Lamellar Orientation Research Articles

Oxidation behavior and mechanical properties of a directionally solidified high Nb TiAl based alloy between 800 °C and 900 °C

The high temperature oxidation behavior and mechanical property response of a directionally solidified Ti-46Al-7Nb-0.4W-0.6Cr-0.1B alloy were investigated. The ultimate tensile strength of the alloy at 800 °C, 850 °C and 900 °C are 647 MPa, 590 MPa and 508 MPa, respectively, and the tensile fracture mode changed from brittle cleavage fracture to micro-void accumulation ductile fracture. At lower temperatures Al2O3 forms first, growing along the γ lamellae to form oxide bands aligned with the lamellar orientation. The oxidation mass gain of the alloy after 900 °C/100 h isothermal oxidation is only 0.91 mg/cm2. The oxidation kinetics results show the microalloyed high Nb TiAl alloy has excellent oxidation resistance, which is due to the formation of a TiO2 layer containing Nb, Cr and W, the AlNb2 phase and an Al/Cr rich transition layer above the directionally solidified lamellar matrix.

Effect of eutectic microstructure on load transfer and creep resistance in Al-Ce alloys

This study investigates the compressive creep response of hypo- and near-eutectic Al-Ce alloys via finite-element modeling (FEM), by considering the composite response of a weak, fast-creeping Al matrix containing slow-creeping Al11Ce3 eutectic reinforcement. In the as-cast microstructure of an eutectic Al-12.5 wt%Ce alloy, the Al11Ce3 eutectic phase is lamellar, regardless of the various cross-sectional geometries (Chinese-script, fish-bone, and comb-like). FEM models based on these various lamellar microstructures investigate the effect of Al11Ce3 reinforcement volume fraction, orientation, and geometry on load transfer performance between matrix and reinforcement during creep deformation. FEM predicts that, when the lamellar Al11Ce3 phase is continuous along the loading direction (where load transfer is most effective), the creep resistance of the alloy is barely affected by cross-sectional geometry of the Al11Ce3 reinforcement or by the solid-solution strengthening of the Al matrix, at constant Al11Ce3 volume fraction. However, alloy creep resistance and load transfer between phases are significantly reduced when applying load parallel to aligned, discontinuous lamellae, and they can be improved by matrix solid-solution strengthening. Furthermore, Al11Ce3 short plates (as created in Al-12.5Ce by coarsening of lamellae upon over-aging at 590 °C/24 h) provide the least creep resistance and load transfer. Lastly, multi-colony FEM models are created by combining colonies with various lamellar orientations to approximate the creep performance of polycrystalline hypo- and near-eutectic alloys which, when compared to experimental data for hypoeutectic Al-7Ce and for near-eutectic Al-(10–13)Ce, provide better predictions than single-colony FEM models or analytical solutions.

The Cahn–Hilliard model of coherent lamellar microstructure: application to alkali feldspar

The temporal evolution of coherent lamellar microstructures is significantly influenced by their elastic properties, particularly when the exsolved phases are coherent. This research utilizes the Cahn–Hilliard model to examine the morphological and energetic evolution of binary alkali feldspar, integrating anisotropic elastic energy into the Gibbs energy equation. The Cahn–Hilliard model successfully simulated the orientation of lamellae observed in natural samples and the elastic strain was consistent with previous research. We also computed the coherent solvus from the annealing simulation of various precursor compositions and temperatures. The temperature difference (ΔT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta T$$\\end{document}) between the strain-free solvus and the coherent solvus was ΔT=85∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta T = 85\\,{}^\\circ \ ext {C}$$\\end{document}, which is slightly lower than previously reported values obtained from similar parameters. This discrepancy is likely due to the presence of non-planar lamellae at the onset of phase separation, which are more stable than planar ones. We also simulated the binodal curves of the coherent solvi for different precursor phase compositions. The computed solvi were not unique but varied depending on the precursor composition. Our model is flexible because it does not assume any specific shapes for the lamellar interfaces and is applicable to various coherent binary systems.

