Search Results (284)

Sn-3Ag-0.5Cu-xBi alloys (SAC305-xBi) represent promising lead-free alternatives for low-temperature soldering. Low Bi concentrations can strengthen SAC-based solders through solid-solution strengthening, refining β–Sn grains and transforming needle-like Ag₃Sn phases into equiaxed morphologies. However, excessive Bi alloying may induce precipitation of brittle Bi particles, cause microstructural instability and interfacial degradation, thereby weakening the solder joint performance. As such, the concentration of Bi in the SAC305 alloys should be carefully controlled. In this work, the microstructure and corrosion behavior of Sn-3Ag-0.5Cu-xBi solder alloys (SAC305-xBi, where x = 0, 1, 2 and 4 wt. %) were investigated. Attention has been paid to the influence of low Bi concentration on the microstructure, morphology, and chemical composition of the phases present in the solder alloys before and after corrosion exposure. The alloys were prepared by induction melting of Sn, Ag, Cu and Bi lumps under Ar gas. The microstructure of the SAC305 and SAC305-1Bi alloys represented a hypoeutectic microstructure with dendritic (Sn) grains and the ternary eutectic, consisting of (Sn), Cu₆Sn₅ and Ag₃Sn, located in inter-dendritic regions. In the SAC305-2Bi and SAC305-4Bi alloys, a segregation of (Bi) particles was observed in addition to dendritic (Sn) and ternary eutectic. The (Bi) particles were located at the (Sn)Ag₃Sn interface in the inter-dendritic spaces of the (Sn) solid solution. The corrosion resistance of the as-cast alloys was studied in aqueous NaCl electrolyte (3.5 wt. %) using electrochemical methods. Open circuit potentials of the alloys were found to increase with increasing concentration of Bi. The highest corrosion current was found for the SAC305-1Bi alloy. It was observed that micro-galvanic cells at the Sn-Ag₃Sn interface were the initiating factors of corrosion in the SAC305-1Bi alloy. The corrosion activity of the SAC305-1Bi alloy is related to the high density of fine Ag₃Sn particles. The higher fraction of Ag₃Sn particles provided a dense network of local galvanic interaction sites, leading to the acceleration of the corrosion rate. The presence of discrete Bi precipitates in the SAC305-2Bi and SAC305-4Bi alloys, on the other hand, partially reduced the risk of galvanic corrosion. Since Bi has a higher standard electrode potential compared to Sn, the Bi/Ag₃Sn and Bi/Cu₆Sn₅ couples were less prone to corrosion. The corrosion mechanism of the SAC305-xBi alloys is discussed, and results are compared to previously studied SAC-Bi alloys. Full article

Polyimide (PI) film is a widely used insulation material in high-frequency power equipment, yet its frequency–lifetime relation and terminal discharge features have rarely been resolved together over a complete ageing trajectory. This paper reports three contributions. First, a condition-specific frequency–lifetime relation for PI surface insulation is presented, in which the discharge inception voltage is frequency-invariant while the flashover voltage and the surface lifetime both fall with frequency. Second, a stage-resolved discharge morphology derived from phase-resolved patterns is proposed, in which a late-stage finger-like cluster serves as a candidate flashover precursor, complemented by a count-aware, time-normalised discharge activity proxy. Third, a space-charge interpretation linking the per-cycle charge injection budget growth at high frequency to the suppressed inter-cycle dissipation, jointly accounting for the lifetime relation and the non-dendritic damage morphology, is presented. The fitted lifetime relation provides a quantitative planning basis over the tested 10–40 kHz grid for insulation design of high-frequency power equipment, and the finger signature provides a candidate device-level morphological criterion for online monitoring. Full article

