterns of CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ correspond to single-phase cubic crystal structures with the space group Fd-3m. Using the Scherrer equation, the crystallite sizes were found to be 9.86 nm, 6.73 nm, and 10.73 nm for CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄, respectively. Other parameters, including crystal structure, micro-strain, lattice constant, unit cell volume, X-ray density, packing factor, and the stacking fault of the calcined powder samples, were determined from data acquired from the X-ray diffractometer. Energy dispersive X-ray spectroscopy (EDX) was employed to confirm the appropriate chromite elements in their expected stoichiometric proportions, removed from other impurities. The identification of the functional groups of the samples was performed using Fourier Transform Infrared Spectroscopy (FTIR). The absorption bands characteristic of tetrahedral and octahedral coordination compounds of the spinel structure are found between 450 and 750 cm⁻¹ for all three samples in the spectrum. From the UV-absorption spectra, and using Tauc’s plot, the energy bandgap values for CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ were measured to be 1.66 eV, 1.82 eV, and 2.01 eV, respectively. The dielectric properties of the chromites were studied using an LCR meter. Frequency-dependent dielectric properties, including Dielectric constant and Tangent loss, were calculated. These findings suggest the feasibility of the use of these synthesized chromites for optical devices and other optoelectronic applications. Full article

Triply Periodic Minimal Surfaces (TPMSs) are mathematically defined surfaces that exhibit periodicity in three dimensions while maintaining a minimal surface property. TPMS-based lattices have gained significant attention in recent years, fueled by advancements in Additive Manufacturing (AM). These structures exhibit exceptional mechanical, thermal, and mass transfer properties, positioning them as a promising class of next-generation materials. However, fully leveraging their potential requires a comprehensive understanding of their design, properties, optimization, and applications. Given the hierarchical nature of TPMSs, achieving optimal performance requires multiscale optimization at the macro- and micro-levels. Addressing these complexities requires advanced computational methods to balance structural integrity and functional performance. In this narrative review, design strategies like functional grading and hybridization to create optimized TPMS-based lattices are summarized. Herein, the performance of such lattices in the mechanical, thermal, and mass transfer domains is focused upon. The role of topology optimization (TO) in the creation of architectured materials for specific application is discussed along with the emerging integration of machine learning. Furthermore, multidisciplinary applications of TPMS structures are examined, particularly in heat sinks, interpenetrating phase composites (IPCs), and biomimetic scaffolds, with their potential to enhance heat dissipation, structural resistance, and biomimicry of biological scaffolds. In addition, various additive manufacturing technologies for fabricating TPMS structures are reviewed, emphasizing how additive manufacturing allows high reproducibility construction of their complex geometry in a precise manner. Further unexplored areas of research are also discussed. Full article

Additive manufacturing enables the fabrication of lightweight structures with complex geometries, offering significant potential in aerospace and biomedical applications. Triply periodic minimal surface (TPMS) lattice structures are of particular interest due to their geometry. However, their intricate geometries pose challenges for both experimental characterization and numerical simulation. This study numerically investigates the effective mechanical properties and dynamic response of AlSi10Mg TPMS structures produced by laser powder bed fusion (PBF-LB/M). Using a micro–mesoscale approach with periodic boundary conditions, Young’s modulus, shear modulus, and Poisson’s ratio in the elastic region using the Johnson–Cook plasticity model are analyzed. Finite element simulations of the representative volume element (RVE) are employed to assess energy absorption and damage evolution under high strain rates, incorporating a ductile damage model. The performance of sheet-based TPMS lattices, namely, Schwarz–Primitive, Gyroid, Schwarz–Diamond, and IWP, is compared with strut-based lattices, namely, BCC and FCC, across volume fractions of 20–40%. Results demonstrate the superior stiffness and energy absorption of TPMS lattices, where Schwarz–Diamond and IWP outperformed the other structures, highlighting their advantages over conventional strut-based designs. This comprehensive numerical framework provides new insights into the high strain-rate behavior of TPMS structures and supports their design for demanding engineering applications. Full article

