Search Results (166)

This work reports the combination of pentagonal grain morphology, high phase purity, and non-monotonic thermal conductivity behavior over a wide temperature range (25–1200 °C). The SrZrO₃ coatings with different processing parameters are deposited using atmospheric plasma spraying (APS). Unlike conventional atmospheric plasma-sprayed oxide coatings, distinct pentagonal-shaped grains with multi-directional orientation suggest a unique solidification pathway and anisotropic growth mechanism. The pentagonal morphology may come from the impingement of five radially columnar grain sectors during rapid solidification of a highly undercooled melt splat, constrained by local thermal gradients. This atypical morphology, not commonly reported for SrZrO₃ coatings, is further supported by electron backscatter diffraction (EBSD) results, which confirm a remarkably high phase fraction (~94.5%) of SrZrO₃ despite rapid quenching inherent to APS processing. The combination of high phase purity and unusual grain geometry represents a significant advancement in tailoring the microstructures of environmental barrier materials. Moreover, the non-linear thermal conductivity response with temperature shows a pronounced decrease up to ~800 °C (0.737 W·m⁻¹·K⁻¹) stabilization between 800 and 900 °C, and a subsequent increase at higher temperatures. This behavior indicates a complex interplay between phonon scattering, defect structures, and possible radiative heat transfer contributions at elevated temperatures. Full article

In pursuit of a composite coating for tunnel boring machine (TBM) disc cutters that offers both high wear resistance and self-lubricating functionality, we fabricated Fe-based composite coatings reinforced with WC and MoS₂ through laser cladding. Seven coating compositions with systematically tailored MoS₂ contents were prepared to investigate the concentration-dependent effects of MoS₂ on microstructural evolution and tribological properties, and to evaluate their performance under various rock-contact conditions. XPS results reveal that MoS₂ decomposed during laser cladding, leading to the in situ formation of metal sulfides in the Fe-based matrix. These sulfides, characterized by low shear strength, readily form a continuous and stable lubricating tribofilm at the hob–rock interface. The tribofilm effectively lowers the coefficient of friction (COF), curtails friction-induced energy dissipation and surface degradation, and ultimately enhances the wear resistance of the disc cutter. Simultaneously, the rapid non-equilibrium solidification inherent in laser cladding stabilizes metastable phases, which refine the microstructure, improve densification, and bolster phase stability. Among the tested compositions, the coating containing 4 wt.% MoS₂ exhibited the most favorable dry-sliding tribological performance, as evidenced by an average coefficient of friction of 0.409, a hardness of 749.5 HV1, and consistently low wear mass losses below 2.1 × 10⁻³ g under different rock-contact conditions. Mechanistically, XRD and SEM analyses further attributed the superior performance of the 4 wt.% MoS₂ coating to concurrent strengthening mechanisms: grain refinement, dispersion strengthening from uniformly distributed second-phase particles, and increased dislocation density. Collectively, these effects substantially improve the wear resistance of the disc cutter, thereby extending its durability and service life under complex operating conditions. Full article

The efficient treatment and resource utilization of shield tunnel spoil (STS) are important for sustainable underground construction in China. To improve the early mechanical performance and microstructural compactness of stabilized STS, this study investigated the solidification effect of a novel early-strength cementitious agent (ESCA) and compared it with ordinary Portland cement (P.O 42.5). Macroscopic mechanical tests, including unconfined compressive strength (UCS), stress–strain behavior, mass, and P-wave velocity measurements, were combined with scanning electron microscopy (SEM) and computed tomography (CT) analyses to reveal the mechanical response and microstructural mechanisms of stabilized STS. The results indicate that, compared with P.O 42.5, ESCA exhibits superior fluidity at lower water-to-solid (w/s) ratios, significantly shorter setting times, and higher compressive strength at all curing ages. The solidification efficiency of ESCA for STS is notably superior to that of P.O 42.5, with the peak strength, elastic modulus, mass, and P-wave velocity of ESCA-solidified specimens being higher than those of P.O 42.5-solidified specimens across the five dosages. Furthermore, ESCA material bonds more tightly with STS particles, resulting in lower porosity and a denser microstructure under the same stabilizer dosage. Overall, the combination of macroscopic mechanical properties and microstructural characterization demonstrates that ESCA material exhibits significant advantages in the efficient solidification and resource utilization of shield tunnel spoil. Full article

