Metals

14 pages, 4680 KB

Open AccessArticle

Performance Evaluation of Five-Axis CNC Milling via Spindle Current and Vibration Monitoring

by Beatriz Cardoso, José Ferreira, Tiago E. F. Silva, Pedro Sá Couto, Ana Reis and Abílio M. P. de Jesus

Metals 2026, 16(1), 129; https://doi.org/10.3390/met16010129 - 22 Jan 2026

Viewed by 423

Abstract

The digitalization of machining processes is increasingly recognized as essential for achieving higher productivity, reliability, and traceability. However, access to reliable in-process sensor data remains limited, particularly in multi-axis CNC machining, where dimensional accuracy and surface integrity strongly depend on stable and optimized [...] Read more.

The digitalization of machining processes is increasingly recognized as essential for achieving higher productivity, reliability, and traceability. However, access to reliable in-process sensor data remains limited, particularly in multi-axis CNC machining, where dimensional accuracy and surface integrity strongly depend on stable and optimized process conditions. This study investigates sensor-based monitoring as a practical approach for evaluating process performance in five-axis CNC milling. Electric current and vibration signals were acquired during three machining operations, under distinct cutting parameters, using current clamps and a plug-and-play MEMS accelerometer. The signals were processed using the root mean square method to assess the correlation between sensor data and machining conditions. Dimensional inspection of each workpiece was carried out to verify geometric conformity. The results show that spindle current measurements exhibit a strong linear correlation with material removal rate and cutting power, supporting their use as indicators of cutting forces and energy consumption. Vibration signals revealed pronounced dynamic behaviour for specific tool orientations, particularly in transverse to tool axis direction. The proposed methodology provides a simple and low-cost framework for integrating sensor-based monitoring into five-axis CNC milling, particularly relevant for semi-roughing operations, and offers a basis for future studies on process optimization and real-time condition monitoring. Full article

(This article belongs to the Special Issue Numerical and Experimental Advances in Metal Processing, 2nd Edition)

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17 pages, 8142 KB

Open AccessArticle

The Combined Influence of the Detonator Position and Anvil Type on the Weld Quality of Explosively Welded A1050/AZ31 Joints

by Bir Bahadur Sherpa, Shu Harada, Saravanan Somasundaram, Shigeru Tanaka and Kazuyuki Hokamoto

Metals 2026, 16(1), 128; https://doi.org/10.3390/met16010128 - 22 Jan 2026

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Abstract

The present study systematically investigates, for the first time, the combined influences of detonator position (top-edge and bottom-edge initiations) and anvil material (steel and sand) on the interfacial microstructure and mechanical performance of explosively welded A1050/AZ31 dissimilar joints. When welding was conducted using [...] Read more.

The present study systematically investigates, for the first time, the combined influences of detonator position (top-edge and bottom-edge initiations) and anvil material (steel and sand) on the interfacial microstructure and mechanical performance of explosively welded A1050/AZ31 dissimilar joints. When welding was conducted using a steel anvil with the detonator positioned at the top edge, significant cracking occurred both at the surface and along the weld interface. In contrast, placing the detonator at the bottom edge noticeably reduced these defects. Moreover, the use of a sand anvil nullified these defects by damping the reflecting shockwaves and minimizing vibrations. Hardness measurements revealed substantial increase at the interface under all the conditions, with the highest value observed with the steel anvil. Welds subjected to top-edge detonation showed higher hardness values compared to those of welds subjected to bottom-edge detonation. Overall, the results suggest that sand anvils with bottom-edge detonation provide the optimal weld quality. The rigid steel anvil reflects the shockwave, generating high pressure and velocity at the interface, whereas the sand anvil absorbs a part of the shock energy, suppressing high-magnitude reflections. The position of the detonator influences the propagation dynamics of the detonation wave and the resulting collision velocity, which in turn, affect the interfacial morphology and overall quality of the weld. Full article

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16 pages, 11984 KB

Open AccessArticle

Research on the Shear Forces and Fracture Behavior of Self-Riveting Friction Stir Lap Welding Joints with Medium-Thick Aluminum/Steel Plates

by Xiongwen Tian, Jianxin Wang, Chang Zhai, Yabin He, Shujin Chen, Yiming Jin, Rui Yu and Sergii Maksymov

Metals 2026, 16(1), 127; https://doi.org/10.3390/met16010127 - 22 Jan 2026

Viewed by 389

Abstract

The self-riveting friction stir lap welding (SRFSLW) method was utilized to improve the bonding strength of lap welding joints with medium-thick aluminum/steel plates and to realize structural lightweighting. The effect of plunge depth on the shear force and the microstructure of the joint [...] Read more.

The self-riveting friction stir lap welding (SRFSLW) method was utilized to improve the bonding strength of lap welding joints with medium-thick aluminum/steel plates and to realize structural lightweighting. The effect of plunge depth on the shear force and the microstructure of the joint was studied, and the influence of groove structure (rectangular groove and dovetail groove) on the failure behavior of the joint under shear load was obtained, simultaneously. The EBSD results indicate that the aluminum alloy grains in the stir zone (SZ) of groove joints have been refined compared to the non-groove joint. Meanwhile, due to the presence of grooves, the proportion of high-angle grain boundaries of the SZ is increased, and more dynamic recrystallization has emerged; thus, the KAM value of the SZ is reduced to a certain extent. The non-groove joint exhibits {111}//ND fiber texture, while the groove joint shows F-plate texture. In self-riveting joints, due to the increased metallurgical bonding area and the weakened effect of external loads, the failure of metallurgical bonding in the joint requires higher external load, and the separation of the self-riveted structure from the groove requires greater bending moment, thereby improving the strength of the joint. Full article

(This article belongs to the Special Issue Properties and Residual Stresses of Welded Alloys)

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17 pages, 5227 KB

Open AccessArticle

Synergistic Regulation of Microstructure and Mechanical Property in TiAl Alloys via Rolling and Cyclic Heat Treatment

by Shiwei Tian, Zhiqian Liao, Dejun Song, Chong Li, Kuishan Sun, Lin Yuan and Haitao Jiang

Metals 2026, 16(1), 126; https://doi.org/10.3390/met16010126 - 22 Jan 2026

Viewed by 228

Abstract

The presence of the brittle β/B2 phase in TiAl alloys often deteriorates their mechanical properties, posing a significant challenge for manufacturing large-sized, high-performance sheets. To address this issue, this study systematically investigates the synergistic effect of pack rolling and subsequent heat treatment on [...] Read more.