Deformation behavior of PST-TiAl bicrystals at 800 °C

PST (polysynthetic twinned) TiAl crystal exhibits excellent mechanical properties, and thus, it has been regarded as a critical candidate for turbine blades in the aero-engine industry. For the first time, the deformation behavior of PST-TiAl bicrystals with two different α2/γ lamellar orientations was studied in this work. Ti-46Al-6Nb bicrystals were cut from directionally solidified ingots, and three bicrystals of B1 (10°–14°), B2 (10°–19°), B3 (6°–75°) together with a single crystal of S1 (3°) were stretched at 800 °C. Then, the deformation behaviors, including fracture morphology, crack propagation, and deformation mechanism, were analyzed. Interestingly, these bicrystals show good high-temperature tensile performance, and their deformation behaviors seem to be very anisotropic. The findings indicate that the misorientation disparity in bicrystals primarily determines their deformation coordination capacity and corresponding mechanical performance. Subsequently, the difference in deformation orientation between the two lamellae significantly controls fracture behavior and deformation compatibility. High slip potential and abundant variant choices in γ phases are supposed to be beneficial for deformation capacity improvement. Meanwhile, the deformation potential of ordinary dislocation and superlattice dislocation slip systems in the α2 phase was also examined. Results show that the disparity in dislocation motion ability between γ variants gradually amplifies the advantages of the easy-mode phase in deformation through strain coordination, while mitigating the disadvantages associated with the difficult-mode phase. During further deformation, the relatively low bicrystal misorientation and small deformation capacity differences between the two lamellae determine high deformation coordination and improved performance. Overall, our work reveals that bicrystal deformation initiates at the relatively softer lamellae and proceeds to the harder lamellae, and its final comprehensive performance is determined by the deformation coordination capacity between the two lamellae.

Toward durable polylactic acid/poly(methyl methacrylate) polyblend fibers with high performance

AbstractPolylactic acid/poly(methyl methacrylate) (PLA/PMMA) composite fibers with high performance were fabricated using melt spinning technique. The crystallization, lamellae orientation and physical properties of composite fibers were investigated systematically. The addition of PMMA (0–20 wt%) has improved the hydrolysis resistance of composite fibers by preventing water molecules from penetrating and diffusing through the fibers, but the strength and heat resistance were reduced at the same time. The stereocomplex crystallites (SC) formed before spinning by introducing poly(D‐lactide) (PDLA) (3 wt%) in poly(L‐lactide) (PLLA) matrix and acted as nucleating agents to enhanced the crystallization and lamellae orientation of PLLA matrix, which improved the physical properties of PLA composite fibers resultful. The tensile strength of PLA fibers with 3 wt% PDLA and 5 wt% PMMA was increased 31% as well as the boiling water shrinkage and the hydrolysis rate were decreased 30% and 33% in relation to PLLA fibers. Finally, the hydrolysis resistance was further enhanced on the basis of realizing high strength and heat resistance, which is of great significance for preparing durable PLA fiber materials and expanding their application.

Double cross-linking system for constructing tortuosity-lowered and strength-enhanced porous MXene films with superior capacitive performance and electromagnetic shielding efficiency