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

Thermo-electromagnetic force plays a crucial role in tailoring the solidification microstructure by altering thermal-solutal buoyancy. However, while in situ synchrotron experiments offer some observations of microstructural evolution, their restricted spatial resolution and beam intensity prevent the full characterization of fluid flow and solute transport during solidification. To address this limitation, a calibrated model of a cellular automaton method coupled with a Eulerian multiphase approach is employed in this study to comprehensively investigate the impact of solute distribution on grain evolution during the directional solidification of an Al-2.5 wt.% Cu alloy under varying steady magnetic fields from 0.5 T to 4.0 T. The model incorporates heat and solute transport, nucleation, grain growth, and complex melt flows driven by thermal-solutal buoyancy, alongside thermo-electromagnetic effects and induced Lorentz forces. Simulations reveal that under a steady 0.5 T magnetic field, an elliptical copper-rich region forms near the solidification front. This solute redistribution significantly influences the development of a tilted solid–liquid interface, consistent with experimental observations. As the magnetic field strength increases, this copper-rich region transitions from an elliptical to a circular morphology. Notably, under a 4.0 T magnetic field, the tilted interface is effectively stabilized due to the suppression of grain growth. Furthermore, significant grain refinement is observed under a steady magnetic field, as the average grain size decreases from 209.3 μm without magnetic field to 122.5 μm of 0.5 T. This refinement is driven by redistribution of the copper concentration, which increases the undercooling from 1.4 K to 3.7 K and generates new nucleation zones. This solute-driven mechanism is identified as the primary cause of grain refinement under steady magnetic fields and is successfully validated by experimental results. These results shed new light on the mechanism of grain growth evolution under a steady magnetic field. Full article

Aiming at the challenging issue of nonlinear coupling control between cooling intensity and solidification rate in the secondary cooling zone of round billet continuous casting, this study proposes an efficient 3D temperature field modeling method that integrates hybrid coordinate systems with equal-area meshing. The model is applicable to the temperature range of 800–1520 °C during the continuous casting process. With the modeling strategies of constructing an r-θ-z hybrid coordinate system and designing a dynamic equal-area meshing method, and combined with a topological structure optimization algorithm, the geometric adaptability and numerical stability of the model are significantly improved. Based on this, an explicit-semi-implicit dual-mode finite difference solution model is developed, where the explicit scheme meets real-time online calculation requirements, and the semi-implicit scheme combined with preconditioned Gauss–Seidel iteration enables high-precision offline simulation. Furthermore, a boundary condition model incorporating adaptive mold heat flux correction and multi-mechanism heat transfer in the secondary cooling zone is established. Based on Microsoft Visual Studio 2019 (Version 16.11) C++ development, SIMD vectorization and temperature gradient threshold optimization technologies are employed, resulting in a 35% improvement in computational efficiency. Industrial validation results show that, taking 42CrMo steel with a casting speed of 0.24 m/min and a cross-section of φ600 mm as an example, the deviation between the calculated surface temperature (887 °C) and the measured value (876 °C) of the round billet in the straightening zone is only 11 °C, and the calculation error of the cold billet diameter is only 0.325% (with a calculated value of 597.548 mm and a measured average value of 599.5 mm), both meeting the accuracy requirements for engineering applications. The model breaks through the limitations of traditional empirical formulas and provides theoretical support for digital control of continuous casting processes and quality optimization of high-alloy steels. Full article

