Search Results (83)

The mechanical performance of cast iron is strongly governed by the morphology of its graphite phase, yet establishing a quantitative link between microstructure and macroscopic properties remains a challenge. In this study, a three-dimensional finite element method (FEM)-based micromechanical framework is proposed to analyze and predict the mechanical behavior of cast iron with representative graphite morphologies, spheroidal and flake graphite. Realistic representative volume elements (RVEs) are reconstructed based on experimental microstructural characterization and literature-based X-ray computed tomography data, ensuring geometric fidelity and statistical representativeness. Cohesive zone modeling (CZM) is implemented at the graphite/matrix interface and within the graphite phase to simulate interfacial debonding and brittle fracture, respectively. Full-field simulations of plastic strain and stress evolution under uniaxial tensile loading reveal that spheroidal graphite promotes uniform deformation, delayed damage initiation, and enhanced ductility through effective stress distribution and progressive plastic flow. In contrast, flake graphite induces severe stress concentration at sharp tips, leading to early microcrack nucleation and rapid crack propagation along the flake planes, resulting in brittle-like failure. The simulated stress–strain responses and failure modes are consistent with experimental observations, validating the predictive capability of the model. This work establishes a microstructure–property relationship in multiphase alloys through a physics-informed computational approach, demonstrating the potential of FEM-based modeling as a powerful tool for performance prediction and microstructure-guided design of cast iron and other heterogeneous materials. Full article

It is known that the addition of SrO heterogeneous nucleation site particles can refine the microstructure of SUS316L stainless steel additively manufactured (AMed) by powder bed fusion (PBF). In this study, this idea was confirmed by directed energy deposition (DED). However, there are several types of DED machines, and the energy system and the material supply system of these machines are different depending on each machine. In this study, the grain refinement behavior and the formability of AMed SUS316L stainless steel with the addition of SrO heterogeneous nucleation site particles are evaluated using a single-beam type LAMDA 200 machine and a multi-beam type ALPION Series machine. The size of the melt pool made by the ALPION Series machine is smaller than that of the LAMDA 200 machine, which results in a shorter residence time in the liquid state of the melt pool for the ALPION Series machine. The grains formed in the inoculated sample manufactured by the ALPION Series machine under the unidirectional scanning strategy are found to be refined compared to those in the uninoculated sample. On the other hand, it is found that the formation of defects and the crystallographic texture observed in the samples manufactured by the LAMDA 200 machine is suppressed by the addition of SrO heterogeneous nucleation site particles. These differences between the ALPION Series and LAMDA 200 machines would come from the differences in the melting state, including temperature, cooling conditions, and re-heating. Full article

Heterogeneous ice nucleation is a key process for ice cloud formation, snowfall, and freezing of water bodies. Ice nucleating particle (INP) cloud feedbacks are one of the largest sources of uncertainties in Earth’s Energy Budget. Although INPs are essential in the development of mixed-phased and glaciated clouds, their composition, sources, and cloud feedbacks remain poorly constrained. Previous studies have shown mixed results on the potential of light-absorbing particles (LAP), such as black carbon (BC) and high latitude dust (HLD), serving as INPs. However, many of these studies use laboratory or model-generated particles that may not represent the complex morphology and behaviors of ambient light-absorbing particles sufficiently. Here, we use in situ surface snow samples, collected during Spring 2018 in Svínafellsjökull, Iceland. The samples were analyzed by an immersion freezing mechanism for their ice nucleation activity (INA). Portions of the filtered samples were concentrated by lyophilization to observe the potential enhancement of INA. We investigated environmental samples of deposited aerosols to better understand the role activity of HLD and BC in ice nucleating activity in mixed-phase clouds in Iceland. We found concentrations of 16 ± 27 ng g⁻¹ and 33 ± 66 × 10⁶ ng g⁻¹ for BC and HLD, respectively. However, we found that isolated methanol-soluble organic aerosols have a more prominent role than BC and HLD in Iceland. We conclude that BC and HLD are insignificant INP but that they can inhibit INA from other INP. Full article

