Search Results (653)

Cementite (Fe₃C) plays a key role in determining the mechanical performance of pearlitic and heat-resistant steels, where both its intrinsic elastic properties and interfacial bonding with ferrite are critical. In this study, first-principles calculations based on density functional theory were employed to systematically investigate the elastic anisotropy of orthorhombic Fe₃C and the interfacial stability of α-Fe/Fe₃C with three typical orientation relationships (Isaichev, Bagaryatsky, and Pitsch–Petch). The calculated elastic constants of Fe₃C satisfy the mechanical stability criteria and reveal pronounced anisotropic behavior, indicating strong directional dependence of its deformation resistance. Interfacial models with optimized lattice matching demonstrate that the Isaichev orientation exhibits the lowest lattice mismatch (~1.71%), the smallest interface energy (0.55 J/m²), and the highest work of adhesion (4.29 J/m²), suggesting superior thermodynamic stability and interfacial bonding strength. In contrast, the Bagaryatsky and Pitsch–Petch interfaces exhibit larger lattice mismatch and more pronounced local interfacial distortion, resulting in higher interface energies and reduced interfacial stability. These findings provide atomic-scale insights into the structure–property relationship of Fe₃C and highlight the critical role of orientation relationships in governing interface stability. The results offer theoretical guidance for interface engineering and microstructure optimization in high-performance steels. Full article

Directed Energy Deposition (DED) is an additive manufacturing technology rapidly consolidating for the fabrication and repair of complex aerospace Ti-6Al-4V components, ensuring high deposition rates and large build volumes. However, in high build-rate regimes, process-induced phenomena, such as oxygen pick-up, overheating, and residual porosity, introduce material anisotropy. While residual porosity can largely be mitigated by Hot Isostatic Pressing (HIP), dissolved oxygen cannot be removed by any post-processing method, raising uncertainties regarding the final mechanical properties of large DED parts and limiting the predictive performance of design simulation tools. To fully exploit the advantage of design for additive manufacturing methods, it is fundamental to assess how the DED process influences the material performance of large Ti-6Al-4V builds. This work investigates the effect of build orientation and process parameter set on the final mechanical behaviour of DED Ti-6Al-4V samples in high-build-rate conditions. Compared to cast and annealed Ti-6Al-4V, all the realized samples exhibit an average 14% and 22.5% increase in yield strength and ultimate tensile strength, respectively, but 38% lower Elongation at Break. Microstructural analysis reveals that both the process parameter set and the build orientation influence DED material anisotropy, particularly ductility, with vertically built specimens showing 68% and 33% higher elongation at break than longitudinal and lateral specimens, respectively, highlighting a direction-dependent mechanical response consistent with the columnar prior β-grain morphology and extension. LECO analysis confirms that oxygen pick-up also occurs in an enclosed deposition environment and strongly increases material strength at the expense of ductility. Oxygen content varies with build orientation, from 0.15 ± 0.02 wt.% in vertical to 0.19 ± 0.01 wt.% in longitudinal specimens. Finally, fracture surface analysis indicates that lack-of-fusion defects act as preferential crack initiation sites. Full article

In this work, the cobalt ferrite ceramic was synthesized by using Pechini and densified using two different sintering routes: conventional sintering (CS) at 1200 °C for 3 h and microwave sintering (MS) at 1200 °C for 15 min. The influence of both sintering methods on the structural, microstructural, magnetic, and magnetostrictive properties was investigated. X-ray diffraction and Rietveld refinement confirmed the formation of a single-phase cubic spinel structure (Fd-3m) without secondary phases for both samples, and the crystal structure parameters exhibited only minor variations, indicating that the crystal structure remained essentially unaffected by the sintering route. In contrast, SEM micrographs revealed a remarkable reduction in average grain size from 7.72 µm (CS) to 0.74 µm (MS), demonstrating the effectiveness of microwave sintering in controlling grain growth (≈90% reduction in grain size). The magnetic measurements showed slightly higher saturation magnetization and coercive field values for sample MS, which were associated with the refined microstructure and enhanced magnetic anisotropy. Magnetostriction curves at room temperature yielded saturation values of −120 × 10⁻⁶ (CS) and −110 × 10⁻⁶ (MS) for samples, respectively. Despite the lower saturation magnetostriction, the microwave-sintered sample exhibited a significantly higher piezomagnetic coefficient (66 × 10⁻⁵ T⁻¹) compared with the conventional sintered sample (35 × 10⁻⁵ T⁻¹), it showed ≈8% decrease in saturation magnetostriction and ≈89% increase in piezomagnetic coefficient. Furthermore, a sign reversal of the magnetostrictive response was observed near 0.40 T for the MS sample, suggesting competition between magnetoelastic contributions associated with different crystallographic directions. The unstressed magnetostriction model successfully reproduced the experimental magnetostriction curves, confirming that grain-size refinement and grain-boundary effects play a dominant role in governing the magnetomechanical response of magnetic ceramics. Full article