Porous MXene films are ideal materials for flexible electronics because of their various porous structures and rich surface chemistry. However, the typical problem, especially as flexible supercapacitors, is that MXene lamellae are still prone to stacking. Many channels are disconnected from each other, facing high ion transport resistance. Herein, an optimal 3D structure is built by ion-molecular double cross-linking system and subsequent freeze-casting with lowered-tortuosity and enhanced-strength for porous MXene films. Ionic cross-linking is used to adjust the orientation of the MXene lamellae by coulombic attraction, while optimized terminal and ion intercalation widens the layer spacing. Molecular cross-linking is used to adjust the backbone of the porous structure through hydrogen bonding interactions. As a result, due to the porous structure of connectivity, the porous MXene-OH/BC (MOB) delivers a capacitance of 527 F g-1, mechanical property of 41.5 MPa (140 % and 367 % of the MXene film, respectively), and the shielding efficiency of 67.2 dB (X-bond). In addition, the assembled NAC//MOB device achieves high energy density of 56.28 Wh kg-1 and 85.6 % capacitance retention after 50,000 cycles. This work shows a well-designed porous film with lightweight, flexible and strong mechanical properties, expanding the competitiveness of MXene materials for real-world applications.

Lamellar orientation control of TiAl-based alloy by uniaxial compressive deformation at high-temperature in (α+β) two-phase region

In this study, the orientation of (α+γ) lamellar structure in the TNM alloy (Ti-43.7Al-4 Nb-1Mo-0.1B) is controlled by high-temperature uniaxial compression conducted in the (α+β) two-phase region. The control of the lamellar orientation is focused on a control of α phase orientation because of being decisive for lamellar γ orientation. All true stress-true strain curves indicated the work softening due to dynamic recrystallization. The stress-strain curve behaviors were consistent with microstructure observation. The peak stress increased with a decrease in lamellar colony size. After deformation in the (α + β) two-phase region at 1543 K and 1573 K, where the content of α phase was dominant, a fiber texture with the (0001)α2 plane tilted 35° away from the compression plane was formed by the deformation mechanism of α phase. On the other hand, at 1623 K where the content of β phase was dominant, a double (0001)α2 fiber texture tilted at 35°- 45° and 80°- 90° away from the compression plane was observed. The double (0001)α2 fiber texture is considered to be caused by β→α phase transformation during cooling according to Burgers orientation relationship. Single-step uniaxial compressions conducted at the (α + β) two-phase region at different temperature (1543 K−1623 K) led to an inclination of (0001)α2to compression plane and subsequently lamellar interfaces of one colony unparallel to those of other colonies.

Effects of recrystallization on interfacial microstructure evolution and shear strength of TiAl alloy joints

The effects of dynamic recrystallization (DRX) and post-bonding heat treatment (PBHT) on the interfacial microstructure evolution and mechanical properties enhancement of Ti-43Al-4Nb-1Mo-0.2B alloy joints, subjected to various bonding parameters, were thoroughly investigated through detailed microstructural characterization and shear performance tests. A strip-like DRX area was observed at the interface when bonding at 1100 °C, ≥30 MPa, for 60 min. Equiaxial- γ grains underwent discontinuous dynamic recrystallization during the bonding process, and tended to form flat grains parallel to the lamellae direction during recrystallization annealing (1000 °C/6 h) owing to the hindrance imposed by the lamellae on both sides. The orientations of lamellae on the both sides of bonding interface affects the lamellae's stress distribution and deformation behavior at the bonding interface, subsequently influencing the DRX behavior and the width of the DRX zone. Static recrystallization (SRX) during the recrystallization annealing treatment can eliminate bonding defects of joints bonding at lower pressures or temperatures. Optimal joints with fully lamellar interfacial microstructure and excellent shear properties can be obtained through single-α phase annealing treatment. Lamellae microstructure tailored through PBHT can significantly enhance the quality of joints, attributed to the homogeneity of the microstructure between the interface and matrix. The highest shear strength of 478 MPa, accounting for 82 % of the matrix strength, was obtained under the bonding parameters of 1100 °C/30 MPa/60 min-1290 °C/15 min. This work provides important DB process parameters for fabricating of complex structural parts of TiAl alloy.

Determination of α lamellae orientation in a β-Ti alloy using electron backscatter diffraction.

