Metals doi: 10.3390/met16060598

Authors: Lei Zhang Xiaoyang Luo Jiawei Shen Jie Sheng Xuefeng Lu Xingchang Tang

The segregation of niobium (Nb) at the FeΣ3(111) grain boundary and its influence on interfacial cohesion were investigated via spin-polarized density functional theory calculations. Nb atoms exhibit strong site-selective segregation, with Site 1 being the most thermodynamically favorable one (segregation energy of –2.47 eV), owing to its largest local Voronoi volume. Electronic structure analyses reveal pronounced Nb-4d/Fe-3d orbital hybridization and localized charge accumulation between Nb and neighboring Fe atoms, enhancing covalent bonding at the boundary. First-principles tensile simulations show that single-Nb segregation increases the critical strain from 13.58% to 15.76% and the theoretical tensile strength from 16.32 GPa to 19.64 GPa. However, double-Nb segregation reduces the work of separation to 3.26–4.24 J/m2, revealing a competition between segregation strengthening and solute-induced weakening that implies an optimal Nb concentration window for grain boundary engineering.

Metals doi: 10.3390/met16060597

Authors: Jie Li Jianxin He Hao Liu Yunhan Hou Zhiming Dong Qian Zhang

Rotary kiln shell temperature monitoring is essential for metallic shell protection and refractory lining maintenance in high-temperature industrial processes, while smoke, dust, thermal diffusion and non-kiln heat sources make valid shell temperature extraction difficult. This study develops a multi-scale cascaded network with low-resolution space-to-depth downsampling (MSC-LSTD) for infrared kiln shell segmentation and temperature recognition. Global infrared thermal images and local laser temperature measurements are used to construct a calibrated rotary kiln infrared dataset, and predicted kiln shell masks are mapped to temperature matrices for valid shell temperature analysis. MSC-LSTD achieves 99.82% aAcc, 99.14% mAcc and 97.03% mIoU on the rotary kiln infrared dataset, showing robust segmentation performance under complex thermal interference. The proposed framework provides a practical image-based solution for kiln shell overheating warning and refractory lining degradation assessment.

Metals doi: 10.3390/met16060596

Authors: Hangbin Tang Zhenyun Ma Haiwen Ge Wei Hua Pengpeng Dong

Additive manufacturing (AM), also known as three-dimensional (3D) printing, has emerged as a revolutionary digital near-net-shape manufacturing technology, offering innovative solutions for the design and fabrication of complex, high-performance structures and equipment. This paper reviews the recent advancements and applications of metal AM technologies in the marine sector. Firstly, the principles and characteristics of three most widely adopted metal AM processes in this field are introduced: laser powder bed fusion (L-PBF), directed energy deposition (DED), and wire arc additive manufacturing (WAAM). Subsequently, the application status of metal AM is summarized in four key marine sectors: propulsion systems, underwater vehicle housings and structures, hull structures and shipboard equipment and components, as well as marine equipment repair and emergency support. Building on this, the major challenges for metal AM applications in the marine environment are further discussed, including the fabrication of large-scale components, standardization of materials and processes, integration of smart manufacturing and digital technologies, and sustainability and circular manufacturing. Finally, future trends are projected toward higher efficiency, intelligence, and environmental sustainability. It is indicated that metal AM will fundamentally reshape the manufacturing mode of marine equipment and support its high-performance, low-cost, intelligent and rapid-response development.

Metals doi: 10.3390/met16060595

Authors: Jovana Djokić Stefan Nikolić Stevan Dimitrijević Shuiping Zhong Željko Kamberović

Gold (Au) is a strategically critical metal whose technological relevance and increasing demand contrast with the long-term decline in primary ore grades. This review discusses gold recovery from primary ores providing the metallurgical and technological baseline for the comparative evaluation of unconventional Au-bearing resources. Emphasis is placed on electronic waste and copper anode slimes as highly valuable secondary raw materials containing gold concentrations comparable to, or exceeding, those in natural deposits. The review examines the origin, chemical and mineralogical characteristics, impurity profiles, and processing routes associated with these materials, including conventional and emerging pyro-, hydro-, and biometallurgical approaches. Material-specific constraints, matrix complexity, recovery efficiency, process limitations, and environmental aspects are discussed in relation to process applicability and technological feasibility. Particular attention is given to the differences between geologically constrained primary ores and heterogeneous secondary Au-bearing materials, whose engineered and continuously evolving compositions influence recovery strategies, limiting the direct application of conventional routes to secondary resources. Finally, the review highlights that primary ores remain the dominant source of global Au production, whereas secondary resources currently represent a complementary component, and outlines key challenges and future directions relevant to the broader utilization of these materials.

Metals doi: 10.3390/met16060594

Authors: Hongjin Zhang Guangsheng Wei Fuhai Liu Shenghai Han Xiaodan Zhong Jianzhong Wang Xiaoyun Luo

Improving energy efficiency of electric arc furnace (EAF) steelmaking is a key pathway for the iron and steel industry to achieve carbon neutrality. Based on statistical data from 56 industrial EAFs, this study established and validated a comprehensive mass and energy balance model with a verification error of less than 5% and systematically quantified the effects of furnace type, furnace capacity, hot metal charging ratio, and scrap preheating on EAF energy efficiency through statistical analysis and scenario simulation. The results show that furnace type is the decisive factor for energy efficiency; Consteel and shaft furnace EAFs with scrap preheating are significantly more efficient than conventional EAFs, with the shaft furnace exhibiting the highest preheating efficiency and best stability. The scale effect of furnace capacity on energy efficiency is weak and fully overshadowed by furnace type. Each 10% increase in hot metal ratio reduces specific power consumption by about 50 kWh/t in conventional furnaces, and the optimal hot metal ratio is 40–50% to balance power consumption and total energy consumption. Scrap preheating saves electricity by recovering physical heat, with each 100 °C temperature increase reducing power consumption by 25 kWh/t; compared with the Consteel process, the shaft furnace process reduces total energy consumption by approximately 14% and increases energy efficiency by 9%. This study provides theoretical support and practical guidance for process optimization in the low-carbon transformation of EAF short-flow steelmaking.

Metals doi: 10.3390/met16060593

Authors: Zbigniew Pater

This study proposes a new method for rolling steel balls using spiral discs. The aim of the study was to investigate whether the proposed method could be used to produce balls with a diameter of 63 mm, as well as to determine the effect of tool geometry and the number of billets on process stability, force, and the energy parameters of the rolling process. Numerical simulations were performed using Forge® NxT v.4.0. The billet for rolling was made of C60 steel and preheated to 1050 °C. The following cases of ball rolling were simulated: Ball rolling using flat discs with single, double, and triple spiral impressions made on their working surface, and ball rolling using tapered discs for two different configurations of the working system. The rolling process was examined in terms of ball shape, internal defect formation, temperature distribution, as well as force and energy parameters. The results showed that the rolling process conducted using tapered discs and by flat discs with single and double impressions produced correctly shaped balls without internal cracks. It was also found that discs with double impressions were more advantageous than the single-impression ones in terms of energy consumption, while the use of discs with triple spiral impressions led to higher tool load and reduced product quality despite the high efficiency of these discs. The system comprising one disc with an external conical working surface and one disc with an internal conical working surface yielded the best results with the lowest energy consumption and power demand. The findings of this study demonstrate that ball rolling using spiral discs is a promising alternative to standard skew rolling methods.

Metals doi: 10.3390/met16060592

Authors: Miao Yang Shuangtian Qin Xiaohan Yang Xiaobo Liu Zhiqiang Cao

To develop novel biodegradable magnesium alloys with suitable corrosion resistance and mechanical properties for orthopedic applications, this study investigated the microstructure, mechanical properties, corrosion behavior and wear resistance of as-cast and near-solidus heat-treated Mg-3Zn-0.3Mn alloys with and without Gd/Nd additions (RE-free, 1Gd, 1Gd1Nd). Rare earth addition refined the grains and transformed the secondary phase from Mg7Zn3 to the W-phase (Mg3RE2Zn3). The as-cast 1Gd1Nd alloy showed the finest grains, highest hardness (51.3 HB), best tensile strength (189.38 MPa), lowest corrosion rate (2.80 mm/y) and lowest wear rate (0.614 × 10−3 mm3/(N·m)). Near-solidus heat treatment slightly decreased hardness (1–3%) but significantly reduced corrosion rate (e.g., RE-free alloy from 3.61 to 2.78 mm/y) and wear rate. The heat-treated 1Gd1Nd alloy gave the best overall performance: corrosion rate 2.68 mm/y, tensile strength 213.71 MPa and elongation 12.96%. Gd promoted grain refinement and film stability, while Nd stabilized the W-phase, showing a clear combined addition benefit. Notably, the heat-treated RE-free alloy performed similarly to the as-cast 1Gd1Nd alloy, indicating that heat treatment can partially mimic rare earth addition. This work provides a baseline for precursor materials before further processing (e.g., extrusion) toward biodegradable implant applications.

Metals doi: 10.3390/met16060591

Authors: Jiancheng Jiao Lifeng Chen Fengfeng Zhan Deqian Zeng Shunyan Ning Dongqiao He Jiaxu Zheng Shaoying Wang Zhongyuan Zhou Xufeng Li Yuezhou Wei

The sustainable development of nuclear energy requires a secure long-term uranium supply. Seawater uranium extraction offers a nearly inexhaustible resource; however, its commercialization is limited due to high costs. To improve economic viability, this study proposes a synergistic strategy for simultaneously recovering uranium and vanadium using amidoxime-based adsorbents, with vanadium as a valuable co-product. Herein, a porous silica-supported poly(amidoxime) adsorbent was synthesized and characterized. The material possesses a well-developed porous structure with a specific surface area of 49.8 m2 g−1. Spectroscopic analyses confirmed the successful grafting of amidoxime groups onto the silica framework, whereas X-ray photoelectron spectroscopy revealed that uranium adsorption occurs via coordination with nitrogen and oxygen donor atoms. Batch experiments demonstrated rapid adsorption equilibrium within 2 h and a maximum Langmuir uranium capacity of 48.5 mg g−1 at 45 °C. The adsorbent exhibited high selectivity toward uranium over vanadium and competing ions at near-neutral pH. Dynamic column experiments demonstrated efficient stepwise separation using 0.1 mol L−1 HNO3 for uranium and a Na2CO3–H2O2 system for vanadium, even in simulated seawater containing high concentrations of competing ions. Under the controlled model conditions employed, this study demonstrates a promising adsorbent and a feasible co-recovery strategy that may contribute to enhancing the economic feasibility of seawater uranium extraction, warranting further validation in natural seawater.

Metals doi: 10.3390/met16060590

Authors: Joel de Jesus Luis Filipe Borrego Luis Vilhena José Martins Ferreira Ricardo Claudio

The increasing demand for porous stainless-steel materials produced by selective laser melting (L-PBF) for biomedical implants, filtration systems, heat exchangers, and energy devices has created an urgent need to improve their mechanical performance. Optimizing process parameters and microstructural properties is therefore critical for enhancing the overall functionality and reliability of L-PBF porous stainless-steel structures. This paper studies the effect of an aging heat treatment on the mechanical properties of L-PBF specimens, manufactured with stainless steel Uddeholm Corrax powders. The porosity was selected to be about 3%, based on manufacturer’s experience on the production injection mold inserts, with the ability to drain air. To reach this porosity, a set of manufacturing variables were selected, quantified in terms of VED (Volumetric Energy Density) of 59.01 J/mm3. The analysis of the mechanical behavior was focused on the compressive and flexural strength, dynamic Young’s modulus and the energy dissipation during earlier fatigue loading cycles. This study concluded that the heat treatment produces a negligible effect on dynamic Young’s modulus and increases the bending strength by about 25% and the compressive plateau strength by about 17%. Both specimens’ batches exhibit similar fatigue strain accumulation for cyclic compressive tests.

Metals doi: 10.3390/met16060589

Authors: Chang Ho Jung Jei-Pil Wang

This study investigates the production behavior of Fe–Ni–S matte from synthetic nickel ore designed to simulate low-grade saprolitic laterite. The synthetic feed was formulated based on XRF and XRD analyses of magnetically upgraded laterite concentrate. Thermodynamic modeling, including phase stability analysis, Ellingham evaluation, viscosity prediction, and sulfidation equilibria, was employed to define optimal smelting conditions. Carbothermic reduction at 1550 °C enabled selective reduction in NiO and FeO, leading to the formation of Fe–Ni alloy droplets, which subsequently reacted with FeS to produce Fe–Ni–S matte. The carbon ratio played a critical role in controlling FeO content in slag, thereby influencing slag basicity and viscosity. An optimal carbon ratio of 0.2–0.4 mol maintained slag viscosity within the industrially favorable range (2–5 poise) and minimized crucible dissolution. Thermodynamic analysis confirmed that FeS is the only stable sulfide phase at high temperature and dissolves into the Fe–Ni melt, promoting stable matte formation. Under optimized carbon and FeS addition conditions, a maximum nickel recovery of approximately 88% was achieved, attributed to improved slag composition, controlled viscosity, and enhanced matte–slag separation. These results demonstrate that simultaneous carbothermic reduction and sulfidation is an effective route for Fe–Ni–S matte production from saprolite-derived oxide feed. Control of carbon ratio, FeS addition, and Al2O3 flux is essential for achieving stable matte formation and efficient metal–slag separation.

Metals doi: 10.3390/met16060588

Authors: Rongzheng Yao Yilai Zhong Xiyun Yang Yongqiang Huang

Neutralization residue results from the hydrometallurgical extraction of magnesium in serpentine, and contains abundant Fe3+, Mg2+, and Al3+. The recovery of these metals involves acid leaching and precipitation. Fe3+ often causes co-precipitation and makes separation difficult. The reduction of Fe3+ into Fe2+ can separate iron from other metals. The reduction kinetics of Fe3+ by SO2 in the acidic leachate from the neutralization residue was studied systematically within the temperature range of 323 to 363 K. The results indicate that SO2 reduction follows first-order kinetics with respect to Fe3+ and 0.71-order with respect to SO2. SO2 reduction undergoes dissolution, hydrolysis, complex and reduction. SO2 dissolution is an exothermic process with ΔHsol = −42.88 kJ mol−1, the reduction step has an activation energy of 14.52 kJ mol−1. The reduction process is controlled by dissolution and hydrolysis. High pH accelerate the reduction while the co-existing Al3+, Mg2+ and Ni2+ ions inhibit the reduction. A multi-factor-controlled kinetic equation for the reduction of Fe3+ by SO2 was built. This study provides a reference for the establishment of a multi-factor control system dynamics model.

Metals doi: 10.3390/met16060587

Authors: Ravi Govindram Kewalramani Ingo Riehl Jan Hantusch Tobias Fieback

The quality and integrity of aluminothermic rail welds are strongly governed by the thermal conditions involved during preheating, pouring and cooling stages of the process. In this study, a simplified numerical framework is presented, based on the finite volume method and implemented in the open-source software OpenFOAM® version 7, to predict the heat transfer and solidification processes. Within this framework, the preheating stage is simulated by employing a heat flux profile derived from experimental measurements, while the mould filling stage is neglected under the assumption of instantaneous pouring of the molten metal. The steel–slag multiphase system is treated using the Volume of Fluid method, whereas melting and solidification are captured using the enthalpy-porosity approach on a fixed Eulerian grid. The numerical framework is validated for a rapid welding process with short preheating procedure, consistent with typical industrial practice for rail welding. The predicted temperature histories during the preheating stage show sufficiently good agreement with the experimental measurements. Subsequently, the cooling stage is validated for a molten metal temperature of 2200∘C (≈2200+273K). The predicted width of the fusion zone is compared with experimental data, showing reasonably good agreement in the railhead region, while an underestimation is observed in the rail web and rail foot regions. Furthermore, a systematic parametric investigation is conducted by varying two key process parameters, namely the molten metal temperature examined at four distinct levels ranging from 1800∘C (≈1800+273K) to 2400∘C (≈2400+273K), and the active preheating duration, varied across six values ranging from 90s ( 90/60min)– 390s ( 390/60min), in order to assess their influence on the cooling stage. The numerical results provide detailed insight into the temporal evolution of the thermal field and its influence on the formation and extent of the fusion zone and heat-affected zone. The results demonstrate that, despite simplifications, the model captures the dominant thermal phenomena of the process and offers a computationally efficient tool for parameter studies and process optimisation.

Metals doi: 10.3390/met16060586

Authors: Ting Jing Yang Yu Qiang Liu

Acoustic emission (AE) technology was used to monitor the fatigue crack growth process of superalloy. The analysis results show that both the cumulative values and the K-entropy values of AE parameters have good correspondences with the three stages described by fracture mechanics, which makes it possible to characterize the process of fatigue crack growth. Since K-entropy is more sensitive to changes in fatigue state, the turning points between the second stage and the third stage are earlier than those defined by fracture mechanics, indicating that it has an early warning capability. The K-entropy of AE parameter was first proposed to represent the growth rate of fatigue crack. This method not only effectively decreased the large dispersion of change rate of AE parameters but also ensured the similarity with the fatigue crack growth rate, thereby optimizing the characterization of fatigue crack growth.