This study systematically investigated the mechanism of micro-segregation reduction in a high-Mn austenitic cryogenic steel continuous casting slab using thermodynamic calculations and homogenization experiments. The high-Mn austenitic cryogenic steel continuous casting slab exhibits obvious non-equilibrium solidification characteristics, with severe interdendritic segregation of C and Mn. The solidus temperatures of equilibrium, Scheil, and Scheil–Back solidification are 1324 °C, 953 °C, and 1272 °C, respectively. According to thermodynamic calculations, there is only a slight decrease in the highest segregation C content when the homogenization temperature is 900 °C. When the specimens were homogenized at 1000 °C, the segregation of C and Mn was significantly alleviated, and the segregation degree further decreased when the homogenization temperature was 1100 °C. Two feasible and industrially applicable strategies for alleviating the micro-segregation of a high-Mn steel continuous casting slab are proposed. First, reduce the cooling intensity of the secondary cooling stage during continuous casting, slow down the cooling rate around 1000 °C, and promote the limited diffusion of solute elements to reduce initial segregation. Second, introduce a holding stage at around 1000 °C during slab reheating prior to hot rolling, eliminating residual segregation and stabilizing the local solidus temperature above 1200 °C. Full article

The solidification process is crucial for preparing high-performance superconductors and is strongly dependent on the characteristics of the starting powder, including particle size, morphology, and phase purity. This review concisely examines the study on four key superconductors: REBCO, Bi-2212, FeSeTe, and MgB₂. In REBCO, additives such as CeO₂, Pt, or BaO₂ powder can refine the RE-211 phase. In Bi-2212, Pb doping stabilizes the high-T_c phase. For FeSeTe, doping with F or Co modifies phase separation and introduces Δκ pinning. Meanwhile, in MgB₂, the incorporation of SiC nanoparticles powder generates effective pinning centers. Concurrently, processing conditions exert a decisive influence on the final microstructure, as demonstrated by the TSMG/TSIG route in REBCO, partial melting parameters for Bi-2212, specific cooling protocols and thermal treatments for FeSeTe, and optimized sintering and post-annealing processes for MgB₂. Future research directions should prioritize fundamental understanding of phase separation mechanisms during powder processing, development of multi-component doping strategies for powder modification, and advancement of scalable powder processing routes for practical conductor architectures. Full article

Stereolithography (SL) based additive manufacturing technology facilitates fabricating structurally complicated silicon-based ceramic cores. However, SL fabricates ceramic component by layer-by-layer solidification of ceramic slurries. The instability of ceramic slurries often leads to the phenomenon of ceramic particle gradient distribution in the prepared ceramic component, which can damage the mechanical properties, porosity, and dimensional accuracy of ceramic component, hindering the application of SL in the preparation of ceramic component. Herein, we systematically investigated and optimized such impacting factors, including particle size distributions, addictive (nanopowder) and solid loading, which result in appropriate viscosity and high stability of SiO₂ ceramic slurries. A SiO₂ ceramic slurry for SL showed the viscosity (26.1 Pa·s) and after 264 h sedimentation time with 80 wt.% of solid loading. Using the slurry, we prepared a ceramic with a shrinkage rate maintained below 4%, a porosity of 21.56%, and a flexural strength of 20.53 MPa. Full article

