Search Results (774)

With the continuous development of plastic products toward larger dimensions, higher precision, and extended service life, plastic mold steels are required to simultaneously possess superior wear resistance, strength, and toughness. The effects of five alloying elements (V, Nb, Si, Mo, and Mn) on the microstructural evolution and mechanical properties of P20 plastic mold steel were systematically investigated after air-cooling from 860 °C, followed by tempering at 525 °C, and the underlying strengthening and toughening mechanisms were elucidated. The results revealed that, in the 0.2 V steel, approximately 62.6% of V existed in the form of fine VC carbides after austenitization at 860 °C, effectively inhibiting austenite grain coarsening. The remaining dissolved V atoms subsequently precipitated as nanoscale V–Mo-rich MC-type carbides during tempering, with an average size of less than 50 nm. This precipitation strengthening contributed an estimated strengthening increment of approximately 760 MPa, corresponding to a measured tensile strength increase of 326 MPa relative to the P20. In contrast, in the 0.1 Nb specimen, solubility calculations indicate that over 99% of Nb remains in undissolved NbC particles; TEM observations show these particles range from coarse 1–3 μm to finer 100–200 nm in size. The contribution of coarse NbC particles to material strength improvement is limited. The addition of Mo promoted the formation of abundant nanoscale MoC-type carbides (2–10 nm), which also exhibit a notable precipitation strengthening effect. Meanwhile, Si mainly contributed to solid-solution strengthening, whereas Mn enhanced the strength through solid-solution strengthening and grain refinement. Charpy impact tests demonstrated that, despite the remarkable strengthening induced by nanoscale carbide precipitation in the 0.2 V steel (tensile strength: 1237 MPa), the impact toughness deteriorated severely, dropping to 21 J. This severe toughness loss is proposed to be associated with local stress concentration around the fine carbides, which promotes secondary crack propagation. Similarly, coarse micrometer-sized NbC particles acted as detrimental sites for crack initiation and impaired impact toughness. Comparative analysis indicated that the steels containing 0.75 wt.% Si, 0.7 wt.% Mo, and 1.5 wt.% Mn achieved a favorable balance between strength, ductility, and toughness. In particular, the 0.7 Mo steel exhibited the most outstanding combination of mechanical properties, attaining a tensile strength of 1207 MPa and an impact energy of 136 J. Full article

Surface roughening is a common defect in plastic deformation processing, directly affecting product surface quality and service performance. This study investigates the mechanisms of surface roughness evolution during plastic deformation by considering both intrinsic and extrinsic factors. A macro–meso-scale modelling framework is developed by coupling crystal plasticity finite element modelling, fluid–solid interaction modelling, and macro–meso boundary conditions. The crystal plasticity model incorporates a constitutive model based on crystal plasticity theory, a Voronoi-based geometric model, and a real rough-surface topography model to capture non-uniform grain-scale plastic deformation. Fluid–solid interaction modelling is introduced to analyze the influence of liquid lubricant on the deforming solid material. Boundary interpolation and continuous displacement theories are then used to transfer macro-scale boundary constraints to the meso scale. The proposed framework is numerically implemented and applied to the aluminum alloy tube drawing process. The effects of intrinsic factors, including grain size, grain orientation, and initial surface roughness, and extrinsic factors, including deformation path, strain rate, and lubrication condition, are systematically examined. From a practical point of view, effective strategies to improve surface quality are by reducing grain size, lowering initial surface roughness, decreasing the strain rate and using low-viscosity lubricants. Full article