Metals doi: 10.3390/met16060585

Authors: Yunchuan Zhang Puwei Dang Huiyu Xu

To improve temperature uniformity and reduce thermal stress-induced cracking during laser directed energy deposition (laser DED) repair of TiAl blades, this study proposes a refined induction heating coil design based on coupled electromagnetic-thermal finite element simulation. A temperature-dependent model of the induction heating process for a cast 45XD TiAl blade was established and used to compare circular and elliptical coil cross-sectional shapes. The elliptical coil reduced the magnetic field concentration at the leading and trailing edges and decreased the maximum temperature difference across the blade cross-section to below 100 K, thereby improving transverse temperature uniformity. To further improve the temperature distribution along the blade length, a variable-pitch solenoid coil with sparse turns in the middle and dense turns near both ends was designed. This arrangement improved the balance between local heat generation and heat dissipation and reduced the temperature variation within the central 10 cm region of the blade to about 10 K. Experimental validation showed engineering-level agreement with the simulation results, and the blade body was stably maintained at 1020–1030 K, satisfying the preheating requirement for laser DED repair of TiAl blades within the tested design set.

Metals doi: 10.3390/met16060583

Authors: Qingrui Lai Zhiguo Luo Yongjie Zhang Zongshu Zou

In a steel continuous casting mold, argon bubbles injected through the submerged entry nozzle undergo transport, coalescence, and turbulent breakup, producing a polydisperse bubble swarm that affects flow stability and defect formation. In this study, an Euler–Lagrange model coupled with bubble collision coalescence and turbulence-induced breakup sub-models was established and validated using water model observations. Three daughter-bubble volume distribution models were compared in terms of bubble-cloud morphology, number-fraction distribution, and median-diameter evolution at different gas flow rates. For the median bubble diameter at different gas flow rates, the M-type model gives the lowest mean absolute error of 0.0349 mm. Large bubbles with diameters greater than 2.5 mm accounted for about 4% of the total number and were mainly concentrated near the SEN, whereas small bubbles with diameters of 1.0–1.5 mm accounted for about 60% and were dispersed throughout the upper recirculation region. Mechanism analysis further shows that bubble transport is drag-dominated in the high-velocity jet region, while buoyancy becomes more important in weaker flow regions; turbulent breakup is localized mainly in high-dissipation regions.

Metals doi: 10.3390/met16060584

Authors: Xi Chen Guojin Zhang Songtao Chang Yuhui Sha Fang Zhang

Intragranular orientation gradients play a critical role in deformation and recrystallization texture evolution of silicon steel. In this study, the dependence of intragranular orientation gradients on grain orientation in a cold-rolled Fe-3%Si alloy was systematically investigated through electron backscatter diffraction (EBSD), complemented by a rate-dependent crystal plasticity model, incorporating grain boundary resistance. A comparative assessment of intragranular orientation gradients in the grain core and grain boundary regions revealed that they are markedly sensitive to grain orientation, with the grain boundary region exhibiting a higher orientation gradient than the grain core. The formation of intragranular orientation gradients is governed by the orientation stability during plastic deformation: stable convergent α (<110>//RD, rolling direction) and γ (<111>//ND, normal direction) orientations develop lower orientation gradients, whereas grains with unstable divergent λ (<001>//ND) orientations exhibit higher orientation gradients. Furthermore, intergranular interactions during rolling reduce orientation stability near grain boundaries, thereby promoting higher orientation gradients in the grain boundary region compared to the grain core.

Metals doi: 10.3390/met16060582

Authors: Junjie Fei Hongfang Qi Bei Yuan Minbiao Wan Linlang Zhang

A transverse fracture occurred in U75V pearlitic rail after 5 months of service on a sharp radius curved track of mixed passenger-freight railway. Systematic tests including chemical composition analysis, mechanical properties testing, macroscopic fracture inspection, metallographic observation and microscopic morphology characterization were conducted on the failed rail sample. The results indicate that the rail base metal has qualified metallurgical quality. Its chemical composition, fundamental mechanical properties and microstructure fully meet the requirements of Chinese railway standard TB/T 2344.1-2020. The failure mode is identified as instantaneous brittle fracture. Severe mechanical extrusion and impact cause prominent plastic deformation on the rail foot, leading to surface plastic flow and further triggering micro-crack initiation. Under continuous cyclic stress induced by train loads, the micro-crack tips undergo repeated tearing and closing. Severe stress concentration accelerates the formation of transgranular cracks, which propagate rapidly and unstably toward the rail interior, eventually resulting in catastrophic transverse fracture. Standardized procedures in rail transportation, hoisting and laying are essential to avoid mechanical damage, while regular line inspection and timely replacement of damaged rails should be strictly enforced.

Metals doi: 10.3390/met16060581

Authors: Wissal Yangui Rami Ghorbel Farid Takali Wafa Naifar Ahmed Ktari Khaled Elleuch Nader Haddar

Hot-rolled A283 Gr C carbon steel/A240 TP 316L stainless steel-clad plates are widely used in structural applications. However, the hot-rolling process introduces residual stresses and microstructural heterogeneities near the interface, which can adversely affect mechanical performance. This study aims to optimize stress-relief annealing parameters for hot-rolled A283 Gr C/A240 TP 316L-clad steel in order to enhance toughness while preserving microstructural integrity. A Taguchi experimental design based on an L9 orthogonal array was employed to evaluate the effects of holding temperature, holding time, and heating/cooling velocity on Charpy impact toughness. Signal-to-noise (S/N) ratio analysis and ANOVA were used to identify the most influential parameters. Microstructural observations, microhardness profiling, and Charpy impact testing were conducted before and after heat treatment. The results indicate that stress-relief annealing does not alter the base microstructures of either the carbon steel substrate or the austenitic stainless steel-clad layer, nor does it induce carbide precipitation or secondary phase formation in the A240 TP 316L stainless steel. A noticeable reduction in the thickness of the decarburized ferrite zone near the interface was observed, suggesting improved interfacial stability. Microhardness measurements revealed a moderate decrease in hardness near the interface, accompanied by a significant increase in Charpy impact toughness under optimized conditions. ANOVA results show that holding temperature is the dominant factor influencing toughness, followed by heating/cooling velocity, while holding time has a minor effect. The optimal stress-relief annealing conditions were identified as 550 °C for 45 min, with a heating/cooling velocity of 100 °C/h. These findings demonstrate that the Taguchi method is an effective approach for optimizing heat treatment parameters and improving the mechanical integrity of hot-rolled stainless steel-clad plates.

Metals doi: 10.3390/met16060580

Authors: Natalija Dolić Zdenka Zovko Brodarac Franjo Kozina Anita Begić Hadžipašić

The corrosion behavior of the EN AW-5083 alloy was investigated due to its widespread use in marine and transportation applications. The study examined the influence of microstructure development on corrosion behavior in both as-cast and homogenized conditions. Thermodynamic calculations, differential scanning calorimetry, and metallographic characterization were used to analyze solidification and microstructure development, while electrochemical testing was applied to evaluate corrosion resistance in a solution simulating severe outdoor exposure conditions, primarily marine, industrial, and transportation environments. The results show that the as-cast microstructure contains a heterogeneous distribution of anodic and cathodic intermetallic phases, which promotes localized corrosion. Homogenization at 520 °C led to the dissolution of the Al8Mg5 (β) phase, resulting in reduced sensitization effects and slightly improved corrosion resistance. However, high corrosion rates were observed in both metallurgical conditions, indicating limited resistance under the applied testing conditions. The study confirms that microstructural modification through homogenization influences corrosion mechanisms in EN AW-5083.

Metals doi: 10.3390/met16060579

Authors: Xinqiang Li Shengdun Zhao Mingjun Qiu Tianlong Lian Yongfei Wang Jing Zeng Shaobo Ma Xiaochen Du Shuqin Fan

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.

Metals doi: 10.3390/met16060578

Authors: Xiaohui Li Yuhong Lin Mingjia Wu Lijie Chen Lianhao Liu Guolin Song

Electrically assisted processing of metallic materials has emerged as a promising paradigm for reducing deformation resistance while concurrently tailoring microstructure and service-related properties under coupled electrical, thermal, and mechanical fields. This review focuses on deformation-dominated and surface-strengthening scenarios, examining recent advances from three interconnected perspectives: fundamental mechanisms, microstructural evolution, and property responses. Available evidence suggests that Joule heating typically constitutes the dominant contribution under high-duty-cycle or near-steady-state current conditions, whereas non-thermal electroplastic effects become increasingly pronounced under short-pulse, high-current-density, and temporally decoupled loading regimes. Current assistance can accelerate recovery and recrystallization, refine grain structure, modify crystallographic texture, and alter phase transformation and precipitation kinetics. Additionally, it can relax or redistribute residual stresses while reducing flow stress and forming forces. In select hybrid surface treatments, these microstructural modifications translate into enhanced resistance to fatigue, wear, and corrosion. Nevertheless, the available evidence precludes a single universal explanation, given that current crowding, defect-selective heating, electron–dislocation interactions, and magnetic effects operate concurrently, with their relative importance varying across material systems and processing conditions. Moving forward, establishing a unified framework that links electrical parameters, defect evolution, microstructure, and performance is imperative, with focused efforts on the quantitative delineation of thermal and non-thermal contributions, predictive constitutive modeling, residual stress stability, and industrial scalability.

Metals doi: 10.3390/met16060577

Authors: Sherzod Kurbanbekov Mazhyn Skakov Tolegen Kaisaruly Yulduz Amangeldiyeva Sherzod Ramankulov Aidyn Tussupzhanov Yerkhat Dauletkhanov

High-entropy alloys and the broader class of compositionally complex alloys have recently attracted significant attention as promising materials for solid-state hydrogen storage. Their potential arises not only from high configurational entropy but also from the possibility of tailoring phase composition, crystal structure, local chemical environment, and defect states that govern hydrogen sorption thermodynamics and kinetics. This review summarizes current understanding of hydrogen interaction mechanisms in HEAs and discusses the role of body-centered cubic (BCC), face-centered cubic (FCC), and Laves phases in determining hydrogen capacity, reversibility, and cyclic stability. The limitations of commonly used descriptors, including valence electron concentration (VEC), atomic size mismatch δ, enthalpy of mixing ΔHmix, and Ω parameter, in predicting hydrogen storage behavior are critically analyzed. Particular attention is given to the effects of processing methods, phase transformations during hydrogenation/dehydrogenation, and the energetic heterogeneity of interstitial sites in multicomponent systems. The review highlights that future progress will depend on the transition from empirical alloy discovery toward physically informed multiparametric design integrating CALPHAD, DFT modeling, machine learning, and in situ/operando characterization techniques for the development of efficient and durable hydrogen storage materials.

Metals doi: 10.3390/met16060576

Authors: Rui Wang Xuhui Bai Lihong Su Guangyang Jiang Yu Sun Yu Liu Yu Zhu Xi Huang

In this study, the stability of the {112}<111> rolling texture component during asymmetric accumulative roll-bonding (AARB) was systematically investigated using a crystal plasticity finite element method (CPFEM) model. The CPFEM predictions showed that the plastic deformation was inhomogeneous along the thickness for all five asymmetric ratios (1.0, 1.2, 1.5, 0.83, and 0.66). To characterize the plastic deformation and texture evolution, through-thickness shear strain, slip-system shear strain, crystal rotation behaviour, pole figures, and the retained area fraction of the {1 1 2}<1 1 1> texture component were analyzed. It was found that the asymmetric ratio, surface friction, and cutting-stacking pattern in AARB played a critical role in the preservation of initial {1 1 2}<1 1 1>.

Metals doi: 10.3390/met16060575

Authors: Liguang Zhu Xin Wang Yihua Han

Sulfur-containing medium-carbon microalloyed steel blooms are widely used for high-load automotive components, and reducing surface defects is important for improving product yield and lowering downstream processing costs. To address surface defects such as star cracks and microcracks in the continuous casting of these steel blooms, this study redesigned the mold flux on the basis of the steel’s solidification characteristics and crack susceptibility and carried out a twin-strand industrial comparative casting trial. Thermodynamic and thermophysical analyses indicated that the relatively high contents of S, Mn, and Ti/N in the steel promoted the precipitation of MnS and TiN–MnS complex inclusions along grain boundaries, severely weakening grain boundary cohesion. Meanwhile, the high specific heat capacity and low thermal conductivity further intensified thermal stress concentration in the solidifying shell, rendering the steel highly susceptible to cracking. Evaluation of the originally used mold flux (Flux A) revealed that its high melting temperature (1189 °C), long melting time (106 s), high break temperature (1170 °C), and poor crystallization behavior resulted in an excessively thin liquid slag layer (<5 mm) within the mold, making it difficult to provide adequate lubrication and stable heat transfer; these were key external factors inducing surface defects. Accordingly, the optimized mold flux (Flux B) was designed and prepared by increasing the basicity from 0.95 to 1.1, raising the Al2O3 content from 9.48% to 11.16%, increasing the F content from 4.93% to 5.58%, and reducing the carbon content from 13.85% to 6.97%. The rheological and crystallization properties of the flux were optimized in a coordinated manner, allowing uniform heat transfer through the crystalline slag layer while maintaining adequate lubrication. Industrial comparative trials demonstrated that Flux B stabilized the liquid slag layer at 8–10 mm, increased slag consumption to 0.56 kg/t, and significantly reduced surface defects such as star cracks and microcracks on blooms. The ultrasonic testing acceptance rate for rolled products increased to 98.6%, thereby meeting stringent quality requirements for the continuous casting of sulfur-containing, medium-carbon, microalloyed steel blooms.

Metals doi: 10.3390/met16060574

Authors: Chaoxiong Qu Chenyang Zhou Chao Fang Zhixu Mao Jin Liu Xinlei Li Tingyu Deng Dean Deng

316LN stainless steel is widely used in critical nuclear fusion structural components due to its excellent mechanical properties and machinability. However, its high thermal expansion coefficient and low thermal conductivity promote welding distortion, while work hardening causes residual stress accumulation. Thermo-elastic–plastic finite element modeling (FEM) is the primary numerical method for predicting these effects. Yet, despite hardware advances, full-scale simulations—especially for thick plates with multi-pass welds—remain computationally expensive, hindering the balance between efficiency and accuracy. To address the inherent trade-off between welding efficiency and dimensional accuracy in multi-pass, multi-layer welding of thick-section components, this study employs MSC. Marc to develop a finite element model of a 15 mm thick butt-welded joint fabricated from 316LN stainless steel. Three distinct heat source models—instantaneous, enhanced moving, and moving element-set—are systematically implemented to simulate transient temperature fields, residual stress distributions, and welding deformation. All numerical predictions are rigorously validated against experimental measurements to comprehensively assess both accuracy and computational efficiency. Results indicate that: (i) the predicted molten pool geometries and characteristic thermal cycle profiles from all three models exhibit strong agreement with experimental observations; (ii) longitudinal residual stress distributions predicted by all models align closely with measured values; (iii) transverse residual stresses predicted by the moving element-set and enhanced moving heat sources agree well with experiments, whereas those from the instantaneous heat source show marked deviation; (iv) angular distortion predictions from the moving element-set heat source achieve over 90% conformity with experimental data, while the instantaneous heat source substantially underestimates angular distortion, and the enhanced moving heat source yields approximately 65% agreement; and (v) in terms of computational efficiency, the instantaneous heat source requires only ~40% of the computation time needed by the moving heat source.

Metals doi: 10.3390/met16060573

Authors: Boris Yanachkov Kateryna Valuiska Yana Mourdjeva Vanya Dyakova Krasimir Kolev Tatiana Simeonova Rumen Krastev Stivan Vasilev Rumyana Lazarova

This study investigates hydrogen embrittlement in welded joints of X52 (L360) pipeline steel obtained from an operating natural gas transmission network after 31 years of service, with particular emphasis on production (longitudinal) and girth (circumferential) welds. The aim is to elucidate the influence of microstructural heterogeneity across the pipe wall and within different welded joint types on hydrogen transport, trapping behavior, and fracture mechanisms. The investigation combines X-ray diffraction, electrochemical hydrogen permeation testing, fractographic analysis, and transmission electron microscopy. X-ray diffraction results show that the base metal and girth weld consist predominantly of body-centered cubic ferrite, whereas the production weld additionally contains retained austenite associated with an elevated manganese content. These phase-related differences are consistent with transmission electron microscopy observations of martensite–austenite constituents within the weld microstructure. Electrochemical hydrogen permeation measurements reveal pronounced microstructure-dependent hydrogen transport behavior. The production weld exhibits a significantly lower apparent diffusion coefficient and a markedly higher hydrogen trap density, approximately five times greater than those of the base metal and girth weld, providing a mechanistic explanation for the observed differences in hydrogen uptake behavior. Fractographic analysis demonstrates a transition from ductile microvoid coalescence in the uncharged condition to predominantly brittle fracture following hydrogen charging. This transition is accompanied by a substantial increase in the fraction of brittle fracture zones, reaching approximately 53% in hydrogen-charged specimens. A pronounced gradient in hydrogen embrittlement susceptibility is observed across the pipe wall thickness, with outer-wall specimens consistently exhibiting greater susceptibility than inner-wall specimens. This behavior reflects the combined influence of long-term soil corrosion and hydrogen-assisted degradation. Transmission electron microscopy reveals that plastic deformation governs dislocation generation, while hydrogen significantly modifies dislocation behavior by promoting dislocation pile-ups near martensite–austenite constituents and non-metallic inclusions. These observations indicate strong interactions between hydrogen, dislocations, and microstructural heterogeneities. A clear size-dependent role of non-metallic inclusions is identified. Sub-micron inclusions act primarily as irreversible hydrogen trapping sites that contribute to hydrogen redistribution within the microstructure, whereas larger inclusions serve as preferential crack initiation sites under hydrogen charging conditions. Overall, the results demonstrate that hydrogen embrittlement behavior is governed by the combined effects of microstructural state, welded joint type, and long-term service-induced degradation, resulting in distinct hydrogen transport characteristics and fracture responses across the pipe wall.