The presence of the brittle β/B2 phase in TiAl alloys often deteriorates their mechanical properties, posing a significant challenge for manufacturing large-sized, high-performance sheets. To address this issue, this study systematically investigates the synergistic effect of pack rolling and subsequent heat treatment on the microstructure evolution and mechanical properties of a Ti-44Al-4Nb-1.5Mo-0.1B-0.1Y alloy. Sheets with two different deformation levels (R7: 69.8% and R11: 83.0% reduction) were prepared via pack rolling. This was followed by a series of heat treatments at different temperatures (1150–1350 °C) and cyclic heat treatments at 1250 °C (3, 6, and 9 cycles). The results demonstrate that the higher deformation level (R11) promoted extensive dynamic recrystallization, resulting in a uniform microstructure of equiaxed γ, α₂, and β phases, while the lower deformation (R7) retained a significant fraction of deformed γ/α₂ lamellae. Heat treatment at 1250 °C was identified as optimal for transforming the microstructure into fine lamellar colonies while effectively reducing the β/B2 phase. Cyclic heat treatment at this temperature further decreased the β-phase content to 4.1% after 9 cycles. The elimination mechanism was determined to follow the β→ α → γ + α₂ phase transformation sequence, driven by the combined effect of rolling-induced defects and cyclic thermal stress. Cyclic heat treatment at this temperature was particularly effective in generating a high density of nucleation sites within the lamellar colonies, leading to significant refinement of the lamellar structure. Consequently, the R11 sheet subjected to 9 cycles of heat treatment exhibited a 15.5% increase in tensile strength and an 8.3% improvement in elongation compared to the hot-isostatically pressed state. This enhancement is primarily attributed to the significant refinement of lamellar colonies and the reduction in interlamellar spacing. This work presents an effective integrated processing strategy for fabricating high-performance TiAl alloy sheets with superior strength and toughness. Full article

(This article belongs to the Special Issue Microstructure and Deformation Mechanisms of Alloys)

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20 pages, 2130 KB

Open AccessArticle

Microstructural, Hardness, and Abrasive Wear Properties of Functionally Graded Al/ZrB₂ Composites Produced by In Situ Centrifugal Casting

by İbrahim Güney, Ömer Faruk Demirok, Yunus Emre Benkli, Çağlar Yüksel and Ömer Savaş

Metals 2026, 16(1), 125; https://doi.org/10.3390/met16010125 - 21 Jan 2026

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Abstract

Functionally graded aluminum matrix composites are of interest for applications requiring region-dependent mechanical and tribological performance. In this study, the micro-structure, hardness, and abrasive wear properties of functionally graded Al/ZrB₂ compo-site materials produced by an in situ centrifugal casting method were investigated. [...] Read more.

Functionally graded aluminum matrix composites are of interest for applications requiring region-dependent mechanical and tribological performance. In this study, the micro-structure, hardness, and abrasive wear properties of functionally graded Al/ZrB₂ compo-site materials produced by an in situ centrifugal casting method were investigated. The ZrB₂ reinforcement phase was synthesized in situ within the molten aluminum matrix, and functional grading was achieved through the action of centrifugal force during solidification. Samples taken from cylindrical castings were characterized using optical microscopy, scanning electron microscopy (SEM), X-Ray diffraction (XRD), density measurements, Brinell hardness testing, and abrasive wear experiments. Phase analyses con-firmed the successful in situ formation of ZrB₂ and verified that the phase distribution in-creased toward the direction of centrifugal force. Hardness increased with reinforcement content, rising from approximately 28 HB in the matrix-rich region to 68 HB and 72 HB in regions reinforced with 12% and 15% ZrB₂, respectively. Abrasive wear behavior was evaluated using the pin-on-disk method, and a Taguchi L (3⁵) orthogonal array was employed for experimental design. Statistical analyses showed that the composite region was the most influential parameter affecting wear performance, followed by abrasive particle size and applied load, while sliding distance and sliding speed were not statistically significant. These findings demonstrate that in situ centrifugal casting is an effective approach for producing functionally graded Al/ZrB₂ composites with improved hardness and wear resistance. Full article

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44 pages, 2586 KB

Open AccessReview

Cellular Automata and Phase-Field Modeling of Microstructure Evolution in Metal Additive Manufacturing: Recent Advances, Hybrid Frameworks, and Pathways to Predictive Control

by Łukasz Łach

Metals 2026, 16(1), 124; https://doi.org/10.3390/met16010124 - 21 Jan 2026

Viewed by 1453

Abstract

Metal additive manufacturing (AM) generates complex microstructures through extreme thermal gradients and rapid solidification, critically influencing mechanical performance and industrial qualification. This review synthesizes recent advances in cellular automata (CA) and phase-field (PF) modeling to predict grain-scale microstructure evolution during AM. CA methods [...] Read more.

Metal additive manufacturing (AM) generates complex microstructures through extreme thermal gradients and rapid solidification, critically influencing mechanical performance and industrial qualification. This review synthesizes recent advances in cellular automata (CA) and phase-field (PF) modeling to predict grain-scale microstructure evolution during AM. CA methods provide computational efficiency, enabling large-domain simulations and excelling in texture prediction and multi-layer builds. PF approaches deliver superior thermodynamic fidelity for interface dynamics, solute partitioning, and nonequilibrium rapid solidification through CALPHAD coupling. Hybrid CA–PF frameworks strategically balance efficiency and accuracy by allocating PF to solidification fronts and CA to bulk grain competition. Recent algorithmic innovations—discrete event-inspired CA, GPU acceleration, and machine learning—extend scalability while maintaining predictive capability. Validated applications across Ni-based superalloys, Ti-6Al-4V, tool steels, and Al alloys demonstrate robust process–microstructure–property predictions through EBSD and mechanical testing. Persistent challenges include computational scalability for full-scale components, standardized calibration protocols, limited in situ validation, and incomplete multi-physics coupling. Emerging solutions leverage physics-informed machine learning, digital twin architectures, and open-source platforms to enable predictive microstructure control for first-time-right manufacturing in aerospace, biomedical, and energy applications. Full article

(This article belongs to the Special Issue Characterization and Modeling of Microstructure Evolution During Metallic Material Processing)

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18 pages, 5019 KB

Open AccessArticle

A High-Solid-Content and Low-Surface-Treatment Epoxy-Polysiloxane Ceramic Metal Coating for Metal Anti-Corrosion in Harsh Environments

by Xiufen Liao, Liang Fan, Qiumei Jiang, Maomi Zhao, Songqiang Huang, Junxiang Lai, Congtao Sun and Baorong Hou

Metals 2026, 16(1), 123; https://doi.org/10.3390/met16010123 - 21 Jan 2026

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Abstract

Conventional anticorrosive coatings suffer from limitations of low solid content and rigorous surface pretreatment, posing environmental and cost challenges in field applications. In this study, a novel high-solid-content (>95%) epoxy-polysiloxane (Ep-PSA) ceramic metal coating was prepared that enables low-surface-treatment application. The originality lies [...] Read more.