The Pulse Magneto Oscillation (PMO) solidification homogenization technique has been successfully applied in the continuous casting production of GCr15 bearing steel. To further investigate the effects of PMO technology on the precipitation mechanisms of primary carbides in GCr15 bearing steel, a series of directional solidification experiments were conducted under the influence of PMO. Characterization and analysis of the area proportion, number density, particle-size distribution, elemental distribution, and types of primary carbides in the as-cast bearing steel under various PMO parameters were conducted using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), and Electron Backscatter Diffraction (EBSD). The findings reveal that the predominant carbide species precipitated in GCr15 bearing steel is M₃C type, characterized by a higher Cr content. As the PMO peak current and pulse frequency increase, there is a significant reduction in both the area proportion and number density of primary carbides. Compared to non-PMO conditions, the application of PMO results in a maximum decrease in carbide area proportion by up to 75.6% and a reduction in number density by up to 58.4%, leading to a more dispersed and uniform carbide distribution. Moreover, under the influence of PMO, the local solidification duration of the solution shortens, leading to an increase in the quantity of inclusions such as MnS, which undergo refinement. This facilitates the refinement of primary carbides that utilize inclusions as heterogeneous nucleation sites. Additionally, the reduction in dendritic arm spacing within the solidification structure and the enhancement of solute distribution near the solid–liquid interface, induced by PMO, also create favorable conditions for the reduction in size and quantity of primary carbides. Based on the distinctive characteristics of primary carbides under varying PMO parameters, an innovative dynamic model for the formation of primary carbides during the solidification process of GCr15 bearing steel has been proposed. Full article

Scaphopod molluscs are marine, infaunal, cosmopolitan animals. They encase their soft tissue with an aragonitic tusk-shaped shell that has at its two ends an orifice, the aperture and the apex. We investigated the shell of the dentaliid species Fissidentalium metivieri and Antalis weinkauffi and characterized shell crystal organization with electron backscatter diffraction (EBSD) and laser confocal and scanning electron microscopies. Based on crystal size, morphology, organization and growth-line spacing, we distinguish five different crystal arrangement motifs in the investigated shells. We find two slightly different microstructures for the shell proper, two microstructures for the attachment of muscles to the shell and one microstructure for a secondary hard tissue growth product, secreted at the apical orifice. Crystal organization motifs are crossed-lamellar, dendritic and prismatic. Crystal textures are crossed-lamellar, axial-like and crossed-lamellar-like. Crystal organization with a crossed arrangement is utilized for shell formation by representatives of many Ca-carbonate shell-secreting mollusc classes/subclasses: Scaphopoda, Gastropoda, Bivalvia, Polyplacophora (crossed-lamellar), and Patellogastropoda (crossed-foliated). Based on structural–crystallographic attributes, we highlight a basic shell structure that is broadly similar for the species of these mollusc classes/subclasses. However, this basic crystal arrangement motif is significantly modulated by the specific crystal organization that is inherent for a particular mollusc class/subclass. Full article

Aluminum metallic foams are lightweight porous materials characterized by low density, high stiffness, and remarkable energy absorption capacity. The mechanical performance of these materials strongly depends on the microstructure of the metallic matrix and the porous structure. In this study, closed-cell A356 aluminum foams were produced by the Alporas melt-foaming method using barite (BaSO₄) as a thickening agent and calcium carbonate (CaCO₃) as a foaming agent. The effect of grain refinement on the microstructure and energy absorption behavior under quasi-static compression was investigated. Grain refinement was evaluated by adding four concentrations of Al-5Ti-1B master alloy (0.02, 0.05, 0.08, and 0.10 wt.%) to the unrefined foam. The addition of Al-5Ti-1B reduced the secondary dendrite arm spacing (SDAS) from 41.85 µm to a minimum of 32.96 µm at 0.05 wt.%, producing stronger and more homogeneous cell walls that increased the plateau stress from 0.525 to 1.549 MPa and the energy absorption capacity from 0.299 to 0.735 MJ/m³—improvements of 195% and 145%, respectively. The energy absorption efficiency analysis confirmed that any refiner concentration improved the compressive performance compared to the unrefined foam. In addition, the energy absorption efficiency (E) and the ideality energy absorption efficiency (I) confirm that the refinement of the dendritic structure through Al-5Ti-1B addition strengthens the foam cell walls, improving their mechanical behavior and performance as an energy-absorbing material under quasi-static compression. Full article