Metals doi: 10.3390/met16060572

Authors: Luis Olmos Armando Michel Garcia-Carrillo Jose Lemus-Ruiz Omar Jiménez Dante Arteaga Julio Cesar Villalobos-Brito Melina Velasco-Plascencia

This study aims to develop CoCrMo/xCu composites through liquid phase sintering. The primary focus is on investigating how the addition of copper influences sintering kinetics, microstructure, and mechanical properties. The copper volume fraction ranged from 10 to 25 wt.% relative to CoCrMo. Sintering was conducted at 1150 °C under an argon atmosphere. Characterization methods included scanning electron microscopy, computed microtomography, and X-ray diffraction analysis. It was observed that molten copper, which forms upon reaching its melting temperature, can fill the interparticle spaces left by CoCrMo particles in the green compacts. During sintering, densification is further enhanced by the dissolution of CoCrMo, resulting in the formation of intermetallic phases enriched in Cr and Mo, as well as a ternary Co-Cr-Cu compound. Both densification and intermetallic formation contribute to increased microhardness as Cu content rises. It is concluded that the CoCrMo/25Cu composite exhibits the best mechanical and corrosion properties because its densification was improved by the Cu liquid.

Metals doi: 10.3390/met16060571

Authors: Aiwei Lv Dong Feng Xudong Luo Siyao Liu Jiegang You Dabin Qi

To improve steel cleanliness during continuous casting, tundish flow-control devices must effectively regulate molten-steel flow and promote the removal of non-metallic inclusions. In this study, a numerical investigation was conducted to clarify the coupled effects of pore number and pore elevation angle in an inclined porous tundish filter on molten-steel flow behavior and inclusion removal. Twenty-five filter configurations were compared by varying the pore number from 2 to 32 pores and the pore elevation angle from 20° to 40° while maintaining an identical total flow-through area. The results show that inclusion removal is governed by the combined effects of flow guidance, velocity-field uniformity, and post-filter streamline distribution, with the filter containing 8 pores and a 40° pore elevation angle achieving the highest average inclusion removal efficiency of 74.33% for 20–80 μm inclusions. These findings provide a quantitative basis for optimizing tundish filter geometry and improving steel cleanliness during continuous casting.

Metals doi: 10.3390/met16060569

Authors: Linru Xia Weihuang Wu Huan Luo Fengkang Wang Xianjun Lei Baoqiang Xu

Gold, as a critical material with both financial and industrial value, is widely used across numerous fields such as finance, aerospace and medical care. Under the global background of increasing geopolitical risks and the advancement of high-tech industries, the demand for gold continues to grow steadily. The main raw materials for extracting gold are mainly divided into ore and electronic waste. Currently, conventional cyanidation remains the dominant industrial method for gold recovery. However, issues such as pollution and high toxicity of cyanide tailings are driving global efforts to explore environmentally friendly alternatives. Therefore, the development of green and efficient gold extraction technology has become a global research hotspot. This article focuses on cyanide-free leaching technologies, providing a detailed review of their current developments, advantages, and limitations, and proposing future trends in gold extraction. The future development directions of gold extraction include the development of thiosulfate–glycine leaching systems, the combination of multi-technology collaborative processes such as ultrasonic assistance and biological treatment to enhance efficiency, the strengthening of microbial metallurgy technology, and the construction of a resource recycling system for electronic waste. This review provides new insights and development directions for extracting gold for sustainable development.

Metals doi: 10.3390/met16060570

Authors: Yaojian Ren Tailin Yang Honglian Deng Junjie Feng Qingkun Meng Jiqiu Qi Fuxiang Wei Yanwei Sui

AlCrFeNi-based high-entropy alloys (HEAs) have attracted considerable interest owing to their adjustable phase constitution and attractive mechanical performance. In this study, AlCr1.6FexNi(3.2−x)Si0.2 HEAs (x = 1.0–2.0) were fabricated by vacuum arc melting to systematically evaluate the influence of the Fe/Ni ratio on phase evolution, microstructural characteristics, and mechanical behavior. The results indicate that, with increasing Fe content, the phase constitution gradually changes from BCC+B2+σ to BCC+B2. Correspondingly, the microstructure evolves from floral and cellular eutectic morphologies to branch-like BCC-rich regions with inter-branch/intercellular eutectic constituents. At the same time, the Vickers hardness decreases from 584.1 HV to 365.7 HV as the Fe content increases. Compression results show a gradual reduction in alloy strength, whereas the deformation ability is noticeably improved. Fracture surface analysis further reveals that the alloys with x ≤ 1.4 exhibit typical brittle fracture features, while those with x ≥ 1.6 display incomplete fracture and enhanced plastic deformation. These results clarify the relationship among Fe/Ni ratio, phase constitution, microstructural evolution, and mechanical properties in AlCrFeNiSi-based HEAs.

Metals doi: 10.3390/met16060568

Authors: Tetsuji Saito Daisuke Nishio-Hamane

Electric motors that use neodymium–iron–boron (Nd–Fe–B) magnets are at the forefront of global efforts to reduce greenhouse gas emissions. However, a major problem associated with these motors is thermal demagnetization driven by eddy current (EC) losses in the magnets; the relatively low electrical resistivity of Nd–Fe–B magnets means that the magnetic fields in the motor generate considerable EC losses. In this study, Nd–Fe–B magnets with 0–20 wt% Si additives were produced through hot pressing to investigate the effects of Si addition on magnetic properties and electrical resistivity. Small amounts of Si significantly increased electrical resistivity without negatively affecting the magnetic properties. The high coercivity of the Nd–Fe–B magnets, 12.5 kOe, did not decrease even in the presence of up to 15 wt% Si content. The electrical resistivity of Nd–Fe–B magnets increased monotonically as the Si content increased, from 1.43 μΩm for pure Nd–Fe–B magnets to 8.17 μΩm with 20% Si. As the electrical resistivity increased, the associated EC losses decreased; the estimated EC losses were halved with the addition of ~8 wt% Si, and further decreased to one-third through the addition of ~12 wt% Si, while simultaneously maintaining high coercivity.

Metals doi: 10.3390/met16060567

Authors: Xingwang He Yanan Lu Xinke Kang Kuo Liu Guozhen Wang Han Yang Lang Liu Haigang Dong Jiachun Zhao Yong Wang Chao Wang Jibiao Han

Rhodium is a high-value strategic platinum-group metal extensively applied in automotive exhaust purification, fine chemicals, glass production and high-temperature materials. Restricted by uneven primary resource distribution and volatile market prices, recovering rhodium from secondary resources has become increasingly critical. Solvent extraction is regarded as a promising technology for continuous and selective separation of rhodium, yet direct extraction of Rh(III) from chloride media faces severe industrial limitations. These bottlenecks are mainly attributed to diversified chloro-aqua complexes, kinetic inertness of low-spin Rh(III), strong hydration capacity and polynuclear species generation, while solution aging and inconsistent thermodynamic-experimental results further complicate extraction behaviors. This review systematically summarizes recent advances in rhodium solvent extraction from chloride media, correlating aqueous speciation regulation, activation chemistry, extractant molecular structure and extraction-stripping mechanisms. Special emphasis is placed on SnCl2-, ascorbic acid-, trichloroacetic acid- and malonate-assisted activation systems, as well as amine-, phosphorus-, sulfur-based, synergistic, ionic-liquid and deep-eutectic-solvent extractants. Key factors affecting extraction efficiency, distribution ratio, selectivity and stripping performance are clarified, and current challenges are outlined. Future research should focus on quantitative speciation analysis, in situ mechanistic characterization, targeted extractant design, and integrated evaluation of extraction, stripping, recyclability, cost and real-feed adaptability, so as to provide theoretical support for efficient and clean rhodium recovery.

Metals doi: 10.3390/met16060566

Authors: Yongan Huang Jingyao Gao Changji Wang Caihong Dou Kunming Pan

The three-phase region of Mo3Si-Mo5Si3-Mo5SiB2(MoSiB) exhibits excellent high-temperature oxidation resistance and is considered a highly promising high-temperature structural material. However, the presence of porous structures significantly increases the surface area exposed to oxidation. Metallic porous materials often suffer from inadequate corrosion resistance and insufficient high-temperature oxidation resistance, whereas ceramic porous materials are plagued by high brittleness. Intermetallic compounds offer a combination of the advantages of both metals and ceramics. Nevertheless, the high-temperature oxidation behavior of porous MoSiB has not yet been systematically elucidated. The study systematically investigates the effect of pore structure on the high-temperature oxidation behavior of porous MoSiB at 1000 °C and 1300 °C, with a focus on oxidation kinetics, phase evolution, surface and cross-sectional morphology and underlying oxidation mechanisms. The effects of porosity and temperature on the oxidation process are also analyzed. The results indicate that at 1000 °C, the material exhibits uniform oxidation, with lower porosity contributing to better oxidation resistance. At 1300 °C, oxidation is limited to the surface layer, where low-viscosity SiO2(B) rapidly seals the pores to form a dense protective layer. This research reveals the high-temperature oxidation mechanism and phase evolution of porous MoSiB, providing a theoretical foundation for its application in high-temperature structural fields.

Metals doi: 10.3390/met16060565

Authors: Eunhye Park Byounglok Jang

This study examines the microstructural characteristics and tensile properties of autogenous orbital gas tungsten arc (GTA) circumferential butt welds produced on commercially rolled 304 stainless steel seam pipes (outer diameter 38.1 mm, wall thickness 2.0 mm) for high-purity fluid distribution systems. A three-segment current profile was employed using an AMI 8-4000 orbital system, with peak currents of 70, 67, and 65 A for the penetration, remelting, and downslope (crater-fill) segments, respectively, under high-purity Ar (99.999%) shielding with back purging. Electron backscatter diffraction (EBSD) analysis, including image quality (IQ), inverse pole figure (IPF), and kernel average misorientation (KAM) mapping, showed that the weld metal consists of epitaxially grown columnar austenite grains strongly oriented along the solidification direction, whereas the heat-affected zone (HAZ) exhibits finer equiaxed grains with an increased Σ3 twin boundary fraction and elevated low-angle boundary fraction, indicative of partial recrystallization. Only sparse, discontinuous δ-ferrite stringers were detected in the fusion zone, and no non-metallic inclusions were observed on fracture surfaces, supporting the weld metal’s suitability for semiconductor-grade cleanliness. Vickers microhardness profiles revealed modest hardness differences (typically within 10–20 HV) between the weld metal, HAZ, and base metal, with no pronounced HAZ softening. Cross-weld tensile tests conducted in accordance with ASTM E8/E8M-22 yielded yield strengths above 200 MPa, ultimate tensile strengths of 650–680 MPa, and total elongations approaching 40%, comparable to the as-received pipe. Scanning electron fractography confirmed fully ductile failure via microvoid coalescence without evidence of cleavage, intergranular decohesion, or weld-defect-induced embrittlement. Collectively, these results demonstrate that the three-segment autogenous orbital GTAW procedure produces structurally sound, particle-clean joints suitable for 304 stainless steel seam pipes used in high-purity industrial piping.

Metals doi: 10.3390/met16060564

Authors: Hamad Alarfati Gordana Kastratović Aleksandar Grbović Martina Balać Nenad Vidanović

In this study, fatigue crack propagation due to unexpected damage caused by fretting in an aero engine high-pressure turbine (HPT) blade slot is analyzed. Two different numerical crack models were applied and studied to simulate fatigue crack propagation caused by amplitude service loading. Also, the goal was to demonstrate the capacities of numerical simulations, including their limitations, especially when the crack propagation behavior should be predicted for critical parts of the real structure. It is shown that the structural integrity of the analyzed component is not jeopardized by the existing damage.

Metals doi: 10.3390/met16060563

Authors: Taoyu Zhou Guanglin Zhu Cean Guo Xiahe Liu

The structural stability of high-temperature-formed oxide films (HTOFs) on SAC305 solder plays a critical role in determining corrosion reliability during long-term thermal exposure, yet the coupled effects of oxide evolution and substrate microstructure changes remain unclear. In this work, SAC305 solder was thermally aged at 150 °C for 10–60 days, and the evolution of the oxide film structure and substrate microstructure was systematically investigated using SEM, XRD, XPS, and electrochemical techniques. The results reveal that HTOF mainly consists of a SnO/SnO2-layered structure with thickness increasing slightly from approximately 16.5 nm to 18 nm, while increasing micro-cracks and Ag3Sn coarsening induced by the Kirkendall effect lead to significant reductions in impedance parameters and corrosion resistance. These findings demonstrate that the degradation of HTOF is governed by the coupled effects of oxide defect accumulation and intermetallic phase coarsening, providing a mechanistic insight into the corrosion failure of SAC305 solder under long-term thermal aging conditions.

Metals doi: 10.3390/met16060562

Authors: Jiangzilin Liu Zhiguo Luo Jiayu Luo Xiaozhuang Liu

To achieve carbon emission reduction in the long ironmaking process with blast furnace-basic oxygen furnace (BF-BOF), the Hebei Iron & Steel Group and Northeastern University have jointly developed the Reduction Smelting Furnace with Carbon-Cycling, Hydrogen-Rich, and Pure-Oxygen (CHORSF) ironmaking process. This new process employs advanced technology to overcome the hydrogen enrichment limitation of traditional BFs and the problems of “hot at the lower part and cold at the upper part” in all-oxygen BFs. This paper establishes an operating line for the CHORSF ironmaking process, systematically analyzes the influence mechanisms of key smelting parameters on CHORSF, and provides guidance for optimizing the process. The results show that the slopes of the operating lines in the indirect reduction zone can characterize the reducing gas consumption under actual conditions; under the smelting conditions of this study, the reducing gas consumption falls within a specific range. The slope of the operating line in the softening–melting–dripping zone can be used to quantify the coke ratio. Furthermore, increasing the metallization ratio at the bottom of the indirect reduction zone leads to a slight increase in reducing gas consumption, while a 1% increase in the same metallization ratio results in a notable decrease in the coke ratio.

Metals doi: 10.3390/met16060561

Authors: Junhyuk Son Daeyong Kim

Ultra-high-strength steel (UHSS) cross-members with a high height-to-width ratio are prone to forming defects, such as splitting and wrinkling, due to localized stress concentration during the drawing process. In this study, the addendum geometry in first-stage of a two-stage drawing process was optimized to improve the formability of a cross-member made of 1 GPa-grade UHSS. The optimization was performed using the Sigma module of AutoForm, and Latin hypercube sampling was adopted for the design of experiments. The punch opening width, upper bar radius, wall angle, and lower die radius of the addendum were selected as design parameters, and multi-objective optimization was conducted to simultaneously minimize the maximum failure index and maximum wrinkle value, the two AutoForm forming-defect indicators used in this study. In the initial design, the maximum failure index was 1.044, exceeding the splitting criterion of 1.0; however, this value was reduced to 0.961 in the optimized design, thereby mitigating the risk of splitting. In addition, the maximum wrinkle value was reduced by 11.7% compared with that of the initial design. Pareto analysis was performed to quantitatively evaluate the effects of the design parameters on the forming defects, and the results confirmed that the punch opening width and lower die radius were the dominant parameters affecting both splitting and wrinkling. These results demonstrate that die addendum geometry optimization is effective for reducing splitting and wrinkling in 1 GPa-grade UHSS cross-members.

Metals doi: 10.3390/met16050560

Authors: Yu Li Xueting Chen Yinglong Liang Shuai Zhang Guili Yin

The microstructure of Ti-Al-Si coatings prepared by direct laser deposition (DLD) requires further refinement and homogenization to enhance coating performance. In this study, an electrostatic field (EF) was introduced to assist the DLD process, and a thermal-flow-electrical multiphysics coupling model was established using COMSOL Multiphysics 6.3 software. The solidification behavior of the molten pool under the EF was investigated, focusing on the mechanism by which the EF influences the nucleation and growth of grains and reinforcing phases. Experimental results revealed that the external EF disrupted the molten pool flow, thereby altering the internal heat dissipation mechanism and affecting the morphology and size of the solidified grains. Under an external EF of 150 V/cm, the coating exhibited the most refined grains, with an average size of 0.417 μm (a 46% reduction non-EF). Concomitantly, the application of the EF increased the concentration of Ti4+ and Si4+ ions at the solid–liquid interface, promoting the formation of a substantial quantity of Ti5Si3 reinforcing phases. The average microhardness of the coating reached 1393 HV0.2, which is 21% higher than that of the coating without an EF. The surface roughness decreased to 0.551 μm, with a minimum wear percentage of 1.4%. Moreover, the EF modified the wear mechanism of the DLD Ti-Al-Si coating. The findings of this study hold scientific significance and practical value for advancing DLD-fabricated high-performance titanium alloy components, offering critical insights into microstructure optimization and process control strategies.