The spatial orientation of α lamellae in a metastable β-Ti matrix of Timetal LCB (Ti-6.8 Mo-4.5 Fe-1.5 Al in wt%) was examined and the orientation of the hexagonal close-packed α lattice in the α lamella was determined. For this purpose, a combination of methods of small-angle X-ray scattering, scanning electron microscopy and electron backscatter diffraction was used. The habit planes of α laths are close to {111}β, which corresponds to (1320)α in the hexagonal coordinate system of the α phase. The longest α lamella direction lies approximately along one of the 〈110〉β directions which are parallel to the specific habit plane. Taking into account the average lattice parameters of the β and α phases in aged conditions in Timetal LCB, it was possible to index all main axes and faces of an α lath not only in the cubic coordinate system of the parent β phase but also in the hexagonal system of the α phase.

Anisotropic Semicrystalline Homopolymer Dielectrics for High‐Temperature Capacitive Energy Storage

AbstractHigh‐temperature dielectric polymers are in high demand for powering applications in extreme environments. Here, we have developed high‐temperature homopolymer dielectrics with anisotropy by leveraging the hierarchical structure in semicrystalline polymers. The lamellae have been aligned parallel to the surface in the dielectric films. This structural arrangement resembles the horizontal alignment of nanosheet fillers in polymer nanocomposites and nanosheet‐like lamellae in block copolymers, which has been proven to provide the optimal topological structure for electrical energy storage. The unique ordering of lamellae in our dielectric films endue a significantly increased breakdown strength and a reduced leakage current compared to amorphous films. This novel approach of enhancing the capacitive energy storage properties by controlled orientation of lamellae in homopolymer offers a new perspective for the design of high‐temperature polymer dielectrics.

Anisotropic Semicrystalline Homopolymer Dielectrics for High-Temperature Capacitive Energy Storage.

High-temperature dielectric polymers are in high demand for powering applications in extreme environments. Here, we have developed high-temperature homopolymer dielectrics with anisotropy by leveraging the hierarchical structure in semicrystalline polymers. The lamellae have been aligned parallel to the surface in the dielectric films. This structural arrangement resembles the horizontal alignment of nanosheet fillers in polymer nanocomposites and nanosheet-like lamellae in block copolymers, which has been proven to provide the optimal topological structure for electrical energy storage. The unique ordering of lamellae in our dielectric films endue a significantly increased breakdown strength and a reduced leakage current compared to amorphous films. This novel approach of enhancing the capacitive energy storage properties by controlled orientation of lamellae in homopolymer offers a new perspective for the design of high-temperature polymer dielectrics.

Effect of mechanical stretching and low amount of silica adding on gas transport properties of poly(butylene succinate-co-adipate) films

This work aimed at studying the influence of a post drawing process on the morphology and the gas permeability of a PBSA (Polybutylene succinate-co-adipate) film. Two films were studied, one of neat PBSA and one filled with 1%wt of silica. The influence of silica was also studied. Reference films of PBSA and PBSA + Si presented a spherulitic morphology despite a difference of spherulites sizes and long period. After stretching, this isotropic morphology changed to an oriented one, as shown by WAXS measurements. SAXS analysis revealed that stretching led to a lamellae organization in the stretching direction, with lamellae oriented perpendicular to the stretching direction. Thermal characterizations have shown that stretching did not modified the degree of crystallinity for both systems. The helium, carbon dioxide and oxygen permeability increased with stretching, mainly due to the orientation of crystalline lamellae, decreasing the diffusion path. Moreover, for PBSA + Si stretched films, small non-percolating voids were evidenced around the silica particles which could also make gas transport easier. Thus, for both systems, this increase in gas permeability happened in a different way.