Chromium slag, a chromium-bearing solid waste characterized by substantial environmental hazards yet with appreciable resource potential, has become a focal topic in solid-waste pollution control and the circular economy. Centered on the overarching logic of “evidence chain–system boundary–scalable and verifiable acceptance,” this review systematically synthesizes recovery technologies, industrial-scale utilization pathways, and the key challenges associated with the detoxification and resource utilization of chromium slag. From the perspective of recovery technologies, we examine pyrometallurgical and hydrometallurgical routes, solidification/stabilization (S/S), and bioelectrochemical coupling approaches, elucidating their fundamental principles, applicability boundaries, and critical nodes where environmental burdens may be transferred across media. We emphasize that process design should concurrently consider detoxification efficiency, resource recovery performance, and whole-process pollution control. Regarding utilization pathways, this review highlights three major routes with strong scale-up relevance—metallurgical process co-treatment (CAP–sintering–blast furnace), bulk utilization in construction materials, and high-value utilization—and analyzes their industrial potential and engineering constraints. Particular attention is given to the lack of long-term leaching and durability evidence, which represents a central bottleneck limiting product-side credibility. Furthermore, we discuss cross-cutting challenges including the long-term stabilization of Cr(VI), the verifiability of “green utilization” concepts, cost and economic feasibility, and standardized acceptance criteria. We propose that future research should shift from single-process optimization toward multi-objective, system-level evaluation, and establish a full-chain evidence system covering “speciation/mineral phases–process mechanisms–environmental behavior–risk assessment–engineering scale-up–standardized acceptance.” This review aims to provide a systematic analytical framework and practical reference for improving comparability across resource-utilization technologies and supporting engineering decision-making for chromium slag management. Full article

High-speed laser cladding shows significant potential for application in the field of high-performance surface hardening due to its low heat input and high cladding efficiency. However, the pool solidification time is significantly reduced at high scanning speeds, resulting in a narrower process window and making it more difficult to ensure coating formation stability and control performance. Therefore, this study employed high-speed laser cladding technology to prepare FeCrNiB alloy coatings, and systematically conducted research on process parameter optimization and friction properties. Firstly, the response surface method (RSM) was used to establish quantitative relationship models between laser power, scanning speed, and powder feed rate and the dilution ratio, forming coefficient, and microhardness. Then, the hybrid differential evolution and NSGA-II algorithm (DE-NSGA-II) was employed for multi-objective optimization. Finally, a systematic analysis was conducted on the friction and wear properties of the coatings produced under the optimal process parameters. The results indicate that the interaction between laser power and scanning speed has a significant impact on the dilution behavior of the coating, while the coupling between scanning speed and powder feed rate governs the formation characteristics and microhardness evolution of the coating. The experiment verified that the prediction error for the optimal parameters is controlled within 5%, demonstrating good engineering applicability. Further analysis indicates that grain refinement and the formation of strengthening phases in the optimal coating are the key mechanisms behind the significant improvement in hardness and wear resistance, and the coating primarily exhibits a mild abrasive wear mechanism. This work realizes the multi-objective optimization of the high-speed laser cladding process via RSM and DE-NSGA-II algorithm, which provides a novel and efficient method for parameter optimization and engineering application of high-speed laser cladding. Full article

This study investigates the valorization of dredged sludge as a sustainable subgrade fill material through stabilization with a nano-calcium carbonate–cement composite. Unconfined compressive strength (UCS) tests were systematically conducted to determine the optimal dosage of nano-CaCO₃ as a supplementary additive at a fixed cement content of 8% by dry soil mass. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and quantitative pore structure analysis were employed to elucidate the underlying solidification mechanisms. The results demonstrate that the addition of 2% nano-CaCO₃ yields the highest 28-day UCS of 721 kPa, representing a statistically significant 21% improvement over the cement-only reference (596 kPa) and a more than threefold increase relative to untreated sludge (213 kPa). Conversely, increasing the nano-CaCO₃ dosage to 2.5% leads to a significant strength reduction, attributed to nanoparticle agglomeration and hindered cement hydration. Microstructural characterization reveals that the optimal nano-CaCO₃ dosage accelerates early-age hydration through a nucleation effect, promotes the consumption of portlandite, and enhances the formation of calcium silicate hydrate (C–S–H) gel. Semi-quantitative XRD analysis further confirms the conversion of less stable monosulfate (AFm-SO₄) into stable monocarboaluminate (AFm-CO₃) phases. These synergistic mechanisms—nucleation, physical pore filling, and chemical reaction—result in a densified matrix with a refined pore structure, reduced total porosity, and a more homogeneous pore-size distribution. The findings provide a robust theoretical basis for the resource-oriented utilization of dredged sludge and the design of low-carbon composite stabilizers for soft soil treatment. Full article