Metals doi: 10.3390/met16050559

Authors: Tong Wu Shuming Xing

In this paper, the supersaturated solid solution of Al-Cu3-Si-Mg alloy prepared by molten metal die forging (MMDF) was used as the research object. The formation and evolution of precipitates during aging treatment were investigated through experiments at different temperatures and times, and the precipitation mechanisms and sequences of various precipitates were analyzed. The main precipitated phases formed in the supersaturated solid solution of the Al-Cu3-Si-Mg alloy after aging treatment are θ(Al2Cu), θ′(Al3.6Cu2), γ′(Al0.63Mg0.37), and η′(Cu, Si). Based on XRD and TEM analysis under different aging treatment conditions, the precipitation sequence is determined as follows: SSS → GP0 → GP0 + γ′ → GP0 + (γ′ + γ) + θ″ + η′ → (γ′ + γ) + (θ″ + θ′) + (η′ + η) → (γ′ + γ) + (θ + θ′) + (η′ + η) → (γ′ + γ) + (θ + θ′) + η → γ + θ + η. After aging treatment at 165–185 °C for 4 h, chain-like θ(Al2Cu) precipitates are discontinuously distributed at the α-Al grain boundaries, and disc-shaped θ′(Al3.6Cu2) and θ″(Al2Cu) phases mainly precipitate within the grains. When the temperature exceeds 185 °C, the chain-like θ(Al2Cu) precipitates at the grain boundaries gradually become continuous, and the fraction increase from 1.5% to 15.2%. The amount of the θ(Al2Cu) phase in the grains increases from 2 to 6, and the size of θ′(Al3.6Cu2) decreases obviously. After aging treatment at 185 °C for 5–6 h, the chain-like θ(Al2Cu) precipitates become more continuous, and the fraction continues to increase from 32.1% to 52.6%. The effect of chain-like precipitates at grain boundaries on the mechanical properties of the matrix is opposite to the strengthening contribution of dispersed intragranular precipitates. When the aging condition exceeds 185 °C × 5 h, the excessive formation of chain-like grain boundary precipitates causes both the strength and hardness of the alloy to show a decreasing trend.

Metals doi: 10.3390/met16050558

Authors: Madhuri Birare Adam Dębski Władysław Gąsior Wojciech Gierlotka

Magnesium antimonide (Mg3Sb2) has emerged as a promising high-performance thermoelectric material, yet its efficiency is fundamentally determined by intrinsic point defects. In this study, we present a comprehensive investigation of defects in the intermetallic compound Mg3Sb2 using first laws of thermodynamics and density functional theory (DFT) within the generalized gradient approximation (GGA). By calculating the energy of defect formation and the charge transition energy between energy levels, it was determined how the change in chemical potential associated with phase synthesis affects the phase stability and carrier concentrations. Calculations show that donor defects dominate in Mg-rich alloys, primarily antimony vacancies and magnesium atoms in interstitial positions. This means that in a phase with a slight magnesium excess, e.g., Mg3.01Sb1.99 at 1400 K, n-type conductivity dominates. In the opposite case, i.e., in an Sb-rich alloy, magnesium vacancies spontaneously form in the Wyckoff 1a position. These ionized acceptors induce strong self-compensation, blocking the Fermi level about 0.38 eV above the valence band maximum. As a result of this process, the Mg3Sb2 phase, at elevated temperatures, becomes the non-stoichiometric Mg2.99Sb2.01 phase, which causes the material to retain p-type conductivity and actively block doping-induced n-type conductivity. The conducted studies demonstrate that the homogeneity range of the Mg-Sb system, although traditionally considered narrow, has a significant impact on the semiconducting properties of the material. Furthermore, they also point to the need for continued research on high temperature in the area of synthetic defect engineering, interface engineering, and optimization of the thermoelectric properties of materials based on Mg-Sb alloys.

Metals doi: 10.3390/met16050557

Authors: Suyi Gu Xiaobin Zhu Qiang Wang

In this paper, a ternary Tb65Co25Ni10 amorphous tape was successfully prepared, and the glass forming ability (GFA), magnetic properties, and magnetocaloric characteristics of the amorphous tape were studied in detail. The values of the reduced glass transition temperature Trg, parameter γ and critical section thickness Zc indicate the good GFA of the Tb65Co25Ni10 amorphous tape. The Tb65Co25Ni10 amorphous tape exhibits spin-glass-like behavior, with a Curie temperature of 83 K and a spin-freezing temperature (Tf) of 73 K, and a large coercivity below Tf. The spin-glass-like behavior significantly deteriorates the magnetic entropy change (−∆Sm) of the Tb65Co25Ni10 amorphous tape at low temperatures, resulting in the deviation of magnetic entropy change behavior from the predicted results. However, the Tb65Co25Ni10 amorphous tape still shows an excellent magnetocaloric effect (the peak value of −∆Sm of 9.46 J kg−1 K−1 and the refrigeration capacity of 569.5 J kg−1 under 5 T, both of which are higher than those of most other heavy rare earth-based amorphous alloys), indicating the great application potential in the field of magnetic refrigeration for the amorphous tape.

Metals doi: 10.3390/met16050556

Authors: Ben Lin Ying Li Xiwu Li Yongan Zhang Kai Wen Changlin Li Lizhen Yan Yanan Li Hongwei Yan Zhihui Li Baiqing Xiong

To address the insufficient strength of friction-stir-welded (FSW) ultra-high-strength Al–Cu–Li alloy joints, the effects of post-weld heat treatment (PWHT) on microstructural evolution and mechanical properties were systematically investigated. The as-welded joint showed a “W”-shaped microhardness profile, with the minimum value located in the thermo-mechanically affected zone (TMAZ), mainly caused by the dissolution of T1 phases and precipitation of coarse AlCu, AlCuMg, and AlCuMn phases during welding. Direct artificial aging at 155 °C for 24 h failed to improve joint strength due to solute depletion induced by pre-existing coarse secondary phases. Solution treatment re-dissolved coarse precipitates into the matrix, and subsequent aging led to uniform precipitation dominated by T1 and θ′ phases, with a consistent microhardness of ~155 HV across all zones. By introducing pre-stretching deformation after solution treatment, T1 became the dominant strengthening phase in all regions, accompanied by a remarkable increase in both microhardness and tensile strength. With 3% pre-stretching, the microhardness reached 185 HV, and the ultimate tensile strength of the joint reached 600 MPa, corresponding to a joint efficiency as high as 95%, which is superior to most reported values for Al–Li alloy FSW joints. This study clarifies the precipitation evolution mechanism under tailored PWHT and provides an effective strategy for property regulation of high-performance Al–Cu–Li alloy FSW structures in aerospace applications.

Metals doi: 10.3390/met16050555

Authors: Nursultan Ulmaganbetov Maral Almagambetov Yerbolat Makhambetov Armat Zhakan Zhadiger Sadyk Zhalgas Saulebek Ruslan Toleukadyr Diana Isagulova

This study investigates the agglomeration of chromium-containing dust from ferroalloy production using rigid vacuum extrusion. Direct utilization of fine technogenic materials in submerged arc furnaces is limited due to poor gas permeability, increased dust generation, and unstable smelting conditions. The aim of this work was to compare bentonite and polymer binders in brex production and evaluate their metallurgical applicability. Chromium-containing dust from the gas-cleaning system of the Aktobe Ferroalloy Plant (TNC Kazchrome JSC, ERG) was characterized using chemical analysis and SEM/EDS methods. The material exhibited a heterogeneous structure composed mainly of chromium-containing spinel, silicate, and oxide phases. Pilot-industrial extrusion tests were performed using J.C. Steele & Sons equipment with bentonite (10 wt.%) and polymer binder TD 021.005.BS (2.5 wt.%). The polymer binder provided improved brex geometry and significantly higher mechanical strength, achieving impact strength values up to 89.5% after curing. SEM/EDS analysis of the obtained brexes confirmed the formation of a dense agglomerated structure with uniform distribution of chromium-containing phases. Thermodynamic modeling using FactSage 8.4 showed that brex addition does not significantly affect slag composition, phase equilibria, or metal quality during high-carbon ferrochrome smelting. The results demonstrate the feasibility of polymer binders for efficient recycling of chromium-containing technogenic wastes by rigid vacuum extrusion.

Metals doi: 10.3390/met16050552

Authors: Omar Alejandro González Noriega Alejandro Flores Nicolás Jorge Uruchurtu Chavarín Laura Montserrat Alcantar Martínez María Yesenia Díaz Cárdenas César Augusto García Peréz Susana López Ayala Elsa Carmina Menchaca Campos

The corrosion of carbon steel in marine–industrial atmospheric environments remains a significant challenge due to the combined effect of aggressive ions such as chlorides and sulfates. In this context, this study aims to explore the inhibitory action of expired omeprazole applied to mild steel AISI 1018 evaluated on a solution simulating atmospheric corrosion (0.1 M Na2SO4 + 3% wt NaCl) over 72 h. The material was characterized using EDS to determine its composition of AISI 1018 steel, while Raman spectroscopy was employed to identify the functional groups and heteroatoms present on the molecular structure of omeprazole. Electrochemical noise (EN) measurements were used to evaluate the corrosion rate, type of corrosion and mechanism. Also, quantum chemical calculations of density function theory (DFT) were performed to predict the relationship between molecular structure and inhibition efficiency. The results indicate that 50 ppm provides the most stable and effective corrosion inhibition over time, as evidenced by increases in noise resistance and inhibition efficiency. In contrast, 75 ppm exhibits improved surface morphology at the end of the exposure period, which indicates enhanced surface coverage. The DFT results reveal that omeprazole possesses suitable electronic properties for corrosion inhibition, including moderate reactivity, electron-donating ability, and favorable charge distribution that promotes adsorption onto the metal surface. SEM analysis corroborates that surface damage is significantly reduced in the presence of the inhibitor, particularly at 75 ppm. This study provides new insights into the use of expired pharmaceutical compounds as corrosion inhibitors and demonstrates the capability of combining electrochemical noise analysis with DFT to evaluate both inhibition efficiency and film stability.

Metals doi: 10.3390/met16050554

Authors: Yulu Su Dan Wang Xulei Wu

In this study, 310S austenitic stainless-steel was welded using a laser with varying amounts of Nb to systematically investigate the effect of Nb on solidification cracking susceptibility, mechanical properties, and corrosion resistance of the weld. Under the present experimental conditions, the critical restraint width was higher for the 0.58 wt.% Nb and 1.45 wt.% Nb welds than for the Nb-free and 2.3 wt.% Nb welds, indicating that Nb addition affected the solidification cracking response of the weld. At low-to-moderate Nb contents, Nb can aggravate compositional segregation and increase the presence of low-melting-point liquid films, thereby increasing cracking susceptibility. At higher Nb contents, the reduced cracking susceptibility was accompanied by microstructural refinement and changes in the distribution of Nb-rich constituents during solidification. With increasing Nb content, the number of precipitated phases in the weld increases, mainly distributed at the austenite grain boundaries in granular, elongated, and chain-like forms. The introduction of Nb generally increases the microhardness and tensile strength of the welded joint, attributed to grain refinement strengthening and solid-solution strengthening. The reduction in area first increased and then decreased, suggesting that excessive Nb addition may reduce ductility because of the increased amount of grain-boundary precipitates and local strengthening heterogeneity. With increasing Nb content, the Ir/Ia ratio decreased from 67.6% to 52.2%, suggesting improved intergranular corrosion resistance. This improvement is likely related to the preferential reaction of Nb with carbon, which may suppress the formation of Cr-depleted zones at grain boundaries. Overall, Nb addition improved the corrosion resistance and increased the hardness and tensile strength of the weld; however, its effect on solidification cracking susceptibility was non-monotonic, indicating that careful control of Nb content is required to balance cracking susceptibility, mechanical properties, and corrosion resistance.

Metals doi: 10.3390/met16050553

Authors: Hesong Guo Shengzhe Chang Jianliang Sun Yafei Lei Chong Yang Wei Zheng

To achieve early perception and accurate prediction of flatness quality, a partial least squares–particle swarm optimization–multi-output support vector regression (PLS-PSO-MSVR) is proposed. Firstly, we parameterized the flatness and used it as an evaluation indicator for flatness. Then, the prediction model was constructed using multi-output support vector regression (MSVR). In the modeling process, particle swarm optimization is used to optimize the parameters. To overcome the problem of information redundancy, reduce data dimensions to reduce computational time, and improve the prediction performance of the algorithm, this paper combines partial least squares and PSO-MSVR to achieve accurate prediction of the flatness features. Finally, the actual industrial process data from the hot rolling 1580 production line was used for validation, and the predicted performance was evaluated using mean absolute error (MAE), mean square error (MSE), root mean square error (RMSE), and coefficient of determination (R2). MAE decreased to 0.15, MSE decreased to 0.038, and RMSE decreased to 0.195. The R2 approaches 1, indicating excellent model fit. This study achieves accurate prediction of the flatness characteristic coefficient, which not only enhances the diagnostic efficiency of steel flatness quality but also helps avoid unnecessary economic losses. Moreover, the prediction model provides a reliable basis for flatness control, offering operators a user-friendly reference tool. This approach compensates for the time lag inherent in the original system and contributes to improved accuracy in flatness control.

Metals doi: 10.3390/met16050551

Authors: Xisheng Yang Shaohai Ma Xu Zhu Jia He Ning Bai Tianyi Zhang

This study investigated the high-temperature (600 °C, 650 °C, 700 °C, 750 °C and 800 °C) mechanical property and failure analysis of GH2070P alloy in boiler elbow pipe. The results show that the microstructures of GH2070P alloy at three typical positions (outer radius (OR), middle radius (MR) and inner radius (IR)) of the bent pipe exhibit distinct gradient features to some degree, and the unsignificant difference in the morphology and composition of the second phase can be found in OR, MR and IR. Below 700 °C, the mechanical properties at different positions show differences affected by the stress states of different positions. Among them, the tensile strength and yield strength of OR under tensile stress states are lower than those of IR under compressive stress states at the same temperature. However, above 700 °C, the mechanical properties of the three positions show no significant difference, which is related to stress release at high temperatures. From 700 °C to 800 °C, the degree of brittle fracture of the material increases, which is related to the performance degradation caused by the coarsening of the second phase at high temperatures. It is worth noting that within the temperature range of less than 700 °C, the yield strength increases with the rise in temperature, while the tensile strength and plasticity remain at a certain level without decreasing. This indicates that the GH2070P alloy has good service performance at 700 °C.

Metals doi: 10.3390/met16050550

Authors: Fulong Li Jianliang Zhang Yang Li Tengfei Wang Ben Feng Yaozu Wang Chunmei Yu Zhengjian Liu

The use of hydrogen for smelting reduction ironmaking can effectively reduce the consumption of coke, as well as the CO2 emission. However, the dynamic mechanism of this process is not clear. In this paper, isothermal thermogravimetric analysis (TGA) was used to study the reduction process of wustite by hydrogen at 1673–1773 K. Results show that wustite can be entirely reduced, and with the increase in temperature, the reduction reaction becomes more intense, and the time required for the entire reduction decreases. The hydrogen reduction of wustite at 1673–1773 K fits the Mampel power model: f(α) = 2α1/2. When the reactants are molten and the products are solid, the apparent activation energy of the reduction process calculated by the iso-conversional method is 9.15 kJ·mol−1. Molecular dynamics simulation results show that the adsorption of hydrogen molecule on FeO surface is spontaneous. With the increase in temperature, FeO substrate becomes more active, and hydrogen molecules move more violently. The average distance between a certain hydrogen atom and its neighboring atom was analyzed statistically. The increase in temperature will increase the average bond length of hydrogen molecules, reduce their bond energy, and facilitate the adsorption of hydrogen molecules on the FeO surface.

Metals doi: 10.3390/met16050549

Authors: Turar Kusmanovich Sarsembekov Tatyana Alexandrovna Chepushtanova Yerik Serikovich Merkibayev Rustam Khassanovich Sharipov Nauryzbek Bakhytuly

Niobium commonly occurs as a minor component in Fe–Ti–O oxide systems associated with ilmenite ores and titanium-bearing metallurgical materials, yet its speciation and incorporation mechanisms remain insufficiently resolved. This study investigates the distribution, structural incorporation, and microphase localization of niobium in the Fe–Ti–O system, with emphasis on TiO2-rich domains. Electron probe microanalysis with EDS/WDS, X-ray diffraction, thermal analysis, and thermodynamic modeling in HSC Chemistry were combined to characterize niobium-bearing phases in natural and model oxide systems. Niobium was found to occur in two principal modes: as a low-level isomorphic impurity in Fe–Ti oxide matrices and as localized enrichments in TiO2-rich domains, particularly rutile lamellae. A first-order area-based estimate for representative analyzed grains suggests that approximately 60–80% of the detected niobium is associated with the lamellar TiO2 channel. The combined observations are consistent with a sequential mechanism involving isomorphic substitution of Nb in Ti sites, followed by microphase enrichment and segregation into more compositionally distinct niobium-bearing oxide or titanate microphases. In the studied material, integrated mapped-field Nb is about 0.04 wt.%, whereas matrix Nb commonly lies at trace levels of about 0.02–0.05 wt.% under the applied analytical conditions, consistent with low-level background incorporation, whereas locally Nb-enriched rutile-like domains reach about 0.70–1.00 wt.%. TiO2-rich domains are therefore identified as the principal concentrators of niobium in Fe–Ti oxide systems. Taken together, the natural observations, model experiments, and thermodynamic calculations support an integrated mechanistic sequence of Nb evolution in the Fe–Ti–O system: isomorphic substitution → microphase enrichment in TiO2-related domains → segregation into distinct Nb-bearing oxides/niobates. These findings provide a practical framework for interpreting Nb behavior in natural and technological Fe–Ti–O materials.