Molecular dynamics simulations of nanoindentation were conducted to compare the dislocation behavior in a pure V and a TiVTa multi-principal element alloy (MPEA) with [100] and [111] crystal orientations. It is found that the significant resistance to dislocation motion and loop formation in the TiVTa MPEA compared to pure V, attributed to its substantial lattice distortion. While dislocation nucleation was heterogeneous in both materials with similar activation volumes and nucleation stresses (approximately 0.2 G), the dislocation density and plastic zone volume in TiVTa were substantially lower. Under standard indentation conditions, independent dislocation loops readily formed in pure V but were absent in TiVTa. With a larger indenter size and a greater nanoindentation depth, the results demonstrated that forming loops in TiVTa requires significantly higher force, directly linking this effect to the hindrance of dislocation glide by chemical disorder and lattice distortion. This study provides atomic-scale insights into the deformation mechanisms of TiVTa MPEAs, offering guidelines for future alloy design. Full article

This study aimed to solve two problems of polyethylene terephthalate (PET) films, namely, their slow crystallization rate and insufficient thermal stability, by using polyethylene naphthalate (PEN) as a modifier to prepare PET-PEN blends with varying PEN contents (0%, 0.9%, 1.8%, and 9%). Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and other methods were used to systematically investigate the effects of the PEN content and cooling rate (5–40 °C/min) on the non-isothermal crystallization behavior and kinetics of the blends. The results indicate that PET and PEN exhibit excellent compatibility. As the PEN content increases, the glass transition temperature (T_g) of the blend increases, while the melting point (T_m) and relative crystallinity decrease. PEN exerts an effect on the crystallization temperature (T_c)—“heterogeneous nucleation—diffusion control—steric hindrance effect”. The cold crystallization behavior depends on the PEN content and cooling rate. Samples with PEN content did not exhibit cold crystallization at low cooling rates. The observed non-isothermal crystallization kinetics show that PEN transforms the growth dimension of PET crystals from three-dimensional to two-dimensional, significantly reducing the absolute values of the crystallization rate constant (Z_c) and crystallization activation energy (ΔE). ΔE tends to stabilize when the PEN content reaches or exceeds 1.8%. In summary, PEN achieves precise control of PET non-isothermal crystallization through the mechanism of “heterogeneous nucleation—diffusion control—steric hindrance effect”. The research results provide theoretical support for the optimization of processing technology for PET-PEN blend films in high-end fields such as food packaging and electronic insulation. Full article

Amorphous hydrogenated germanium–carbon alloys (Ge_1−xC_x:H) were synthesized by X-ray-activated Chemical Vapor Deposition and investigated to evaluate the effects of annealing on their structure, composition, and properties given the limited information available on their behavior at high temperatures. Thermogravimetric and elemental analyses showed that the materials are stable up to 573 K; above this temperature, the carbon and hydrogen content progressively decrease, favoring structural reorganization. XRPD and Raman analyses demonstrate that the as-deposited films are fully amorphous, while annealing promotes the progressive formation of crystalline Ge. This crystallization occurs heterogeneously through the nucleation of small “islands” embedded within the sample matrix. Optical measurements reveal a narrowing of the band gap with increasing annealing temperature and time. The weak contribution of sp²-carbon observed in some Raman spectra indicates that band gap reduction is mainly governed by the overall composition and the variation of germanium hydrogen bonding configuration, rather than by graphitization. The study also notes that the parameter B^1/2 does not follow a regular trend due to the complex nature of the material’s microstructural evolution during annealing. These results provide a comprehensive picture of the annealing-driven transformations in Ge–C:H alloys relevant for the design of thermally stable optoelectronic materials. Full article

Polyaniline (PANI) nanofibers (NFs) were synthesized via two chemical oxidative polymerization approaches: a rapid mixing process and a conventional stirred tank method. PANI is a promising electrode material for supercapacitors due to its conductivity, stability, and pseudocapacitive redox behavior. The rapid mixing route proved especially effective, as fast polymerization promoted homogeneous nucleation and yielded thin, uniform, and interconnected NFs, whereas conventional stirring produced thicker, irregular fibers through heterogeneous nucleation. Structural characterization (FTIR, UV-Vis, XRD, XPS, TGA) confirmed that both samples retained the typical emeraldine form of PANI, but morphological analyses (SEM, BET) revealed that only the rapid process preserved nanofiber uniformity and porosity. This morphological control proved decisive for electrochemical behavior: symmetric supercapacitor devices fabricated from rapidly synthesized NFs delivered higher specific capacitances (378.8 F g⁻¹ at 1 A g⁻¹), improved rate capability, and superior cycling stability (90.33% retention after 3000 cycles) compared to devices based on conventionally prepared NFs. These findings demonstrate that rapid polymerization offers a simple and scalable route to morphology-engineered PANI electrodes with enhanced performance. Full article

