Metals

20 pages, 2125 KB

Open AccessArticle

A New Continuous Bending and Straightening Curve Based on the High-Temperature Creep Property of a Low-Alloy Steel Continuous Casting Slab

by Yunhuan Sui, Haiqing Lu and Xingzhong Zhang

Metals 2025, 15(9), 1059; https://doi.org/10.3390/met15091059 - 22 Sep 2025

Viewed by 146

Abstract

The existing continuous caster layout curves cause plastic deformation of slabs during bending and straightening segments, while no effective deformation occurs in the basic arc segment, which tends to induce defects, such as cracks, and compromise slab quality. High-temperature creep deformation is generally [...] Read more.

The existing continuous caster layout curves cause plastic deformation of slabs during bending and straightening segments, while no effective deformation occurs in the basic arc segment, which tends to induce defects, such as cracks, and compromise slab quality. High-temperature creep deformation is generally regarded as detrimental to material performance. If the significant and inevitable creep deformation of a slab could be utilized to accomplish bending and straightening deformation during continuous casting, it would turn a potential harm into an advantage, ultimately enhancing both production efficiency and final product quality. Therefore, a new continuous bending and straightening curve based on the high-temperature creep property of a low-alloy steel slab was designed. The new curve cancelled the original basic arc segment and smoothly connected the bending and straightening segments, which not only substantially prolonged the effective bending and straightening deformation time but also extended the creep time. The locations within the slab corresponding to the temperature range of 1100 °C to 1200 °C were obtained from the simulated temperature field results. Comparing the calculated strain rates with the steady-state creep rates revealed that within the temperature range exhibiting favorable hot ductility, the bending and straightening deformation of the slab could be accomplished entirely through creep deformation. Full article

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17 pages, 10023 KB

Open AccessArticle

Research on Hybrid Blue Diode-Fiber Laser Welding Process of T2 Copper

by Xiangkuan Wu, Na Qi, Shengxiang Liu, Qiqi Lv, Qian Fu, Yue Kang, Min Jin and Miaosen Yang

Metals 2025, 15(9), 1058; https://doi.org/10.3390/met15091058 - 22 Sep 2025

Viewed by 218

Abstract

This research proposes a non-penetration lap welding process for joining T2 copper power module terminals in high-frequency and high-power electronic applications, using a hybrid laser system combining a 445 nm blue diode laser and a 1080 nm fiber laser. The composite laser beam, [...] Read more.

This research proposes a non-penetration lap welding process for joining T2 copper power module terminals in high-frequency and high-power electronic applications, using a hybrid laser system combining a 445 nm blue diode laser and a 1080 nm fiber laser. The composite laser beam, formed by coupling a circular blue laser beam with a spot-shaped fiber laser beam, was oscillated along circular, sinusoidal, and 8-shaped trajectories to control weld geometry and joint quality. Results indicate that all trajectories produced U-shaped weld cross-sections with smooth toe transitions and good surface quality. Specifically, the circular trajectory provided uniform energy distribution and stable weld formation; the 8-shaped trajectory achieved a balanced width-to-depth ratio; and the sinusoidal trajectory exhibited sensitivity to welding speed, often resulting in uneven fusion width. Increased welding speed promoted grain refinement, but excessive speed led to porosity and poor surface quality in both 8-shaped and sinusoidal trajectories. Oscillating laser welding facilitated equiaxed grain formation, with the circular and 8-shaped trajectories yielding more uniform microstructures. The circular trajectory maintained consistent weld dimensions and hardness distribution, while the 8-shaped trajectory exhibited superior tensile strength. This work highlights the potential of circular and 8-shaped trajectories in hybrid laser welding for regulating weld microstructure, enhancing mechanical performance and ensuring weld stability. Full article

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

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44 pages, 5603 KB

Open AccessArticle

Optimization of Different Metal Casting Processes Using Three Simple and Efficient Advanced Algorithms

by Ravipudi Venkata Rao and Joao Paulo Davim

Metals 2025, 15(9), 1057; https://doi.org/10.3390/met15091057 - 22 Sep 2025

Viewed by 211

Abstract

This paper presents three simple and efficient advanced optimization algorithms, namely the best–worst–random (BWR), best–mean–random (BMR), and best–mean–worst–random (BMWR) algorithms designed to address unconstrained and constrained single- and multi-objective optimization tasks of the metal casting processes. The effectiveness of the algorithms is demonstrated [...] Read more.

This paper presents three simple and efficient advanced optimization algorithms, namely the best–worst–random (BWR), best–mean–random (BMR), and best–mean–worst–random (BMWR) algorithms designed to address unconstrained and constrained single- and multi-objective optimization tasks of the metal casting processes. The effectiveness of the algorithms is demonstrated through real case studies, including (i) optimization of a lost foam casting process for producing a fifth wheel coupling shell from EN-GJS-400-18 ductile iron, (ii) optimization of process parameters of die casting of A360 Al-alloy, (iii) optimization of wear rate in AA7178 alloy reinforced with nano-SiC particles fabricated via the stir-casting process, (iv) two-objectives optimization of a low-pressure casting process using a sand mold for producing A356 engine block, and (v) four-objectives optimization of a squeeze casting process for LM20 material. Results demonstrate that the proposed algorithms consistently achieve faster convergence, superior solution quality, and reduced function evaluations compared to simulation software (ProCAST, CAE, and FEA) and established metaheuristics (ABC, Rao-1, PSO, NSGA-II, and GA). For single-objective problems, BWR, BMR, and BMWR yield nearly identical solutions, whereas in multi-objective tasks, their behaviors diverge, offering well-distributed Pareto fronts and improved convergence. These findings establish BWR, BMR, and BMWR as efficient and robust optimizers, positioning them as promising decision support tools for industrial metal casting. Full article