Metals doi: 10.3390/met16050548

Authors: Ahmed Nabil Elalem Xin Wu

Wire Arc Additive Manufacturing (WAAM) is a cost-effective and scalable technique for producing large metallic components; however, coarse columnar microstructures, strong crystallographic texture, and significant residual stresses limit its widespread adoption. Hybrid WAAM processes that integrate deformation-based techniques have been developed to address these limitations. This review provides an analysis of deformation-assisted WAAM, covering interlayer rolling, friction stir processing (FSP), machine hammer peening, laser shock peening, and ultrasonic-vibration-assisted techniques. These hybrid techniques introduce additional thermomechanical parameters (strain, strain rate, and applied stress) that significantly influence microstructure evolution. The governing physical metallurgy mechanisms are discussed in detail, including dislocation accumulation, recovery, static and dynamic recrystallization, and severe plastic deformation. Studies from 2022 to 2025 are critically reviewed, highlighting the effectiveness of hybrid WAAM in promoting columnar-to-equiaxed grain transformation, reducing anisotropy, mitigating defects, and improving mechanical properties across aluminum, titanium, steels, and nickel-based alloys. The integration of auxiliary processes such as in situ machining and heat treatment is also discussed. This review establishes a process–structure–property framework for hybrid WAAM and provides guidance for the development of advanced additive manufacturing systems for the production of near-net-shape components, with reported yield-strength gains of 20–40%, elongation gains of 10–30%, and fatigue-life improvements of up to 60% relative to as-built WAAM.

Metals doi: 10.3390/met16050547

Authors: Jatupong Pantri Panya Wiman Thanasak Nilsonthi Somrerk Chandra-ambhorn

Ferritic stainless steels are widely used as interconnects of solid oxide fuel cells (SOFCs) due to their high temperature stability and thermal expansion similar to that of the electrolyte. To help commercialise SOFCs, commercial-grade ferritic stainless steel with a coating, i.e., Type 430, has been considered a promising material for this application. In this work, we developed a Mn-Co oxide coating via anodic electrodeposition followed by heat treatment processes in Ar and oxygen at 800 °C. The proposed coating helped reduce the formation of Cr-rich oxide at the interface between the coating and substrate relative to a sample coated without annealing in Ar. It also provided a relatively dense coating layer and better withstood the applied load, provoking the first spallation of the coating layer assessed by the scratch test. A diagram used to assess the effects of pore density and size on the coating’s protectiveness is included in the manuscript.

Metals doi: 10.3390/met16050546

Authors: Saurabh Tiwari Nokeun Park Nagireddy Gari Subba Reddy

Hydrogen embrittlement is a critical degradation mechanism in microalloyed and pipeline steels used in hydrogen-economy infrastructure. We present a physics-informed neural network (PINN) framework that embeds Fick’s second law and the Arrhenius temperature dependence directly into the loss function, trained on 22 temperature-dependent data points spanning pure α-Fe and API X65 pipeline steels (modern and vintage microstructures). The PINN recovered the pure-iron activation energy (4.2 kJ mol−1 vs. literature 4.15 kJ mol−1, R2 = 1.00) and yielded Arrhenius activation energies of 28.5 and 45.2 kJ mol−1 for modern and vintage X65, respectively, indicating substantially stronger trapping in older microstructures. McNabb–Foster analysis of ten ternary Fe–Me–C,N alloys revealed flat-trap binding enthalpies of 19 ± 2 kJ mol−1 and deep-trap free energies of 57 ± 2 kJ mol−1, with effective diffusivities spanning three orders of magnitude governed primarily by flat-trap density. The framework provides a computationally efficient and physically consistent tool for hydrogen transport prediction, with a clear roadmap for multi-feature extension incorporating compositional and microstructural descriptors.

Metals doi: 10.3390/met16050545

Authors: Kyu-Dong Lee Wi-Geol Seo Aman Gupta Shi-Hoon Choi

Ring formation in rotary kilns is a major operational problem in the ferronickel dry smelting process, in which nickel laterite ore undergoes drying, calcination, and partial reduction. Excessive ring accretion reduces thermal efficiency and disrupts stable kiln operation. In this study, the mechanism of ring formation was investigated through a combined approach integrating laboratory-scale experiments and long-term operational data obtained from a large-scale industrial rotary kiln. The effects of ore composition, particle size, and temperature on melting and sintering behavior were examined, and their correlations with operating variables such as fuel input and kiln rotational speed were analyzed. The results show that ring formation is governed by the selective melting and adhesion of low-melting constituents, particularly in ores with low basicity (MgO/SiO2 < 0.55) and high Fe content (>14 wt.%). A high fraction of fine particles (<75 μm) further promotes adhesion due to their lower melting temperature and enhanced mechanical retention on the refractory surface. In industrial operation, localized overheating near the burner zone and low kiln rotational speeds (0.9–1.1 rpm) significantly accelerate ring growth. These findings provide a mechanistic understanding of ring formation and suggest that appropriate ore blending and optimized control of fuel input and kiln rotation are effective strategies for mitigating ring accretion in commercial ferronickel rotary kilns.

Metals doi: 10.3390/met16050544

Authors: Jiwoo Byeon Dongwook Seo Seunghyo Lee

Austenitic stainless steels exhibit excellent corrosion resistance owing to the formation of passive films composed of a dense Cr-rich inner layer and porous Fe-rich outer layer. The corrosion resistance and passive film characteristics of N-containing austenitic stainless steel (NASS) were investigated in various pH and Cl−-containing environments and compared with those of commercial 304 SS. Microstructural analysis revealed that NASS had larger grains but more favorable crystal structures for the adsorption of passivating species. NASS exhibited a lower corrosion current density, higher pitting potential, and superior repassivation behavior in acidic and neutral environments, whereas 304 SS exhibited better corrosion resistance under strongly alkaline conditions. NASS formed a passive film with lower defect density and a higher fraction of compact Cr-rich species, contributing to its enhanced passive film stability and repassivation ability. Immersion tests demonstrated that pit initiation was delayed in the NASS group compared with the 304 SS group. These results indicate that the corrosion resistance of NASS in acidic and neutral environments originates from the improved stability and protective characteristics of the passive film.

Metals doi: 10.3390/met16050542

Authors: Shilei Zhang Yaoyi Cheng Peijun Liu Ruijun Yan Yongli Jin Yifan Chai

Against the backdrop of global climate warming and energy shortages, China proposed the “dual-carbon strategy” in 2020 to address climate change and promote ecological civilization. As a high-carbon emission industry, the iron and steel sector faces an urgent need to accelerate low-carbon transformation. In 2024, China’s crude steel production accounted for over 50% of the total global crude steel production, with the blast furnace–basic oxygen furnace route remaining the dominant process. As a natural iron-bearing raw material, lump ore features high iron grade and low cost, eliminating the requirements of high-temperature processing steps such as sintering or pelletizing. Therefore, increasing the proportion of lump ore in the blast furnace burden represents an effective approach to achieving energy conservation and emission reduction. However, constrained by technical constraints, the current utilization rate of natural lump ore in Chinese steel enterprises remains generally low. Research indicates that despite their higher iron content, lump ores exhibit deficiencies in metallurgical properties such as thermal shock resistance and softening–melting drip characteristics, limiting their large-scale application. Therefore, it is typically necessary to perform pre-treatment such as preheating before charging into the furnace. In actual blast furnace burden design, it is essential to balance metallurgical performance and economic considerations by appropriately combining lump ore with high-basicity sinter and pellets. This approach leverages high-temperature interactions among the burden materials to optimize the overall softening and melting behavior of the mixed charge, thereby ensuring smooth furnace operation while simultaneously advancing the low-carbon transition of the iron and steel industry.

Metals doi: 10.3390/met16050543

Authors: Min Zhao Jing Zhang Rui Wang Yunsheng An Hao Yu Zhiyuan Meng Yuxin Shu Kui Xiao

This study investigated the degradation behavior of a polyurethane acrylate coating/Q345B steel system under the coastal atmospheric conditions of Wenchang, Hainan, and evaluated the correlation between indoor accelerated tests and outdoor exposure. Outdoor exposure tests, single-factor accelerated tests (UV irradiation and neutral salt spray), and a multi-factor cyclic accelerated test combining UV, salt spray, humidity, and thermal cycling were conducted. Coating degradation was characterized by morphological observation, gloss measurement, adhesion testing, and electrochemical impedance spectroscopy. The results showed that after 8 months of outdoor exposure, localized rust spots, blistering, and under-film corrosion appeared on the coating surface. The gloss loss rate reached 15.72% after 3 months, while adhesion decreased from 5.83 MPa to 2.39 MPa during prolonged exposure. UV irradiation mainly affected gloss degradation, whereas corrosive media penetration played a dominant role in adhesion loss and electrochemical deterioration. Compared with single-factor tests, the multi-factor cyclic accelerated test exhibited the highest correlation with outdoor exposure. The corresponding correlation coefficients for gloss loss, adhesion, and low-frequency impedance modulus were 0.9764, 0.9988, and 0.9929, respectively, while the gray relational coefficients reached 0.8334, 0.8467, and 0.7977. These results demonstrate that the multi-factor cyclic accelerated test more accurately reproduces the degradation behavior and failure characteristics observed in the coastal atmosphere of Hainan. The proposed method provides a practical approach for indoor–outdoor correlation analysis and durability evaluation of protective coatings in marine atmospheric environments.

Metals doi: 10.3390/met16050541

Authors: Liang Wang Jie Zhou Rui Xia Tao Zhang Kaibo Xia Yilun Wang

Picosecond laser drilling is characterized by a minimal heat-affected zone (HAZ) and superior surface quality, making it widely utilized for fabricating film-cooling holes in aeroengine turbine blades. However, maintaining consistent drilling quality remains a significant challenge. This study conducts picosecond laser trepanning drilling experiments on a GH4169 nickel-based superalloy to investigate the quality of inclined holes. Due to its excellent high-temperature resistance, creep resistance, and corrosion resistance, GH4169 is a primary material for turbine blades. A control variable method was employed to evaluate the effects of power ratio (60–95%), number of scanning passes (5–40), and defocus amount (−0.2 mm to 0.2 mm) on the quality of inclined holes with tilt angles of 7° and 15° and a sample thickness of 0.5 mm. Entrance diameter, exit diameter, and taper angle were utilized as the key quality indicators. The results indicate that due to the distribution of laser energy flux, both the geometric dimensions and taper angles of 15° inclined holes are significantly larger than those of 7° holes. As the power ratio increases, the entrance and exit diameters exhibit non-linear expansion; a “topographic stability window” is achieved at a 75% power ratio due to the equilibrium in energy coupling. An increase in the number of scanning passes leads to larger diameters; however, excessive scanning slows down the expansion of the exit diameter due to multiple reflection losses within the hole and the accumulation of slag, thereby intensifying taper evolution. The defocus amount exerts a bidirectional regulatory effect: positive defocusing increases the entrance diameter while decreasing the exit diameter, whereas negative defocusing facilitates the expansion of the exit. Optimal hole wall quality is observed at zero defocusing. This work provides data support for parameter optimization and the selection of inclination angles in subsequent laser machining of inclined holes.

Metals doi: 10.3390/met16050540

Authors: Halil Ahmet Gören

In this study, the effects of cadmium (Cd) on 4 different alloys developed by casting the Mg-Al-Mn ternary composition, in which the second element is aluminum (Al), and the third element is manganese (Mn), based on magnesium (Mg) metal, which is known as the lightest of the metallic materials in the field of engineering, were investigated. The base alloy Mg-Al-Mn (AM60) (Q1) and the Q2, Q3, and Q4 alloys were produced by adding Cd to the base alloy at rates of 0.2%, 0.5%, and 1.0%, respectively. The effects of element addition were determined by conducting Optical Microscopy (OM), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), Energy-Dispersive X-Ray Spectroscopy (EDX), hardness tests, potentiodynamic polarization corrosion tests in a 3.5% NaCl environment, and wear tests under 20 N and 40 N loads. The effect of 3.5% NaCl on the alloys in corrosion and wear tests was tested. In the Mg-Al-Mn ternary alloy, the expected α-Mg, β-Mg17Al12, Al8Mn5 and AlMn phases were observed, and Cd was found to be predominantly dissolved in the matrix at the micro-level. Cd showed a fine, uniform distribution in the structure. In the hardness tests, the hardness of the alloy containing 1.0% Cd increased by approximately 16%. According to the potentiodynamic polarization corrosion test values, the corrosion potentials of the alloys were negative, but the corrosion rate (CR) increased with increasing Cd content of the alloys. In corrosive wear tests, based on the aggressive corrosive wear mechanism in a 3.5% NaCl environment, an increase in wear of approximately 25% was observed at the end of 400 m as the load increased from 20 N to 40 N. The effect of hardness on corrosive wear was found to be limited. However, it can be stated that the Cd content of the Q2 alloy, being insufficient in accelerating galvanically induced wear, may reduce friction. In the Q3 and Q4 alloys, the increasingly discontinuous β-phase morphology altered the galvanic coupling geometry, contributing to accelerated abrasive wear. In corrosive wear, only the Q2 samples performed well under both 20 N and 40 N loads in a NaCl environment.

Metals doi: 10.3390/met16050539

Authors: Xirui Gao Lei Zhou Xinru Liu Mengyang Shen Gaoda Zheng Lin Zhang Shiyu Zhang

5G communication commercialization is accelerating in many countries. At present, a large number of communication materials are deployed to transmit millimeter waves for 5G base stations. However, it brings huge energy consumption due to the shortcomings of the current materials. Therefore, a novel soft magnetic material with high magnetic permeability and low dielectric constant is urgently needed to reduce the energy loss of 5G base stations. In this work, a series of CoBiNi alloys were prepared using the hydrothermal reduction method, with bismuth (Bi) as the dopant. The results indicate that Bi can regulate the magnetic permeability of soft magnetic materials; the permeability of the Co20Bi5Ni75 alloy fluctuates stably around 1.50 within the frequency range of 14.00–18.00 GHz. The saturation magnetization exhibits an upward trend with increasing Bi doping, with the Co20Bi5Ni75 sample reaching a saturation magnetization of 73.11 emu/g. The coercivity and residual magnetization characteristics confirm that Co20Bi5Ni75 is a typical soft magnetic material. The microwave return loss (RL) of the Co20Bi5Ni75 alloy was consistently higher than −6.89 dB across the 1.00–18.00 GHz frequency range when the sample thickness was 5 mm. The increased magnetic permeability of the Co20Bi5Ni75 alloy is attributed to the ability of Bi3+ to suppress carrier migration, thereby increasing the resistivity of the crystal structure and consequently improving the material’s magnetic permeability. These findings provide new insights into the preparation of high-permeability soft magnetic materials.

Metals doi: 10.3390/met16050538

Authors: Tao Niu Chun Wu Zhihao Wang Chu Chu Xingrong Chu Zhiwei Xu

Flexible honeycomb skins offer a promising route for achieving continuous shape adaptation in morphing aircraft. In practical service, however, the skin must simultaneously accommodate large in-plane deformation while maintaining sufficient out-of-plane load-bearing capacity, which poses a fundamental design challenge. To address this trade-off, this study investigates an SMA-based U-shaped honeycomb under combined tensile deformation and aerodynamic pressure. A parametric finite element model incorporating SMA superelasticity is established, and an automated Abaqus–modeFRONTIER framework is developed for multi-objective optimization under dual loading conditions. The curvature radius, parallel-segment length, and middle-beam length are selected as design variables. The optimization objectives are defined as minimizing the maximum local strain under a prescribed tensile displacement and reducing the Z-direction displacement under aerodynamic loading as an indicator of out-of-plane bending resistance. The resulting Pareto front reveals the trade-off between flexibility and load-bearing capacity, and the sensitivities of the key geometric parameters are analyzed. Compared with the initial design, a representative optimized solution reduces the maximum local strain by 58.5% and the Z-direction displacement by 61.3%. These results provide a numerical basis for the design of SMA-based flexible skins for morphing aircraft.

