Metals

15 pages, 4359 KiB

Open AccessArticle

Phase Transformations During Heat Treatment of a CPM AISI M4 Steel

by Maribel L. Saucedo-Muñoz, Valeria Miranda-Lopez, Felipe Hernandez-Santiago, Carlos Ferreira-Palma and Victor M. Lopez-Hirata

Metals 2025, 15(7), 818; https://doi.org/10.3390/met15070818 - 21 Jul 2025

Viewed by 255

Abstract

The phase transformations of Crucible Particle Metallurgy (CPM) American Iron and Steel Institute (AISI) M4 steel were studied during heat treatments using a CALPHAD-based method. The calculated results were compared with experimental observations. The optimum austenitizing temperature was determined to be about 1120 [...] Read more.

The phase transformations of Crucible Particle Metallurgy (CPM) American Iron and Steel Institute (AISI) M4 steel were studied during heat treatments using a CALPHAD-based method. The calculated results were compared with experimental observations. The optimum austenitizing temperature was determined to be about 1120 °C using Thermo-Calc software (2024b). Air-cooling and quenching treatments led to the formation of martensite with a hardness of 63–65 Rockwell C (HRC). The annealing treatment promoted the formation of the equilibrium ferrite and carbide phases and resulted in a hardness of 24 HRC. These findings with regard to phases and microconstituents are in agreement with the predictions derived from a Thermo-Calc-calculated time–temperature–transformation diagram at 1120 °C. Additionally, the primary carbides, MC and M₆C, which formed prior to the heat treatment and had a minor influence on the quenched hardness. In contrast, the tempering process primarily led to the formation of fine secondary M₆C carbides, which hardened the tempered martensite to 57 HRC. The present work demonstrates the application of a CALPHAD-based methodology to the design and microstructural analysis of tool steels. Full article

(This article belongs to the Special Issue Advances in Steels: Heat Treatment, Microstructure and Properties)

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27 pages, 3299 KiB

Open AccessArticle

Corrosion Stability and Biological Activity of Anodized cpTi for Dental Application

by Aleksandra S. Popović, Minja Miličić Lazić, Dijana Mitić, Lazar Rakočević, Dragana Jugović, Predrag Živković and Branimir N. Grgur

Metals 2025, 15(7), 817; https://doi.org/10.3390/met15070817 - 21 Jul 2025

Viewed by 431

Abstract

The anodic oxidation of titanium implants is a practical, cost-effective method to enhance implant success, especially due to rising hypersensitivity concerns. This study investigated the electrochemical behavior, surface characteristics, and biocompatibility of anodized commercially pure titanium (cpTi, grade IV). Anodization is performed on [...] Read more.

The anodic oxidation of titanium implants is a practical, cost-effective method to enhance implant success, especially due to rising hypersensitivity concerns. This study investigated the electrochemical behavior, surface characteristics, and biocompatibility of anodized commercially pure titanium (cpTi, grade IV). Anodization is performed on polished, cleaned cpTi sheet samples in 1 M H₂SO₄ using a constant voltage of 15 V for 15 and 45 min. The color of the oxide layer is evaluated using the CIELab color space, while composition is analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). Additionally, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are performed to identify and monitor the phase transformations of the formed titanium oxides. Corrosion measurements are performed in 9 g L⁻¹ NaCl, pH = 7.4, and show the excellent corrosion stability of the anodized samples in comparison with pure titanium. The biological response is assessed by determining mitochondrial activity and gene expression in human fibroblasts. Anodized surfaces, particularly Ti-45, promote higher mitochondrial activity and the upregulation of adhesion-related genes (N-cadherin and Vimentin) in human gingival fibroblasts, indicating improved biocompatibility and the potential for enhanced early soft tissue integration. Full article

(This article belongs to the Special Issue Feature Paper Collection of “Current Challenges in Corrosion Research" (2nd Edition))

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11 pages, 1293 KiB

Open AccessArticle

DOE-Based Investigation of Microstructural Factors Influencing Residual Stress in Aluminum Alloys

by Nawon Kwak and Eunkyung Lee

Metals 2025, 15(7), 816; https://doi.org/10.3390/met15070816 - 21 Jul 2025

Viewed by 276

Abstract

Residual stresses generated during the casting process significantly affect the reliability of the final product, making accurate prediction and analysis of these stresses crucial. In particular, to minimize the difference between simulation results and actual measurements, it is essential to develop predictive simulations [...] Read more.

Residual stresses generated during the casting process significantly affect the reliability of the final product, making accurate prediction and analysis of these stresses crucial. In particular, to minimize the difference between simulation results and actual measurements, it is essential to develop predictive simulations that incorporate microstructural characteristics. Therefore, in this study, residual stress prediction simulations were conducted for aluminum components manufactured by high-pressure die casting (HPDC), and measurement locations were selected based on the simulation results. Subsequently, the microstructural characteristics at each location (Si and intermetallic compounds) were quantitatively analyzed, and significant factors affecting residual stress were identified through design of experiments (DOE). As a result, Si sphericity (p-value ≤ 0.05) was observed to be the most significant factor among Si area fraction, IMC area fraction, and Si sphericity, and the residual stress and Si sphericity showed a positive interaction due to the rapid cooling rate and inhomogeneous microstructure distribution. Furthermore, the study demonstrated the effectiveness of DOE in clearly distinguishing the significance of variables with strong interdependencies. Full article

(This article belongs to the Special Issue Mechanical Structure Damage of Metallic Materials)

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14 pages, 2948 KiB

Open AccessArticle

Efficient Flotation Separation of Antimonate Minerals from Quartz Using Sodium Dodecyl Sulfonate as Collector

by Feng Jiang, Pengyuan Wang, Jiaxing Qi, Wei Sun, Yulin Zhou, Weishang Zhao, Shuai He, Yuanjia Luo and Honghu Tang

Metals 2025, 15(7), 815; https://doi.org/10.3390/met15070815 - 21 Jul 2025

Viewed by 263

Abstract

The efficient separation of antimonate minerals from quartz remains a significant challenge in mineral processing due to their similar surface properties and strong hydrophilicity. This study explored the application of sodium dodecyl sulfonate (SDS) as a selective collector for antimonate–quartz flotation separation. Micro-flotation [...] Read more.

The efficient separation of antimonate minerals from quartz remains a significant challenge in mineral processing due to their similar surface properties and strong hydrophilicity. This study explored the application of sodium dodecyl sulfonate (SDS) as a selective collector for antimonate–quartz flotation separation. Micro-flotation tests demonstrated that SDS achieved optimal recovery of antimonate minerals (90.25%) at pH 8 with a dosage of 70 mg/L, while quartz recovery remained below 10%. Contact angle measurements revealed a significant increase in the hydrophobicity of antimonate minerals after SDS treatment, whereas quartz remained highly hydrophilic. FTIR and XPS analyses confirmed the selective chemisorption of SDS on antimonate mineral surfaces through Sb-O-S bond formation, while negligible adsorption occurred on quartz. Adsorption isotherms further showed the higher SDS uptake on antimonate minerals compared to quartz. These findings collectively demonstrate the effectiveness of SDS as a selective collector for the flotation of antimonate minerals, providing a promising approach to enhancing the recovery of fine antimonate particles. Full article

(This article belongs to the Section Extractive Metallurgy)

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17 pages, 12649 KiB

Open AccessArticle

Microstructure, Mechanical Properties, and Electrochemical Corrosion Behavior of CoCrFeNiNb and CoCrFeNiV High-Entropy Alloys Prepared via Mechanical Alloying and Spark Plasma Sintering

by Yan Zhu, Yiwen Liu, Zhaocang Meng and Jianke Tian

Metals 2025, 15(7), 814; https://doi.org/10.3390/met15070814 - 21 Jul 2025

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Abstract

This study investigates the microstructural evolution, mechanical behavior, and electrochemical performance of CoCrFeNiNb and CoCrFeNiV HEAs fabricated via mechanical alloying and spark plasma sintering. Microstructural analyses reveal that the alloys have a face-centered cubic (FCC) matrix with Nb-enriched Laves and V-enriched σ phases. [...] Read more.