Conventional anticorrosive coatings suffer from limitations of low solid content and rigorous surface pretreatment, posing environmental and cost challenges in field applications. In this study, a novel high-solid-content (>95%) epoxy-polysiloxane (Ep-PSA) ceramic metal coating was prepared that enables low-surface-treatment application. The originality lies in the synergistic combination of nano-sized ceramic powders, high-strength metallic powders, polysiloxane resin (PSA), and solvent-free epoxy resin (Ep), which polymerize through an organic–inorganic interpenetrating network to form a dense shielding layer. The as-prepared Ep-PSA coating system chemically bonds with indigenous metal substrate via Zn₃(PO₄)₂ and resin functionalities during curing, forming a conversion layer that reduces surface preparation requirements. Differentiating from existing high-solid coatings, this approach achieves superior long-term barrier properties, evidenced by |Z|_0.01Hz value of 9.64 × 10⁸ Ω·cm², after 6000 h salt spray exposure—four orders of magnitude higher than commercial 60% epoxy zinc-rich coatings (2.26 × 10⁴ Ω·cm², 3000 h salt spray exposure). The coating exhibits excellent adhesion (14.28 MPa) to standard sandblasted steel plates. This environmentally friendly, durable, and easily applicable composite coating demonstrates significant field application value for large-scale energy infrastructure. Full article

(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))

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23 pages, 136328 KB

Open AccessArticle

Mechanical Wear and Friction Behavior of 30CrMnSiNi2A Steel Rocket Sled Sliders Under High-Speed and Heavy-Load Conditions: A Finite Element Analysis

by Ye Hao, Naiming Lin, Lin Wu, Kai Yan, Weihua Wang, Yuan Yu, Qing Zhou, Zhiqi Liu, Qunfeng Zeng, Dongyang Li and Yucheng Wu

Metals 2026, 16(1), 122; https://doi.org/10.3390/met16010122 - 20 Jan 2026

Viewed by 305

Abstract

The rocket sled slider is a key connection component between the rocket sled and the track for support, guidance and load-bearing, ensuring the system’s safe and reliable operation. Wear of sliders under high—velocity and heavy—load conditions is crucial for equipment reliability. This study [...] Read more.

The rocket sled slider is a key connection component between the rocket sled and the track for support, guidance and load-bearing, ensuring the system’s safe and reliable operation. Wear of sliders under high—velocity and heavy—load conditions is crucial for equipment reliability. This study establishes a wear prediction model for sled rails using ANSYS, incorporating a dimensionless acceleration factor into the simulation. By analyzing dynamic characteristics of contact friction stress, wear volume, depth, and stress over time, the tribological characteristics of 30CrMnSiNi2A steel sliders were studied. The simulation results showed that during dry—friction sliding, slider wear is highly related to speed and load, increasing significantly as they increase. The slider’s contact surface has non-uniform stress distribution with stress concentration and gradient changes. Quantitative analysis has revealed that friction stress is positively correlated with load, and its sensitivity to speed changes is high at low speeds and relatively low at high speeds. Full article

(This article belongs to the Special Issue Advances in Tribological Performance and Wear Mechanism of Metallic Materials)

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18 pages, 8446 KB

Open AccessArticle

Influence of Post-Processing Temperatures on Microstructure and Hardness of PBF-LB Ti-6Al-4V

by Trung Van Trinh, Trang Huyen Dang, Anh Hoang Pham, Gia Khanh Pham and Ulrich E. Klotz

Metals 2026, 16(1), 121; https://doi.org/10.3390/met16010121 - 20 Jan 2026

Viewed by 434

Abstract

This study investigates the effects of post-build heat treatments—such as annealing, quenching, and aging—on the microstructure and hardness of Laser Powder Bed Fusion (PBF-LB) Ti-6Al-4V. Specimens were subjected to annealing (950 °C, 1010 °C) or solution treatment/quenching (950 °C, 1010 °C), followed by [...] Read more.

This study investigates the effects of post-build heat treatments—such as annealing, quenching, and aging—on the microstructure and hardness of Laser Powder Bed Fusion (PBF-LB) Ti-6Al-4V. Specimens were subjected to annealing (950 °C, 1010 °C) or solution treatment/quenching (950 °C, 1010 °C), followed by aging (350–550 °C). Microstructural evolution was analyzed using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and Vickers hardness testing. Results showed that the as-built sample exhibited high hardness (365.2 HV_0.1) due to fine α′ martensite. Sub-β-transus annealing at 950 °C decomposed α′ into equilibrium α + 1.25% β (329 HV_0.1), while super-β-transus annealing at 1010 °C formed coarse lamellar structures of α + 1.5% β, yielding the lowest hardness (319 HV_0.1). Quenching from 1010 °C produced dominant α′ martensite with high hardness (371.6 HV_0.1). Notably, aging samples quenched from 950 °C increased hardness, peaking at 382.6 HV_0.1 at 450 °C due to precipitation, before decreasing to 364.4 HV_0.1 at 550 °C due to coarsening. These findings demonstrate that optimizing heat treatment temperatures is critical for controlling phase transformations and tailoring mechanical properties in additively manufactured Ti-6Al-4V components. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing for Metallic Materials and Their Applications (4th Edition))

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18 pages, 4995 KB

Open AccessArticle

The Effect of Ultrasonic Vibration Assistance During Laser Lap Welding on the Microstructure and Properties of Galvanized Steel/Mg Joints

by Dan Wang, Chengsen Zhu, Juming Gao, Hongliang Li, Dongdong Zhuang, Nan Xu, Xinyi Zhao, Ke Han and Zeyu Wang

Metals 2026, 16(1), 120; https://doi.org/10.3390/met16010120 - 20 Jan 2026

Viewed by 313

Abstract

In this work, a laser lap-welded joint of galvanized steel/Mg and a laser lap-welded joint of galvanized steel/Mg assisted by ultrasonic vibration were compared. By adjusting the laser beam power and ultrasonic amplitude, the appropriate welding process parameters were obtained. The weld formation, [...] Read more.

In this work, a laser lap-welded joint of galvanized steel/Mg and a laser lap-welded joint of galvanized steel/Mg assisted by ultrasonic vibration were compared. By adjusting the laser beam power and ultrasonic amplitude, the appropriate welding process parameters were obtained. The weld formation, microstructure and mechanical properties were studied and analyzed. The results indicated that the addition of ultrasonic vibration generated an excitation force with a certain frequency and amplitude on the weldment, making the molten metal in the molten pool produce ultrasonic forced vibration, and producing the effects of cavitation, acoustic streaming, mechanical stirring and heat, thus reducing welding residual stress and welding-deformation, porosity and incomplete-fusion defects. In addition, it can make the fusion zone transition evenly, improve the wettability, refine the weld grain, and reduce the average grain area from 583 μm² to 324 μm². Moreover, the distribution of Mg-Zn reinforcing phase at the interface was more uniform and denser, and the maximum tensile shear strength increased from 179.9 N/mm to 290 N/mm, indicating that the addition of ultrasonic vibration was conducive to improving the comprehensive mechanical properties of the joint. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Property Improvement of Welded Metal Joints (2nd Edition))

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25 pages, 16008 KB

Open AccessArticle

The Correlation of Thermodynamic Modelling and Experimental Methods in the Production of Nickel Matte from Saprolite Nickel Ore via CaS

by Erdenebold Urtnasan, Chang-Ho Jung and Jei-Pil Wang

Metals 2026, 16(1), 119; https://doi.org/10.3390/met16010119 - 20 Jan 2026

Viewed by 744

Abstract

Given the importance of nickel in lithium-ion batteries and the expectation of the growth in electric vehicles and electrical devices, the demand for nickel in battery production is expected to increase dramatically. Nickel is primarily sourced from laterite saprolite ore, and there is [...] Read more.