Metals doi: 10.3390/met16050537

Authors: Jose Manuel Costa

Metal additive manufacturing (AM) has progressed from prototyping toward industrial deployment, yet adoption remains uneven because many initiatives are still driven by isolated process demonstrations rather than system-level manufacturing strategy. This framework review proposes a gated decision workflow for integrating metal AM into industrial systems by coupling process-family selection and route definition, Design for Additive Manufacturing (DfAM) and sustainability considerations. The paper consolidates a comparative matrix of six metal AM process families for early down-selection, introduces a minimal evidence checklist linking each decision gate to required artifacts, and contextualizes the workflow through representative part archetypes. The framework is further supported by practical guidance on process-specific DfAM constraints, including support strategy, residual stress, and surface integrity in powder bed fusion; shrinkage-driven design in sinter-based routes; and machining allowances in repair and hybrid manufacturing. Rather than positioning metal AM as a universal substitute for conventional manufacturing, this work defines it as a complementary, strategy-dependent enabler whose sustainability benefits depend on system-level integration and application context.

Metals doi: 10.3390/met16050536

Authors: Zhuang Shao Ke Yang Wenbin Lu Xuezhi Zhu Jianhua Zhao

The reliable joining of ultra-thick aluminum alloy plates remains a critical technical challenge in modern industrial manufacturing, often hindered by defects such as porosity and excessive distortion associated with conventional fusion welding. The novelty of this work lies in the characterization of the intermediate layer overlapping zone in 110 mm ultra-thick plates, which has rarely been reported. The motivation is to overcome the limitations of single-pass FSW for thick plates, such as insufficient material flow and high tool forces, by adopting a sequential double-sided strategy. Furthermore, this technique may help moderate the through-thickness heat input variation, although no direct thermal measurements were made. The weld nugget zone consists of uniformly fine, recrystallized α-Al grains. In contrast, the heat-affected zone displays distinctly laminar grain structures. The overlapping regions within the intermediate layer, which undergo two thermal cycles, exhibit refined grain sizes. A well-defined interface is evident between the advancing-side weld nugget zone and the thermo-mechanically affected zone. The overall tensile strength of the FSW joint is approximately 81% of the base material, and the tensile specimen fractured at the interface between the thermo-mechanically affected zone and the heat-affected zone. Along the thickness of the weld joint, a “W”-shaped microhardness distribution is observed at the surface and subsurface, whereas the intermediate layer exhibits a distinct “V”-shaped profile. The lowest microhardness value is located in the intermediate layer overlapping area due to the insufficient heat input and limited grain growth in this region. In summary, under the specific welding parameters tested (130 rpm, 15 mm/min, 110 mm thick), double-sided friction stir welding produces defect-free joints in AA 5052-H32, suggesting its potential for thick-plate applications, offering a practical and effective solution for manufacturing high-performance aluminum alloy structures. Potential industrial applications include pressure vessels for chemical storage, ship hull structures, and heavy-duty transportation components where ultra-thick aluminum plates are required.

Metals doi: 10.3390/met16050535

Authors: Guiying Deng Yaohui Wang Xu Zheng Xinkui Zhang Kai Ma Bolu Xiao Zongyi Ma

This study investigated how initial ingot thickness (400 mm vs. 520 mm) influences the microstructure and mechanical properties of Al–Zn–Mg–Cu alloys rolled to 80 mm. The combination of smaller initial thickness and lower total reduction (the 400-L route) results in lower dislocation density and a higher fraction of metastable η′ precipitates after T77 treatment. In contrast, the 520-L route, which involves a larger initial ingot thickness coupled with greater rolling reduction, yields higher dislocation density and a greater proportion of stable η phase. Texture also differs: the 400 mm ingot develops a strong S texture and high anisotropy, whereas the 520 mm ingot exhibits Brass texture and reduced anisotropy. Specifically, cross-rolling plus longitudinal rolling of the 520 mm ingot enhances recrystallization texture, giving a short-transverse yield strength of 528 MPa—within 6% of the longitudinal direction. This work offers valuable insights for controlling anisotropy in large 7xxx aluminum plates.

Metals doi: 10.3390/met16050534

Authors: Mario Herrera-Ortega Armin K. Silaen Nicholas J. Walla Chenn Q. Zhou Tomas Ekman Esin Iplik Rudiger Eichler Rafat Hirmiz Joseph Maiolo Bernard Chukwulebe Oscar Lanzi Yong Lee

This work presents an oxidation model that integrates high-temperature steel oxidation kinetics with CFD simulations to predict oxide scale formation during steel reheating under varying combustion atmospheres in the temperature range of 800–1200 °C, over residence times in the rage of 60–160 min. The model accounts for the water vapor content in the furnace atmosphere and evaluates scale thickness under both natural gas and hydrogen combustion, using air or oxygen as oxidizing agents. Oxide scale growth is described using a combined linear–parabolic approach to capture mixed growth mechanisms. Simulation results were validated against experimental measurements of scale thickness obtained for two low-carbon steel grades. The model predictions show good agreement with experimental measurements, with average deviations of approximately 10%, while maximum deviations of up to approximately 17% are observed for specific cases and operating conditions. The model captures scale growth trends under non-isothermal conditions and highlights the impact of water vapor and combustion atmosphere on oxidation behavior.

Metals doi: 10.3390/met16050533

Authors: Zhonglei Wang Jie Meng Qingqiang Chen Shunlong Li Fei Wang Jie Sun

This paper investigates the influence of surface ultrasonic rolling treatment on the fatigue performance of Mg-3Al-1Zn extruded alloy and systematically analyzes the evolution laws of fatigue life and mechanical properties with the thickness of the surface removed layer. The results show that after ultrasonic rolling treatment, the fatigue life of the alloy at a stress amplitude of 240 MPa changes significantly and reaches a peak at a specific removal thickness: when the 80 μm surface layer is removed, the fatigue life reaches 7.79 × 106 cycles, which is much higher than that of the untreated sample (3.87 × 104) and the sample only subjected to ultrasonic surface rolling processing (1.8 × 104). With the increase in the removal thickness, the fatigue life shows a trend of first increasing and then decreasing, and a second increase occurs within the range of 400–500 μm. Microstructure analysis indicates that at a depth of 80 μm from the surface, the strength is enhanced due to grain refinement and the peak hardness, thereby inhibiting the initiation of fatigue cracks, while within the depth range of 400–500 μm, there exist high-density dislocations and deformation layers, which also effectively hinder crack propagation. This study reveals the key role of surface state and subsurface microstructure in the fatigue behavior of magnesium alloys, providing a theoretical basis for improving the fatigue performance of magnesium alloys through surface modification.

Metals doi: 10.3390/met16050532

Authors: Dexin Fan Jiankang Huang Chen Dong Jiaojiao Xie

The phase transformation characteristics of Sn-Pb-Bi ternary alloys with four representative Bi/Pb mass fraction ratios (0, 0.14, 0.33, and 0.60) were systematically investigated using the deep potential molecular dynamics (DeePMD) method over a temperature range of 300–600 K. A high-precision machine-learned interatomic potential was achieved using large-scale ab initio molecular dynamics (AIMD) datasets, reaching chemical accuracy (energy error <5 meV/atom, force error <100 meV/Å). Complete solid–liquid–solid heating–cooling cycle simulations were performed to accurately determine the melting temperature Tm, solidification temperature Ts, and undercooling ΔT. The microscopic mechanisms through which Bi regulates phase transitions were revealed through radial distribution function (RDF), mean square displacement (MSD), self-diffusion coefficient, and viscosity analyses. Our results show that increasing the Bi/Pb ratio monotonically lowers Tm from 475 K to 450 K, while ΔT reaches a maximum of ~48 K at Bi/Pb = 0.14. Bi addition disrupts short-range order, enhances chemical homogeneity, suppresses atomic diffusion, and optimizes liquid viscosity, with the optimal composition found to be Bi/Pb ≈ 0.14, balancing a low melting point, controlled undercooling, and improved flowability. This study provides an atomic-scale theoretical foundation for the precise composition design of low-melting-point Sn-Pb-Bi solders for photovoltaic and electronic packaging applications.

Metals doi: 10.3390/met16050531

Authors: Srđan Stanković Dragana Radovanović Nataša Gajić Sanja Jevtić Marija Štulović Jovana Đokić Željko Kamberović

The asbestos mine “Stragari” (Kragujevac municipality, central Serbia) operated for approximately four decades, exploiting chrysotile asbestos and generating several million tons of tailings composed primarily of finely crushed serpentinite rock. These tailings are rich in magnesium (≈25 wt.%); yet, efficient magnesium recovery is hindered by the high acid consumption associated with serpentinite mineral dissolution. The objective of this study was to optimize the extraction of magnesium as magnesium chloride hexahydrate (MgCl2×6H2O) from asbestos mine tailings using hydrochloric acid as the leaching agent. The effects of key process parameters (including thermal activation—roasting, hydrochloric acid concentration, leaching temperature, and leaching duration) were systematically investigated. Experiments in this study were conducted using concentrations of HCl 0.5, 1, 1.5 and 2 M, temperatures of 60, 70 and 80 °C and durations of 60 and 180 min, with constant stirring speed (350 rpm) and 20% initial pulp density. The resulting pregnant leach solution was purified by controlled neutralization with Mg(OH)2 followed by evaporation to obtain MgCl2×6H2O. A preliminary techno-economic assessment indicates that the proposed process is economically feasible and provides a foundation for future scale-up studies. The results demonstrate that balancing acid consumption with magnesium recovery, rather than pursuing maximum extraction efficiency, can enable profitable industrial-scale production of a value-added magnesium compound while contributing to asbestos tailings remediation.

Metals doi: 10.3390/met16050530

Authors: Kaiyu Cheng Shihao Ma Yuanyuan Fang Wei Guo Xia Xu Guoqiang Chang Henggao Xiang

In high-cycle fatigue, the majority of fatigue life is spent in the crack initiation stage. However, current models fail to accurately capture the fatigue life consumed in the crack initiation stage, resulting in discrepancies in predictions. Here, we propose a fatigue life prediction model based on the crack tip plastic zone, combined with a multi-stage crack growth approach. To quantify the crack initiation life, a modified Tanaka–Mura model is developed by incorporating the effects of localized plastic deformation at the crack tip. The proposed model demonstrates good agreement with experimental observations. Furthermore, a reliability-based fatigue evaluation framework is established by introducing a fatigue safety factor formulation. The results show that the safety factor decreases with increasing applied stress levels, attributed to the reduced standard deviation and lower scatter of fatigue life at higher stresses. The findings provide a practical and physics-informed methodology for fatigue life and safety assessment of aluminum alloy components under complex cyclic loading conditions.

Metals doi: 10.3390/met16050529

Authors: Onur Güler Mücahit Kocaman Yaren Adabaş Serdar Özkaya Temel Varol Serhatcan Berk Akçay Hamdullah Çuvalcı

At particle-level engineering, this study mainly focused on the issues of microstructural heterogeneity and the high oxidation susceptibility of Cu-Al-Ni shape memory alloys (SMAs) suitable for high-temperature actuation. Initial powders of Cu (82–83 wt.%) and Al (14–15 wt.%) were first milled mechanically and the Cu-Al particles were modified using an electroless Nickel (Ni) coating process to achieve a controlled Ni enrichment of 4–5 wt.%. The SEM-EDS, XRD, and TGA findings reveal that the cryogenic milling effectively reforms dendritic Cu and spherical Al particles into a refined composite structure. This process resulted in particle size reduction from 40–70 µm to 5–20 µm, and apparent density values increased from 3.45 g·cm−3 to 4.10 g·cm−3. Microstructural investigations showed that the continuous Ni layer, without generating unwanted intermetallic phases, was obtained with the help of an electroless coating process. In addition, it was confirmed that the crystallite size decreased from 52.10 nm to 41.71 nm. Additionally, the oxidation of nickel-coated and cryogenically milled powders occurred at temperatures above 350 °C owing to the formation of a protective surface layer. In other words, these powders exhibited higher thermal stability. Consequently, this dual processing procedure represents a very useful method for changing particle shape and interfacial composition. These combined methods can help to create a powder structure with a composition optimum for the making of high-performance Cu-Al-Ni SMAs.

Metals doi: 10.3390/met16050528

Authors: Guangya Hou Siqi Chen Jianli Zhang Qiang Chen Yiping Tang

The functional valorization of waste fabrics, particularly their conversion into flexible low-cost, high-performance electrodes, holds significant promise for resource sustainability and the development of advanced energy technologies. Here, a NiB/Cu/polyester fabric (PF) composite electrode was fabricated via two-step electroless plating on waste PF and was demonstrated as a bifunctional electrocatalyst for methanol oxidation (MOR) and urea oxidation (UOR). The morphology, crystal structure, surface chemical state, and wettability of the electrodes were characterized using SEM, TEM, XRD, XPS, and contact angle measurements. The Cu interlayer critically enhanced interfacial wettability, intrinsic catalytic activity and stability. At 0.8 V, the NiB/Cu/PF electrode delivered average current densities of 312 mA·cm−2 for MOR and 288 mA·cm−2 for UOR, outperforming NiB/PF by 27.9% and 9.1%, respectively. After 2000 accelerated degradation cycles with electrolyte renewal, MOR and UOR activities were retained at 91.6% and 105.0%, respectively. Remarkably, the Cu interlayer conferred exceptional mechanical–electrochemical robustness: following 100 sequential bending and twisting deformations, current density retention ranged from 84.6% to 96.7% across multiple test configurations. The Cu interlayer acted as a flexible stress buffer during mechanical deformation, effectively improving the adhesion between the coating and the substrate.

Metals doi: 10.3390/met16050527

Authors: Orhan Gülcan Burak Özcan Umut Çalışkan Güher Pelin Toker

Auxetic metamaterials have outstanding negative Poisson’s ratio characteristics which can be beneficial in different industrial applications. The main aim of the present study is to investigate the effect of thickness-dependent functional grading (FG) on the mechanical response of two widely known auxetic geometries, namely re-entrant and anti-tetrachiral. Three different thickness-dependent FG versions of these geometries were compared against their counterparts without FG by using numerical simulations. The effect of thickness-dependent FG was also compared against non-auxetic geometry (honeycomb) to understand the effect of auxeticity. The validation experiments were performed by the production of sample geometries by laser powder bed fusion technology from Inconel 718 material and quasi-static compression testing. The results revealed that the grading direction is a key variable in design that significantly influences the deformation stability and stress distribution, and it was shown that thickness-dependent FG is a promising way to decrease the weight of auxetic structures without sacrificing SEA considerably.

Metals doi: 10.3390/met16050526

Authors: Zhiwei Liu Xiuhua Gao Changyou Zhu Shuo Gao Zhiyong Chang Linxiu Du Hongyan Wu

To address the strength fluctuation observed in Ti microalloyed steel, the effects of final rolling temperature, coiling temperature, and Ti content on the microstructure, secondary phase precipitation behavior, and grain size were investigated through simulation experiments. Various characterization techniques were employed to elucidate the underlying causes of the strength variation, and key control strategies were proposed. The results indicate that the strength fluctuation is primarily influenced by the presence of nano-sized TiC precipitates. The precipitation behavior of TiC can be effectively controlled by adjusting the content of non-metallic elements as well as the final rolling and coiling temperatures. Higher final rolling temperatures combined with appropriate coiling temperatures promote increased TiC precipitation; however, excessively high temperatures may result in grain coarsening and inhomogeneous precipitate distribution. The optimal processing parameters were determined to be a final rolling temperature of 860 °C and a coiling temperature of 600 °C.

Metals doi: 10.3390/met16050525

Authors: Zongxian Song Zhiwei Gao Lina Zhu Hao Jin Jian Zhao Caiyan Deng

This investigation elucidates the elevated-temperature (650 °C) monotonic mechanical response and very-high-cycle fatigue (VHCF) characteristics of Inconel 718 superalloys additively manufactured via selective laser melting (SLM), with a comparative assessment between the as-built and post-process heat-treated states. The results indicate that mechanical performance improves after heat treatment, primarily due to the formation of γ′ and γ″ precipitates, which interact with dislocations to strengthen the alloy. Relative to the as-built specimens, the fatigue strength of the specimen after heat treatment has increased by more than twice. For the as-built specimen, fatigue cracks nucleate at the specimen surface. However, in the high stress range, crack initiation in the heat-treated specimens consistently occurs at the free surface, whereas under low stress conditions, the crack initiation site transitions to the subsurface region encompassing internal defects. Post heat treatment, the fatigue crack trajectory adopts a markedly ductile and tortuous morphology, engendered by the concerted influence of grain-boundary (Laves/δ) precipitates that enforce repeated crack deflection, matrix-strengthening phases that homogenize plastic strain and the attendant reduction in local strain accumulation under the effect of cyclic load.

Metals doi: 10.3390/met16050524

Authors: Jarupong Charoensuk Takuma Iwai Taiga Hongo Tomoyoshi Maeno Surasak Suranuntchai

This study introduced a pre-holed hot clinching process for hot stamping patchwork blanks, using the lower sheet pre-hole as a forming cavity to facilitate material flow and minimize deformation resistance. Evaluated through mechanical testing and finite element analysis (FEA), the process induced ausforming and maintained material homogeneity (~500 HV), and an optimal interfacial gap up to 10 mm effectively prevented localized soft-zone fractures. Results identified interfacial slip, driven by a critical differential surface expansion rate, as the primary mechanism for geometric anchoring and solid-state bonding. Experimental validation established optimal joining at a 60% penetration ratio and a 0.9 hole-to-punch diameter ratio. While prior studies on forge joining reported average maximum strengths limited to 1.2 kN due to the absence of a mechanical hook, the optimized pre-holed joints in this work achieved a superior tensile shear capacity of 11.5 kN. Furthermore, the cross-tension load reached 0.77 kN, representing a nearly tenfold increase compared to the 0.08 kN observed in the no-hole with offset condition. These results demonstrate that the pre-holed hot clinching method significantly enhances joint integrity while reducing the forming load from 70 kN without a pre-hole to 12 kN with a 10 mm pre-hole.