This study investigates the microstructural evolution, mechanical behavior, and electrochemical performance of CoCrFeNiNb and CoCrFeNiV HEAs fabricated via mechanical alloying and spark plasma sintering. Microstructural analyses reveal that the alloys have a face-centered cubic (FCC) matrix with Nb-enriched Laves and V-enriched σ phases. The CoCrFeNiNb HEA exhibits superior compressive strength and hardness than CoCrFeNiV due to uniform Laves phases distribution. Fracture surface analysis reveals that at lower sintering temperatures, the fracture is primarily caused by incomplete particle bonding, whereas at higher temperatures, brittle fracture modes dominated via transgranular cracking become predominant. The research results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) show that both alloys exhibited superior electrochemical stability in a 3.5 wt.% NaCl solution compared to the CoCrFeNi base alloy. X-ray photoelectron spectroscopy (XPS) analysis confirms the formation of stable oxide layers (Nb₂O₅ and V₂O₃) on the precipitated phases, acting as protective barriers against chloride ion penetration. The selective oxidation of Nb and V improves the integrity of the passive film, reducing the corrosion rates and enhancing the long-term durability. These findings highlight the critical role of precipitated phases in enhancing the corrosion resistance of HEAs, and emphasize their potential for use in extreme environments. Full article

(This article belongs to the Special Issue High-Entropy Alloys: Processing and Properties)

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14 pages, 2552 KiB

Open AccessArticle

Selective Oxidation Depression of Copper-Activated Sphalerite by H₂O₂ During Chalcopyrite Flotation

by Peiqiang Fan, Xiong Tong, Xian Xie, Qiang Song, Yuanlin Ma, Bin Han, Haitao Fu and Zhiming Lu

Metals 2025, 15(7), 813; https://doi.org/10.3390/met15070813 - 21 Jul 2025

Viewed by 299

Abstract

Using hydrogen peroxide (H₂O₂), a simple and easily accessible reagent, as a selective depressant, flotation separation experiments of chalcopyrite and copper-activated sphalerite were conducted. The micro-flotation tests of single minerals indicated that H₂O₂ selectively depresses copper-activated [...] Read more.

Using hydrogen peroxide (H₂O₂), a simple and easily accessible reagent, as a selective depressant, flotation separation experiments of chalcopyrite and copper-activated sphalerite were conducted. The micro-flotation tests of single minerals indicated that H₂O₂ selectively depresses copper-activated sphalerite and exerted almost no depressant effect on chalcopyrite. In the flotation tests of artificially mixed minerals, a copper concentrate with a grade of 29.95% and a recovery of 87.30% was obtained, while the zinc content was only 5.76%, demonstrating a significant separation effect. The results of contact angle measurement, Zeta potential measurement, surface adsorption analysis, and XPS analysis suggested that H₂O₂ had a stronger oxidation capacity on the surface of copper-activated sphalerite than chalcopyrite, generating hydrophilic hydroxyl groups on the surface of sphalerite and preventing further adsorption of the collector Z-200 on the surface of sphalerite. Full article

(This article belongs to the Special Issue Advances in Sustainable Utilization of Metals: Recovery and Recycling)

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22 pages, 16125 KiB

Open AccessArticle

Toward an Efficient and Robust Process–Structure Prediction Framework for Filigree L-PBF 316L Stainless Steel Structures

by Yu Qiao, Marius Grad and Aida Nonn

Metals 2025, 15(7), 812; https://doi.org/10.3390/met15070812 - 20 Jul 2025

Viewed by 624

Abstract

Additive manufacturing (AM), particularly laser powder bed fusion (L-PBF), provides unmatched design flexibility for creating intricate steel structures with minimal post-processing. However, adopting L-PBF for high-performance applications is difficult due to the challenge of predicting microstructure evolution. This is because the process is [...] Read more.

Additive manufacturing (AM), particularly laser powder bed fusion (L-PBF), provides unmatched design flexibility for creating intricate steel structures with minimal post-processing. However, adopting L-PBF for high-performance applications is difficult due to the challenge of predicting microstructure evolution. This is because the process is sensitive to many parameters and has a complex thermal history. Thin-walled geometries present an added challenge because their dimensions often approach the scale of individual grains. Thus, microstructure becomes a critical factor in the overall integrity of the component. This study focuses on applying cellular automata (CA) modeling to establish robust and efficient process–structure relationships in L-PBF of 316L stainless steel. The CA framework simulates solidification-driven grain evolution and texture development across various processing conditions. Model predictions are evaluated against experimental electron backscatter diffraction (EBSD) data, with additional quantitative comparisons based on texture and morphology metrics. The results demonstrate that CA simulations calibrated with relevant process parameters can effectively reproduce key microstructural features, including grain size distributions, aspect ratios, and texture components, observed in thin-walled L-PBF structures. This work highlights the strengths and limitations of CA-based modeling and supports its role in reliably designing and optimizing complex L-PBF components. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing for Metallic Materials and Their Applications (3rd Edition))

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22 pages, 3727 KiB

Open AccessArticle

Johnson–Cook Constitutive Model Parameters Estimation of 22MnB5 Hot Stamping Steel for Automotive Application Produced via the TSCR Process

by Yuxin Song, Yaowen Xu and Gengwei Yang

Metals 2025, 15(7), 811; https://doi.org/10.3390/met15070811 - 20 Jul 2025

Viewed by 2875

Abstract

In the industrial practice of metal forming, the consistent and reasonable characterization of the material behavior under the coupling effect of strain, strain rate, and temperature on the material flow stress is very important for the design and optimization of process parameters. The [...] Read more.

In the industrial practice of metal forming, the consistent and reasonable characterization of the material behavior under the coupling effect of strain, strain rate, and temperature on the material flow stress is very important for the design and optimization of process parameters. The purpose of this work was to establish an appropriate constitutive model to characterize the rheological behavior of a hot-formed steel plate (22MnB5 steel) produced through the TSCR (Thin Slab Casting and Rolling) process under practical deformation temperatures (150–250 °C) and strain rates (0.001–3000 s⁻¹). Subsequently, the material flow behavior was modeled and predicted using the Johnson–Cook flow stress constitutive model. In this study, uniaxial tensile tests were conducted on 22MnB5 steel at room temperature under varying strain rates, along with elevated-temperature tensile tests at different strain rates, to obtain the engineering stress–strain curves and analyze the mechanical properties under various conditions. The results show that during room-temperature tensile testing within the strain rate range of 10⁻³ to 300 s⁻¹, the 22MnB5 steel exhibited overall yield strength and tensile strength of approximately 1500 MPa, and uniform elongation and fracture elongation of about 7% and 12%, respectively. When the strain rate reached 1000–3000 s⁻¹, the yield strength and tensile strength were approximately 2000 MPa, while the uniform elongation and fracture elongation were about 6% and 10%, respectively. Based on the experimental results, a modified Johnson–Cook constitutive model was developed and calibrated. Compared with the original model, the modified Johnson–Cook model exhibited a higher coefficient of determination (R²), indicating improved fitting accuracy. In addition, to predict the material’s damage behavior, three distinct specimen geometries were designed for quasi-static strain rate uniaxial tensile testing at ambient temperature. The Johnson–Cook failure criterion was implemented, with its constitutive parameters calibrated through integrated finite element analysis to establish the damage model. The determined damage parameters from this investigation can be effectively implemented in metal forming simulations, providing valuable predictive capabilities regarding workpiece material performance. Full article