The grain refinement of high-stacking-fault-energy metals during high-pressure torsion (HPT) is governed by dislocation activity and boundary evolution. However, how local misorientation evolves during different stages of grain refinement remains insufficiently clarified. In this study, AA1050 aluminium was processed by HPT to selected equivalent strains of 0, 0.90, 2.69, 10.76 and 53.78, and electron backscatter diffraction (EBSD) was used to analyse grain morphology, boundary fractions and EBSD-derived misorientation parameters. The results reveal strongly stage-dependent grain refinement during HPT. The average grain size decreases rapidly from 12.63 μm in the initial state to 3.29 μm at ε = 0.90 and 2.19 μm at ε = 2.69, remains nearly unchanged at ε = 10.76, and finally decreases to 0.58 μm at ε = 53.78. The fraction of low-angle grain boundaries increases markedly at ε = 0.90, indicating intensive formation of dislocation substructures, whereas high-angle grain boundaries become dominant at high strain. Grain orientation spread (GOS) and grain reference orientation deviation (GROD) exhibit non-monotonic evolution, whereas the geometrically necessary dislocation (GND) density increases markedly at the early deformation stage and subsequently decreases with further deformation. These results indicate that the stage-dependent grain refinement of AA1050 during HPT is closely associated with dislocation-mediated grain subdivision involving alternating grain elongation and fragmentation. Full article

This study investigates the effects of different graded crushing durations in a blade crusher on the crushing mechanics of wheat and the properties of the resulting flour. Mechanical models were established for blade–particle collisions, radial sliding of particles along the blade surface, and particle–chamber wall collisions. Under reasonable simplifying assumptions, the models analytically characterize the theoretical relationships of impact force and crushing energy with blade rotational speed, rotational radius, and particle incidence angle. The models were used to provide a qualitative mechanistic interpretation of the experimental trends rather than to quantitatively predict flour particle size distribution or damaged starch content. Two graded crushing processes were evaluated, with crushing durations of 10 s per pass (F10) and 15 s per pass (F15). Observation of particle-size evolution during the crushing of wheat particles showed that as the number of crushing passes increased, the proportion of coarse particles continuously decreased, the proportion of fine particles gradually increased, and the proportion of intermediate-sized particles initially increased and then decreased, demonstrating a progressive coarse-to-fine fragmentation pattern. Particle size analysis of the resulting wheat flour showed that the particle size distribution for the F15 process peaked below 5 μm and shifted toward smaller particle sizes relative to that for the F10 process. Nevertheless, the wheat flour obtained from both processes exhibited relatively concentrated particle size distributions, with Span values ranging from 2.46 to 2.68. Damaged starch content increased significantly with the number of crushing passes and was generally higher for the F15 process than for the F10 process. Moisture content decreased from 14.30% to 12.86% under the F10 process and from 14.25% to 12.73% under the F15 process, whereas ash content ultimately increased to 0.48% under both processes. Protein content initially increased and subsequently decreased under both processes. These findings provide experimental evidence for the effects of graded milling on grain refinement, starch damage, and physicochemical composition of wheat flour. Full article

Landslide-induced waves are primarily controlled by granular dynamics during landslide–water impact. While particle size, velocity, and volume are recognized influences, the role of internal grain arrangement and segregation remains less clear. This study employs a coupled CFD-DEM model to investigate how vertical permutation of three fixed grain fractions and layered configurations affect surge generation and propagation. Simulations using three particle sizes (1, 3, and 5 mm) in six initial arrangements reveal that fine particles dominate leading wave formation through efficient momentum transfer, yielding an overall wave height growth of 5.22% and a maximum local growth rate of 2.42%. Grain size segregation governs deposit morphology, with larger particles migrating preferentially along the flow direction. Increasing still-water depth systematically shifts surge characteristics from strongly nonlinear, high-amplitude shallow-water waves to more linear, longer-wavelength, smaller-amplitude deep-water features. Energy dissipation, which is linked to reduced equivalent water depth, decreases wave celerity with propagation distance. The model reproduces granular collapse experiments with a relative error below 5%, confirming that granular segregation critically controls surge dynamics and providing a refined framework for simulating natural landslide-generated waves. Full article