Ultrasound-assisted metal additive manufacturing (U-FAAM) has emerged as a promising in situ melt-pool regulation strategy for addressing the challenges of conventional metal additive manufacturing, including process instability, defect formation, and microstructural anisotropy. This review systematically summarizes recent progress in contact and non-contact ultrasound-assisted metal additive manufacturing from the perspective of acoustic energy delivery pathways. The interactions between ultrasonic excitation and melt-pool behavior, thermal transport, solidification-front evolution, defect formation, microstructural transformation, and mechanical performance are comprehensively discussed. Contact ultrasound approaches transmit acoustic energy through solid media. Cavitation can occur only when the melt-side acoustic pressure reaches the required threshold; under such conditions, cavitation-associated effects may act with acoustic streaming and inertial melt flow to enhance mixing, grain refinement, and defect mitigation. Non-contact ultrasound approaches provide improved geometric adaptability and mainly influence melt-pool evolution through acoustic streaming and cyclic pressure fluctuations. The relationships among ultrasonic input conditions, melt-side responses, solidification behavior, and final properties are critically analyzed. Furthermore, current limitations associated with acoustic energy attenuation, coupling efficiency, process scalability, and quantitative characterization of ultrasonic effects within the melt pool are highlighted. This review synthesizes current evidence for ultrasound-driven melt-pool control in the investigated fusion-based AM systems, particularly DED/LDED and WAAM, while recognizing the limited evidence for LPBF. Full article

The growing demand for sustainable binder systems in 3D-printed concrete (3DPC), together with the declining availability of fly ash (FA), has increased the need for alternative supplementary cementitious materials. This study investigates the feasibility of using basaltic rock dust (BRD) as a high-volume replacement of FA in 3DPC through a two-stage experimental programme involving mix optimisation followed by evaluation under printing conditions. Five mortar mixes incorporating BRD at FA replacement levels of 0%, 25%, 50%, 75%, and 100% by mass were first evaluated to identify the optimum replacement level within the investigated range, after which the optimum mix was comprehensively characterised in terms of its fresh properties, rheological behaviour, hydration characteristics, mechanical performance, anisotropy, and microstructure. The results showed that 75% FA replacement by BRD achieved the optimum overall performance among the investigated BRD-containing mixes, based on the combined consideration of high BRD utilisation, flowability, hydration behaviour, and compressive strength. Although its 28-day compressive strength under conventionally cast conditions remained slightly lower than that of the control mix, under printing conditions, the C75 mix increased the flow diameter from 165 mm to 176 mm and the maximum printable layers from 14 to 16 while reducing the shape retention spread diameter from 96 mm to 89 mm. Compared with the control mix, the BRD-incorporated mix also increased the compressive strength by 10.9% in the Y- direction and 22.9% in the Z-direction, respectively, while reducing the compressive anisotropy from 20.97% to 12.39%. Although the flexural strength decreased from 7.66 to 5.02 MPa in the Y-direction and from 7.29 to 5.19 MPa in the Z-direction, the directional dependence decreased from 4.83% to 3.34%. SEM observations revealed a more compact cementitious matrix with fewer visible large pores in C75 than in the control mix. These findings demonstrate that BRD has strong potential as a high-volume replacement for FA in 3D-printed concrete, reducing reliance on fly ash while achieving favourable printability, compressive performance, and structural uniformity. Full article