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19 pages, 4839 KiB

Open AccessArticle

Corrosion Inhibition of C38 Steel in 1 M HCl Using Benzoxazole-2-Thione: Electrochemical, SEM-EDX, and Theoretical Studies

by Mohamed Omari, Khalid Bouiti, Said Jebbari, Nabil Lahrache, Ali Barhoumi, Najoua Labjar, Souad El Hajjaji, Mahado Said-Ahmed, Mounim Lebrini, Hamid Nasrellah, Mohammed El Idrissi and Abdessamad Tounsi

Metals 2025, 15(7), 810; https://doi.org/10.3390/met15070810 - 19 Jul 2025

Viewed by 561

Abstract

This study explores the corrosion inhibition of C38 steel in a 1 M hydrochloric acid (HCl) solution using a novel benzoxazole-2-thione compound. The inhibitor was synthesized and structurally characterized by both ¹H NMR (DMSO-d₆/TMS) and ¹³C NMR spectroscopy. Electrochemical [...] Read more.

This study explores the corrosion inhibition of C38 steel in a 1 M hydrochloric acid (HCl) solution using a novel benzoxazole-2-thione compound. The inhibitor was synthesized and structurally characterized by both ¹H NMR (DMSO-d₆/TMS) and ¹³C NMR spectroscopy. Electrochemical techniques, including Tafel polarization and electrochemical impedance spectroscopy, were employed to evaluate the inhibition performance. The results indicate that the benzoxazole-2-thione significantly reduces the corrosion rate, achieving a maximum inhibition efficiency of 95.25% at a concentration of 10⁻⁴ M. To gain deeper insights into the inhibition mechanism, theoretical methods such as density functional theory, Monte Carlo simulations, and molecular dynamics were applied to investigate the adsorption behavior of the compound on the steel surface. The adsorption process follows the Langmuir isotherm model, suggesting the coexistence of physisorption and chemisorption interactions. Surface morphology and elemental composition analyses using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) confirm the formation of a protective inhibitor film on the steel surface. Full article

(This article belongs to the Special Issue Feature Paper Collection of “Current Challenges in Corrosion Research" (2nd Edition))

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14 pages, 5792 KiB

Open AccessArticle

Weld Formation and Characteristics of Hot-Wire Laser Welding in Aluminum Alloy Narrow-Gap Joints

by Jukkapun Greebmalai, Shun Sadasue, Keita Marumoto, Eakkachai Warinsiriruk and Motomichi Yamamoto

Metals 2025, 15(7), 809; https://doi.org/10.3390/met15070809 - 18 Jul 2025

Viewed by 272

Abstract

This study joins a 20 mm thick 5000-series aluminum alloy using hot-wire insertion combined with narrow-gap laser welding to evaluate the feasibility and welding characteristics of this technique. The findings indicate that weld formation is primarily influenced by the laser energy density and [...] Read more.

This study joins a 20 mm thick 5000-series aluminum alloy using hot-wire insertion combined with narrow-gap laser welding to evaluate the feasibility and welding characteristics of this technique. The findings indicate that weld formation is primarily influenced by the laser energy density and material deposition rate. A strategy for improving weld beads is introduced incorporating a reoriented laser spot during the final pass on narrow-gap joints. This approach improves penetration and produces defect-free joints. The optimal processing conditions result in complete joint formation with four welding passes. Microstructural analysis reveals that the aluminum matrix morphology evolves according to the local thermal history during welding. Measurements show that the weld region is slightly harder than the base metal, whereas slightly lower hardness is observed at the fusion line and inter-pass boundaries, which correlates with the microstructure result. Full article

(This article belongs to the Special Issue Advanced Laser Welding and Joining of Metallic Materials)

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12 pages, 11870 KiB

Open AccessArticle

Structural, Elastic, Electronic, Magnetic, and Half-Metallic Properties of Full-Heusler Compounds Fe₂LiZ (Z = Ge and Si): A First-Principles Study

by Yufeng Wen, Yanlin Yu, Zhangli Lai and Xianshi Zeng

Metals 2025, 15(7), 808; https://doi.org/10.3390/met15070808 - 18 Jul 2025

Viewed by 260

Abstract

The structural, elastic, electronic, magnetic, and half-metallic properties of full-Heusler

{Fe}_{2}

LiSi and

{Fe}_{2}

LiGe compounds were investigated using first-principles calculations. Among the studied configurations, the cubic XA structures in the ferromagnetic state for both compounds are the most stable. They [...] Read more.

The structural, elastic, electronic, magnetic, and half-metallic properties of full-Heusler

{Fe}_{2}

LiSi and

{Fe}_{2}

LiGe compounds were investigated using first-principles calculations. Among the studied configurations, the cubic XA structures in the ferromagnetic state for both compounds are the most stable. They exhibit mechanical stability, elastic anisotropy, and ductility. Compared to

{Fe}_{2}

LiGe,

{Fe}_{2}

LiSi demonstrates higher stability, stronger anisotropy, greater brittleness, higher Debye and melting temperatures, and a smaller Grüneisen parameter. Both compounds exhibit metallic majority-spin channels and semiconducting minority-spin channels. At the equilibrium lattice constant,

{Fe}_{2}

LiSi and

{Fe}_{2}

LiGe exhibit half-metallic gaps of 0.141 eV and 0.179 eV, respectively. Both compounds exhibit 100% spin-polarization ratio in specific lattice constant ranges. The total magnetic moment per formula unit (3.000

μ_{B}

) follows the generalized Slater–Pauling rule and depends on Fe atomic magnetic moments. These properties indicate that

{Fe}_{2}

LiSi and

{Fe}_{2}

LiGe hold promise for spintronic applications. Full article

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22 pages, 9679 KiB

Open AccessArticle

Impact of Multiple-Laser Processing on the Low-Cycle Fatigue Behaviour of Laser-Powder Bed Fused AlSi10Mg Alloy

by Arun Prasanth Nagalingam, Erkan Bugra Tureyen, Abdul Haque, Adrian Sharman, Ozgur Poyraz, Evren Yasa and James Hughes

Metals 2025, 15(7), 807; https://doi.org/10.3390/met15070807 - 18 Jul 2025

Viewed by 517

Abstract

Multi-laser processing is increasingly adopted in laser powder bed fusion (L-PBF) to improve productivity and enable the fabrication of larger components, but its impact on part quality and performance remains a critical concern. This study investigates the microstructure, tensile properties, and fatigue performance [...] Read more.