The Co₄₀Fe₄₀B₂₀ alloy is a key magnetic material that combines high saturation magnetization with excellent soft magnetic properties, offering broad application prospects in fields such as spintronic devices, magnetic tunnel junctions, and tunnel magnetoresistive sensors. Hot pressing can be used to produce fine-grained, highly dense CoFeB alloys. However, there is currently a lack of systematic research on the intrinsic mechanisms by which the particle size of gas-atomized CoFeB powders and their non-equilibrium solidification microstructure regulate phase transformations, microstructural evolution, and densification behavior during hot pressing and sintering—particularly regarding the microstructural inheritance effects of powders with different particle sizes. To address this issue, this study used vacuum induction melting and gas atomization technology to prepare Co₄₀Fe₄₀B₂₀ pre-alloyed powders in three particle size ranges: <38 μm, 38–74 μm, and 74–154 μm. Under identical process parameters, corresponding bulk alloys were produced via vacuum hot-press sintering, and the effects of initial powder particle size on phase transformations and microstructural evolution in the sintered bodies were systematically investigated. Microstructural characterization revealed the complete phase evolution of the alloy from the non-equilibrium solidified powder state to the sintered equilibrium state. During hot-press sintering, the metastable (Fe,Co)₃B phase in the powder completely decomposed, transforming into a stable body-centered cubic bcc-(Fe,Co) phase and a bcc-(Fe,Co)₂B second phase. The dispersed (Fe,Co)₂B phase precipitated after sintering strongly inhibits grain boundary migration via the Zener pinning effect, effectively hindering grain growth and resulting in a uniform, fine-grained, equiaxed microstructure. In coarse powders, due to the presence of a portion of the (Fe,Co)₂B phase, this phase aggregates and grows during sintering, weakening the pinning effect and leading to abnormal grain growth. The Hall–Petch fine-grain strengthening effect resulting from grain refinement couples with and offsets the weakening of second-phase strengthening caused by second-phase coarsening, ultimately leading to sintered bodies prepared from powders of different particle sizes exhibiting similar macroscopic density and hardness properties. Full article

Robot-assisted surgery has significantly expanded the possibilities of minimally invasive procedures by providing enhanced dexterity and visualization. However, the lack of direct haptic feedback still limits the surgeon’s ability to accurately assess instrument–tissue interactions, motivating the need for automatic intraoperative assistance systems. During vesicourethral anastomosis (VUA) in robot-assisted radical prostatectomy (RARP), accurate engagement of the bladder and urethral mucosa is essential to ensure proper tissue approximation and watertight closure. Nevertheless, automatic identification of fine-grained needle–tissue interactions during this phase remains largely unexplored. In this work, we propose a proof-of-concept framework for vision-based needle–tissue interaction analysis in RARP endoscopic videos, combining semantic segmentation, geometric proximity analysis, and motion coherence estimation to identify biomechanically plausible interaction events. Two independent transformer-based models were fine-tuned for semantic segmentation of the mucosal tissue and the surgical needle using a patient-level split of six real-world RARP procedures, comprising four procedures for training, one for validation, and one for independent testing. The models achieved Dice scores of 0.837 and 0.774, respectively. The segmentation outputs were subsequently used to drive a motion-aware interaction analysis pipeline, combining geometric proximity estimation between the needle endpoint and the mucosal tissue with optical-flow motion coherence analysis. The proposed interaction framework was evaluated on an independent test set, achieving a specificity of 0.933 and a recall of 0.667. An ablation study further demonstrated the complementary contribution of geometric proximity and motion coherence cues for needle–tissue interaction detection. Although limited by the retrospective nature and size of the dataset, this study introduces a low-latency, end-to-end framework for interaction-aware surgical scene understanding during RARP. The proposed approach represents an initial step toward the development of context-aware intraoperative guidance systems for robotic urologic surgery. Full article