Self-fluxing Ni-based coatings (NiCrFeBSiC) were deposited through gas-flame spraying and evaluated in three conditions: as-sprayed, flame-remelted, and furnace-heat-treated (1025 °C/5 min). Phase analysis (XRD) revealed FeNi₃ together with strengthening carbides/borides (e.g., Cr₇C₃, Fe₂₃(C,B)₆); post-treatments increased lattice order. Cross-sectional image analysis showed progressive densification (thickness ~805 → 625 → 597 µm) and a drop in porosity from 7.866% to 3.024% to 1.767%. Surface roughness decreased from Ra = 31.860 to 14.915 to 13.388 µm. Near-surface microhardness rose from 528.7 ± 2.3 to 771.6 ± 4.6 to 922.4 ± 5.7 HV, while adhesion strength (ASTM C633) improved from 18 to 27 to 34 MPa. Wettability followed the densification trend, with the contact angle increasing from 53.152° to 79.875° to 89.603°. Under dry ball-on-disk sliding against 100Cr6, the friction coefficient decreased and stabilized (0.648 ± 0.070 → 0.173 ± 0.050 → 0.138 ± 0.003), and the counterbody wear-scar area shrank by ~95.6% (0.889 → 0.479 → 0.0395 mm²). Wear-track morphology evolved from abrasive micro-cutting (as-sprayed) to reduced ploughing (flame-remelted) and a polishing-like regime with a thin tribo-film (furnace). Potentiodynamic tests indicated the lowest corrosion rate after furnace treatment (CR ≈ 0.005678 mm·year⁻¹). Overall, furnace heat treatment provided the best structure–property balance (lowest porosity and Ra, highest HV and adhesion, lowest and most stable μ, and superior corrosion resistance) and is recommended to extend the service life of NiCrFeBSiC coatings under dry sliding. Full article

This study presents a viscosity-controlled epoxy infiltration strategy to mitigate common production defects, such as interlayer bond weaknesses, step gaps, and surface roughness, in 3D-printed polypropylene lattice and tube structures. To address these issues, epoxy resin infiltration was applied at four distinct viscosity levels. The infiltration process, facilitated by ultrasonic assistance, improved epoxy penetration into the internal structure. The results indicate that this method effectively reduced micro-voids and surface irregularities. Variations in epoxy viscosity significantly influenced the final internal porosity and the thickness of the epoxy film formed on the surface. These structural changes directly affected the energy absorption (EA) and specific energy absorption (SEA) of the specimens. While performance was enhanced across all viscosity levels, the medium-viscosity specimens (L-V2 and L-V3), with a mass uptake of ~37%, yielded the most favorable outcome, achieving high SEA (0.84 J/g) and EA (252 J) values. This improvement was mainly attributed to the epoxy filling internal voids and defects. Mechanical test results were further supported by SEM observations and validated through statistical correlation analyses. This work constitutes one of the first comprehensive studies to employ epoxy infiltration for defect mitigation in 3D-printed polypropylene structures. The proposed method offers a promising pathway to enhance the performance of lightweight, impact-resistant 3D-printed structures for advanced engineering applications. Full article

This work evaluates a hydrogen-fueled planar micro-combustor featuring three triply periodic minimal surface (TPMS) structures, namely, gyroid, lidinoid, and Neovius matrix lattices, aiming to advance heat transfer processes and enhance system efficiency in micro-thermophotovoltaic (MTPV) applications. Through three-dimensional numerical investigations, a series of simulations are conducted under varying TPMS lengths, inlet volume flow rate, and inlet equivalence ratios to optimize the design and operating conditions. The outcomes reveal that increasing the length of the TPMS structures is an effective means of improving heat transfer from the combustion zone to the walls, as indicated by significant increases in both mean wall temperature and radiation efficiency. However, longer internal structures reduce the uniformity of wall temperature and slightly increase entropy generation. Of the three topologies, the Neovius lattice demonstrates superior performance in all length scales, exhibiting a marginal improvement over the gyroid and a substantially greater advantage over the lidinoid structure. Increasing the inlet volume flow rate enhances wall temperature and its uniformity; however, the performance parameters decrease for all structures, indicating a limitation of the micro-combustor in benefiting from higher input power. Notably, the gyroid structure shows a lower rate of performance degradation at higher velocities, making it a potentially ideal design under such conditions. Finally, varying the equivalence ratio identifies the stoichiometric condition as optimal, yielding superior performance metrics compared to both lean and rich mixtures. Full article