Given the importance of nickel in lithium-ion batteries and the expectation of the growth in electric vehicles and electrical devices, the demand for nickel in battery production is expected to increase dramatically. Nickel is primarily sourced from laterite saprolite ore, and there is now substantial interest in moving from ferronickel smelting technology to nickel matte technology in its processing to produce high-grade nickel. This research involved a thermodynamic modelling and lab–scale experiment on the smelting of nickel matte. Nickel concentrate from laterite saprolite was used, and CaS, produced from commercially available gypsum, was employed as a sulfurizing agent. The matte smelting experiment was conducted at 1500 °C to optimize CaS and C consumption. During smelting with CaS, matte particles form, although sufficient reduction of nickel and iron from the concentrate is not achieved. By consuming carbon, the reduction potential of iron is increased, and this process, along with enriching the matte with iron, aids in the transportation of nickel. At a nickel grade in the matte with a Ni/Fe ratio of approximately 1, the nickel recovery only reached 63%. Upon achieving a nickel recovery exceeding 93%, the Ni/Fe ratio reached 0.44, corresponding to a nickel grade reduction to 22.78%. By employing analytical techniques and thermodynamic modelling, we have successfully determined the sulfidizing of nickel, identified the ideal CaS and C additions, and characterized the structure and quality of the slag produced during nickel matte smelting, supplying vital technological data necessary for practical application. Full article

(This article belongs to the Special Issue Pyrometallurgy and Waste Recycling: Experiment and Simulation)

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13 pages, 3005 KB

Open AccessArticle

A Study of Effect of Bidirectional Drawing on the Mechanical Properties of 30MnSi6 Non-Heat-Treated Steel

by Jaehan Lim, Jonghyeok Lee and Byounglok Jang

Metals 2026, 16(1), 118; https://doi.org/10.3390/met16010118 - 20 Jan 2026

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Abstract

As the work hardening rate increases during the cold drawing of non-heat-treated steel (NHT steel), a significant loss in ductility and toughness can occur, leading to reduced formability and part quality. In this study, a bidirectional drawing process consisting of alternating forward and [...] Read more.

As the work hardening rate increases during the cold drawing of non-heat-treated steel (NHT steel), a significant loss in ductility and toughness can occur, leading to reduced formability and part quality. In this study, a bidirectional drawing process consisting of alternating forward and reverse passes is proposed to mitigate these issues and enhance the mechanical performance of the steel. Mechanical property evaluations, including tensile testing and three-point bending tests, were conducted to assess the effects of bidirectional drawing compared to conventional unidirectional drawing. The results showed that the bidirectionally drawn wire maintained a similar tensile strength to that of the unidirectionally drawn wire at a 70% area reduction, while exhibiting a 12% improvement in elongation. Microstructural analysis revealed grain refinement and reduced texture anisotropy in the bidirectionally drawn specimens, contributing to the observed enhancement in ductility. These findings indicate that bidirectional drawing is a promising approach for improving the formability and overall quality of high-strength, NHT steel components. Full article

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17 pages, 3423 KB

Open AccessArticle

Effect of Calcination of Manganese Ore on Reducing Hydrogen and Energy Consumptions in Hydrogen-Based Direct Reduction Process

by Jafar Safarian

Metals 2026, 16(1), 117; https://doi.org/10.3390/met16010117 - 19 Jan 2026

Viewed by 417

Abstract

Manganese is a critical raw material and there is currently a great interest in decarbonization in the metallurgical sector for its production. Hydrogen use in manganese and its alloys’ production is in principle possible for sustainable production; however, this requires a technological shift [...] Read more.

Manganese is a critical raw material and there is currently a great interest in decarbonization in the metallurgical sector for its production. Hydrogen use in manganese and its alloys’ production is in principle possible for sustainable production; however, this requires a technological shift from traditional carbothermic processes to completely new processes; like the HAlMan process. To design a process, it is crucially important to optimize the process conditions (such as temperature) and minimize the quantity of hydrogen gas and the related energy consumptions. In the present work, energy and mass balances for a hydrogen-based reduction reactor were carried out employing thermodynamics software and analytical approaches from room temperatures to 900 °C. It was found that the quantity of hydrogen gas required for the pre-reduction of manganese ore can be significantly reduced via coupling the reduction reactor with a calciner and the hot charge of the calcined ore into the reduction reactor. Moreover, hot H₂-H₂O gas mixture from the reduction reactor outlet can be used for preheating the hydrogen feed of the reactor, and the calcination of the ore, while a portion or all its hydrogen can be recovered and looped. The integrated coupled calcination-reduction process was found to be operated with no external energy supply, or insignificant fuel use. Full article

(This article belongs to the Section Extractive Metallurgy)

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14 pages, 2937 KB

Open AccessArticle

Development of a Workflow for Topological Optimization of Cutting Tool Milling Bodies

by Bruno Rafael Cunha, Bruno Miguel Guimarães, Daniel Figueiredo, Manuel Fernando Vieira and José Manuel Costa

Metals 2026, 16(1), 116; https://doi.org/10.3390/met16010116 - 19 Jan 2026

Viewed by 666

Abstract

This study establishes a systematic and reproducible workflow for topology optimization (TO) of indexable face milling cutter bodies with integrated internal coolant channels, designed for Additive Manufacturing (AM) of metallic parts. Grounded in Design for Additive Manufacturing (DfAM) principles, the workflow combines displacement-based [...] Read more.

This study establishes a systematic and reproducible workflow for topology optimization (TO) of indexable face milling cutter bodies with integrated internal coolant channels, designed for Additive Manufacturing (AM) of metallic parts. Grounded in Design for Additive Manufacturing (DfAM) principles, the workflow combines displacement-based TO and computational fluid dynamics analysis to generate simulation-driven tool geometries tailored to the constraints of AM. By leveraging iterative design knowledge, the proposed methodology enhances the scalability and repeatability of the design process, reducing development time and supporting rapid adaptation across various tool geometries. AM is explicitly exploited to integrate support-free internal coolant channels directed toward the insert cutting edge, thereby achieving a 20% mass reduction relative to the initial milling tool designs, and improving material usage efficiency at the design stage. The workflow yields numerically optimized geometries that maintain simulated global stiffness under the considered loading conditions and exhibit coolant flow distributions that effectively target the exposed cutting edges. These simulation results demonstrate the feasibility of an AM oriented, workflow-based approach for the numerical design of milling tools with internal cooling, mass reduction and provide a focused basis for subsequent experimental validation and comparison with conventionally manufactured counterparts. Full article

(This article belongs to the Special Issue Advances in Manufacturing and Machining Processes of Metals)

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20 pages, 3861 KB

Open AccessArticle

Picolinoyl N4-Phenylthiosemicarbazide-Modified ZnAl and ZnAlCe Layered Double Hydroxide Conversion Films on Hot-Dip Galvanized Steel for Enhancing Corrosion Protection in Saline Solution

by Thu Thuy Pham, Anh Son Nguyen, Chien Thang Pham, Hong Nhung Nguyen, Maurice Gonon, Lisa Dangreau, Xavier Noirfalise, Thuy Duong Nguyen, Thi Xuan Hang To and Marie-Georges Olivier

Metals 2026, 16(1), 115; https://doi.org/10.3390/met16010115 - 19 Jan 2026

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Abstract

ZnAl and ZnAlCe layered double hydroxide (LDH) conversion layers modified with picolinoyl N4-phenylthiosemicarbazide (HL) are fabricated on hot-dip galvanized steel (HDG) to improve corrosion protection. X-ray diffraction (XRD) confirms that HL molecules are not intercalated within the LDH interlayers, whereas Fourier [...] Read more.