Graphene-based hybrid magnetic systems are promising platforms for spintronic applications, yet the mechanisms governing magnetic correlations in these two-dimensional (2D) architectures remain incompletely understood. Here, we investigate the magnetic behavior of Co/CoO core–shell nanoparticles electrochemically deposited on graphene, focusing on the 25–50 K range, where the coercivity and exchange bias field reach their maximum values. Using a modified 2D integral-law framework for approaching magnetic saturation, adapted for 2D systems via the Meyer integral transform, we reconstruct the real-space correlation functions (CFs) of the magnetic anisotropy axes and extract the main micromagnetic parameters. The analysis reveals three distinct types of CFs, monotonic, non-monotonic, and jump-like, which we tentatively associate with different microstructural configurations, including isolated nanoparticles, dense clusters, and sparse conglomerates separated by graphene domain boundaries. The monotonic CFs exhibit long-range coherence of the magnetic anisotropy axes extending over nearly one micrometer. We propose that this long-range behavior may arise from a dual-scale mechanism: indirect RKKY-type exchange through the graphene layer, combined with strong local anisotropy from the CoO shells, which pins the magnetization of individual Co cores via exchange bias. These interpretations are presented as plausible hypotheses, and further experimental verification is required. Full article

Uniaxial tensile tests were conducted to investigate the mechanical anisotropy of rolled 2024 aluminum alloy sheets subjected to different cryogenic treatment durations along the rolling direction (0°), diagonal direction (45°), and transverse direction (90°). The experimental results indicate that the mechanical properties of the rolled 2024 aluminum alloy are strongly dependent on the treatment process and exhibit pronounced anisotropy. With increasing cryogenic treatment time, the yield strength first increases and then tends to stabilize. The optimal combination of mechanical properties is achieved after cryogenic treatment for 16 h, with the yield strength increasing to 385–390 MPa. Cryogenic treatment has no significant effect on the grain morphology of the matrix, but promotes dislocation multiplication and a more uniform distribution of precipitation features. The anisotropy analysis shows that the yield strength in the 45° direction is consistently lower than that in the 0° and 90° directions. The in-plane anisotropy parameter (IPA) decreased from 4.8% in the condition without deep cryogenic treatment to 3.0% after 4 h of cryogenic treatment, followed by an increase to 6.7% after 24 h. This result indicates that short-term cryogenic treatment can effectively reduce the in-plane anisotropy of the 2024 aluminum alloy. Full article

Objectives: We investigate the relationship between the loss of consciousness (LOC) and the state of default mode network (DMN) connectivity in diffuse axonal injury (DAI) patients, using diffusion tensor tractography (DTT). Methods: Twenty-one consecutive patients with DAI were recruited in this study. The DMN connectivity [medial prefrontal cortex (mPFC)—posterior cingulate cortex (PCC)/precuneus and retrosplenial cortex (RSC)—medial temporal lobe (MTL)] was reconstructed using DTT. Fractional anisotropy (FA) value, mean diffusivity (MD) value, and tract volume (TV) of the DMN connectivity at the chronic stage were measured in this study. Results: After adjusting for covariates, none of the DTT parameters reached definitive statistical significance at the p < 0.05 level. However, the LOC duration revealed a marginal trend toward a negative correlation with the TV of the mPFC-PCC/precuneus neural connectivity (partial r = −0.466, p = 0.060) and a marginal trend toward a positive correlation with the MD value of the MTL-RSC neural connectivity (partial r = 0.467, p = 0.059). The FA and MD of the mPFC-PCC/precuneus, and the FA and TV of the MTL-RSC, showed no significant associations (p > 0.05). Conclusions: This exploratory study identified a marginal trend between the LOC duration and the state of DMN connectivity (mPFC-PCC/precuneus and MTL-RSC) at the chronic stage in DAI patients. Chronic-stage microstructural changes in the DMN are likely influenced by several factors, including the severity of the initial injury and the time since injury. Therefore, although the LOC duration provides useful clinical information, it should not be considered a direct predictor of chronic DMN deterioration in patients with DAI. Full article