Multi-laser processing is increasingly adopted in laser powder bed fusion (L-PBF) to improve productivity and enable the fabrication of larger components, but its impact on part quality and performance remains a critical concern. This study investigates the microstructure, tensile properties, and fatigue performance of components fabricated by L-PBF using single- and multiple-laser configurations. Both strategies were evaluated under varying layer thicknesses and gas flow conditions with optimized process parameters. Microstructural analysis revealed defects such as lack-of-fusion, porosity and microcracks in multiple-laser builds with reduced gas flow. However, the density and microhardness results showed negligible differences between single and multiple-laser builds. Tensile testing indicated that single-laser builds exhibited superior strength and ductility, whereas multiple-laser builds demonstrated reduced performance due to localized defects such as lack-of-fusion and microcracks. Low-cycle fatigue testing results showed that optimized multiple-laser strategies could achieve performance comparable to that of single-laser builds while improving productivity. The results also revealed that the gas flow becomes more pronounced with multiple-laser processing, where more spatter is generated due to the interactions of the lasers in a small scan area, and that reduced gas flow leads to fatigue degradation due to increased defect density. The results from this study clearly highlight the importance of gas flow, laser overlap, border optimization, and defect mitigation strategies in producing multiple-laser produced components with mechanical properties and fatigue performance comparable to those of single-laser produced L-PBF components. Full article

(This article belongs to the Special Issue Processing, Microstructure and Properties of Aluminium Alloys)

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17 pages, 6308 KiB

Open AccessArticle

Effect of Heat Treatment on Microstructure and Mechanical Properties of (TiB + TiC) /Ti-6Al-4V Composites Fabricated by Directed Energy Deposition

by Hai Gu, Guoqing Dai, Jie Jiang, Zulei Liang, Jianhua Sun, Jie Zhang and Bin Li

Metals 2025, 15(7), 806; https://doi.org/10.3390/met15070806 - 18 Jul 2025

Viewed by 318

Abstract

The titanium matrix composites (TMCs) fabricated via Directed Energy Deposition (DED) effectively overcome the issue of coarse columnar grains typically observed in additively manufactured titanium alloys. In this study, systematic annealing heat treatments were applied to in situ (TiB + TiC)/Ti-6Al-4V composites to [...] Read more.

The titanium matrix composites (TMCs) fabricated via Directed Energy Deposition (DED) effectively overcome the issue of coarse columnar grains typically observed in additively manufactured titanium alloys. In this study, systematic annealing heat treatments were applied to in situ (TiB + TiC)/Ti-6Al-4V composites to refine the microstructure and tailor mechanical properties. The results reveal that the plate-like α phase in the as-deposited composites gradually transforms into an equiaxed morphology with increasing annealing temperature and holding time. Notably, when the annealing temperature exceeds 1000 °C, significant coarsening of the TiC phase is observed, while the TiB phase remains morphologically stable. Annealing promotes decomposition of acicular martensite and stress relaxation, leading to a reduction in hardness compared to the as-deposited state. However, the reticulated distribution of the TiB and TiC reinforcement phases contributes to enhanced tensile performance. Specifically, the as-deposited composite achieves a tensile strength of 1109 MPa in the XOY direction, representing a 21.6% improvement over the as-cast counterpart, while maintaining a ductility of 2.47%. These findings demonstrate that post-deposition annealing is an effective strategy to regulate microstructure and achieve a desirable balance between strength and ductility in DED-fabricated titanium matrix composites. Full article

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16 pages, 1713 KiB

Open AccessArticle

Mass and Heat Balance Model and Its Engineering Application for the Oxygen Blast Furnace Smelting Process of Vanadium–Titanium Magnetite

by Yun Huang, Mansheng Chu, Xian Gan, Shushi Zhang, Zhenyang Wang and Jianliang Zhang

Metals 2025, 15(7), 805; https://doi.org/10.3390/met15070805 - 18 Jul 2025

Viewed by 356

Abstract

The oxygen blast furnace (OBF) process presents a promising low-carbon pathway for the smelting of vanadium–titanium magnetite (VTM). This study develops an innovative mathematical model based on mass and heat balance principles, specifically tailored to the OBF smelting of VTM. The model systematically [...] Read more.

The oxygen blast furnace (OBF) process presents a promising low-carbon pathway for the smelting of vanadium–titanium magnetite (VTM). This study develops an innovative mathematical model based on mass and heat balance principles, specifically tailored to the OBF smelting of VTM. The model systematically investigates the effects of key parameters—including pulverized coal injection ratio, recycling gas volume, hydrogen content in the recycling gas, and charge composition—on furnace productivity, hearth activity, and the tuyere raceway zone. The results show that increasing the pulverized coal injection ratio slightly reduces productivity and theoretical flame temperature: for every 25 kg/tHM increase in the coal ratio, the theoretical flame temperature decreases by 21.95 °C; moreover, indirect reduction is enhanced and the heat distribution within the furnace is significantly improved. A higher recycling gas volume markedly increases productivity and optimizes hearth thermal conditions, accompanied by enhanced blast kinetic energy and an expanded tuyere raceway zone, albeit with a notable drop in combustion temperature. Increased hydrogen content in the recycling gas promotes productivity, but may weaken blast kinetic energy and reduce the stability of the raceway zone. Furthermore, a higher titanium content in the charge increases the difficulty of iron oxide reduction, resulting in lower CO utilization and reduced productivity. Full article

(This article belongs to the Special Issue Innovation in Efficient and Sustainable Blast Furnace Ironmaking)

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14 pages, 3909 KiB

Open AccessArticle

Demonstrating In Situ Formation of Globular Microstructure for Thixotropic Printing of EN AW-4043 Aluminum Alloy

by Silvia Marola and Maurizio Vedani

Metals 2025, 15(7), 804; https://doi.org/10.3390/met15070804 - 17 Jul 2025

Viewed by 280

Abstract

This study explores the feasibility of generating a globular microstructure in situ during the thixotropic 3D printing of the EN AW-4043 alloy, starting from a conventional cold-rolled wire. Thermodynamic simulations using Thermo-Calc software were first conducted to identify the semi-solid processing window of [...] Read more.

This study explores the feasibility of generating a globular microstructure in situ during the thixotropic 3D printing of the EN AW-4043 alloy, starting from a conventional cold-rolled wire. Thermodynamic simulations using Thermo-Calc software were first conducted to identify the semi-solid processing window of the alloy, based on the evolution of liquid and solid fractions as a function of temperature. Guided by these results, thermal treatments were performed on cold-rolled wires to promote the formation of a globular microstructure. A laboratory-scale printing head prototype was then designed and built to test continuous heating and deposition conditions representative of a thixotropic additive manufacturing process. The results showed that a globular microstructure could be achieved in the cold-rolled EN AW-4043 wires by heating them at 590 °C for 5 min in a static muffle furnace. A similar effect was observed when continuously heating the wire while it flowed through the heated printing head. Preliminary deposition tests confirmed the viability of this approach and demonstrated that thixotropic 3D printing of EN AW-4043 alloy is achievable without the need for pre-globular feedstock. Full article

(This article belongs to the Section Additive Manufacturing)

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35 pages, 6745 KiB

Open AccessArticle

The ESTPHAD Concept: An Optimised Set of Simplified Equations to Estimate the Equilibrium Liquidus and Solidus Temperatures, Partition Ratios, and Liquidus Slopes for Quick Access to Equilibrium Data in Solidification Software Part II: Ternary Isomorphous Equilibrium Phase Diagram

by Gergely Kőrösy, András Roósz and Tamás Mende

Metals 2025, 15(7), 803; https://doi.org/10.3390/met15070803 - 16 Jul 2025

Viewed by 210

Abstract

In a previous article, an estimation procedure for calculating the liquidus and solidus lines of binary equilibrium phase diagrams was presented. In this article, keeping the thermodynamic basics, the estimation method for the approximate calculation of the liquidus and solidus surfaces of ternary [...] Read more.