The object of this study is nephrite found on Mount Bikilyar, South Urals, Russia. The purpose of the study is to determine the mineral and chemical composition of the nephrite and host rocks and to develop a model of the nephrite’s formation. The mineral composition was studied using a scanning electron microscope with an energy-dispersive quantitative microanalysis system. We studied the chemical, trace element, and oxygen isotopic composition. The nephrite’s composition is dominated by tangled fibrous and downy aggregates, with large lamellar grains of actinolite. Magnesian hornblende and resorbed diopside grains, as well as chromite, titanite, apatite, chlorite, sulfides, and secondary minerals, are less common. The host rocks are metagabbro of diverse mineral compositions. The nephrite is characterized by a subchondritic trough-like distribution spectrum of REE with a negative Eu anomaly. The chondrite-normalized spectrum of the metagabbro is characterized by significantly higher REE content values. The δ¹⁸O isotopic composition of the nephrite is +5.53 to +5.80‰, indicating the deep origins of oxygen inherited from ultramafic rocks. The extremely heterogeneous and heavier composition of the metagabbro is +4.42 to +11.27‰, reflecting different contributions of the mantle and crustal sources to its formation. The nephrite was formed as a result of ultramafic xenoblock transformation under the influence of gabbro. Initially, serpentine was replaced by diopside, after which actinolite developed to form the nephrite. The Bikilyar nephrite differs in its mineral composition from the nephrite of other deposits. Despite the unique mineral composition, Bikilyar nephrite is a typical serpentinite in terms of paragenesis and chemical composition. The nephrite-specific mineral and chemical composition is explained by the small size of the ultramafic block that is in a significant volume of gabbro. Full article

Deoxidized high-phosphorus (DHP) copper is widely used in marine heat-exchangers and seawater piping, where long-term structural reliability demands both high strength and a deformation-tolerant microstructure to resist damage initiation. Constrained groove pressing (CGP) is a scalable severe plastic deformation route for metallic sheets; however, the sharp trapezoidal junctions of the conventional die impose parasitic bending strains that produce sinusoidal in-plane hardness variations and anisotropic properties. This study introduces a modified CGP (MCGP) process in which the sharp crest and valley of each 45° tooth are replaced by tangent circular arcs (R₁ = 1.6 mm at the crest, R₂ = 4.8 mm at the valley), removing geometric discontinuities while exactly preserving the groove angle, pitch, and die envelope for drop-in compatibility with existing equipment. DHP copper sheets processed by conventional CGP and MCGP were systematically compared using optical microscopy, SEM, XRD, microhardness, tensile testing, and finite-element analysis. MCGP delivered exceptional mechanical performance: yield strength of 281.19 MPa, ultimate tensile strength of 451.94 MPa (96.4% above the as-received state and 23.8% above conventional CGP), mean hardness of 131.38 HV, and the finest apparent (instrument-uncalibrated) coherent diffraction-domain size of 22.75 nm. Finite-element modelling revealed a lower peak equivalent plastic strain with a more continuously distributed through-thickness deformation path, despite an unchanged nominal grooving strain (≈0.56). Notably, while the modified die redistributes deformation rather than amplifying the nominal strain, the measured through-thickness hardness inhomogeneity factor increased from 7.14% to 21.97% due to strain concentration in the mid-thickness region, indicating that full homogenisation requires further arc-radius optimisation. Nevertheless, the substantial gains in strength and microstructural refinement demonstrate that MCGP offers a promising processing route for producing DHP copper components with enhanced strength and refined microstructures, which may contribute to improved damage tolerance. However, it is acknowledged that direct tests on seawater corrosion, corrosion fatigue, and thermal cycling were not performed in this study; the implications for marine service life are inferred from the established literature on the benefits of grain refinement for corrosion and fatigue resistance. Future work incorporating marine environmental performance tests is recommended to validate these implications. Full article

Porous nickel (Ni) coatings were fabricated by wet powder metallurgy using urea and ammonium bicarbonate (NH₄HCO₃) as low-temperature pore-forming additives. Ni powder was mixed with 3 wt.% carboxymethyl cellulose (CMC), coated onto Ni mesh substrates, and sintered in a hydrogen atmosphere at temperatures of 550–900 °C for 30–120 min. The microstructural evolution, phase composition, elemental distribution, and pore characteristics were systematically characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) analyses. The results demonstrate that sintering temperature governs the evolution of the porous structure more strongly than the investigated space holders. With increasing temperature, progressive neck growth, grain coarsening, and densification were observed, consistent with the transition from initial particle contact to the intermediate stage of solid-state sintering. An interconnected porous framework formed at 700 °C, identified as the selected condition due to its balance between interparticle bonding and pore preservation. XRD confirmed a single face-centered cubic (FCC) Ni phase after sintering, while BET analysis showed minor differences in specific surface area but noticeable variations in pore volume and pore-size characteristics. The limited influence of urea and NH₄HCO₃ is attributed to their decomposition at temperatures well below the effective sintering range of Ni. Consequently, the generated gases are likely to escape before a continuous metallic framework is established, resulting in only modest changes in the final pore architecture. These findings indicate that the porous structure is governed predominantly by diffusion-controlled solid-state sintering rather than by the direct pore-forming action of the investigated additives. This study highlights the importance of thermal compatibility between space holders and the sintering window of the metal matrix, providing new insight into the rational design of porous Ni materials prepared by wet powder metallurgy. Full article