Ti65 is a promising structural material for lightweight high-temperature aerospace components, yet the heat-treatment response of Ti65 fabricated by electron beam powder bed fusion (EB-PBF) remains insufficiently understood. In this study, EB-PBF Ti65 specimens were subjected to solution treatments at 800–1000 °C for different holding times followed by aging at 650 °C for 2–8 h. Microstructural evolution was characterized and tensile properties were evaluated at room temperature and 650 °C along the XY and Z directions. The as-built alloy exhibited a fine basketweave α + β lamellar microstructure with evident anisotropy. Increasing the solution temperature promoted α-lamella dissolution, elemental homogenization, discontinuity of grain-boundary α, and microstructural reconstruction. The 1000 °C/2 h + 650 °C/2 h treatment significantly improved room-temperature strength and transverse ductility, giving ultimate tensile strengths of approximately 1050 MPa and reducing anisotropy. At 650 °C, all specimens showed reduced strength but increased ductility; low-temperature solution treatment favored ductility, whereas 1000 °C-based treatments combined with appropriate aging improved elevated-temperature strength. Aging for 4 h provided a balanced strength–ductility combination, while longer aging enhanced yield strength but reduced ductility. These results demonstrate that tailoring solution and aging parameters is essential for optimizing the microstructure and mechanical performance of EB-PBF Ti65 alloy. Specifically, the 1000 °C/2 h + 650 °C/2–4 h regime achieved UTS of ~1050 MPa at room temperature and ~608 MPa at 650 °C, with XY-direction elongation increasing from 5.4% to 11.5%, representing a quantitative anisotropy reduction of approximately 53%. Full article

Hydric deformation can contribute to progressive damage in building stones, particularly when moisture-induced strains interact with pre-existing fabric anisotropy and thermally induced microstructural changes. Six Macigno sandstone prisms (20 mm × 20 mm × 200 mm), three with the longitudinal axis orthogonal to bedding (MTO) and three parallel to bedding (MTP), were examined after drying at 60 °C and after sequential thermal conditioning at 350 and 500 °C. At each stage, hydric deformation was continuously monitored during 8400 min of water immersion, and at the end of each test, water absorption and ultrasonic pulse velocity were measured on the samples. Mean final hydric deformation in the 60 °C reference state was 0.54 mm m⁻¹ for MTO and 0.44 mm m⁻¹ for MTP. Along the sequential conditioning path, it decreased to 0.18 and 0.10 mm m⁻¹, respectively, at 500 °C, whereas water absorption increased from about 0.42 to 0.58–0.59 wt.%. Ultrasonic pulse velocity decreased from 4347 to 3915 m s⁻¹ for MTO and from 4770 to 4437 m s⁻¹ for MTP. Bedding-related anisotropy persisted, while water absorption and hydric deformation followed divergent trends. Continuous acquisition further showed that the general temporal pattern of rapid initial deformation followed by a more gradual approach to a near-stable response was preserved after thermal conditioning, although the initial deformation rate decreased systematically. Full article