In a previous article, an estimation procedure for calculating the liquidus and solidus lines of binary equilibrium phase diagrams was presented. In this article, keeping the thermodynamic basics, the estimation method for the approximate calculation of the liquidus and solidus surfaces of ternary phase diagrams was further developed. It is shown that the procedure has a hierarchical structure, and the ternary functions contain the binary functions. The applicability of the method is checked by calculating the liquidus and solidus surfaces of the Ag-Au-Pd isomorphous ternary equilibrium phase diagram. The application of each level of the developed four-level procedure depends on the data available and the aim. It is shown that in the case of a concentration range close to the base alloy pure element, the liquidus and solidus surfaces of the ternary equilibrium phase diagram can be calculated from the liquidus and solidus functions of the binary equilibrium phase diagrams with a few K errors, which is 0.2 at% at 10 K/at% slope. The equilibrium phase diagrams were available in graphical form, so the data obtained via digitalisation of the diagrams for the calculations was used. The functions describe the slope of the surfaces, and the approximate method developed for the calculation of the partition ratios is also shown. Full article

(This article belongs to the Special Issue Thermodynamic Assessment of Alloy Systems)

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13 pages, 4282 KiB

Open AccessArticle

Cerium Addition Enhances Impact Energy Stability in S355NL Steel by Tailoring Microstructure and Inclusions

by Jiandong Yang, Bijun Xie and Mingyue Sun

Metals 2025, 15(7), 802; https://doi.org/10.3390/met15070802 - 16 Jul 2025

Viewed by 287

Abstract

S355NL structural steel is extensively employed in bridges, ships, and power station equipment owing to its excellent tensile strength, weldability, and low-temperature toughness. However, pronounced fluctuations in its Charpy impact energy at low temperatures significantly compromise the reliability and service life of critical [...] Read more.

S355NL structural steel is extensively employed in bridges, ships, and power station equipment owing to its excellent tensile strength, weldability, and low-temperature toughness. However, pronounced fluctuations in its Charpy impact energy at low temperatures significantly compromise the reliability and service life of critical components. In this study, vacuum-induction-melted ingots of S355NL steel containing 0–0.086 wt.% rare earth cerium were prepared. The effects of Ce on microstructures, inclusions, and impact toughness were systematically investigated using optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Charpy V-notch testing. The results indicate that appropriate Ce additions (0.0011–0.0049 wt.%) refine the average grain size from 5.27 μm to 4.88 μm, reduce the pearlite interlamellar spacing from 204 nm to 169 nm, and promote the transformation of large-size Al₂O₃-MnS composite inclusions into fine, spherical, Ce-rich oxysulfides. Charpy V-notch tests at –50 °C reveal that 0.0011 wt.% Ce enhances both longitudinal (269.7 J) and transverse (257.4 J) absorbed energies while minimizing anisotropy (E_t/E_l = 1.01). Conversely, excessive Ce addition (0.086 wt.%) leads to coarse inclusions and deteriorates impact performance. These findings establish an optimal Ce window (0.0011–0.0049 wt.%) for microstructural and inclusion engineering to enhance the low-temperature impact toughness of S355NL steel. Full article

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16 pages, 5637 KiB

Open AccessArticle

Optimizing High-Al₂O₃ Limonite Pellet Performance: The Critical Role of Basicity in Consolidation and Reduction

by Yufeng Guo, Yixi Zhang, Feng Chen, Shuai Wang, Lingzhi Yang, Yanqin Xie and Xinyao Xia

Metals 2025, 15(7), 801; https://doi.org/10.3390/met15070801 - 16 Jul 2025

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Abstract

With the gradual depletion of high-quality iron ore resources, global steel enterprises have shifted their focus to low-grade, high-impurity iron ores. Using low-grade iron ore to produce pellets for blast furnaces is crucial for companies to control production costs and diversify raw material [...] Read more.

With the gradual depletion of high-quality iron ore resources, global steel enterprises have shifted their focus to low-grade, high-impurity iron ores. Using low-grade iron ore to produce pellets for blast furnaces is crucial for companies to control production costs and diversify raw material sources. However, producing qualified pellets from limonite and other low-grade iron ores remains highly challenging. This study investigates the mechanism by which basicity affects the consolidation and reduction behavior of high-Al₂O₃ limonite pellets from a thermodynamic perspective. As the binary basicity of the pellets increased from 0.01 under natural conditions to 1.2, the compressive strength of the roasted pellets increased from 1100 N/P to 5200 N/P. The enhancement in basicity led to an increase in the amount of low-melting-point calcium ferrite in the binding phase, which increased the liquid phase in the pellets, thereby strengthening the consolidation. CaO infiltrated into large-sized iron particles and reacted with Al and Si elements, segregating the contiguous large-sized iron particles and encapsulating them with liquid-phase calcium ferrite. Calcium oxide reacts with the Al and Si elements in large hematite particles, segmenting them and forming liquid calcium ferrite that encapsulates the particles. Additionally, this study used thermodynamic analysis to characterize the influence of CaO on aluminum elements in high-aluminum iron ore pellets. Adding CaO boosted the liquid phase’s ability to incorporate aluminum, lessening the inhibition by high-melting-point aluminum elements of hematite recrystallization. During the reduction process, pellets with high basicity exhibited superior reduction performance. Full article

(This article belongs to the Special Issue Steelmaking and Ironmaking: Fundamental Research to Technology Innovation)

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14 pages, 5155 KiB

Open AccessArticle

Erosion of AISI 4340 and AISI 8620 Steels with High Ductility Caused by SiC Particles

by Juan R. Laguna-Camacho, Ezequiel A. Gallardo-Hernández, Manuel Vite-Torres, Celia M. Calderón-Ramón, Víctor Velázquez-Martínez, Silvia M. Sánchez-Yáñez and Karla I. Zermeño-De Lojo

Metals 2025, 15(7), 800; https://doi.org/10.3390/met15070800 - 16 Jul 2025

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Abstract

In this study, solid particle erosion tests were conducted to evaluate the resistance of AISI 4340 (EN24) and 8620 alloy steels against silicon carbide (SiC). These steels were selected due to their high hardness, yield strength (σ_y), ultimate tensile strength (σ [...] Read more.