This study systematically investigates the effects of varying Ni doping levels (1.0–7.0 wt.%) on the microstructure, static magnetic properties, and high-frequency dynamic magnetic performance of Fe-5.5 wt.% Si soft magnetic composites (SMCs). Toroidal core samples were fabricated using powder metallurgy combined with silicone resin coating and high-temperature annealing. The influence of Ni doping on phase composition, morphology, saturation magnetization, coercivity, effective permeability, quality factor, total core loss and its components, and DC bias characteristics was comprehensively evaluated by XRD, SEM, EDS, hysteresis loop testing, and DC bias measurements. The results indicate that an appropriate Ni content (3.0–5.0 wt.%) promotes the formation of α-Fe(Si,Ni) solid solution and (Fe,Ni)₃Si ordered phases, optimizes grain size and structural ordering, enhances saturation magnetization, and reduces coercivity. In contrast, excessive Ni doping (7.0 wt.%) leads to Ni segregation at grain boundaries, forming strong pinning centers that significantly increase coercivity and hysteresis loss. Within the wide frequency range of 1–100 kHz, Ni doping improves the permeability retention under DC bias but reduces the initial effective permeability. Notably, the sample with 5.0 wt.% Ni exhibits the highest quality factor (Q value) across the entire frequency range, demonstrating the best overall performance. This study provides experimental evidence and theoretical guidance for developing high-saturation-resistance, low-loss soft magnetic composites for medium-to-high-frequency applications. Full article

Ni–Co γ/γ′-strengthened superalloys are key structural materials for modern energy and flow turbomachinery systems due to their exceptional high-temperature strength, creep resistance, as well as hydrogen and corrosion stability. However, operation in gaseous hydrogen environments typical of hydrogen-cooled generators, cooled gas-turbine blades, and emerging hydrogen-energy technologies can significantly affect their microstructural stability and fracture behavior. This study presents a comprehensive multiscale review of hydrogen-induced nanoscale degradation and crack initiation mechanisms in Ni–Co superalloys produced by wrought, powder metallurgy, and additive manufacturing routes. Transmission electron microscopy combined with quantitative morphometric analysis was employed to characterize the size, morphology, and spatial distribution of γ′ precipitates, revealing a dense population of coherent particles predominantly in the 40–120 nm range, governed by a log-normal distribution. Correlations between precipitate size, aspect ratio, and circularity indicate the onset of partial loss of coherency and coarsening for particles exceeding ~80 nm, creating favorable sites for hydrogen localization. The presence of TCP phases (η, σ, μ, Laves) and carbides at grain boundaries and within grains was shown to enhance microstructural heterogeneity and act as effective hydrogen traps, promoting interfacial decohesion and microcrack initiation. To support microstructural interpretation, convolutional neural network analysis with Grad-CAM visualization was applied to SEM images, enabling the identification of the structural regions most sensitive to hydrogen-assisted damage, particularly γ/γ′ interfaces and defect clusters. The results demonstrate that hydrogen-induced degradation in Ni–Co superalloys is governed by the coupled interactions among microstructure, hydrogen distribution, and local stress state. The findings provide a physically grounded basis for optimizing alloy chemistry, heat treatment, and additive manufacturing parameters, as well as for developing AI-assisted predictive models for the durability of critical components in hydrogen-energy and high-temperature power-generation systems to increase hydrogen safety. Full article