Background/Objectives: Cerebral small vessel disease (SVD) is a heterogeneous condition in which similar conventional MRI findings may be associated with different clinical manifestations and pathogenetic mechanisms. Previously, hierarchical clustering of structural MRI features in patients with severe white matter hyperintensities (Fazekas 3) identified two MRI phenotypes, designated MRI Type 1 and MRI Type 2. Diffusion MRI (dMRI) may provide additional information about the microstructural differences between these phenotypes. To compare white matter microstructure between MRI Type 1 and MRI Type 2 of sporadic age-related SVD using signal-based and biophysical dMRI models. Methods: This cross-sectional study included 75 patients with SVD and 36 age- and sex-matched healthy controls. Among the patients with SVD, 43 had MRI Type 1 and 32 had MRI Type 2. All participants underwent structural and multi-shell dMRI on a 3 Tesla MRI scanner. Diffusion metrics were derived using multiple models: Diffusion Tensor Imaging (DTI), Diffusion Kurtosis Imaging (DKI), Neurite Orientation Dispersion and Density Imaging (NODDI), White Matter Tract Integrity (WMTI), and the Multi-compartment Spherical Mean Technique (MC-SMT). Tract-profile analysis was performed in three corpus callosum segments: the forceps major, forceps minor, and body. Group differences were assessed using age- and sex-adjusted general linear models with correction for multiple comparisons. The combined discriminative value of dMRI metrics was evaluated using regularized Elastic Net logistic regression with repeated nested five-fold cross-validation. Results: After adjustment for age and sex, the overall group effect remained significant for 45 of 48 global dMRI measures following Benjamini–Hochberg correction. Compared with MRI Type 2, MRI Type 1 showed lower fractional anisotropy (FA), neurite density index (NDI), intra-axonal volume fraction (INTRA), axonal water fraction (AWF), mean kurtosis (MK), axial kurtosis (AK), and radial kurtosis (RK), and higher mean diffusivity (MD), radial diffusivity (RD), extra-axonal mean diffusivity (EXTRA_MD), extra-axonal transverse diffusivity (EXTRA_TRANS), and extra-axonal radial diffusivity (radEAD). These differences were generally most pronounced in the body of the corpus callosum. In the segmental analysis, 131 of 144 values showed a significant overall group effect after correction, and 108 demonstrated significant differences between MRI Type 1 and MRI Type 2. The largest effects were observed in the 60–80% interval of the corpus callosum body, particularly for AWF, MK, INTRA, EXTRA_TRANS, RK, FA, RD, radEAD, and MD. An Elastic Net model combining age, sex, and 48 global dMRI measures discriminated MRI Type 1 from MRI Type 2 with an internally validated area under the curve of 0.866 (95% CI, 0.762–0.953), accuracy of 86.7%, sensitivity of 75.0%, and specificity of 95.3%. Ten dMRI features showed a selection frequency of at least 70% across repeated model construction. Conclusions: MRI Type 1 is characterized by more severe and spatially extensive corpus callosum microstructural abnormalities than MRI Type 2, despite broadly similar vascular risk-factor profiles. The findings support the heterogeneity of sporadic age-related SVD and indicate that combined signal-based and biophysical dMRI metrics may improve MRI phenotyping. The observed associations should be interpreted as indirect markers of tissue microstructure and require confirmation in larger, independent, and longitudinal cohorts. Full article

Ta-2.5W alloy is a promising liner material for high-performance shaped-charge warheads because of its high density and excellent dynamic mechanical properties. However, conventional machining and hot-forming routes suffer from low material utilization, limited dimensional accuracy, and oxidation-related defects. In this study, near-net-shape cold pressing and annealing treatments were investigated for Ta-2.5W liners. The initial microstructure and mechanical properties of the starting sheet were characterized, compression tests were performed to establish a room-temperature constitutive model, and 16 combinations of deformation and annealing temperature were designed to clarify the evolution of grain morphology and crack sensitivity. To compensate for elastic die deformation and blank springback, a coupled simulation-based die correction strategy was further developed. The results show that the starting alloy exhibits an excellent strength–ductility balance with weak anisotropy. Increasing cold deformation refines the grains, whereas increasing annealing temperature initially promotes grain refinement but subsequently causes grain coarsening. Excessive deformation combined with high annealing temperature increases crack susceptibility. Based on the single-specimen screening experiments in this study, a preliminary processing range of 20–40% cold deformation and 1200 °C annealing produced the most favorable microstructural condition without obvious cracking. After iterative die compensation, trial-manufactured parts satisfied the target contour requirements and showed uniform, crack-free microstructures after annealing. Full article