Solid-state lithium batteries (SSLBs) have emerged as a promising alternative to conventional lithium-ion systems due to their superior safety profile, higher energy density, and potential compatibility with lithium metal anodes. However, a major challenge hindering their widespread deployment is the formation and growth of lithium dendrites, which compromise both performance and safety. This review provides a comprehensive and structured overview of recent advances in dendrite suppression strategies, with special emphasis on the role played by the nature of the solid electrolyte. In particular, we examine suppression mechanisms and material innovations within the three main classes of solid electrolytes: sulfide-based, oxide-based, and polymer-based systems. Each electrolyte class presents distinct advantages and challenges in relation to dendrite behavior. Sulfide electrolytes, known for their high ionic conductivity and good interfacial wettability, suffer from poor mechanical strength and chemical instability. Oxide electrolytes exhibit excellent electrochemical stability and mechanical rigidity but often face high interfacial resistance. Polymer electrolytes, while mechanically flexible and easy to process, generally have lower ionic conductivity and limited thermal stability. This review discusses how these intrinsic properties influence dendrite nucleation and propagation, including the role of interfacial stress, grain boundaries, void formation, and electrochemical heterogeneity. To mitigate dendrite formation, we explore a variety of strategies including interfacial engineering (e.g., the use of artificial interlayers, surface coatings, and chemical additives), mechanical reinforcement (e.g., incorporation of nanostructured or gradient architectures, pressure modulation, and self-healing materials), and modifications of the solid electrolyte and electrode structure. Additionally, we highlight the critical role of advanced characterization techniques—such as in situ electron microscopy, synchrotron-based X-ray diffraction, vibrational spectroscopy, and nuclear magnetic resonance (NMR)—for elucidating dendrite formation mechanisms and evaluating the effectiveness of suppression strategies in real time. By integrating recent experimental and theoretical insights across multiple disciplines, this review identifies key limitations in current approaches and outlines emerging research directions. These include the design of multifunctional interphases, hybrid electrolytes, and real-time diagnostic tools aimed at enabling the development of reliable, scalable, and dendrite-free SSLBs suitable for practical applications in next-generation energy storage. Full article

The dispersion behavior of ceramic particles in aluminum alloys during rapid solidification critically affects the resulting microstructure and mechanical performance. In this study, we investigated the nucleation and growth of Al₃(Sc,Zr) on TiB₂ surfaces in a 2TiB₂/Al–8Ni–0.6Sc–0.1Zr alloy, fabricated via wedge-shaped copper mold casting and laser surface remelting. Thermodynamic calculations were employed to optimize alloy composition, ensuring sufficient nucleation driving force under rapid solidification conditions. The results show that the formation of Al₃(Sc,Zr)/TiB₂ composite interfaces is highly dependent on cooling rate and plays a pivotal role in promoting uniform TiB₂ dispersion. At an optimal cooling rate (~1200 °C/s), Al₃(Sc,Zr) nucleates heterogeneously on TiB₂, forming core–shell structures and enhancing particle engulfment into the α-Al matrix. Orientation relationship analysis reveals a preferred (111)α-Al//(0001)TiB₂ alignment in Sc/Zr-containing samples. A classical nucleation model quantitatively explains the observed trends and reveals the critical cooling-rate window for composite interface formation. This work provides a mechanistic foundation for designing high-performance aluminum-based composites with uniformly dispersed reinforcements for additive manufacturing applications. Full article