To simultaneously suppress shrinkage-related defects and refine the solidification microstructure of Mn70Ni25Cr5 alloy ingots, ProCAST simulation was combined with Box–Behnken response surface methodology to optimize pouring temperature, filling time, and mold temperature. Porosity in the ingot body and secondary dendrite arm spacing (SDAS) were selected as the response variables, and quadratic regression models were established for both responses. The optimized casting parameters were determined using analysis of variance, response surface analysis, and the desirability function approach. The porosity and SDAS models were both statistically significant, with non-significant lack-of-fit terms and R² values of 0.9906 and 0.9901, respectively. The optimal parameters were a pouring temperature of 1220.74 °C, a filling time of 6.34 s, and a mold temperature of 294.47 °C, corresponding to a predicted porosity of 0.426% and a predicted SDAS of 47.51 μm. A supplementary simulation and a validation casting experiment were then performed using practical process settings derived from the optimized solution. The supplementary simulation indicated that shrinkage-related defects were concentrated mainly in the riser, while metallographic examination revealed no large continuous shrinkage-porosity region in the examined ingot-body sections. The overall measured SDAS across the center, half-radius, and edge positions was 48.54 μm, differing from the response-surface prediction by approximately 2.2%. These results support the applicability of the combined ProCAST–RSM approach for simulation-assisted optimization of Mn70Ni25Cr5 alloy casting parameters within the investigated process range. Full article

This study systematically investigates the synergistic effects of Sr and La-Ce mixed rare earth (RE) additions on the microstructure and mechanical properties of AlSi9Cu3 alloy. The results show that adding 0.02 wt.% Sr and 0.10 wt.% RE together produces the most pronounced refinement, reducing the secondary dendrite arm spacing (SDAS) from 40.12 μm to 26.98 μm and decreasing the aspect ratio of eutectic Si from 12.3 to 7.8. Sr modifies eutectic Si by inducing twin formation and suppressing anisotropic growth, while RE promotes the dispersion distribution of Al₄Ce phases and enhances constitutional undercooling. The synergistic effect leads to a more uniform appearance of dendrites and secondary phases. Consequently, the tensile strength reaches 258.6 MPa, accompanied by a transition in fracture mode from brittle cleavage to ductile dimple fracture. This work provides experimental support for microstructural control and the strengthening–toughening design of AlSi9Cu3 alloys. Full article

In the present study, the influence of microstructural morphology and dendritic refinement on the electrochemical corrosion behavior of directionally solidified aluminum-based structures (columnar and equiaxed) with Si contents between 6 and 12.6 wt. % was investigated in a 0.5% NaCl solution at room temperature. Corrosion resistance was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The directional solidification process was repeated for each of the alloy compositions at different cooling rates, yielding different secondary dendritic spacing values. The columnar-to-equiaxed transition (CET) was observed to occur when the temperature gradient in the melt decreased to values between −1.85 and 0.75 °C/cm. In addition, a small increase in the microhardness values was observed as a function of the Si content. The same applies to tensile strength values. The values of the polarization resistance are used as a basic criterion for the evaluation of the corrosion resistance of alloys. The columnar grain zone presents higher corrosion resistance than the equiaxed grain zone, despite presenting coarser dendritic spacing. This behavior contrasts with the commonly expected improvement in corrosion resistance associated with microstructural refinement and indicates that passive-layer stability and cathodic phase distribution play a dominant role in the electrochemical behavior. When the polarization resistance decreases with the increase in the distance from the base, the grain size and secondary dendritic arm spacings increase. In addition, when the polarization resistance increases, the critical temperature gradient decreases. This work allows us to conclude that the modification of thermal parameters in the solidification process can be used for the development of an optimized microstructure morphology and to optimize corrosion resistance in Al–Si alloys through control of dendritic spacing and passive film formation mechanisms. Full article