The structural use of three-dimensional concrete printing remains limited by the directional weakness introduced during extrusion and layer-by-layer deposition. Although 3DPC offers major advantages in formwork elimination, architectural freedom, and automated construction, its printed architecture produces interfaces, pore networks, and reinforcement discontinuities that do not exist in the same form in conventionally cast concrete. This review examines the anisotropic behavior of 3DPC by linking its architectural arrangement, physical interlayer mechanisms, and chemical durability-related processes. The analysis shows that anisotropy develops from the combined effects of filament orientation, interlayer bonding quality, pore morphology, cold-joint formation, mechanical interlocking, hydration continuity, and reinforcement limitations. Weak interlayer regions act not only as preferred paths for crack initiation and propagation under tensile, flexural, shear, and compressive loading, but also as transport channels that accelerate water absorption, chloride ingress, carbonation, sulfate attack, and freeze–thaw deterioration. The review further highlights that fiber, textile, FRP, and discrete reinforcement strategies can reduce some consequences of anisotropy, but their effectiveness depends on whether they bridge the weaker interlayer regions rather than merely reinforcing the filament direction. SEM-based observations confirm that microstructural discontinuities, fiber-matrix debonding, irregular hydration products, and connected pores provide the material-level basis for the directional response of printed concrete. Overall, anisotropy should be treated as a design-critical feature of 3DPC rather than as a secondary defect. Reliable structural application requires coordinated control of mixture rheology, deposition parameters, interlayer timing, curing, toolpath design, and reinforcement layout. Full article

This work presents an experimental characterization of 17-4PH stainless steel fabricated by Atomic Diffusion Additive Manufacturing (ADAM). The microstructure, porosity, local chemical composition, and residual stresses were investigated using optical microscopy, SEM-EDS, digital image analysis, and sin²ψ X-ray diffraction. Pronounced porosity anisotropy was observed, with a lower porosity area fraction in the transverse section (1.45%) than in the longitudinal section (3.48%), where elongated channel-like inter-layer defects were identified. Isothermal sintering at 1315 °C produced a predominantly martensitic microstructure with equiaxed morphology. Local chemical variations were detected in selected macro-voids and interfacial regions, including elevated concentrations of C, Cr, and Nb, reaching 1.61 wt.%, 42.58 wt.%, and 16.31 wt.%, respectively. These anomalies may be related to localized binder-derived residues or secondary phase formation, although their origin cannot be conclusively determined by EDS alone. Residual stress measurements at 12 surface locations revealed spatial variations, with maximum axial tensile stress of 185.6 ± 21.9 MPa and local compressive stress of −46.7 ± 10.9 MPa. All measured stresses remained below the reported yield strength. The findings highlight the importance of optimizing inter-layer bonding and thermal debinding conditions in ADAM. Full article

Laser Powder Bed Fusion (LPBF) has revolutionized high-end manufacturing, particularly in aerospace and biomedical fields. However, internal defects such as pores, cracks, and inclusions compromise the structural integrity and service reliability of LPBF components. Laser ultrasonics, a non-contact, broadband non-destructive testing (NDT) method, offers a promising solution for detecting and characterizing these defects. This study systematically investigated laser ultrasonic testing technology for LPBF-fabricated Ti6Al4V using a combined approach of physics-driven simulation modeling and experimental validation. To accurately model material anisotropy, a finite element model was developed that integrated Voronoi algorithm-generated polycrystalline microstructures with orientation-dependent elastic tensors, providing a comprehensive representation of the material’s microstructural heterogeneity. Simulation results revealed that while sub-100-μm defects yield weak ultrasonic scattering signals, the Synthetic Aperture Focusing Technique (SAFT) markedly improves the detection and imaging performance for such small-scale defects. Experimental validation using a laser ultrasonic system identified a 90 μm internal defect in the LPBF Ti6Al4V specimen, though a 75 μm defect was undetectable. This highlights the need for enhanced sensitivity. A signal processing method combining time-truncation principal component analysis (PCA) with targeted noise reduction and SAFT was proposed to reduce high-frequency noise and improve high-resolution imaging, enhancing defect detection accuracy. This study provides theoretical foundations and technical support for high-precision defect detection in metal additive manufacturing components, with significant implications for quality control in high-end equipment manufacturing. Full article