ZnAl and ZnAlCe layered double hydroxide (LDH) conversion layers modified with picolinoyl N4-phenylthiosemicarbazide (HL) are fabricated on hot-dip galvanized steel (HDG) to improve corrosion protection. X-ray diffraction (XRD) confirms that HL molecules are not intercalated within the LDH interlayers, whereas Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analyses reveal their surface adsorption. Moreover, scanning electron microscopy (FE-SEM) observations reveal that HL modification induces changes in surface morphology. After 168 h in 0.1 M NaCl, the LDH structure remains intact, and N and S signals are still detected, confirming the persistence of both the LDH layer and adsorbed HL molecules under corrosive conditions. During 168 h immersion in NaCl, electrochemical measurements indicate that the modified LDH layers exhibit higher corrosion resistance than the unmodified ones, with the ZnAlCe LDH/HL coating providing the most effective protection. Full article

(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials)

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18 pages, 8125 KB

Open AccessArticle

EERZ-Based Kinetic Modeling of Ladle Furnace Refining Pathways for Producing Weathering Steels Using CALPHAD TCOX Databases

by Reda Archa, Zakaria Sahir, Ilham Benaouda, Amine Lyass, Ahmed Jibou, Hamza Azzaoui, Sanae Baki Senhaji, Youssef Samih and Johan Jacquemin

Metals 2026, 16(1), 114; https://doi.org/10.3390/met16010114 - 19 Jan 2026

Viewed by 629

Abstract

The design of ladle furnace (LF) refining pathways for weathering steels requires precise control of multi-component steel/slag reactions governed simultaneously by thermodynamics and interfacial mass transfer kinetics. An EERZ-based kinetic modeling strategy was employed using the Thermo-Calc^® (version 2022a) Process Metallurgy Module [...] Read more.

The design of ladle furnace (LF) refining pathways for weathering steels requires precise control of multi-component steel/slag reactions governed simultaneously by thermodynamics and interfacial mass transfer kinetics. An EERZ-based kinetic modeling strategy was employed using the Thermo-Calc^® (version 2022a) Process Metallurgy Module and the CALPHAD TCOX11 database to develop LF refining schedules capable of upgrading conventional S355J2R steel to weathering steel grades: S355J2W and S355J2WP. First, the sensitivity of predicted compositions to key kinetic inputs was quantified. The validated model was then used to simulate deoxidation and desulfurization sequences, predicting the evolution of liquid–steel and slag compositions, slag basicity, and FeO activity throughout the LF cycle. Subsequently, Cr- and P-ferroalloys were introduced to design tap-to-tap schedules that meet the EN 10025-5 chemical specifications for S355J2W and S355J2WP. To correlate simulation outcomes with material performance, plates produced following the modeled schedules were evaluated through a 1000 h accelerated salt spray test. Steel density and steel phase mass transfer coefficients were found to produce the highest prediction sensitivity (up to 7.5 wt.% variation in C and S), whereas slag phase parameters exhibited a lower impact. The predicted steel compositions showed strong agreement with industrial values obtained during plant trials. SEM-EDS analyses confirmed the development of a Cr-enriched protective patina and validated model-based alloying strategies. Full article

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4 pages, 148 KB

Open AccessEditorial

Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes

by Ilhwan Park and Sanghee Jeon

Metals 2026, 16(1), 113; https://doi.org/10.3390/met16010113 - 19 Jan 2026

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Abstract

The global commitment to achieving a carbon-neutral society has accelerated the transition toward renewable energy, electric mobility, and advanced electronic systems [...] Full article

(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)

17 pages, 1285 KB

Open AccessArticle

Surface Modification of Inconel 625 in Nitrate Environment

by Mieczysław Scendo

Metals 2026, 16(1), 112; https://doi.org/10.3390/met16010112 - 19 Jan 2026

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Abstract

The influence of nitrate (NO₃⁻) concentration on the corrosion resistance of the Inconel 625 (superalloy) was investigated. The surface of Inconel 625 was chemically modified by oxidation in an alkaline sodium nitrate(V) solution. The surface and microstructure of specimens were [...] Read more.

The influence of nitrate (NO₃⁻) concentration on the corrosion resistance of the Inconel 625 (superalloy) was investigated. The surface of Inconel 625 was chemically modified by oxidation in an alkaline sodium nitrate(V) solution. The surface and microstructure of specimens were observed by a scanning electron microscope (SEM). The mechanical properties of Inconel 625 were characterized by microhardness (HV) measurements. The corrosion tests of materials were carried out by using the electrochemical method in the acidic chloride solution. The adsorption of the (Me_mO_n)_ads layer effectively separates the Inconel 625 surface from contact with the aggressive corrosive environment. The microhardness (HV10) value increased (about 13%) with the increase in nitrate concentration. A more-than-five-times-lower corrosion rate (CW) value was obtained for the Inconel 625 sample, whose surface was modified in an alkaline solution with the highest NO₃⁻ concentration. Chemical modification improves the structure and surface topography of the superalloy. After exposing Inconel 625 to an oxidizing environment (1.00 M NO₃⁻), the surface coverage degree (SC) was 80%. Full article

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19 pages, 4052 KB

Open AccessArticle

Microstructure and Wear Resistance of (Mg₂Si + SiC_p)/Al Composites

by Dekun Zhou, Xiaobo Liu and Miao Yang

Metals 2026, 16(1), 111; https://doi.org/10.3390/met16010111 - 18 Jan 2026

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Abstract

The microstructure and wear behaviors of Mg₂Si/Al composites with 0 wt.%, 5 wt.%, and 10 wt.% SiC particles were studied using XRD, OM observation, SEM observation, EDS analysis, an extraction experiment, a hardness test, and the dry sliding wear test. It [...] Read more.

The microstructure and wear behaviors of Mg₂Si/Al composites with 0 wt.%, 5 wt.%, and 10 wt.% SiC particles were studied using XRD, OM observation, SEM observation, EDS analysis, an extraction experiment, a hardness test, and the dry sliding wear test. It is shown by the results that after the addition of 10 wt.% SiC particles, the population of primary Mg₂Si particles increased, while the mean size of these particles reduced from 40 ± 10 μm (in the SiC-free composite) to 25 ± 8 μm. Both the matrix and the eutectic structure were refined. The tetrakaidecahedral morphologies of Mg₂Si crystals were confirmed by the results of extraction tests. The wear test results with GCr15 steel as the friction pair show that the Mg₂Si/Al composite with 10 wt.% SiC particles displayed more favorable wear resistance than the specimens with 0 wt.% and 5 wt.% SiC particle additions under both constant load and constant sliding velocity conditions. Under applied loads of 10 N, 20 N, and 30 N at a fixed sliding speed of 300 r/min, the wear rate of the Mg₂Si-Al composites reinforced with 10 wt.% SiC particles was 36.01%, 48.29%, and 23.32% lower than that of the SiC-free composites, respectively. When the sliding speed was set to 300 r/min, 550 r/min, 750 r/min, and 1000 r/min under a constant applied load of 20 N, the wear rate of the 10 wt.% SiC-reinforced Mg₂Si-Al composites was reduced by 40.37%, 40.87%, 26.20%, and 25.78%, respectively, compared with the SiC-free counterparts. The wear failure mechanisms of (Mg₂Si + SiC_P)/Al composites were mainly adhesive wear and abrasive wear, but the proportion of oxidation wear increased after the addition of the SiC particles. Full article

(This article belongs to the Special Issue Recent Advances in Forming Processes of Lightweight Metals)

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18 pages, 4148 KB

Open AccessArticle

Optimizing S20C Steel and SUS201 Steel Welding Using Stainless Steel Filler and MIG Method

by Van Huong Hoang, Thanh Tan Nguyen, Minh Tri Ho, Pham Tran Minh Trung, Nguyen Van Sung, Van-Thuc Nguyen and Van Thanh Tien Nguyen

Metals 2026, 16(1), 110; https://doi.org/10.3390/met16010110 - 18 Jan 2026

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Abstract

The reliable joining of dissimilar stainless steel and carbon steel remains a critical challenge in Metal Inert Gas (MIG) welding due to complex thermal–metallurgical interactions and the formation of brittle phases at the weld interface. In this study, a Taguchi-based design of experiments [...] Read more.