Temper embrittlement (TE) degrades the toughness of high-strength Ni-Cr-Mo steels, typically driven by competing mechanisms of impurity segregation and carbide precipitation. To decouple these effects, this study investigates the influence of prior austenite grain size (PAGS) on TE kinetics in a low-phosphorus (0.0038 wt.%) steel. Varying PAGS microstructures were subjected to isothermal aging and characterized using impact testing and atom probe tomography (APT). APT confirmed negligible phosphorus segregation, proving TE is driven primarily by M₂₃C₆ carbide precipitation. Compositional profiling revealed that carbide growth is kinetically governed by chromium (Cr) diffusion. Kinetic modeling via the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation demonstrated that coarse-grained steel exhibits a higher initial embrittlement rate due to continuous intergranular carbide networks that facilitate crack propagation. Conversely, fine-grained structures promote discontinuous precipitation, delaying early-stage embrittlement, although both microstructures reach comparable degradation after prolonged exposure. By isolating precipitation kinetics from impurity effects, this research demonstrates that PAGS critically dictates the rate of carbide-driven TE, providing predictive insights for the microstructural design and lifetime optimization of high-strength structural alloys. Full article

Filters serve as critical facilities for ensuring the seepage stability of earth-rock dams and tailings dams; their failure poses severe threats to dam safety. Traditional filter design criteria are constrained by the diversity of soil types and fail to account for the influence of pore characteristics (e.g., constriction size) on the soil retention and hydraulic conductivity of filters. Design methods recommended in design codes only provide gradation envelope boundaries without specifying exact gradation curves. This paper proposes a filter design approach based on the natural clogging concept. Using Terzaghi’s interlayer coefficient as the initial parameter, this method induces stable clogging layers of base soil within the filter through sediment-laden seepage, adopting the post-clogging gradation as the design gradation. Experimental results demonstrate that: (1) when the initial interlayer coefficient α of the filter is ≤10.4, the base soil retention rate exceeds 97% (soil loss < 3%), surpassing the conservative limit of α < 4 in Terzaghi’s criterion; (2) the final interlayer coefficient α of filters ZS-2 to ZS-5 ranges between 1.15 and 2.48, with i_b/i_f values between 6.26 and 23.68, simultaneously satisfying Terzaghi’s requirements for soil retention and hydraulic conductivity; (3) this method explicitly defines the specific gradation curve of the filter, with the final gradation curve of ZS-5 largely falling within the envelope recommended by design codes. The proposed method integrates Terzaghi’s interlayer coefficient criterion with the influence of pore characteristics on filter performance, offering a new design strategy for tailings dam filters with fine-grained base soils, preliminarily validated under laboratory conditions. Full article

A recently developed high-strength nickel-based corrosion-resistant alloy has attracted increasing interest for drilling and production operations in unconventional oil and gas fields. Owing to its high resistance to media containing H₂S, CO₂ and chloride ions, together with its ultra-high strength and favorable strength–toughness balance, this alloy is suitable for demanding service conditions. During hot working, dynamic recrystallization (DRX) governs deformation softening, grain refinement and the subsequent microstructural state, and thus has a direct influence on final properties. In this work, isothermal compression experiments were conducted on this ultra-high-strength nickel-based corrosion-resistant alloy using a Gleeble thermal simulator at 1000–1150 °C and strain rates of 0.01–10 s⁻¹. Electron backscatter diffraction (EBSD) was used to quantify grain size, grain-boundary misorientation, kernel average misorientation (KAM) and the DRX volume fraction. The results indicate that higher deformation temperature generally accelerates DRX, lowers the KAM value and increases the recrystallized-grain fraction. Under a constant deformation temperature, the DRX volume fraction changes non-monotonically with strain rate, showing an initial increase followed by a decrease. Based on the EBSD-derived DRX fractions, linear and quadratic single-parameter models using the Zener–Hollomon parameter were examined first, but neither provided satisfactory fitting accuracy. A two-variable empirical model was therefore formulated for a fixed true strain of ε = 0.92 by considering deformation temperature and strain rate separately. The predicted values agree well with the experimental data, giving R² = 0.91278 and an average relative error of 8.53%. The proposed model captures the main variation tendency of the DRX volume fraction within the studied processing window and provides a useful basis for microstructure control and hot-working parameter design for ultra-high-strength nickel-based corrosion-resistant alloys. Full article