Levitation techniques reduce the available heterogeneous nucleation sites and provide stable access to deeply undercooled melts. However, some samples have repeatably demonstrated that, in the presence of strong stirring, solidification may be induced at moderate, sub-critical undercoolings. Dynamic nucleation is a mechanism by which solidification may be induced through flow effects within a sub-critically undercooled melt. In this mechanism, collapsing cavities within the melt produce very high-pressure shocks, which shift the local melting temperature. In these regions of locally shifted melt temperatures, thermodynamic conditions enable nuclei to grow and trigger solidification of the full sample. By deepening the local undercooling, dynamic nucleation enables solidification to occur in conditions where classical nucleation does not. Dynamic nucleation has been observed in several zirconium and zirconium-based samples in the Electromagnetic Levitator onboard the International Space Station (ISS-EML). The experiments presented here address conditions in which a zirconium sample alloyed with 2.5 atomic percent niobium spontaneously solidifies during electromagnetic levitation experiments with strong melt stirring. In these experimental conditions, classical nucleation predicts the sample to remain liquid. This solidification behavior is consistent with the solidification behavior observed in prior experiments on pure zirconium. Full article

Progressive damage evolution in rock masses serves as the fundamental mechanism driving geological hazards by controlling deformation patterns and failure predictability. To address the critical challenge of predicting fracture behaviors in heterogeneous geological media, this study pioneers the integration of real-time computed tomography (CT) scanning and acoustic emission (AE) monitoring to investigate self-organized criticality and fracture predictability in Cretaceous sandstone under uniaxial compression. By systematically analyzing internal structural evolution and damage parameters, this established a multiparameter framework to characterize self-organized processes and critical phase transitions during progressive fracturing. Key findings include the following: (1) Distinct critical thresholds emerge during yield-stage self-organization, marked by abrupt transitions in AE signals and crack metrics—from microdamage coalescence initiating volumetric expansion (first critical point) to macrocrack nucleation preceding peak strength (second critical point). (2) AE-crack evolution follows power–law statistics, where elevated scaling exponents (r > 0.85) correlate with intensified nonlinear damage, accelerated localization, and progressive rate enhancement. Yield-stage power–law acceleration provides quantifiable failure precursors. (3) Yield-stage damage patterns exhibit 85% similarity with terminal failure configurations, confirming yield-stage as the definitive precursor with critical temporal signatures for failure prediction. A conceptual framework integrating multiparameter responses (AE signals, crack metrics) was developed to decipher self-organized critical phase transitions during deformation-failure processes. This work establishes methodological foundations for investigating damage mechanisms and predictive strategies in heterogeneous rock systems. Full article

Titanium oxynitride (TiNO) thin films represent a multifaceted material system applicable in diverse fields, including energy storage, solar cells, sensors, protective coatings, and electrocatalysis. This study reports the synthesis of TiNO thin films grown at different substrate temperatures using pulsed laser deposition. A comprehensive structural investigation was conducted by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Non-Rutherford backscattering spectrometry (N-RBS), and X-ray absorption spectroscopy (XAS), which facilitated a detailed analysis that determined the phase, composition, and crystallinity of the films. Structural control was achieved via temperature-dependent oxygen in-diffusion, nitrogen out-diffusion, and the nucleation growth process related to adatom mobility. The XPS analysis indicates that the TiNO films consist of heterogeneous mixtures of TiN, TiNO, and TiO₂ phases with temperature-dependent relative abundances. The correlation between the structure and electrochemical behavior of the thin films was examined. The TiNO films with relatively higher N/O ratio, meaning less oxidized, were more electrochemically active than the films with lower N/O ratio, i.e., more oxidized films. Films with higher oxidation levels demonstrated enhanced crystallinity and greater stability under electrochemical polarization. These findings demonstrate the importance of substrate temperature control in tailoring the properties of TiNO film, which is a fundamental part of designing and optimizing an efficient electrode material. Full article