Effect of forging routes on the microstructure and mechanical properties of newly-developed Ti-44Al-5.5Nb-0.5W-0.5Cr-0.3Si-0.1C alloys

In this study, the effects of forging routes on the microstructure and tensile properties of Ti-44Al-5.5 Nb-0.5 W-0.5Cr-0.3Si-0.1 C (at%) alloys was comparatively investigated. Results showed that the bare ingot forged at 1400 ℃ (BH) exhibited refined lamellar colonies with narrow lamellar spacing. In contrast, dynamic recrystallized γ grains and lamellar structure with thick lamellar spacing formed in the canned sample deformed at 1320 ℃ (CA). In addition, the heat-treated BH-HT sample showed fully recrystallized texture, while the lamellar structure in the CA-HT presented a preferred orientation, i.e., lamellar interfaces were parallel to rolling direction (RD). The mechanical properties of the CA-HT sample test results showed superior room-temperature ductility of 1.68 % and tensile strength of 515 MPa at 950 ℃ due to the lamellar orientation alignment to tensile direction. According to the temperature drop calculation results, both BH and CA forging routes exhibited rapid cooling rates. The initial microstructure at the pre-heating temperature was maintained until a hot deformation sequence was initiated. Therefore, the BH route could be performed in the α+β region, while the CA route could be carried out in the α-forging condition with the 1101̅12 γ texture.

Crystal plasticity modeling fatigue behavior in bimodal Ti–6Al–4V: Effects of microdefect and lamellar orientation

AbstractInvestigating fatigue failure in titanium alloys is crucial for material design and engineering. Fatigue behavior in dual‐phase titanium alloys is strongly correlated with microstructural features and microdefects. This work formulates an improved modeling method to investigate fatigue behavior of bimodal Ti–6Al–4V, emphasizing the effects of lamellar orientation and microdefects. Using an improved Voronoi tessellation method, we establish representative volume element (RVE) models with various grain size distributions. Crystal plasticity finite element modeling (CPFEM) is used to analyze fatigue deformation in bimodal Ti–6Al–4V, considering microdefects and lamellar orientation. Fatigue indicator parameters are then incorporated into CPFEM to predict fatigue life and verified with experimental data. Numerical results highlight the significant influence of lamellar orientation and microdefects on fatigue behavior, with predicted life within the 3‐error band. This method efficiently overcomes challenges in quantitatively characterizing microstructural lamellae that experiments are short of, paving the way for designing fatigue‐resistant alloy materials with similar microstructures.

Experimental and numerical investigation of the yield point phenomenon and strain partitioning behavior in a dual-phase steel with lamellar structure

Severe rolling techniques show potential for enhancing the strength and ductility of metallic materials, but the resulting microstructural anisotropy affects the mechanical behavior. The study investigated the anisotropic yield point phenomenon (YPP) and strain partitioning behavior in a dual-phase steel with ultrafine lamellar structure, fabricated through severe cold- and warm-rolling procedures. Experimental results show that tensile specimens aligned parallel to the rolling direction exhibit YPP and higher ductility, while those oriented normal to the rolling direction show continuous yielding behavior and decreased ductility. Using Digital Image Correlation techniques, we studied the evolution of the strain distribution on the surface of the gauge segment, revealing that the strain within the Lüders band was almost constant during the Lüders band propagation. Strain-induced martensitic transformation (SIMT) was observed within the Lüders band and the volume fraction of martensite keeps almost constant during the Lüders band propagation. Numerically, we integrated the mechanisms of SIMT and YPP into a dislocation density-based J2 plasticity constitutive framework. Simulated tensile tests indicate a smaller Lüders strain resulted from the initial higher strain hardening rate. Additionally, SIMT suppresses local instability and therefore promotes the stable propagation of Lüders bands. Simulations verify that the lamellar orientation and SIMT significantly affect the strain hardening rate and void growth. Our findings provided a new perspective on the intrinsic mechanism of the anisotropic YPP and ductility in lamellar dual-phase steels.