In this study, solid particle erosion tests were conducted to evaluate the resistance of AISI 4340 (EN24) and 8620 alloy steels against silicon carbide (SiC). These steels were selected due to their high hardness, yield strength (σ_y), ultimate tensile strength (σ_uts) and elongation (%), which are significant parameters, influencing wear resistance. An erosion rig based on the ASTM G76-95 standard was used to perform the testing. Tests were carried out using different impact angles, 30°, 45°, 60° and 90°, with a particle velocity of 24 ± 2 m/s. The abrasive flow rate was 0.7 ± 0.5 g/min and the temperature was between 35 °C and 40 °C. Characterization techniques such as SEM were employed to identify the chemical composition of AISI 4340 and AISI 8620 steels and optical microscopy to determine the morphology of SiC abrasive particles. In addition, the SiC particle size was between 350 and 450 µm; it was determined by the particle size distribution technique. SEM micrographs were obtained to classify the wear mechanisms, characterized by micro-cutting, micro-ploughing, grooves, pitting actions and embedded particles on the surface at 30° and 90°. The results showed that AISI 8620 steel exhibited higher erosion resistance than AISI 4340 steel. Finally, AFM was used to evaluate the roughness variations before and after erosion tests, specifically in the central zone of the wear scars at 30° and 90° for both materials. Full article

(This article belongs to the Special Issue Research on Microstructure and Performance Mechanisms of Advanced Steels and Alloys)

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17 pages, 343 KiB

Open AccessReview

Recovery of Tungsten from Raw and Secondary Materials Using Hydrometallurgical Processing

by Francisco Jose Alguacil and Manuel Alonso

Metals 2025, 15(7), 799; https://doi.org/10.3390/met15070799 - 15 Jul 2025

Cited by 1 | Viewed by 421

Abstract

As in the case with other metals, tungsten is an element with a number of uses in different fields, which is why its recovery from both primary and secondary materials continues to be of great interest. Various hydrometallurgical processes, considered as unit operations, [...] Read more.

As in the case with other metals, tungsten is an element with a number of uses in different fields, which is why its recovery from both primary and secondary materials continues to be of great interest. Various hydrometallurgical processes, considered as unit operations, can be used for the recovery, separation and concentration of tungsten from any source, with ease of scaling-up a potential factor when considering the best process for practical use. The present work reviewed investigations into the use of such unit operations for the recovery of tungsten which were published during 2024 and the first half of 2025. Because most if not all of these investigations were conducted on a laboratory scale, there is still much room for improvement before deciding on the best option for tungsten recovery. In all cases, however, this recovery is based on a series of steps from leaching to separation technologies (ion exchange resins, liquid–liquid extraction, etc.) to the tungsten end-product. Full article

(This article belongs to the Special Issue Tungsten and Tungsten Alloys)

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25 pages, 14812 KiB

Open AccessArticle

The Effect of Yttrium Addition on the Solidification Microstructure and Sigma Phase Precipitation Behavior of S32654 Super Austenitic Stainless Steel

by Jun Xiao, Geng Tian, Di Wang, Shaoguang Yang, Kuo Cao, Jianhua Wei and Aimin Zhao

Metals 2025, 15(7), 798; https://doi.org/10.3390/met15070798 - 15 Jul 2025

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Abstract

This study focuses on S32654 super austenitic stainless steel (SASS) and systematically characterizes the morphology of the sigma (σ) phase and the segregation behavior of alloying elements in its as-cast microstructure. High-temperature confocal scanning laser microscopy (HT-CSLM) was employed to investigate the effect [...] Read more.

This study focuses on S32654 super austenitic stainless steel (SASS) and systematically characterizes the morphology of the sigma (σ) phase and the segregation behavior of alloying elements in its as-cast microstructure. High-temperature confocal scanning laser microscopy (HT-CSLM) was employed to investigate the effect of the rare earth element yttrium (Y) on the solidification microstructure and σ phase precipitation behavior of SASS. The results show that the microstructure of SASS consists of austenite dendrites and interdendritic eutectoid structures. The eutectoid structures mainly comprise the σ phase and the γ₂ phase, exhibiting lamellar or honeycomb-like morphologies. Regarding elemental distribution, molybdenum displays a “concave” distribution pattern within the dendrites, with lower concentrations at the center and higher concentrations at the sides; when Mo locally exceeds beyond a certain threshold, it easily induces the formation of eutectoid structures. Mo is the most significant segregating element, with a segregation ratio as high as 1.69. The formation mechanism of the σ phase is attributed to the solid-state phase transformation of austenite (γ → γ₂ + σ). In the late stages of solidification, the concentration of chromium and Mo in the residual liquid phase increases, and due to insufficient diffusion, there are significant compositional differences between the interdendritic regions and the matrix. The enriched Cr and Mo cause the interdendritic austenite to become supersaturated, leading to solid-state phase transformation during subsequent cooling, thereby promoting σ phase precipitation. The overall phase transformation process can be summarized as L → L + γ → γ → γ + γ₂ + σ. Y microalloying has a significant influence on the solidification process. The addition of Y increases the nucleation temperature of austenite, raises nucleation density, and refines the solidification microstructure. However, Y addition also leads to an increased amount of eutectoid structures. This is primarily because Y broadens the solidification temperature range of the alloy and prolongs grain growth perio, which aggravates the microsegregation of elements such as Cr and Mo. Moreover, Y raises the initial precipitation temperature of the σ phase and enhances atomic diffusion during solidification, further promoting σ phase precipitation during the subsequent eutectoid transformation. Full article

(This article belongs to the Special Issue Synthesis, Processing and Applications of New Forms of Metals)

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18 pages, 8196 KiB

Open AccessArticle

Enhancing Aluminum Alloy Properties Through Low Pressure Forging: A Comprehensive Study on Heat Treatments

by Silvia Cecchel and Giovanna Cornacchia

Metals 2025, 15(7), 797; https://doi.org/10.3390/met15070797 - 15 Jul 2025

Viewed by 325

Abstract

The weight reduction is a key objective in modern engineering, particularly in the automotive industry, to enhance vehicle performance and reduce the carbon footprint. In this context aluminum alloys are widely used in structural automotive applications, often through forging processes that enhance mechanical [...] Read more.

The weight reduction is a key objective in modern engineering, particularly in the automotive industry, to enhance vehicle performance and reduce the carbon footprint. In this context aluminum alloys are widely used in structural automotive applications, often through forging processes that enhance mechanical properties compared to the results for casting. However, the high cost of forging can limit its economic feasibility. Low pressure forging (LPF) combines the benefits of casting and forging, employing controlled pressure to fill the mold cavity and improve metal purity. This study investigates the effectiveness of the LPF process in optimizing the mechanical properties of AlSi7Mg aluminum alloy by evaluating the influence of three different magnesium content levels. The specimens underwent T6 heat treatment (solubilization treatment followed by artificial aging), with varying aging times and temperatures. Microstructural analysis and tensile tests were conducted to determine the optimal conditions for achieving superior mechanical strength, contributing to the design of lightweight, high-performance components for advanced automotive applications. The most promising properties were achieved with a T6 treatment consisting of solubilization at 540 °C for 6 h followed by aging at 180 °C for 4 h, resulting in mechanical properties of σ_y 280 MPa, σ_m 317 MPa, and A% 3.5%. Full article

(This article belongs to the Special Issue Advances in Lightweight Alloys, 2nd Edition)

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13 pages, 3560 KiB

Open AccessArticle

Experimental Study on the Parameter Optimization of an Ultra-High-Pressure Water Jet for Grade-A Marine Steel Based on Surface Roughness

by Wuyang Shan, Yupeng Cao, Weidong Shi, Zhengang Wang, Qingbo Zhang, Yongfei Yang and Rui Zhou

Metals 2025, 15(7), 796; https://doi.org/10.3390/met15070796 - 15 Jul 2025

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Abstract

The selection of process parameters for an ultra-high-pressure water jet directly affects the adhesion ability of the subsequent coating on the ship’s surface. This study investigates the effect of jet pressure, standoff distance, and nozzle traverse speed on the surface roughness of grade-A [...] Read more.