The citrate–nitrate method was employed to synthesize the magnesium chromite (MgCr₂O₄) spinel, followed by calcination at 700 °C for 3 h. The synthesized compound was analyzed using techniques including powder XRD, SEM-EDAX, FTIR, UV-DRS, and LCR Meter. The structural analysis was conducted using an X-ray diffractometer, which revealed the formation of the cubic crystal symmetry of the sample with the corresponding Fd-3 m space group. The average crystallite size of the sample was calculated around 15.38 nm. Using tetrahedral and octahedral positions, the lattice vibrations of the associated chemical bonds were identified using Fourier transform infrared (FTIR) spectroscopy. SEM (scanning electron microscopy) micrographs showed that the spherical nature of the particles and the constituent particles were between 10 and 40 nm in size. The optical bandgap value was evaluated using Tauc’s plot. Pellets of the powdered sample were prepared for determining the dielectric aspects, such as the dielectric constant (ε′) and tangent loss (tanδ), in the frequency range of 10 Hz–8 MHz at room temperature. The charge transport mechanism was explored from the complex impedance spectroscopy study. The obtained results indicate that magnesium chromite may be a potential candidate in the fabrication of sensors, micro-electronic devices, etc. Full article

Laser powder bed fusion (L-PBF) enables the fabrication of complex lattice-type structures composed of thin struts, offering lightweight, high-strength advantages in aerospace and biomedical applications, among others. While extensive research has examined full lattices and process parameter effects individually, the combined influence of strut geometry, configuration, and processing conditions on mechanical properties remains less understood. This study investigates how the strut number, strut size, cross-sectional shape, and laser energy input affect the mechanical properties of thin-strut L-PBF tensile specimens. Ti-6Al-4V struts were designed and fabricated using an EOS M270 system using five linear energy density (LED) levels. The fabricated specimens were measured in porosity using micro-scaled computed tomography and further evaluated using a tensile tester. The results showed that increasing the strut number leads to significant reductions in tensile strength, even with the same overall cross-sectional area, especially at low LED levels. Size effects on mechanical strengths were observed, though mostly minimal, except at the smallest strut size, where defects tend to be more critical. Circular and square shapes performed similarly under general LED conditions; however, square struts exhibited inferior behavior at the lowest LED level. Overall, LED is the most influential factor, with the greatest tensile strength occurring near 0.2 J/mm; further decreasing or increasing the LED both increase the porosity, degrading mechanical strengths. Full article

Hierarchically porous polymers can unite macro-scale architected voids with micro-scale pores, enabling unique combinations of low density, high surface area, and controlled transport properties that are difficult to achieve with traditional methods. This review outlines the current advancements in creating such multiscale architectures using fused filament fabrication (FFF), the most widely used polymer additive manufacturing technique. Unlike earlier reviews that consider lattice architectures and foaming chemistries separately, this work integrates both within a single analysis. It begins with an overview of FFF fundamentals and how process parameters affect macropore formation. Design strategies for achieving macroporosity (≳100 µm) with a single thermoplastic are presented and categorized: 2D infill patterns, strut-based lattices, triply periodic minimal surfaces (TPMS), and Voronoi structures, along with functionally graded approaches. The discussion then shifts to functional filaments incorporating chemical or physical blowing agents, thermally expandable or hollow microspheres, and sacrificial porogens, which create microporosity (≲100 µm) either in situ or through post-processing. Each material approach is connected to case studies that demonstrate its application. A comparative analysis highlights the advantages of each method. Key challenges such as viscosity control, thermal gradient management, dimensional instability during foaming, environmental concerns, and the absence of standardized porosity measurement techniques are addressed. Finally, emerging solutions and future directions are explored. Overall, this review provides a comprehensive perspective on strategies that enhance FFF’s capability to fabricate hierarchically porous polymer structures. Full article