The reliable joining of dissimilar stainless steel and carbon steel remains a critical challenge in Metal Inert Gas (MIG) welding due to complex thermal–metallurgical interactions and the formation of brittle phases at the weld interface. In this study, a Taguchi-based design of experiments was employed to systematically optimize MIG welding parameters for SUS201/S20C dissimilar joints using a SUS201 filler wire, with particular attention to the welding current, voltage, travel speed, and electrode stick-out. The welding process was performed using an automatic welding robot. Tensile specimens were tested on a universal testing machine. Microstructural analysis was performed using a metallurgical microscope. The microstructure reveals that the development of the carbon side’s large ferrite and the stainless steel side’s δ-ferrite both significantly degrade joint quality. Among all process parameters, electrode stick-out is identified as the most influential parameter governing both tensile and bending performance, highlighting a critical process sensitivity that has received limited attention in prior studies. Optimized parameter combinations are required to maximize tensile and flexural responses. The highest tensile strength is 450.96 MPa. These findings advance the understanding of parameter–microstructure–property relationships in dissimilar MIG welding. Future work applying numerical welding simulations and advanced evaluation techniques is recommended. Full article

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18 pages, 10356 KB

Open AccessArticle

Chlorella vulgaris Powder as an Eco-Friendly and Low-Cost Corrosion Inhibitor Against Carbon Steel Corrosion by HCl

by Zhong Li, Xiaolong Li, Jianfeng Lai, Shaohua Cao, Guoqiang Liu, Xiaowan Wang, Yan Lyu, Junlei Wang and Jike Yang

Metals 2026, 16(1), 109; https://doi.org/10.3390/met16010109 - 18 Jan 2026

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Abstract

In this study, dried biomass of the alga Chlorella vulgaris was ground into a powder as an eco-friendly, low-cost inhibitor to mitigate the corrosion of carbon steel in acidic solutions. Electrochemical and weight loss measurements, surface morphology observations, adsorption isotherms, activation energy, and [...] Read more.

In this study, dried biomass of the alga Chlorella vulgaris was ground into a powder as an eco-friendly, low-cost inhibitor to mitigate the corrosion of carbon steel in acidic solutions. Electrochemical and weight loss measurements, surface morphology observations, adsorption isotherms, activation energy, and potential of zero charge calculations were applied to evaluate the inhibition performance. Electrochemical results indicate that C. vulgaris powder can simultaneously inhibit both the anodic and cathodic corrosion processes of carbon steel, demonstrating good inhibition performance and classifying it as a mixed-type inhibitor with both anodic and cathodic characteristics. Weight loss data further confirm that at a concentration of 300 mg/L, the corrosion inhibition efficiency reaches 88%. The fitted adsorption isotherm reveals that the adsorption of Chlorella vulgaris powder on the carbon steel surface follows the Langmuir model. Density functional theory (DFT) and molecular dynamics simulations indicate that the excellent inhibition performance is attributed to the combined effects of physisorption and chemisorption of constituents such as amino acids and cellulose present in C. vulgaris. Full article

(This article belongs to the Special Issue Advances in Microbiological Corrosion of Metals, Alloys, and Metallic Compounds)

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24 pages, 12498 KB

Open AccessArticle

Study on Surface Properties and Microstructural Evolution of LA103Z Mg-Li Alloy by Friction Stir Processing

by Jiqiang Zhai, Kai Hu, Zihan Kong and Xinzhen Fang

Metals 2026, 16(1), 108; https://doi.org/10.3390/met16010108 - 18 Jan 2026

Viewed by 375

Abstract

Magnesium–lithium alloys are the lightest structural metals and offer high specific strength, good damping capacity, and excellent thermal conductivity; however, their limited room-temperature strength restricts wider engineering applications. In this study, friction stir processing (FSP) was applied to LA103Z magnesium–lithium alloy to modify [...] Read more.

Magnesium–lithium alloys are the lightest structural metals and offer high specific strength, good damping capacity, and excellent thermal conductivity; however, their limited room-temperature strength restricts wider engineering applications. In this study, friction stir processing (FSP) was applied to LA103Z magnesium–lithium alloy to modify its surface microstructure and mechanical properties. The effects of tool rotational speed and travelling speed on dynamic recrystallization behavior, grain refinement, and phase evolution in the stirred zone (SZ) and thermomechanically affected zone (TMAZ) were systematically investigated. FSP induced significant grain refinement accompanied by the precipitation of a reticular α-Mg phase along β-Li grain boundaries, as well as Li₃Mg₇ and Li₂MgAl phases within the stirred zone, leading to pronounced strengthening. Under optimized processing conditions, substantial improvements in hardness and tensile properties were achieved compared with the base material. The optimal condition was obtained at 600 rpm and 100 mm/min, yielding an average hardness of 79.17 HV_0.2, a tensile strength of 243.6 MPa, and an elongation of 17.9%, corresponding to increases of 47.5% in hardness and 53.3% in tensile strength. Quantitative relationships between heat input, grain size, and mechanical properties further demonstrate that heat input governs microstructural evolution and strengthening behavior during FSP of LA103Z alloy. Full article

(This article belongs to the Special Issue Surface Modification and Characterization of Metals and Alloys)

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17 pages, 10848 KB

Open AccessArticle

Creep Deformation Estimation of Single Crystal Ni-Based Superalloy by Optimized Geometrically Necessary Dislocation Density Evaluation

by Cristina Motta, Francesco Mastromatteo, Niccolò Baldi, Elisabetta Gariboldi and Luca Bernardini

Metals 2026, 16(1), 107; https://doi.org/10.3390/met16010107 - 17 Jan 2026

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Abstract

In the framework of high temperature components, the need to evaluate the accumulated creep damage during service life is fundamental to extend the life of components which are currently deemed as scrap as per design intent. Thus, the life assessment of Ni-based superalloys [...] Read more.