The selection of process parameters for an ultra-high-pressure water jet directly affects the adhesion ability of the subsequent coating on the ship’s surface. This study investigates the effect of jet pressure, standoff distance, and nozzle traverse speed on the surface roughness of grade-A marine steel, aiming to optimize the process parameters and improve the quality of surface treatment. Based on single-factor experiments and orthogonal experiments, a three-factor, three-level experimental design was employed, considering jet pressure, standoff distance, and nozzle traverse speed. Scanning electron microscopy (SEM) and a confocal microscope were used to analyze the surface morphology and roughness of grade-A marine steel. The experimental results proved that surface roughness exhibited a nonlinear relationship with jet pressure, initially increasing and then decreasing as pressure rose. Conversely, surface roughness showed negative correlations with both standoff distance and nozzle traverse speed, progressively decreasing with increases in these parameters. Through hierarchical analysis, the effect hierarchy of the three factors on surface roughness was determined as follows: jet pressure > standoff distance > nozzle traverse speed. Parametric optimization revealed that a jet pressure of 150 MPa, a standoff distance of 25 mm, and a nozzle traverse speed of 180 mm/min collectively yielded a peak surface roughness of 62.549 μm. This value aligns with the pre-coating surface preparation standards for grade-A marine steel substrates, ensuring optimal adhesion for subsequent anti-corrosion treatments. Full article

(This article belongs to the Special Issue Fabricating Advanced Metallic Materials)

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17 pages, 3800 KiB

Open AccessArticle

Characterizing the Substructural Changes in Metals by Microindentation and Various Numerical Approaches

by János György Bátorfi and Jurij J. Sidor

Metals 2025, 15(7), 795; https://doi.org/10.3390/met15070795 - 14 Jul 2025

Viewed by 189

Abstract

This contribution compares various theories dealing with the assessment of dislocation density in metals subjected to different straining levels. The paper examines both substructure development and the evolution of dislocation densities in 1xxx, 5xxx, and 6xxx Al alloys. Barlat’s dislocation model, Kocks–Mecking–Estrin (K-M-E) [...] Read more.

This contribution compares various theories dealing with the assessment of dislocation density in metals subjected to different straining levels. The paper examines both substructure development and the evolution of dislocation densities in 1xxx, 5xxx, and 6xxx Al alloys. Barlat’s dislocation model, Kocks–Mecking–Estrin (K-M-E) theory, and Kubin–Estrin (K-E) type modeling approaches were analyzed. The dislocation model parameters were determined from the microindentation profiles for the rolled Al alloys. It was shown that a strong correlation exists between the K-E and K-M-E models, confirming their reliability in describing the relationship between strain, stress, and dislocation density. These numerical approaches effectively capture the evolution of dislocation density with strain, making them suitable for the analysis of the accumulation of stored energy during deformation. The development of substructure during straining was inferred from the microindentation experiments, and the resulting dependencies tended to align with the characteristic curve observed in various metals. Full article

(This article belongs to the Special Issue Formation, Microstructure, and Properties of Light Alloys)

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18 pages, 2268 KiB

Open AccessArticle

Effects of a Novel Mechanical Vibration Technology on the Internal Stress Distribution and Macrostructure of Continuously Cast Billets

by Shuai Liu, Jianliang Zhang, Hui Zhang and Minglin Wang

Metals 2025, 15(7), 794; https://doi.org/10.3390/met15070794 - 14 Jul 2025

Viewed by 272

Abstract

In this paper, a new mechanical vibration technology applied to continuous casting production is studied, which is used to break the dendrite at the solidification front, expand the equiaxed dendrite zone, and improve the center quality of the billet. The exciting force of [...] Read more.

In this paper, a new mechanical vibration technology applied to continuous casting production is studied, which is used to break the dendrite at the solidification front, expand the equiaxed dendrite zone, and improve the center quality of the billet. The exciting force of this vibration technology is provided by a new type of vibration equipment (Vibration roll) independently developed and designed. Firstly, an investigation is conducted into the impacts of vibration acceleration, vibration frequency, and the contact area between the Vibration roll (VR) and the billet surface on the internal stress distribution within the billet shell, respectively. Secondly, the billet with and without vibration treatment was sampled and analyzed through industrial tests. The results show that the area ratio of equiaxed dendrites in transverse specimens treated with vibration technology was 11.96%, compared to 6.55% in untreated specimens. Similarly, for longitudinal samples, the linear ratio of equiaxed dendrites was observed to be 34.56% in treated samples and 22.95% in untreated samples. Compared to the specimens without mechanical vibration, the billet treated with mechanical vibration exhibits an increase in the area ratio and linear ratio of equiaxed dendrite ratio by 5.41% and 11.61%, respectively. Moreover, the probability of bridging at the end of solidification of the billet treated by vibration technology was significantly reduced, and the central porosity and shrinkage cavities of the billet were significantly improved. This study provides the first definitive evidence that the novel mechanical vibration technology can enhance the quality of the billet during the continuous casting process. Full article

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33 pages, 20199 KiB

Open AccessReview

Composition Optimization in Alloy Design for Nickel-Based Single Crystal Superalloy: A Review

by Yu Zhou, Xinbao Zhao, Yunpeng Fan, Quanzhao Yue, Wanshun Xia, Qinghai Pan, Yuan Cheng, Weiqi Li, Yuefeng Gu and Ze Zhang

Metals 2025, 15(7), 793; https://doi.org/10.3390/met15070793 - 13 Jul 2025

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Abstract

This article presents a review of the composition optimization progress of nickel-based single crystal (SC) superalloy design in recent years in order to obtain better high-temperature performance for the development of the aviation industry. The influence of alloying elements on the creep resistance, [...] Read more.

This article presents a review of the composition optimization progress of nickel-based single crystal (SC) superalloy design in recent years in order to obtain better high-temperature performance for the development of the aviation industry. The influence of alloying elements on the creep resistance, microstructure characteristics, oxidation resistance, castability, density, and cost of superalloys is analyzed and discussed. In order to obtain better high-temperature performance, the content of refractory elements (Ta + Re + W + Mo) and Co was increased gradually. The addition of Ru was added in the fourth-generation nickel-based SC superalloy to stabilize the microstructures and suppress the precipitation of the topologically close-packed (TCP) phase. However, the content of the antioxidant element Cr significantly decreased, while the synergistic effect of Al, Cr, and Ta received more attention. Therefore, synergistic effects should also receive more attention to meet the practical needs of reducing the content of refractory elements to reduce costs and density in future single crystal alloy designs without compromising critical performance. Full article

(This article belongs to the Special Issue Advances in Lightweight Alloys, 2nd Edition)

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16 pages, 3348 KiB

Open AccessArticle

Response and Failure Behavior of Square Tubes with Varying Outer Side Lengths Under Cyclic Bending in Different Directions

by Chin-Mu Lin, Min-Cheng Yu and Wen-Fung Pan

Metals 2025, 15(7), 792; https://doi.org/10.3390/met15070792 - 13 Jul 2025

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Abstract

This paper primarily investigates the response and failure behavior of 6063-T5 aluminum alloy square tubes with varying outer side lengths under symmetric curvature-controlled cyclic bending in different bending directions. The response is characterized by the moment–curvature relationship and the variation in the outer [...] Read more.