Stabilization/solidification (S/S) is a crucial technology for the engineering reuse of oil-contaminated soil. A key challenge, however, is preventing the migration of residual oil under varying hydraulic conditions. This study investigates the efficacy of a lime and fly ash binder in treating oil-contaminated soil. We systematically compared the performance of untreated (UOCS) and treated (TOCS) soils under different aqueous environments (humidity injection, water injection, and permeation). We evaluated oil migration, water-holding capacity, and permeability characteristics. The results demonstrate that the lime–fly ash treatment effectively adsorbed and immobilized oil contaminants, restricting their mobility to a remarkably low range of 0.54% to 4.90%. Furthermore, the S/S treatment significantly improved the soil’s hydraulic properties: it enhanced the water-holding capacity, reduced the soil-water characteristic curve hysteresis, and counteracted the oil-induced hydrophobicity. Consequently, the effective permeation channels were restored, leading to a higher permeability coefficient in TOCS compared to UOCS. Crucially, the hydro-mechanical performance of the treated soil met the criteria of the Solidification/Stabilization Resource Guide, confirming its suitability for engineering applications. Full article

Industrialization has led to the substantial release of heavy metals and organic pollutants into soil and groundwater, resulting in severe contaminated site issues that pose significant threats to ecosystems and human health. This review aims to systematically review the current development status and challenges of contaminated site remediation technologies, and explore the potential of artificial intelligence (AI) applications in site remediation, to provide a theoretical reference for advancing intelligent remediation. Conventional remediation technologies mainly include physical methods (e.g., solidification/stabilization (S/S), soil vapor extraction (SVE), thermal desorption, pump and treat (P&T), groundwater circulation wells (GCWs)), chemical methods (e.g., chemical oxidation/reduction, electrokinetic remediation (EKR), soil washing), and biological methods (phytoremediation, microbial remediation), along with combined strategies that integrate multiple approaches. Although these technologies have achieved certain successes in engineering practice, they still face common challenges such as risks of secondary pollution, long remediation periods, high costs, poor adaptability to complex hydrogeological conditions, and insufficient long-term stability, making it difficult to fully meet the remediation demands of complex contaminated sites. Subsequently, the potential of emerging technologies—including nanomaterial-based remediation, bioelectrochemical systems, and molecular biology-assisted remediation—is introduced. On this basis, the forefront applications of AI in contaminated site remediation are discussed, covering site monitoring and characterization, risk assessment, remedial strategy selection, process prediction and parameter optimization, material design, and post-remediation intelligent stewardship. Machine learning (ML), explainable AI (XAI), and hybrid modeling approaches have markedly improved remediation efficiency and decision-making. Looking forward, with advancements in XAI, mechanism-data fusion models, and environmental foundation models, AI is poised to drive a paradigm shift toward intelligent and precision remediation. However, challenges related to data quality, model interpretability, and interdisciplinary expertise remain key barriers to overcome. Full article

This study investigates the mechanical behavior of polyurethane (PU)-stabilized calcareous sand with varying PU contents and relative sand densities using unconfined compression and direct shear tests. The results demonstrate that PU stabilization significantly enhances compressive and shear strength and induces a transition from brittle to ductile failure with increasing PU content. Strength and stiffness exhibit nonlinear growth as an interconnected polymer bonding network develops. Relative density controls the timing and efficiency of strength mobilization, with dense specimens strengthening earlier and loose specimens exhibiting accelerated strength development at higher PU contents. SEM and XRD analyses confirm that stabilization is dominated by a bonding–solidification mechanism, without altering the mineralogical composition. Overall, PU stabilization provides an effective approach for achieving rapid strength development and stable mechanical performance in calcareous sand. Full article