In the framework of high temperature components, the need to evaluate the accumulated creep damage during service life is fundamental to extend the life of components which are currently deemed as scrap as per design intent. Thus, the life assessment of Ni-based superalloys could be performed in relation to the accumulated creep deformation which represents the limiting factor for serviced components. Despite the different microstructural changes that occur in service life, this work focuses on the possibility to evaluate the material strain by means of electron backscattered diffraction (EBSD). The key point is the identification of the correlation between geometrically necessary dislocation (GND) density derived from EBSD analyses and the reached creep strain for a single crystal Ni-based superalloy. However, the results of GND density are affected by the settings’ parameters adopted to perform the analysis by the magnification level and the step size. These two parameters have been optimized by analyzing specimens from interrupted creep tests at strain levels between 0.5% and 10%, in the temperature range between 850 °C and 1000 °C. Full article

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16 pages, 7668 KB

Open AccessArticle

Heterogeneity of Microstructure and Mechanical Response in Steel–Titanium Multilayer Wires Subjected to Severe Plastic Deformation

by Bartłomiej Pabich, Paulina Lisiecka-Graca, Marcin Kwiecień and Janusz Majta

Metals 2026, 16(1), 106; https://doi.org/10.3390/met16010106 - 17 Jan 2026

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Abstract

This study addresses the fundamental problem of representing the rheological properties of heterostructured materials composed of metals that differ significantly in their crystal structure, stacking fault energy, and related characteristics. The necessity of accounting for essential strengthening mechanisms is highlighted. The study is [...] Read more.

This study addresses the fundamental problem of representing the rheological properties of heterostructured materials composed of metals that differ significantly in their crystal structure, stacking fault energy, and related characteristics. The necessity of accounting for essential strengthening mechanisms is highlighted. The study is based on experimental results related to the fabrication of a multilayer, heterogeneous system via multistage wire drawing, supported by microstructural analysis, microhardness measurements, and numerical simulations employing various flow-stress models. A discussion is presented regarding the effectiveness of these models in representing the deformation behavior of the investigated materials. The primary materials examined were a multilayer system composed of microalloyed steel and titanium. The obtained results indicate that, in addition to incorporating strengthening mechanisms, it is necessary to consider significant microstructural changes affecting microstructure evolution—particularly grain refinement induced by continuous recrystallization and the effects of strain hardening. Moreover, the findings point to the potential intensification of strengthening associated with pile-up mechanisms, linked to the development of dislocation substructures and the possible fragmentation of the hard phase in the vicinity of the more ductile microalloyed steel phase. In conclusion, the discussion integrates measurements of rheological properties obtained through tensile tests, supported by microstructural analysis, digital image correlation (DIC), and microhardness measurements, which collectively demonstrate the effectiveness of the adopted analytical approach. Full article

(This article belongs to the Special Issue Advances in the Forming and Processing of Metallic Materials)

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15 pages, 5606 KB

Open AccessArticle

Effect of Deposition Angle and Arc Current on the Structure and Optical Properties of Ti Coatings Deposited by Cathodic Arc Evaporation

by Iulian Pana, Anca C. Parau, Mihaela Dinu, Adrian E. Kiss, Lidia R. Constantin, Nicolae C. Zoita, Alina Vladescu (Dragomir) and Catalin Vitelaru

Metals 2026, 16(1), 105; https://doi.org/10.3390/met16010105 - 17 Jan 2026

Viewed by 471

Abstract

This study investigates the effects of deposition angle and arc current on the surface morphology and optical response of Ti coatings obtained by unfiltered cathodic arc evaporation for spectrally selective solar-thermal applications. 100 nm-thick Ti films were deposited at normal (0°) and oblique [...] Read more.

This study investigates the effects of deposition angle and arc current on the surface morphology and optical response of Ti coatings obtained by unfiltered cathodic arc evaporation for spectrally selective solar-thermal applications. 100 nm-thick Ti films were deposited at normal (0°) and oblique (80°) angles of incidence, with arc currents of 65 A and 90 A, respectively. The SEM measurements revealed the characteristic arc-generated microdroplet population. At normal incidence (0°), droplets are predominantly spherical and relatively uniformly distributed, whereas at 80° incidence, many droplets exhibit elongated footprints aligned with the incoming flux from the Ti cathode. This behavior is consistent with oblique-angle deposition (OAD), where the arrival geometry can promote self-shadowing and transient droplet spreading before solidification. AFM confirms an increase in nanoscale roughness, whereas GIXRD indicates nanocrystalline α-Ti and cubic TiO, with maximum crystallinity for 0°/65 A. Contact-angle measurements demonstrate a transition from hydrophobic 316L (~103°) to moderately hydrophilic Ti-coated surfaces (~68–72°), with only minor dependence on deposition geometry. Optical reflectance in the 400–800 nm range is significantly lower for Ti-coated glass and is further reduced for OAD films, indicating enhanced solar absorptance. Full article

(This article belongs to the Special Issue Metallic Coatings Synthesized by Magnetron Sputtering)

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19 pages, 6581 KB

Open AccessArticle

Data-Driven Design of HPDC Aluminum Alloys Using Machine Learning and Inverse Design

by Seunghyeok Choi, Sungjin Kim, Junho Lee, Jeonghoo Choi, MiYoung Lee, JaeHwang Kim, Jae-Gil Jung and Seok-Jae Lee

Metals 2026, 16(1), 99; https://doi.org/10.3390/met16010099 - 16 Jan 2026

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Abstract

This work proposes a data-driven design framework for high-pressure die-cast (HPDC) aluminum alloys that integrates robust data refinement, machine learning (ML) modeling, explainability, and inverse design. A total of 1237 tensile-test records from T5-aged HPDC alloys were aggregated into a curated dataset of [...] Read more.

This work proposes a data-driven design framework for high-pressure die-cast (HPDC) aluminum alloys that integrates robust data refinement, machine learning (ML) modeling, explainability, and inverse design. A total of 1237 tensile-test records from T5-aged HPDC alloys were aggregated into a curated dataset of 382 unique composition–heat-treatment combinations. Four regression models—Ridge regression, Random Forest (RF), XGBoost (XGB), and a multilayer perceptron (MLP)—were trained to predict yield strength (YS), ultimate tensile strength (UTS), and elongation (EL). Tree-based ensemble models (XGB and RF) achieved the highest accuracy and stability, capturing nonlinear interactions inherent to industrial HPDC data. In particular, the XGB model exhibited the best predictive performance, achieving test R² values of 0.819 for UTS and 0.936 for EL, with corresponding RMSE values of 15.23 MPa and 1.112%, respectively. Feature-importance and SHapley Additive exPlanations (SHAP) analyses identified Mn, Si, Mg, Zn, and T5 aging temperature as the most influential variables, consistent with metallurgical considerations such as microstructural stabilization and precipitation strengthening. Finally, RF-based inverse design suggested new composition–process candidates satisfying UTS > 300 MPa and EL > 8%, a region scarcely represented in the experimental dataset. These results illustrate how interpretable ML can expand the feasible design space of HPDC aluminum alloys and support composition–process optimization in industrial applications. Full article

(This article belongs to the Special Issue Solidification and Casting of Light Alloys)

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13 pages, 5889 KB

Open AccessArticle

Metallic Structures and Tribological Properties of Ti-15mass%Nb Alloy After Gas Nitriding and Quenching Process

by Yoshikazu Mantani, Riho Takahashi, Tomoyuki Homma and Eri Akada

Metals 2026, 16(1), 98; https://doi.org/10.3390/met16010098 - 16 Jan 2026

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Abstract

This study aimed to experimentally investigate the differences in metallic structures owing to the gas nitriding and quenching process (GNQP) temperature of the Ti-15mass%Nb alloy and differences in the tribological properties of the surface layer. The GNQP heating temperature was 1023 K or [...] Read more.