This paper primarily investigates the response and failure behavior of 6063-T5 aluminum alloy square tubes with varying outer side lengths under symmetric curvature-controlled cyclic bending in different bending directions. The response is characterized by the moment–curvature relationship and the variation in the outer side length with respect to curvature, whereas failure is characterized by the relationship between the controlled curvature and the number of cycles required to initiate buckling. The outer side lengths studied are 20 mm, 30 mm, 40 mm, and 50 mm, and the bending directions considered are 0°, 22.5°, and 45°. The moment–curvature curves exhibited cyclic hardening, and stable loops were formed for all outer side lengths and bending directions. An increase in the outer side length resulted in a higher peak bending moment, while a greater bending direction led to a slight increase in the peak bending moment. For a fixed bending direction, the curves representing the variation of the outer side length (defined as the change in length divided by the original length) with respect to curvature displayed symmetry, serrated features, and an overall increasing trend as the number of cycles increased, irrespective of the specific outer side length. In addition, increasing either the outer side length or altering the bending direction led to a larger variation in the outer side length. As for the relationship between curvature and the number of cycles required to initiate buckling, the data for each bending direction and each of the four outer side lengths formed distinct straight lines on a double-logarithmic plot. Based on the experimental observations, empirical equations were developed to characterize these relationships. These equations were then used to predict the experimental data and showed excellent agreement with the measured results. Full article

(This article belongs to the Special Issue Mechanical Structure Damage of Metallic Materials)

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16 pages, 8314 KiB

Open AccessArticle

Effect of the Heat Affected Zone Hardness Reduction on the Tensile Properties of GMAW Press Hardening Automotive Steel

by Alfredo E. Molina-Castillo, Enrique A. López-Baltazar, Francisco Alvarado-Hernández, Salvador Gómez-Jiménez, J. Roberto Espinosa-Lumbreras, José Jorge Ruiz Mondragón and Víctor H. Baltazar-Hernández

Metals 2025, 15(7), 791; https://doi.org/10.3390/met15070791 - 13 Jul 2025

Viewed by 417

Abstract

An ultra-high-strength press-hardening steel (PHS) and a high-strength dual-phase steel (DP) were butt-joined by the gas metal arc welding (GMAW) process, aiming to assess the effects of a high heat input welding process on the structure-property relationship and residual stress. The post-weld microstructure, [...] Read more.

An ultra-high-strength press-hardening steel (PHS) and a high-strength dual-phase steel (DP) were butt-joined by the gas metal arc welding (GMAW) process, aiming to assess the effects of a high heat input welding process on the structure-property relationship and residual stress. The post-weld microstructure, the microhardness profile, the tensile behavior, and the experimentally obtained residual stresses (by x-ray diffraction) of the steels in dissimilar (PHS-DP) and similar (PHS-PHS, DP-DP) pair combinations have been analyzed. Results indicated that the ultimate tensile strength (UTS) of the dissimilar pair PHS-DP achieves a similar strength to the DP-DP joint, whereas the elongation was similar to that of the PHS-PHS weldment. The failure location of the tensile specimens was expected and systematically observed at the tempered and softer sub-critical heat-affected zone (SC-HAZ) in all welded conditions. Compressive residual stresses were consistently observed along the weldments in all specimens; the more accentuated negative RS were measured in the PHS joint attributed to the higher volume fraction of martensite; furthermore, the negative RS measured in the fusion zone (FZ) could be well correlated to weld restraint due to the sheet anchoring during the welding procedure, despite the presence of predominant ferrite and pearlite microstructures. Full article

(This article belongs to the Special Issue Welding and Joining of Advanced High-Strength Steels (2nd Edition))

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24 pages, 6554 KiB

Open AccessArticle

Modeling Mechanical Properties of Industrial C-Mn Cast Steels Using Artificial Neural Networks

by Saurabh Tiwari, Seongjun Heo, Nokeun Park and Nagireddy Gari S. Reddy

Metals 2025, 15(7), 790; https://doi.org/10.3390/met15070790 - 12 Jul 2025

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Abstract

This study develops a comprehensive artificial neural network (ANN) model for predicting the mechanical properties of carbon–manganese cast steel, specifically, the yield strength (YS), tensile strength (TS), elongation (El), and reduction of area (RA), based on the chemical composition (16 alloying elements) and [...] Read more.

This study develops a comprehensive artificial neural network (ANN) model for predicting the mechanical properties of carbon–manganese cast steel, specifically, the yield strength (YS), tensile strength (TS), elongation (El), and reduction of area (RA), based on the chemical composition (16 alloying elements) and heat treatment parameters. The neural network model, employing a 20-44-44-4 architecture and trained on 400 samples from an industrial dataset of 500 samples, achieved 90% of test predictions within a 5% deviation from actual values, with mean prediction errors of 3.45% for YS and 4.9% for %EL. A user-friendly graphical interface was developed to make these predictive capabilities accessible, without requiring programming expertise. Sensitivity analyses revealed that increasing the copper content from 0.05% to 0.2% enhanced the yield strength from 320 to 360 MPa while reducing the ductility, whereas niobium functioned as an effective grain refiner, improving both the strength and ductility. The combined effects of carbon and manganese demonstrated complex synergistic behavior, with the yield strength varying between 280 and 460 MPa and the tensile strength ranging from 460 to 740 MPa across the composition space. Optimal strength–ductility balance was achieved at moderate compositions of 1.0–1.2 wt% Mn and 0.20–0.24 wt% C. The model provides an efficient alternative to costly experimental trials for optimizing C-Mn steels, with prediction errors consistently below 6% compared with 8–20% for traditional empirical methods. This approach establishes quantitative guidelines for designing complex multi-element alloys with targeted mechanical properties, representing a significant advancement in computational material engineering for industrial applications. Full article

(This article belongs to the Special Issue Advances in Constitutive Modeling for Metals and Alloys)

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24 pages, 11312 KiB

Open AccessArticle

Effect of Thermomechanical Processing on Porosity Evolution and Mechanical Properties of L-PBF AISI 316L Stainless Steel

by Patrik Petroušek, Róbert Kočiško, Andrea Kasperkevičová, Dávid Csík and Róbert Džunda

Metals 2025, 15(7), 789; https://doi.org/10.3390/met15070789 - 12 Jul 2025

Viewed by 364

Abstract

Thermomechanical processing has a significant impact on the porosity and mechanical properties of AISI 316L stainless steel produced by laser powder bed fusion (L-PBF). This work evaluated the effect of three heat treatment conditions: as-built (HT0), annealed at 650 °C for 3 h [...] Read more.

Thermomechanical processing has a significant impact on the porosity and mechanical properties of AISI 316L stainless steel produced by laser powder bed fusion (L-PBF). This work evaluated the effect of three heat treatment conditions: as-built (HT0), annealed at 650 °C for 3 h with air cooling (HT1), and annealed at 1050 °C for 1 h followed by water quenching (HT2), combined with cold and hot rolling at different strain levels. The most pronounced improvement was observed after 20% hot rolling followed by water quenching (HR + WQ), which reduced porosity to 0.05% and yielded the most spherical pores, with a circularity factor (

f_{c i r c l e}

) of 0.90 and an aspect ratio (AsR) of 1.57. At elevated temperatures, the matrix becomes more pliable, which promotes pore closure and helps reduce stress concentrations. On the other hand, applying heat treatment without causing deformation resulted in the pores growing and increasing porosity in the build direction. The fractography supported these findings, showing a transition from brittle to more ductile fracture surfaces. Heat treatment combined with plastic deformation effectively reduced internal defects and improved both structural integrity and strength. Full article

(This article belongs to the Special Issue Metal Forming and Additive Manufacturing)

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