High-speed electrical discharge machining (EDM) is crucial for drilling aerospace components, but the fatigue effects of its recast layer are still not well understood. This study investigates the fatigue behavior of high-speed EDM-processed specimens using ultrasonic fatigue testing and microscopic analysis. The recast layer showed a 20.4% increase in hardness and a 16.5% decrease in elastic modulus compared to the base material. Fatigue cracks originated from microcracks, pores, and inclusions within the recast layer, as well as at its interface with the substrate. Microscopic crack initiation was influenced by defect interactions, while macroscopic crack initiation occurred near the maximum hole diameter perpendicular to the loading direction due to stress concentration. The specimens exhibited bimodal fatigue life: shorter lifetimes were observed when macroscopic stress concentrations overlapped with recast layer defects such as cracks and voids, while defect-free regions significantly extended durability. The non-uniform distribution of the recast layer critically links microstructural heterogeneity to variations in fatigue failure. These findings highlight how recast layer characteristics influence crack nucleation and life variability in EDM-processed components, offering valuable insights for optimizing machining parameters to reduce fatigue risks in critical aerospace applications. Full article

Application of rare earths (RE) as grain refiners is well-known in the technology of aluminum alloys for the automotive industry. In the current study, Al-2.4%Cu-0.4%Mg alloy (coded 220) and Al-7.5%Si-0.35%Mg alloy (coded 356.1), were prepared by melting each alloy in a resistance furnace. Strontium (Sr) was used as a modifier, while titanium boride (TiB₂) was added as a grain refiner. Measured amounts of Ce and La were added to both alloys (max. 1 wt.%). The alloy melts were poured in a preheated metallic mold. The main part of the study was conducted on tensile testing at room temperature. The results show that although RE would cause grain refining to be about 30–40% through the constitutional undercooling mechanism, grain refining with TiB₂ would lead to approximately 90% refining (heterogenous nucleation mechanism). The addition of high purity Ce or La (99.9% purity) has no modification effect regardless of the alloy composition or the concentration of RE. Depending on the alloy ductility, the addition of 0.2 wt.%RE has a hardening effect that causes precipitation of RE in the form of dispersoids (300–700 nm). However, this increase vanishes with the decrease in alloy ductility, i.e., with T6 treatment, due to intensive precipitation of ultra-fine coherent Mg₂Si-phase particles. There is no definite distinction in the behavior of Ce or La in terms of their high affinity to interact with other transition elements in the matrix, particularly Ti, Fe, Cu, and Sr. When the melt was properly degassed using high-purity argon and filtered using a 20 ppi ceramic foam filter, prior to pouring the liquid metal into the mold sprue, no measurable number of RE oxides was observed. In conclusion, the application of RE to aluminum castings would only lead to formation of a significant volume fraction of brittle intermetallics. In Ti-free alloys, identification of Ce- or La-intermetallics is doubtful due to the fairly thin thickness of the precipitated platelets (about 1 µm) and the possibility that most of the reported Al, Si, and other elements make the reported values for RE rather ambiguous. Full article

Epitaxial growth can be used to guide the controllable growth of one metal on the surface of another substrate by matching the interface lattice, thus improving the dendrite tendency of metal growth. The atomic arrangement of the Cu (111) crystal plane of the FCC structure is similar to that of the Zn (0002) crystal plane of the HCP structure, which is theoretically expected to promote the heterogeneous epitaxial nucleation growth of metal zinc under low strain. In this paper, the molecular dynamics method is used to simulate the atomic process of zinc film growth on the Cu (111) surface. It is found that the behavior of zinc-adsorbed atoms on the substrate surface conforms to the epitaxial growth mode. The close-packed structure grown along the (0002) direction of the layered clusters is tiled on the Cu (111) surface, forming a highly ordered low-lattice-mismatch interface. When a large area of layered zinc clusters cover the substrate, the growth mode will change from heteroepitaxial growth to homoepitaxial growth of Zn atoms on the zinc film, forming a lamellar distribution composed of FCC and HCP structure grains. Polycrystalline zinc film with a planar structure with a (0002) surface preferred a crystal plane. The increase in incident energy is helpful in improving the quality of zinc films, while the deposition rate, corresponding to the deposition temperature and electrolyte ion concentration, has no significant effect on the surface morphology and crystal structure of single metal films. In summary, the atomic arrangement of the Cu (111) surface has a strong guiding effect on the atomic ordered arrangement in the zinc film crystal, which is suitable for the epitaxial deposition of the substrate to induce the ordered growth of the Zn (0002) crystal plane. Full article