Metals doi: 10.3390/met16050523

Authors: Haolong Cheng Jun Peng Yingtie Xu Jing Li Fei Huang Lixia Liu

The precise control of non-metallic inclusions is crucial for high-end GCr15 bearing steel. This study investigates cerium (Ce)-induced inclusion modification mechanisms. Smelting experiments with 0 to 0.017 wt% Ce additions, high-temperature in situ observations, thermodynamics, and first-principles calculations were used to evaluate inclusion evolution and aggregation behaviors. Without Ce, coarse Al2O3 and MnS phases dominate. As Ce increases to 0.017 wt%, inclusions evolve sequentially into CeAlO3, Ce2O3, and ultimately, finely dispersed Ce2O2S and CeS. Thermodynamics indicate CeAlO3 nucleates preferentially, acting as heterogeneous nucleation sites for MnS. In situ observations and interparticle force calculations reveal an aggregation tendency order of Al2O3 > CeAlO3 > Ce2O3 > Ce2O2S. Furthermore, first-principles simulations confirm that Ce2O2S possesses the lowest formation energy and optimal stability, wherein Ce effectively modifies coarse inclusions into fine, well-dispersed spherical particles. Coupled with its intrinsic deoxidizing and desulfurizing effects, Ce addition synergistically modifies coarse inclusions into fine, well-dispersed spherical particles. These findings elucidate the rare-earth modification micro-mechanisms, providing a theoretical foundation for manufacturing high-quality bearing steel.

Metals doi: 10.3390/met16050522

Authors: Sanat Tolendiuly Nursultan Rakhym Kaster Kamunur Sharafkhan Assylkhan Lyazzat Mussapyrova Sandugash Tanirbergenova

Chromium-containing ferroalloy wastes represent an important secondary resource; however, chromium is mainly bound in thermodynamically stable spinel phases, which complicates its reduction. Unlike previous studies focusing on pure oxide systems, this work demonstrates the enhanced destabilization and subsequent reduction of MgCr2O4 spinel in real ferroalloy wastes under SHS conditions, revealing a non-monotonic relationship between activation time and reduction efficiency. A critical activation threshold (~30 min) was identified, beyond which particle agglomeration suppresses reaction kinetics. Powder mixtures based on HShP and KEK wastes with Al–C–Si reducing agents were mechanically activated for 10–120 min and subsequently subjected to SHS at 950 °C. The combustion parameters, phase composition (XRD), microstructure (SEM), and elemental composition (EDS) were analyzed. The results show a pronounced non-monotonic dependence of combustion temperature and front velocity on activation time, with maximum values at ~30 min (1920 °C and 1.10 mm/s for HShP; 1765 °C and 0.98 mm/s for KEK). XRD analysis indicates that MgCr2O4 was not detected within the XRD detection limits and that the highest relative amount of metallic chromium phase (~8% for HShP and ~6.8% for KEK) was observed at the same activation time. SEM observations reveal the formation of a more dispersed and porous structure, while EDS indicates an increase in chromium content up to ~15 wt.% in local regions. At longer activation times, overgrinding and agglomeration reduce process efficiency. Mechanical activation enhances chromium reduction through improved mass transfer, with an optimal activation time of ~30 min. The chromium reduction efficiency was evaluated using a semi-quantitative approach based on XRD phase analysis and supported by EDS data, allowing comparative assessment of reduction efficiency rather than absolute extraction values. These results highlight the existence of a critical mechanochemical activation threshold governing the balance between enhanced reactivity and agglomeration effects.

Metals doi: 10.3390/met16050521

Authors: Bo Fu Jialiang Sun Boya Wang Yang Yu Wenjun Ye Yumeng Luo Yanfeng Li Songxiao Hui

The α-phase microstructure and texture of a Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy hot-rolled plate can easily lead to anisotropy in impact toughness. This study observed the microstructure and texture of the alloy plate on different planes, conducted impact toughness tests using four combinations of loading direction and crack propagation plane, analyzed the fracture morphology, and investigated the effects of texture and microstructure on the anisotropy of impact toughness. The differences in crack initiation and propagation behavior are discussed. The results show that the impact toughness of the four types of specimens exhibits strong anisotropy. Among them, the L-S specimen (fracture on TD-ND plane, loading along ND) shows the highest impact toughness (97.75 J/cm2), while the T-L specimen (fracture on RD-ND plane, loading along RD) shows the lowest (46.7 J/cm2). Analysis suggests that the strong T-type texture in the plate makes activating slip systems significantly easier for fracture on the TD-ND plane compared to the RD-ND plane. Consequently, the former demonstrates better plastic deformation ability during both crack initiation and propagation. Additionally, the elongated characteristic of α laths along the RD/TD direction and the grain boundary features cause a more tortuous crack path and greater energy consumption when the crack propagates along the ND direction. The combined effect of texture and microstructure determines the anisotropy of impact toughness in this alloy.

Metals doi: 10.3390/met16050520

Authors: Jordan Maximov Galya Duncheva Angel Anchev Vladimir Dunchev Kalin Anastasov Mariana Ichkova

Burnishing technologies are a cheap and effective means of improving the surface integrity (SI) and performance of metal components. However, there is practically no information about the integral influence of the preceding turning process on the initial (pre-burnishing) SI. This study answers the question of how the white layer resulting from flank wear on the cutting insert in pre-turning affects the SI and fatigue limit, and determines the extent to which subsequent diamond burnishing (DB) is able to improve the SI and rotating bending fatigue limit of normalised, quenched and high-temperature-tempered C45 steel. The (DB)–SI–fatigue limit correlation was investigated using a holistic approach that took into account the effects of the dynamic pattern of flank wear on the initial SI. An explicit relationship was established between the flank wear, the affected surface layer structure and the fatigue limit. Increasing flank wear to the 60th minute intensified the formation of a gradient layer with finer and thinner grains that formed a texture. As a result, a synergistic effect was observed from turning with an insert operating for 60 min and subsequent DB, which maximised the fatigue limit (741 MPa). After 60 min, the structure of the affected layer changed qualitatively towards the formation of a nanostructured (white) layer, which reversed the trend, worsening the fatigue behaviour. As the thickness of the white layer increased, the fatigue limit was sharply reduced to below 560 MPa after the 90th minute. Regardless of the degree of flank wear, DB significantly improved the SI characteristics and increased the fatigue limit after turning with a worn insert, although the absolute dimensions of the positive DB effect depend on the initial SI and fatigue limit due to pre-turning. To achieve a synergistic effect, the cutting insert should be replaced with a new one after every 60 min of operation.

Metals doi: 10.3390/met16050519

Authors: Avinash Kandalam Markus Andreas Reuter Michael Stelter Andreas Richter Christian Kupsch Alexandros Charitos

Top Submerged Lance (TSL) technology is widely used in non-ferrous smelting, yet in-situ bath dynamics remain challenging to quantify because the process operates in a closed, high-temperature, highly turbulent and optically inaccessible environment. The absence of direct diagnostics limits the ability to relate operating conditions to bubble dynamics, gas penetration and bath agitation and constrains validation of multiphase CFD models under realistic conditions. This study introduces a multimodal sensing framework that combines spectral acoustic analysis with lance-mounted inertial motion sensing to characterize dynamic bath behavior across cold-model, laboratory-scale and pilot-scale systems. Water-glycerin experiments establish repeatable acoustic signatures of individual bubble-collapse events, with dominant emission bands in the 300–900 Hz range and higher-frequency components extending into the kilohertz domain. High-temperature laboratory trials using fayalitic slag reproduce these frequency regions while exhibiting depth-dependent attenuation and clear spectral separation between submerged and non-submerged lance operation. Power Spectral Density (PSD) and cumulative spectral power analyses resolve the influence of gas flow rate and lance submersion depth on acoustic spectral power distribution, while inertial measurements capture corresponding increases in vertical lance acceleration associated with back-pressure fluctuations. Pilot-scale trials at 120 Nm3/h air and 13 L/h diesel confirm that shallow lance submersion substantially increases measured acoustic spectral power below 3 kHz, whereas deeper penetration enhances periodic vertical acceleration response measured by the inertial sensor. The combined acoustic-inertial methodology provides a physically interpretable and cross-scale framework for assessing bubble collapse activity, plume interaction and bath agitation under high-temperature TSL conditions. The approach enables frequency-based diagnostics that can be systematically compared with CFD predictions of plume oscillation and collapse-related dynamics. Once baseline frequency ranges are established for a given slag system, the method can support process monitoring and may provide indirect indicators related to changes in surface agitation or foaming tendency, enabling structured data-driven analysis. The framework thus provides a practical bridge between cold-model experiments, high-temperature measurements, multiphase modeling and industrial TSL operation.

Metals doi: 10.3390/met16050518

Authors: Suli Li Zhijie Guo Yang Gao Jing Guo

To address issues such as thermal stress concentration in metal bone implants produced via high-energy beam direct additive manufacturing, a method was proposed to fabricate porous titanium scaffolds. This approach combined Fused Deposition Modeling (FDM) with a debinding–sintering process. Ti/ABS composite filaments with titanium volume fractions of 35%, 40%, and 45% were successfully developed via a single-screw extrusion process. Their feasibility in the FDM process was subsequently verified. The effects of different processing parameters on the forming quality and dimensional accuracy of the green bodies were investigated. After debinding and sintering the composite scaffolds prepared with optimized parameters, structurally intact porous titanium scaffolds were obtained. Microscopic characterization shows that the scaffold surface consists primarily of titanium, and the pore structure remains intact. Furthermore, compression tests were performed on three types of porous titanium scaffolds with different porosities. The results indicate that the combination of ABS/titanium alloy composite filaments, FDM technology, and debinding–sintering post-processing enables the high-quality and efficient production of porous titanium scaffolds. The elastic modulus of the resulting scaffolds ranges from 1.2 to 1.6 GPa, and the compressive strength is between 25.7 and 68.3 MPa. The elastic modulus matches that of human cancellous bone. Meanwhile, the compressive strength is significantly higher than that of cancellous bone and falls between the values for cancellous and cortical bone. These mechanical properties meet the requirements for human bone, providing a new approach for the manufacture of orthopedic implants.

Metals doi: 10.3390/met16050517

Authors: Ming-Jun Xie Peng-Fei Wang Lin Gao Yan-Fei Bian Zhi Cheng

Aiming at the urgent heat dissipation demands of high-power, high-integration electronic devices, Cu/Al composite heat sinks combine the high thermal conductivity of copper and the lightweight advantage of aluminum, becoming a mainstream solution for advanced thermal management systems. The significant physicochemical differences between Cu and Al, however, make high-quality joining a technical bottleneck. In this study, flux-free ultrasonic brazing with a Zn-based filler metal was used to join 6061 aluminum alloy and industrial pure copper. Gradient heat treatment (55–300 °C) was subsequently applied to systematically investigate its effect on the microstructure, microhardness, and thermal properties of the joints. The results show that the as-brazed joint exhibited excellent bonding (97.3% bonding rate) and shear strength (95.24 MPa). The weld seam consisted of Zn solid solution, Cu solid solution, and Al-Cu-Zn ternary compounds. Heat treatment did not induce new phases but led to the coarsening of Zn-Al-Cu compounds and aggregation of the eutectic structure, reducing grain boundaries. Consequently, the microhardness at the weld center varied non-monotonically, and the thermal conductivity of the joint showed an overall increasing trend with rising heat treatment temperature. This enhancement is attributed to reduced phonon scattering at diminished grain boundaries. This study clarifies the heat treatment–microstructure–thermal properties relationship, providing important guidance for the thermal performance optimization of Cu/Al composite heat sinks.

Metals doi: 10.3390/met16050516

Authors: Xiangqian Liu Wei Wang Yanmo Li Peiyue Li Yaozong Li Xiaoyi Guo Linlin Zhang Zhihua Sun Gaosong Wang

We designed a specialized structure for friction stir-welded hollow extrusions for high-speed trains in order to fulfill security and economic requirements. A sequentially coupled thermo-mechanical model was used to investigate the thermal stress distribution in the designed structure. The results show that stress concentration was the most important factor in high calculated stress and that increasing the supporting rib width and the arc radius on the advancing side of the supporting rib can effectively improve structural security. Finally, an optimized structure was obtained, and friction stir welding experiments were carried out to verify the simulation’s precision.

Metals doi: 10.3390/met16050514

Authors: Guanglin Zhu Jianmin Song Jinpeng Yang Liang Hu Cean Guo Wenhuan Shen

High-load sliding components, including gun barrels, are susceptible to accelerated wear and damage due to coupled thermal-mechanical stresses and reciprocating frictional conditions. Therefore, enhancing their operational lifespan requires the application of wear-resistant coatings with high melting points for effective surface protection. In this study, Ta-10W alloy coatings were deposited on CrNi3MoVA steel substrates through electricspark deposition, focusing on deposition voltage as a critical parameter. Experimental results indicate that the Ta-10W coatings are primarily composed of α-Fe, α-Ta2O5, δ-Ta2O5, α-Ta(W), and Fe-W intermetallic phases. An increase in deposition voltage facilitates enhanced melting and mass transfer, thereby promoting solid solution and oxidation strengthening, which results in improved hardness. However, higher voltages also induce defects such as porosity and microcracks. Hardness measurements and friction-wear tests demonstrate that coatings deposited at 80 V exhibit optimal performance, attaining the highest hardness (~753 HV) and a friction coefficient similar to that at 60 V. Conversely, the friction coefficient increases at 100 V due to defects and coating spalling. The wear mechanism transitions from adhesive wear at 60 V to adhesive wear with minor plastic deformation at 80 V and ultimately to spalling wear at 100 V. Finite element thermomechanical simulations reveal that increasing voltage significantly elevates the equivalent interfacial stress (600–1150 MPa), thus correlating with the propensity for microcracks to propagate into longitudinal semi-penetrating cracks at elevated voltages. This study establishes a theoretical foundation for optimizing electricspark deposition process parameters and contributes to the reliability design of Ta-W alloy coatings.

Metals doi: 10.3390/met16050515

Authors: Tengfei Ma Xuanran Gao Zhifeng Ma Ziqi Hao

The L-shaped columns of recycled aggregate concrete-filled steel tubes (L-RACFSTs) with a 40% coarse aggregate replacement ratio were selected as the research subject, and axial compression and eccentric compression tests were conducted. Based on validated finite element numerical simulation methods, a parametric analysis was carried out, incorporating key parameters such as steel strength, width-to-thickness ratios of the square steel tube and connecting plate, and load eccentricity. The mechanical properties of L-RACFSTs under axial compression and eccentric compression loads were studied. The results show the following: (1) At a 40% replacement rate, axial compression specimens exhibited obvious in-plane deformation of the column limbs, whereas eccentric compression specimens showed overall bending toward the inner side of the column. (2) As the strength of the steel increases, the axial and eccentric compressive bearing capacities of the specimens gradually increase. It is recommended that structural steel with a strength grade of Q355 is adopted. (3) When the width of a square steel tube is fixed, the axial and eccentric compressive bearing capacities of the test specimen gradually increase as the width-to-thickness ratio decreases. (4) In contrast, for a connecting plate of a fixed width, an increase in the width-to-thickness ratio results in a decrease in bearing capacity. Additionally, due to the increased width of the connecting plate, bearing capacity will decrease in some cases. (5) The bearing capacity under eccentric loading decreases gradually as the eccentricity increases; it is recommended that the eccentricity be kept below 120 mm.

Metals doi: 10.3390/met16050513

Authors: Shuilin Tan Qian Wang Chaobin Lai

Hot deformation effectively refines the microstructure and homogenizes the composition of high-nitrogen martensitic stainless steel (HNMSS), but its influence on austenite stability during subsequent cooling remains unclear. In this study, the effect of the hot deformation strain on austenite stability in HNMSS 30Cr15Mo1N0.37 was investigated by means of a Gleeble thermomechanical simulator, X-ray diffraction (XRD), electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM). The austenite stability is evaluated by the austenite fraction measured via XRD at room temperature. The results show that the austenite content in HNMSS 30Cr15Mo1N0.37 gradually increases with the strain range from 0 to 0.8. The austenite fractions are 69.5%, 73.1%, and 80.7% when the strains are 0, 0.4, and 0.8, respectively. At a strain of 0.14, dislocation accumulation leads to the formation of dislocation cells and sub-grains within austenite, which enhances its stability. When the strain exceeds 0.36, the austenite grains are significantly refined, the austenite stability is attributed to the synergistic effects of dislocation accumulation and grain refinement, which collectively increase the resistance to martensitic transformation. Furthermore, both recrystallized grains and dislocation cells influence the morphology and size of martensite laths. The martensite laths are significantly refined from 100 nm at a strain of 0 to 35 nm as the strain reaches 0.8, and their morphology changes from straight to curved.