Neurons achieve their highly polarized architecture by coordinating cytoskeletal systems across space and time, enabling axons to extend over remarkable distances and dendrites to elaborate complex arbours. Early neuroanatomists described intracellular “neurofibrils,” yet these structures remained poorly understood until electron microscopy resolved them into three distinct polymer systems: microtubules, actin filaments, and intermediate filaments. Although this framework clarified neuronal ultrastructure, it simultaneously established a conceptual hierarchy in which microtubules and actin were regarded as the principal drivers of neurite growth, while intermediate filaments were relegated to a passive, supportive role. Unlike prior reviews that document vimentin dynamics primarily from a cell-biological standpoint, this review integrates historical, conceptual, and epistemological perspectives to examine both how and why that hierarchy arose and how it has been dismantled. This review traces how that hierarchy arose and why it has been increasingly reconsidered in favour of intermediate filaments, focusing on vimentin as a case study. Evidence from live cell imaging, molecular manipulation, and genetic models shows that vimentin is dynamically regulated rather than static. Vimentin networks remodel continuously, exchange subunits with soluble pools, and move in coordination with microtubules. Most recently, sparse single-filament labelling combined with correlative volume electron microscopy has demonstrated that individual vimentin filaments remain motile even within dense perinuclear networks previously assumed to be static, a finding that fundamentally redefines what filament density implies about cytoskeletal organization. In neural and neural precursor cells, vimentin expression is developmentally regulated and is prominent during early differentiation stages associated with neurite initiation giving way to neurofilaments in mature neurons. Functional studies further link vimentin to neurite formation and extension, cytoskeletal coordination, organelle positioning, and cellular stress responses. Philosophical analysis reveals that these empirical advances were inseparable from shifts in imaging technology and conceptual framing, and that epistemic risks including model dependency and confirmation bias can be mitigated through methodological pluralism and explicit model disclosure. Taken together, these findings support a revised understanding of intermediate filaments as active, context-dependent contributors to neuronal development and plasticity, and illustrate the value of integrating biological evidence with historical and philosophical reflection. Full article

The influence of Cu content on the thermal conductivity and mechanical properties of Al-9Si-0.7Fe casting alloy were investigated in this paper. The results show that as the Cu content increases from 0.1 wt.% to 2.0 wt.%, the thermal conductivity of the alloy decreases from 173.6 W/(m·K) to 154.8 W/(m·K), while the yield strength increases from 72.2 MPa to 90.9 MPa. Metallographic, XRD, and EPMA analyses revealed that Cu has a relatively small impact on the secondary dendrite arm spacing of α-Al and the morphology of eutectic silicon. Its influence on the thermal conductivity and mechanical properties primarily stems from Cu atoms dissolving in the α-Al matrix, leading to a decreased lattice constant, increased lattice distortion, enhanced electron scattering, and improved solid solution strengthening effect. Based on the measured solubility of Cu, the Maxwell and Hashin–Shtrikman thermal conductivity models were modified. The correlation coefficients between the predicted values of the modified models and the experimental data were 92.77% and 93.11%, respectively, indicating a significant improvement in prediction accuracy. Full article

This study investigates the effect of complex nanomodification combined with the simultaneous application of magnetic fields and mechanical vibration on the structure formation and performance properties of medium-alloy steel 40CrNi3MoV. Improving the structural homogeneity and operational characteristics of such steels remains an important task due to their widespread use in components operating under severe loading and wear conditions. The introduction of the nanostructured modifier InSteel-7 at a concentration of 0.03%, together with simultaneous magnetic and vibrational treatment of the melt, resulted in pronounced structural homogenization and grain refinement. Quantitative metallographic analysis using Thixomet Pro image analyzer revealed a significant refinement of the dendritic structure, with the secondary dendrite arm spacing decreasing from 73.9 μm to 27.9 μm. X-ray phase analysis confirmed the preservation of phase composition while indicating increased structural uniformity of the BCC matrix. Energy-dispersive spectroscopy and elemental micro-mapping demonstrated high chemical purity of the alloy and a uniform distribution of the modifier components. The combined treatment significantly improved the mechanical and tribological characteristics of the material. The average hardness increased from 390 HV to 510 HV, while tribological tests showed a reduction in wear track depth from 5.16 μm to 0.87 μm and a decrease in surface roughness from Ra 2.13 μm to 0.20 μm, indicating enhanced wear resistance. Full article