Representation of the microstructure of pearlitic steels for DEM simulations of fatigue

The fatigue behavior of pearlitic steels in wheel-rails is correlated to the microstructure. However, existing models do barely take this correlation into account. In this work, we propose a hierarchical meshing to describe the microstructure of pearlitic steels. The mesh includes grain and block/colony boundaries, lamellae orientations, and orientation perpendicular to lamellae. We use the Voronoi Tessellation method to generate elements with the specific area fraction distribution for pearlite colony areas. The colony and block information is obtained from SEM and EBSD measurements of R260 steel to construct the mesh that represents the microstructure. Finally, we obtained the deformed microstructure via simple geometrical shearing. This meshing method is the first step for modeling fatigue crack growth anisotropy due to plastic deformation.

Preparation and Characterization of High-Density Polyethylene with Alternating Lamellar Stems Using Molecular Dynamics Simulations.

Mechanical recycling is the most efficient way to reduce plastic pollution due to its ability to maintain the intrinsic properties of plastics as well as provide economic benefits involved in other types of recycling. On the other hand, molecular dynamics (MD) simulations provide key insights into structural deformation, lamellar crystalline axis (c-axis) orientations, and reorganization, which are essential for understanding plastic behavior during structural deformations. To simulate the influence of structural deformations in high-density polyethylene (HDPE) during mechanical recycling while paying attention to obtaining an alternate lamellar orientation, the authors examine a specific way of preparing stacked lamella-oriented HDPE united atom (UA) models, starting from a single 1000 UA (C1000) chain of crystalline conformations and then packing such chain conformations into 2-chain, 10-chain, 15-chain, and 20-chain semi-crystalline models. The 2-chain, 10-chain, and 15-chain models yielded HDPE microstructures with the desired alternating lamellar orientations and entangled amorphous segments. On the other hand, the 20-chain model displayed multi-nucleus crystal growth instead of the lamellar-stack orientation. Structural characterization using a one-dimensional density profile and local order parameter {P2(r)} analyses demonstrated lamellar-stack orientation formation. All semi-crystalline models displayed the total density (ρ) and degree of crystallinity (χ) range of 0.90-0.94 g/cm-3 and ≥42-45%, respectively. A notable stress yield (σ_yield) ≈ 100-120 MPa and a superior elongation at break (ε_break) ~250% was observed under uniaxial strain deformation along the lamellar-stack orientation. Similarly, during the MD simulations, the microstructure phase change represented the average number of entanglements per chain (<Z>). From the present study, it can be recommended that the 10-chain alternate lamellar-stack orientation model is the most reliable miniature model for HDPE that can mimic industrially relevant plastic behavior in various conditions.

Keratoconus cone location influences ocular biomechanical parameters measured by the Ocular Response Analyzer.

Keratoconus is characterized by asymmetry in the biomechanical properties of the cornea, with focal weakness in the area of cone formation. We tested the hypothesis that centrally-measured biomechanical parameters differ between corneas with peripheral cones and corneas with central cones. Fifty participants with keratoconus were prospectively recruited. The mean ± standard deviation age was 38 ± 13 years. Axial and tangential corneal topography were analyzed in both eyes, if eligible. Cones in the central 3mm of the cornea were considered central, and cones outside the central 3mm were considered peripheral. Each eye was then measured with the Ocular Response Analyzer (ORA) tonometer. T-tests compared differences in ORA-generated waveform parameters between cohorts. Seventy-eight eyes were analyzed. According to the axial topography maps, 37 eyes had central cones and 41 eyes had peripheral cones. According to the tangential topography maps, 53 eyes had central cones, and 25 eyes had peripheral cones. For the axial-topography algorithm, wave score (WS) was significantly higher in peripheral cones than central cones (inter-cohort difference = 1.27 ± 1.87). Peripheral cones had a significantly higher area of first peak, p1area (1047 ± 1346), area of second peak, p2area (1130 ± 1478), height of first peak, h1 (102 ± 147), and height of second peak, h2 (102 ± 127), than central cones. Corneal hysteresis (CH), width of the first peak, w1, and width of the second peak, w2, did not significantly differ between cohorts. There were similar results for the tangential-topography algorithm, with a significant difference between the cohorts for p1area (855 ± 1389), p2area (860 ± 1531), h1 (81.7 ± 151), and h2 (92.1 ± 131). Cone location affects the biomechanical response parameters measured under central loading of the cornea. The ORA delivers its air puff to the central cornea, so the fact that h1 and h2 and that p1area and p2area were smaller in the central cone cohort than in the peripheral cone cohort suggests that corneas with central cones are softer or more compliantcentrally than corneas with peripheral cones, which is consistent with the location of the pathology. This result is evidence that corneal weakening in keratoconus is focal in nature and is consistent with localized disruption of lamellar orientation.