Metals doi: 10.3390/met16050512

Authors: Aitbala Narembekova Kalkaman Zhumashev Pheruza Berdikulova Yelena Zhinova Anna Bogdanova

This article presents the results of developing a hydrometallurgical method for processing polymetallic sublimates containing arsenic, zinc, copper, and lead. Using sublimates from “BalkhashPolymetal” LLP (Kazakhstan) as an example, the optimal conditions for sulfuric acid leaching were determined as follows: t = 80–85 °C, H2SO4 = 25 g/dm3, τ = 60 min. Under these conditions, extraction of arsenic was 93%, zinc 80%, and copper 42% was achieved. Iron(II) hydroxide was used to remove arsenic from the solution, which made it possible to reduce the residual As content in the solution to 0.02 g/L and return approximately 97% of copper to the process cycle. Eh–pH analysis of the Fe–As–Cu–H2O system confirmed the thermodynamic stability of Fe(II/III) arsenates in the selected pH range 3–5. The obtained results can be used to develop safe and resource-saving technologies for processing technogenic raw materials.

Metals doi: 10.3390/met16050511

Authors: Gauhar Yerekeyeva Bauyrzhan Kelamanov Vera Tolokonnikova Bakyt Suleimen

This study presents a thermodynamic analysis of the dissociation and association behavior of the Fe–Si system using the Bjerrum–Guggenheim osmotic coefficient. An equilibrium thermodynamic approach was applied to evaluate the Gibbs free energy, equilibrium constant, and degree of association of the congruently melting compound FeSi over a wide temperature range. The Fe–Si system was analyzed across three characteristic crystallization regions: Fe-rich, FeSi, and Si-rich. It was established that the Fe-rich region exhibits behavior approaching ideality with a nearly linear dependence of the osmotic coefficient, whereas the Si-rich region is characterized by strong deviations from ideality due to intensive association processes. The FeSi crystallization region represents a transitional regime in which association and dissociation processes occur simultaneously. The formation and partial dissociation of [FexSiy] clusters significantly affect the thermodynamic behavior of the melt. It was shown that accounting for FeSi dissociation leads to a linearization of the osmotic coefficient dependence and improves the accuracy of thermodynamic description. The proposed analytical approximations demonstrate high correlation coefficients (R2 ≈ 0.99), confirming the reliability of the developed approach. The results provide a consistent thermodynamic framework for describing phase transformations and structural evolution in Fe–Si melts and can be applied to the optimization of metallurgical processes involving silicon-containing alloys.

Metals doi: 10.3390/met16050510

Authors: Lu Cheng Chenxi Shao Peng Cheng

Accurate constitutive modeling of TC4 titanium alloy at elevated temperatures is critical for process design and numerical simulation in aerospace manufacturing. However, purely data-driven deep neural networks (DNNs) often suffer from severe overfitting and may yield physically unreasonable predictions in data-sparse or strictly out-of-distribution (OOD) regions. To address this issue, this study proposes a physics-guided two-stage neural network framework, termed NN-PhysicsInit, for the constitutive modeling of TC4 alloy. In Stage I, a large synthetic dataset generated from a strain-compensated Arrhenius-type constitutive equation is used to pre-train the network, thereby introducing analytical prior knowledge into the initial topological space. In Stage II, the pre-trained model is fine-tuned using rigorously corrected experimental data obtained from isothermal compression tests conducted over 800–980 °C and 0.001–1 s−1 to improve material-specific predictive accuracy. To evaluate generalization capability, a rigorous dual-perspective extrapolation validation scheme is designed separately in the temperature (1010 °C) and strain-rate (10 s−1) dimensions. The results demonstrate that, compared with direct black-box training, the proposed framework successfully prevents non-physical divergence and better preserves macroscopic thermodynamic smoothness in unseen domains. Specifically, the extrapolation average absolute relative error (AARE) is significantly reduced from 34.21% to 14.34% in the temperature extrapolation task, and from 27.91% to 8.92% in the strain-rate extrapolation task. These findings confirm that physics-based initialization acts as a powerful implicit regularizer, effectively mitigating the extrapolation catastrophe while maintaining high fitting accuracy. The proposed framework provides a robust and practical strategy for the constitutive modeling of complex alloys under limited-data conditions.

Metals doi: 10.3390/met16050509

Authors: Taoran Shao Bingbing Wu Yanxin Wu Zhenli Mi

High-manganese steel has emerged as a potential alternative material to austenitic stainless steel for liquid hydrogen storage and transportation environments, owing to its superior mechanical characteristics and limited hydrogen diffusivity. However, its hydrogen embrittlement (HE) susceptibility limits its engineering applications. This study investigates the effect of microstructural regulation through trace titanium (Ti, 0.021 wt%) addition on HE resistance in high-manganese steel. By means of Electron Backscatter Diffraction (EBSD), TEM, SEM, and Slow Strain Rate Tensile (SSRT) tests, the effects of Ti on the microstructure, mechanical properties, and HE susceptibility of high-manganese steel are systematically investigated. The results show that the addition of Ti did not significantly alter the average austenite grain size or phase composition, but it generated a large number of Ti(C,N) nanoscale precipitates with sizes ranging from 20 to 70 nm within the matrix. The elongation loss of the 25Mn-Ti specimen was significantly lower than that of the 25Mn specimen when hydrogen-charged for 72 h, decreasing from 18.4% to 9.3%. The fracture surfaces consistently exhibited ductile dimple morphology, whereas 25Mn steel demonstrated significant cleavage-induced brittle fracture. EBSD analysis revealed that hydrogen-charged 25Mn-Ti steel exhibited higher Kernel Average Misorientation (KAM) value retention rate and more uniform grain strain distribution, indicating enhanced microstructural deformation compatibility. The main mechanism was that Ti pre-formed nanoscale Ti(C,N) precipitates during the preparation of 25Mn high-manganese steel, which played a key role in inhibiting HE. These precipitates altered hydrogen diffusion behavior and distribution patterns, reduced stress concentration levels, and inhibited hydrogen-induced crack initiation. This work is of great significance for improving the HE resistance of high-manganese steels.

Metals doi: 10.3390/met16050508

Authors: Askhat Akuov Alibek Baisanov Bauyrzhan Kelamanov Aidana Baisanova Nina Vorobkalo Yerulan Samuratov

This study investigates the thermodynamic and kinetic features of chromium reduction from chromium ore using complex Fe–Si–Cr and Al–Si–Cr alloys as reducing agents for the refined ferrochrome production. The thermodynamic probability of Cr2O3 reduction by silicon and aluminum was evaluated using thermodynamic equilibrium calculations based on reference thermodynamic data, including determination of the standard Gibbs free energy change over the studied temperature range. The results showed that both reduction routes are thermodynamically feasible, while aluminum exhibits a higher affinity for oxygen and a greater reducing capacity. The thermal behavior of chromium ore and its mixtures with Fe–Si–Cr and Al–Si–Cr alloys was studied by differential thermal and thermogravimetric analysis. The use of Al–Si–Cr, especially in briquetted form, was found to shift several thermal transformation stages to lower temperatures and to reduce the apparent activation energy of the high-temperature interaction stages compared with Fe–Si–Cr-containing mixtures. The obtained results indicate that Al–Si–Cr alloy is a promising complex reductant for intensifying chromium recovery and improving process conditions in refined ferrochrome production.

Metals doi: 10.3390/met16050507

Authors: Tomasz Chmielewski Piotr Siwek Marcin Chmielewski Anna Piątkowska Agnieszka Grabias Dariusz Golański

The journal retracts the article “Structure and Selected Properties of Arc Sprayed Coatings Containing In-Situ Fabricated Fe-Al Intermetallic Phases” [...]

Metals doi: 10.3390/met16050506

Authors: Vinamra Bhushan Sharma Saurabh Tewari Susham Biswas Bharat Lohani Umakant Dhar Dwivedi Deepak Dwivedi Ashutosh Sharma Jae Pil Jung

There were some errors in the original publication [...]

Metals doi: 10.3390/met16050505

Authors: Rongxin Lan Zhengbing Meng Meiqiao Wu Jiangbo Deng Dinghua Feng

S136 mold steel is widely used in the injection molding industry due to its excellent properties. However, during actual production, the mold is inevitably exposed to harsh service conditions involving high temperature, high pressure, chemical corrosion, and mechanical wear, leading to risks of failure caused by pitting corrosion, intergranular corrosion, electrochemical corrosion, selective dissolution, and surface fatigue wear. To enhance the surface protection performance of the mold, a TiC-reinforced 440C stainless steel composite coating was fabricated on the S136 substrate using plasma spray welding technology. Composite powders with different TiC contents (wt.%) were prepared via mechanical mixing. The phase composition, microstructure, microhardness, corrosion resistance, and wear resistance of the coatings were characterized by XRD, SEM, Vickers microhardness tester, electrochemical workstation, and vertical universal friction and wear tester. Furthermore, the corresponding strengthening mechanisms were elucidated. The results show that the incorporation of TiC refines the microstructure and synergistically enhances both corrosion and wear resistance. Among the tested coatings, the one with 1.0 wt.% TiC exhibits the best overall performance, with a significantly increased microhardness of 858.85 HV (approximately 1.5 times that of the substrate), an Ecorr of –0.286 ± 0.002 V, an Icorr of 4.51 × 10−7 A·cm−2, and a friction coefficient of 0.591. This study provides important theoretical and technological insights for the surface strengthening of S136 mold steel using plasma spray welding of TiC/440C composite coatings to improve corrosion and wear resistance and extend service life.

Metals doi: 10.3390/met16050504

Authors: Fakhri Ali Salem Mohammed Yahui Zhang

As critical rare earth elements (REEs), the industrial demand for neodymium (Nd) and dysprosium (Dy) increases rapidly due to their specific physical and chemical properties. Recycling these REEs from secondary resources such as spent NdFeB magnetic materials is an efficient approach for sustainable production. However, the separation of neodymium and dysprosium in aqueous solutions is an arduous task because of their close chemical properties. Recovering and purifying neodymium and dysprosium from a simulated leaching solution of spent NdFeB magnets were conducted by employing selective ion exchange resins. It was found that Purolite S950 PLUS resin functionalized with aminophosphonic groups demonstrated selective adsorption toward Nd3+ and Dy3+ while maintaining low affinity for Fe(II) at low pH (i.e., 0.65), which could realize efficient iron removal from the solution. Purolite MTX7010 resin impregnated with di-(2-ethylhexyl) phosphoric acid (D2EHPA) had a strong adsorption preference for Dy3+ over Nd3+, which is highly suitable for Dy separation from their mixed solutions under optimized conditions. By employing a multistage adsorption–elution process analogous to distillation, a prospective purity of 98.51% for Dy and a purity over 99.90% for Nd were realized with high metal recoveries from the synthetic leaching solution of spent NdFeB magnets. This research demonstrates that recovery and purification of single REEs from leaching solutions containing mixed REEs and other metals can be achieved with selective resin adsorption processes analogous to distillation despite large concentration differences in the metals in the solutions, which presents a new approach.

Metals doi: 10.3390/met16050503

Authors: Pengyu Gao Yali Huang Hong Xiao Xindu Chen Yanxi Zhang Xiangdong Gao

Accurate and interpretable weld-quality assessment is essential for ensuring the reliability of resistance spot welding in industrial production. This study develops a data-efficient classification framework that integrates dual-interval mean discretization (DIMD) of dynamic-resistance signals with gradient-boosting models. The proposed DIMD method applies fine discretization during the rapid heating–melting and coarse discretization during the subsequent slow-evolving period, effectively preserving the peak–valley morphology of resistance curves while reducing feature dimensionality. Using these compact features, XGBoost and CatBoost classifiers were trained on a dataset of DC01 low-carbon steel, covering five weld conditions. CatBoost achieved the highest accuracy of 98.9%, attributed to its ordered-boosting mechanism and symmetric-tree structure. Validation on an independent 198-sample dataset confirmed the generalization capability of the proposed approach. SHapley Additive exPlanations (SHAP)-based interpretability analysis further revealed that resistance-peak characteristics and energy-related descriptors dominate model decisions, aligning with the physical process of nugget formation and expulsion. Experimental results demonstrate that the DIMD–CatBoost framework provides a physically consistent, interpretable, and high-accuracy solution for intelligent weld-quality inspection.

Metals doi: 10.3390/met16050502

Authors: Iurii Dovgaliuk Yaroslav Tokaychuk Roman Gladyshevskii Viktor Hlukhyy

Lithium-containing intermetallic compounds, in particular tin-based systems, are attracting significant attention as potential anode materials for battery applications. In this work, we present the crystal structure of a new ternary compound, Li11Co1.8Sn20, which was solved and refined from single-crystal X-ray diffraction data: new structure type, space group C2/m, Pearson symbol mS66; a = 15.2320(5), b = 6.3334(2), c = 14.8033(4) Å, β = 99.758(4)°. The structure consists of a framework of pentagonal, square and trigonal prisms formed by Sn atoms and partially centered by Li or Co atoms.

Metals doi: 10.3390/met16050501

Authors: Yuli Zhou Huilin Zhang Yuxin Chen Fan Li Cai Chen Mohammed El Ganaoui Hélène Elias-Birembaux Mourad Khelifa Shuai Zhang Peijian Wang Dunming Liao

The influence of Cu content on the thermal conductivity and mechanical properties of Al-9Si-0.7Fe casting alloy were investigated in this paper. The results show that as the Cu content increases from 0.1 wt.% to 2.0 wt.%, the thermal conductivity of the alloy decreases from 173.6 W/(m·K) to 154.8 W/(m·K), while the yield strength increases from 72.2 MPa to 90.9 MPa. Metallographic, XRD, and EPMA analyses revealed that Cu has a relatively small impact on the secondary dendrite arm spacing of α-Al and the morphology of eutectic silicon. Its influence on the thermal conductivity and mechanical properties primarily stems from Cu atoms dissolving in the α-Al matrix, leading to a decreased lattice constant, increased lattice distortion, enhanced electron scattering, and improved solid solution strengthening effect. Based on the measured solubility of Cu, the Maxwell and Hashin–Shtrikman thermal conductivity models were modified. The correlation coefficients between the predicted values of the modified models and the experimental data were 92.77% and 93.11%, respectively, indicating a significant improvement in prediction accuracy.

Metals doi: 10.3390/met16050500

Authors: Matúš Gavalec Mária Dománková Marek Kudláč Katarína Bártová Gabriela Stachová

Extending the service life of nuclear power plant components beyond their originally designed operational period requires a detailed understanding of the microstructural stability of the materials used. This study focuses on low-temperature precipitation in the austenitic stainless steel 08CH18N10T, which is employed in the main circulation piping of pressurized water reactors. During long-term operation in the temperature range of 100–320 °C, secondary phases such as M23C6 carbides and intermetallic phase sigma (σ) can precipitate, which can lead to local chromium depletion at grain boundaries, subsequent sensitization of the steel, and susceptibility to intergranular corrosion. The research includes the analysis of samples taken from the decommissioned V1 unit of the Jaslovské Bohunice Nuclear Power Plant, which has been in operation for 28 years. The samples were subjected to thermal aging under laboratory conditions, with an emphasis on evaluating microstructural changes and their impact on corrosion resistance. Based on the experimental results, it can be concluded that the thermal stability of all tested materials is suitable for the operation of the main circulation piping, as the service temperatures to which the main circulation piping is exposed during operation remain below the activation of precipitation that would lead to sensitization and, consequently, susceptibility to intergranular corrosion. Activation of low-temperature precipitation was observed only at 450 °C, while at temperatures up to 400 °C, the structural stability of the material was confirmed, demonstrating its suitability for operation within the specified temperature range of the nuclear power plants’ main circulation piping.

Metals doi: 10.3390/met16050499

Authors: Airat M. Fairushin Elena Yu. Tumanova Andrey S. Tokarev Natalya B. Mulyashova Azamat S. Ilalov Alsu R. Kanaeva Arseny M. Kazakov Galiia F. Korznikova

Martensitic chromium-molybdenum steels such as 15Kh5M are widely used in high-temperature oil and gas equipment, but their weldability is limited by high hardenability and susceptibility to cold cracking, which usually necessitate energy-intensive preheating. This study evaluates an alternative route based on the combination of root-pass mechanical vibration (50 Hz, ~1 mm amplitude) and post-pass water-air jet cooling during mechanized GMAW. Three welding variants were compared: conventional preheated welding, vibration-assisted welding without preheating, and hybrid thermo-vibrational welding with active cooling. Among the tested conditions, the hybrid route produced the narrowest heat-affected zone, reducing its width from about 7 mm to about 3 mm, which is consistent with a compressed thermal cycle. Microhardness in the heat-affected zone decreased from 380 to 440 HV in the preheated condition to 330–370 HV in the hybrid condition. Optical microscopy further indicated a finer and more homogeneous transformed microstructure in the hybrid case. Results indicate that simultaneous vibro-treatment and controlled cooling effectively mitigate harmful metallurgical effects typically induced by rapid cooling, enabling preheat-free fabrication of thick-walled components. The proposed hybrid approach may offer energy savings, shorter production cycles, and improved automation compatibility in field welding applications.