The present study investigates passive microdroplet generation in a T-junction microchannel using microscopic observations, microscale particle image velocimetry (Micro-PIV) visualization, and lattice Boltzmann simulations. The key flow regimes, i.e., dripping, threading, and parallel flow, are characterized by analyzing the balance between hydrodynamic forces and surface tension, revealing the critical role of the flow rate ratio of the continuous to dispersed fluids in regime transitions. Micro-PIV visualizes velocity fields and vortex structures during droplet formation, while a lattice Boltzmann model with wetting boundary conditions captures interface deformation and flow dynamics, showing good agreement with experiments in the dripping and threading regimes but discrepancies in the parallel flow regime due to neglected surface roughness. The present experimental results highlight non-monotonic trends in the maximum head interface and breakup positions of the dispersed fluid under various flow rates, reflecting the competition between the squeezing and shearing forces of the continuous fluid and the hydrodynamic and surface tension forces of the dispersed fluid. Quantitative analysis shows that the droplet size increases with the flow rate of continuous fluid but decreases with the flow rate of dispersed fluid, while generation frequency rises monotonically with the flow rate of dispersed fluid. The dimensionless droplet length correlates with the flow rate ratio, enabling tunable control over droplet size and flow regimes. This work enhances understanding of T-junction microdroplet generation mechanisms, offering insights for applications in precision biology, material fabrication, and drug delivery. Full article

The effect of surface roughness in laminar flow has been the focus of recent research related to drag reduction. However, although particle transport is governed by laminar flow in most applications, the effect of surface texture on the drag of a sphere has mostly been addressed in the transitional and turbulent regimes. The aim of the present study is to explore the drag behavior of rough spherical micro-particles in laminar flow. The spheres’ roughness has been structured based on a 3D complex Weaire–Phelan model, as well as on a simpler orthogonal lattice one, and quantified as per various definitions. The emerging surface roughness comprises irregular elements in terms of shape and size. The investigation has been performed at Reynolds numbers ranging from 2 to 8. The drag coefficient is found to drop quadratically with increasing roughness. Relative roughness can reduce the total drag on the particle by over 21%. The key physical mechanism is explained by the particles’ surface cavities, which contain recirculating, nearly stagnant fluid, thus creating a self-lubricating effect that reduces skin friction, as the main flow skims over the top without entering the cavities. A reduction in total drag arises when skin friction drag reduction is larger than the increase in form drag. Understanding the drag behavior of spherical particles with irregular surface texture provides new and useful insight into low Reynolds number transport phenomena related to a variety of engineering applications. Full article

The structural features of Sb–doped (Ti,Zr)NiSn and (Ti,Zr,Hf)NiSn half-Heusler (HH) thermoelectrics have been identified down to the atomic scale using a combination of transmission electron microscopy (TEM) techniques. TEM sheds light on the morphology, phases present, size distributions and elemental variations between the two samples. Both materials consist of the HH phase, at both micro- and nanoscale levels, and comprise particles with two size ranges, 115 and 223 nm, on average, for large HH particles and 4–17 nm for nanoparticles for both materials. Hf incorporation in the HH lattice brought upon significant elemental fluctuations, manifested in chemical profiles and lattice parameter variations measured by post-experimental image analysis. The increased elemental variations induced by Hf substitution significantly contributed to the low thermal conductivity values and high power factor, leading to an enhanced figure of merit of 0.76 at 762 K for (Ti,Zr,Hf)NiSn, demonstrating the capability of TEM to confirm the structural features that are responsible for improved TE performance. Full article

The single-crystal diamond (SCD), owing to its extreme physical and chemical properties, serves as an ideal substrate for quantum sensing and high-frequency devices. However, crystal anisotropy imposes significant challenges on fabricating high-quality micro-nano structures, directly impacting device performance. This work investigates the effects of femtosecond laser processing on the SCD under two distinct crystallographic orientations via single-pulse ablation. The results reveal that ablation craters along the <100> orientation exhibit an elliptical shape with the major axis parallel to the laser polarization, whereas those along the <110> orientation form near-circular craters with the major axis at a 45° angle to the polarization. The single-pulse ablation threshold of the SCD along <110> is 9.56 J/cm², representing a 7.8% decrease compared to 10.32 J/cm² for <100>. The graphitization threshold shows a more pronounced reduction, dropping from 4.79 J/cm² to 3.31 J/cm² (31% decrease), accompanied by enhanced sp² carbon order evidenced by the significantly intensified G-band in the Raman spectra. In addition, a phase transition layer of amorphous carbon at the nanoscale in the surface layer (thickness of ~40 nm) and a narrow lattice spacing of 0.36 nm are observed under TEM, corresponding to the interlayer (002) plane of graphite. These observations are attributed to the orientation-dependent energy deposition efficiency. Based on these findings, an optimized crystallographic orientation selection strategy for femtosecond laser processing is proposed to improve the quality of functional micro-nano structures in the SCD. Full article