Synergistic control of microstructures and properties in eutectic high-entropy alloys via directional solidification and strong magnetic field

The AlCoCrFeNi2.1 eutectic high-entropy alloy (Ni2.1 EHEA), as an exemplary representative of the high-entropy alloy family, has garnered significant research attention owing to its exceptional comprehensive properties. In this study, we investigated the influence of various growth velocities on the microstructure, lamellar spacing, and mechanical properties of the Ni2.1 EHEA. We observed that at lower growth velocities, the structure consisted of an alternating face-centered-cubic (FCC) phase and B2 phase lamellae aligned in a single direction, with the lamellae orientation parallel to the direction of the heat flow. The yield strength increased with the growth rate, while the ultimate tensile strength decreased with increasing the growth velocity. Ductility remained relatively consistent, and a double yield phenomenon was observed in the elastic-plastic deformation region. Under conditions of high growth velocities, the microstructure transitioned from a single-directional full lamellar structure to a multi-stage lamellar arrangement. The most favorable comprehensive mechanical properties were achieved at a growth rate of 200 μm/s, resulting in a yield strength of 450 MPa, an ultimate tensile strength of 1092 MPa, and a remarkable ductility of ∼32% in the directionally solidified samples—double that of the arc-melted sample. The evolution law of directional solidification structures under the coupling effect of different magnetic fields and different growth rates was studied. The interaction of the thermoelectric-magnetic force and thermoelectric-magnetic convection and the potential mechanism of microstructure evolution under the effect of magnetic field were deeply analyzed. The results reveal that at a growth rate of 2 μm/s, the spacing between eutectic layers decreases as the magnetic induction intensity increases, leading to the transformation of some regular layers into spherical layers. Similarly, at a growth velocity of 10 μm/s, the eutectic structure exhibited a Columnar-to-equiaxed transition (CET). However, as the growth rate further increases, the limited exposure time to the magnetic field prevented significant structural changes.

Unveiling the secrets of unusual long-pitch periodic assembly of poly(ʟ-Lactide) ring-banded spherulites

Although polymer physicists have conducted extensive research over the decades, the molecular assembly in lamellae of ring-banded spherulites (RBS) remains a puzzle that has yet to be solved. Nonetheless, a breakthrough has occurred in this field where long-pitch banded rings made of a model poly(ʟ-lactide) (PLLA) were examined using advanced synchrotron X-ray micro-focused diffraction techniques. Through the microbeam diffraction mapping and microscopy 3D dissection morphology, the periodic banded structure of RBS is composed of lamellae that self-assemble as structural gratings. Furthermore, a comparison of optical micrograph image with the mapping results revealed the sequential arrangement and orientation of lamellae in these gratings. These extensive experimental findings now provide a comprehensive and novel explanation for the formation of long-pitch lamellar assembly in RBS. This new methodology is adaptable to a wide variety of polymers and allows for the analysis of spherulites displaying periodically self-assembled patterns. The novel methodology employed here has a versatile applicability for a diverse range of polymers. This technique can be extended to analyze spherulites showcasing periodically self-assembled patterns. Such revelation provides valuable understanding into the complex structures and behaviors of polymers, and this discovery opens up new frontiers in materials science research and its practical applications.