Directional solidification technology is the core process for manufacturing single-crystal blades in aero-engines, but transverse grain boundaries caused by the competitive growth of polycrystals severely degrade blade performance. To gain a deeper understanding of polycrystalline competitive growth behavior, this study investigates the competitive growth of polycrystals during directional solidification under natural convection based on the phase field and lattice Boltzmann coupling model. By adjusting the solutal expansion coefficient, grain configuration, and pulling velocity, the influence of the flow field on polycrystalline competitive growth is analyzed. The results indicate that changes in the solutal expansion coefficient affect the dendritic competition process and outcome, particularly for dendrites with larger favorably oriented (FO) angles, which are more likely to be eliminated at higher solutal expansion coefficients. Additionally, grain configurations with greater orientation differences between adjacent dendrites are more sensitive to changes in the solutal expansion coefficient, whereas configurations with smaller orientation differences are less affected. It was also found that as the pulling velocity increases, the primary dendrite arm spacing decreases and the growth direction of the dendrites deflects towards the temperature gradient direction. This leads to a reduction in vortices at the dendrite tips and grain boundaries, thereby decreasing the overall flow field intensity. During dendrite growth, solute is rejected from the solid phase, creating a concentration gradient between the dendrite tips and the liquid region. This induces convection in the liquid phase. The interaction between the flow field and the solute concentration in the liquid phase causes the flow field strength and solute concentration to exhibit periodic fluctuations. Full article

Nickel-based superalloy GH3625 is widely used in extreme environments due to its exceptional high-temperature strength and corrosion resistance; however, optimizing its comprehensive performance through precise microstructural control remains a critical challenge. In this study, the effect of withdrawal rate (10–200 μm/s) on the microstructural evolution, mechanical properties, and corrosion resistance of GH3625 alloy was investigated using a liquid-metal-cooled directional solidification system. The microstructural characteristics, elemental segregation, and phase distributions were systematically analyzed via OM, SEM, and EDS, followed by uniaxial tensile and electrochemical polarization tests. The results show that with increasing withdrawal rate, the solid–liquid interface morphology evolves from cellular to cellular-dendritic and finally to fully dendritic. Correspondingly, the primary dendrite arm spacing decreases from 270.4 μm to 100.2 μm, and the secondary dendrite arm spacing decreases from 66.5 μm to 12.3 μm. The area fraction of the detrimental Laves phase first decreases and then increases, reaching a minimum at 100 μm/s. Correspondingly, the yield strength increases from 282 MPa to 409 MPa, and the corrosion resistance is optimized at 100 μm/s. The microstructure–property relationships are discussed based on second-phase strengthening theory and microstructural refinement. This study provides a theoretical basis and practical process windows for optimizing directional solidification parameters to achieve enhanced mechanical and corrosion performance in GH3625 alloy. Full article

Laser-directed energy deposition (DED) using wire or powder feedstock is a promising way to fabricate prototypes in rapid time, including complex metal parts for advanced engineering applications. In this work, AISI 316L stainless steel—a well-known, weldable alloy model—was used to perform a foundational comparative study of wire-fed (LW-DED) and powder-fed (LP-DED) processes, establishing a baseline before progressing to high-temperature alloys. Hollow cylindrical specimens were fabricated and characterized microstructurally and mechanically. LP-DED produced a refined cellular–dendritic structure with primary dendrite arm spacing of 3.29 ± 0.49 µm and slightly higher average hardness (226 ± 8 HV0.2), accompanied by fine, spherical porosity inherent to the powder feedstock. LW-DED generated coarser epitaxial columnar dendrites (5.15 ± 0.69 µm) and slightly lower hardness (206 ± 10 HV0.2) but achieved nearly full density and high material catching efficiency. The results indicate that both methods yield comparable deposits when parameters are controlled, with LP-DED offering enhanced microstructural refinement and LW-DED providing faster deposition and higher build volume. These findings provide practical guidance for the additive manufacturing of high-performance parts and establish a baseline for the application of DED processes to advanced alloys. Full article

In this study, we examine an ex-service, Ni-base single-crystal blade made of alloy PWA1483, which was in service for 6000 h. Using light optical, scanning, and transmission electron microscopy, we analyzed the microstructure at the blade’s tip, middle, and root. Key focus areas included surface features, dendrite spacings, γ’-particle sizes, and dislocation densities. The findings reveal that the bulk microstructure hardly evolved. Dendrite spacings exhibited a consistent microstructure across all locations and there were no significant differences between the local alloy chemistries of dendritic and interdendritic regions, indicating high-quality processing. A bimodal γ’-particle distribution was observed. Variations in γ’-sizes and γ-channel widths were noted, with the tip showing rounded γ’-particles. Small spherical particles occurred only in the root and middle of the blade. The middle location exhibited the highest hardness. Dislocation densities were low and uniform, with the highest density correlating with the highest hardness. Full article