This study aimed to experimentally investigate the differences in metallic structures owing to the gas nitriding and quenching process (GNQP) temperature of the Ti-15mass%Nb alloy and differences in the tribological properties of the surface layer. The GNQP heating temperature was 1023 K or 1223 K, and the holding time was set to 1 h. In the X-ray diffraction profiles, the diffraction peak of the (10

\bar{1}

1) plane of the hexagonal close-packed phase exhibited a shift toward lower angles, following the sequence AN:α, AQ:α′, and GNQP:α-TiN_0.3. In both the 1023 K and 1223 K GNQP specimens, the α″ phase exhibited lower values than the α′ phase; nonetheless, it still exhibited larger values than the annealed α phase. Based on transmission electron microscopy observations, the high core hardness of the 1223 K GNQP specimen was attributed to solid-solution strengthening caused by nitrogen diffusion or to strain hardening associated with the diffusion and was not attributed to the influence of precipitation phases, such as the ω phase. In the friction and wear tests, both the 1023 K and 1223 K GNQP specimens exhibited narrower wear track widths, clearly demonstrating that the GNQP enhanced the wear resistance. Moreover, the TiO₂ layer was effective in maintaining a low coefficient of friction. Full article

(This article belongs to the Section Crystallography and Applications of Metallic Materials)

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14 pages, 3394 KB

Open AccessArticle

Softening and Melting Behavior of Lead Blast Furnace Slags

by Josué López-Rodríguez, Cancio Jiménez-Lugos, Manuel Flores-Favela, Aurelio Hernández-Ramírez, Alejandro Cruz-Ramírez, Carmen Martínez-Morales, Miguel Pérez-Labra and Antonio Romero-Serrano

Metals 2026, 16(1), 104; https://doi.org/10.3390/met16010104 - 16 Jan 2026

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Abstract

In this work, the characteristic temperatures (solidus and liquidus) of selected lead blast furnace slags were investigated using in situ high-temperature optical microscopy. The effects of the basicity of the slag (CaO/SiO₂), the Fe/SiO₂ ratio, and the Zn content were [...] Read more.

In this work, the characteristic temperatures (solidus and liquidus) of selected lead blast furnace slags were investigated using in situ high-temperature optical microscopy. The effects of the basicity of the slag (CaO/SiO₂), the Fe/SiO₂ ratio, and the Zn content were investigated. The deformation temperature associated with the rounding of the sample edges and the temperature at which 75% of the sample height decreases were experimentally considered as the solidus and liquidus temperatures, respectively. The pseudoternary phase diagrams CaO-SiO₂-Fe_0.63Zn_0.37O and FeO-Ca_0.54Si_0.46O_1.46-ZnO were calculated, along with the crystallization curves, using the thermodynamic software FactSage to estimate the characteristic temperatures and phase evolution during the cooling of the slag. The difference between the calculated and experimental solidus and liquidus temperatures was about 70 °C. The results of XRD, SEM, and DSC analysis at high temperatures showed that spinel (ZnFe₂O₄), melilite (Ca₂ZnSi₂O₇), and andradite (Ca₃Fe₂Si₃O₁₂) were the base crystals for all slag samples. The liquidus temperature increases with decreasing slag basicity (CaO/SiO₂), while the liquidus temperature increases with increasing Fe/SiO₂ ratio or Zn content. Full article

(This article belongs to the Section Extractive Metallurgy)

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19 pages, 5077 KB

Open AccessArticle

The Influence of Microstructure on Decisions Regarding Repurposing Natural Gas Pipelines for Hydrogen Service

by Jonathan Parker, Mike Gagliano and Eeva Griscom

Metals 2026, 16(1), 103; https://doi.org/10.3390/met16010103 - 16 Jan 2026

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Abstract

Empirical approaches alone have significant limitations for accurate estimation of the fracture toughness of welds in gas line pipes being considered for repurposing to hydrogen service. These problems arise because most samples machined from ex-service welds contain a range of microstructures. The different [...] Read more.

Empirical approaches alone have significant limitations for accurate estimation of the fracture toughness of welds in gas line pipes being considered for repurposing to hydrogen service. These problems arise because most samples machined from ex-service welds contain a range of microstructures. The different microstructural zones have different properties and even when compact tension samples with side grooves are utilized, it is unlikely that plane strain conditions are achieved during laboratory testing. Thus, the measured toughness may not be directly relevant to assessing in-service performance. The present research has been undertaken as part of an integrated series of projects seeking to define a robust protocol for assessing the damage tolerance of piping used for the transmission of hydrogen, especially when considering repurposing existing infrastructure. The key work described in this paper involved establishing heat treatments which produced microstructures relevant to the constituents found in ex-service welds of X46 type steel. Following comprehensive microstructural characterization, these heat treatments were applied to steel sections which allowed for the fabrication of standard compact tension specimens, which were subsequently tested in hydrogen to measure fracture toughness. The results obtained showed that the fracture behavior varied for different microstructures. To identify the influence that hydrogen gas has on the performance of pipeline steels, it is important to assess microstructures relevant to the welds present, as testing only on base metal may not provide conservative information. However, the results from well-planned and carefully executed programs can be used to identify the relative performance in hydrogen. The data can also be used as critical input to models which form part of an integrated approach to structural integrity assessment. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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14 pages, 6748 KB

Open AccessArticle

Roller Joining of AA1050 and AA6061 Aluminum Foam Immediately After Heating Process

by Yoshihiko Hangai, Shingo Nagatake, Ryosuke Suzuki, Kenji Amagai and Nobuhiro Yoshikawa

Metals 2026, 16(1), 102; https://doi.org/10.3390/met16010102 - 16 Jan 2026

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Abstract

Aluminum foam is attracting attention as a multifunctional, ultra-lightweight material. To apply this aluminum foam to actual industrial materials, aluminum foam plates are required. In addition, it is expected that a multi-layer aluminum foam composed of dissimilar aluminum alloy foam layers can further [...] Read more.

Aluminum foam is attracting attention as a multifunctional, ultra-lightweight material. To apply this aluminum foam to actual industrial materials, aluminum foam plates are required. In addition, it is expected that a multi-layer aluminum foam composed of dissimilar aluminum alloy foam layers can further enhance its functionality. In this study, we attempted to fabricate a three-layer aluminum foam composed of commercially pure aluminum AA1050 and Al-Mg-Si aluminum alloy AA6061 by heating and foaming a total of three pieces of AA1050 precursor and AA6061 precursor arranged alternately, followed by immediate roller joining. It was found that, by traversing a roller immediately after foaming the AA1050 and AA6061 precursors, the aluminum foam could be joined while forming it into a flat plate. In addition, X-ray CT images of the fabricated samples revealed that material flow induced by roller traversing ruptured the surface skin layer. Numerous pores were observed within the sample, indicating pores were maintained during the roller traversing and no significant differences in porosities were identified between AA1050 aluminum foam and AA6061 aluminum foam. Furthermore, from the four-point bending test and the observation of samples after bending test, although quantitative mechanical properties were not obtained due to the as-joined samples were used for the bending test, pores were observed at the fracture surfaces, confirming that roller joining achieved seamless joining. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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