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

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20 pages, 13705 KB

Open AccessArticle

Harnessing Hydrothermal Treatments to Control Magnesium Alloy Degradation for Bioresorbable Implants: A Comprehensive Evaluation of Bath Chemistry Effect

by Matteo Pavarini, Nadia Milanesi, Monica Moscatelli and Roberto Chiesa

Metals 2025, 15(9), 1056; https://doi.org/10.3390/met15091056 - 22 Sep 2025

Viewed by 227

Abstract

Magnesium alloys have been recently recognized as promising materials for temporary orthopedic applications, thanks to their biocompatibility, nontoxicity and biodegradability, combined with bone-like mechanical properties; nevertheless, their clinical viability is still hindered by their excessively rapid corrosion in physiological environments. In this context, [...] Read more.

Magnesium alloys have been recently recognized as promising materials for temporary orthopedic applications, thanks to their biocompatibility, nontoxicity and biodegradability, combined with bone-like mechanical properties; nevertheless, their clinical viability is still hindered by their excessively rapid corrosion in physiological environments. In this context, hydrothermal surface modification offers a simple and inexpensive option to form thick ceramic conversion films capable of protecting magnesium and delaying the initial stages of corrosion. In this study, magnesium samples were hydrothermally treated in various aqueous baths to systematically assess the influence of their chemistry on the resulting coating features. The obtained coatings were characterized in terms of physicochemical properties, electrochemical corrosion behavior in SBF, and long-term degradation with volumetric loss quantification by µ-CT. The results highlighted how corrosion resistance is dictated by coating uniformity rather than thickness. Moreover, XRD analyses revealed that all the best-performing coatings contained a stable magnesium oxide phase in addition to magnesium hydroxide, a feature absent in less protective films. A simple sodium nitrate solution was found to produce the most protective layer, showing the lowest volumetric losses after immersion testing. Full article

(This article belongs to the Special Issue Recent Advances in Surface Modification of Metallic Materials)

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23 pages, 5240 KB

Open AccessArticle

The Effect of Electrolytic Temperature on the Purity of Electrolytic Pure Iron

by Di Zhang, Tengshi Liu, Gangsheng Xie, Bo Wang, Xin Cao, Jiaxin Bai, Mingyue Zhong and Han Dong

Metals 2025, 15(9), 1055; https://doi.org/10.3390/met15091055 - 21 Sep 2025

Viewed by 198

Abstract

The influence of electrolytic temperature on the purity grade of electrolytic pure iron, variations in elemental content, macroscopic morphology, and microstructural characteristics was studied using electrodeposition experiments alongside glow discharge mass spectrometry and scanning electron microscopy. As electrolyte temperature increased, the total impurity [...] Read more.

The influence of electrolytic temperature on the purity grade of electrolytic pure iron, variations in elemental content, macroscopic morphology, and microstructural characteristics was studied using electrodeposition experiments alongside glow discharge mass spectrometry and scanning electron microscopy. As electrolyte temperature increased, the total impurity content in electrolytic pure iron decreased; the iron reached a purity level of 4N1 (99.991%) when electrolyzed at 75 °C. The content of gaseous elements also decreased with increasing temperature, with a total content of only 46.07 ppm during electrolysis at 75 °C. Among the major metallic elements, the Ni content was minimally affected by temperature, while the concentrations of other metallic elements were at their lowest during electrolysis at 75 °C, remaining below 0.5 ppm, except for elements such as Co, Cu, Ni, and Zn. With an increase in the electrolyte temperature, the macroscopic morphology evolved into a smooth, silver-white surface. The microstructure on the surface evolved into an irregular polygonal nucleus structure, and the microstructure on the cross-section exhibited a striped characteristic. Therefore, electrolytic pure iron with a purity exceeding 4N, exhibiting both excellent macroscopic and compact structures, can be prepared at an electrolytic temperature of 75 °C. Full article

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15 pages, 9033 KB

Open AccessArticle

Evaluation of the Resistance of APS-Developed Woka-Diamalloy Carbide Coatings to High-Temperature Damage

by Yildiz Yarali Ozbek, Okan Odabas, Yasin Ozgurluk and Abdullah Cahit Karaoglanli

Metals 2025, 15(9), 1054; https://doi.org/10.3390/met15091054 - 21 Sep 2025

Viewed by 226

Abstract

This study was conducted to evaluate the high-temperature protection performance of new hard coating systems. Woka 7202 (Cr₃C₂-NiCr) and Diamalloy 2002 (WC-NiCrFeBSiC) powders were coated onto 316L stainless steel substrates using the atmospheric plasma spraying (APS) method and subjected [...] Read more.

This study was conducted to evaluate the high-temperature protection performance of new hard coating systems. Woka 7202 (Cr₃C₂-NiCr) and Diamalloy 2002 (WC-NiCrFeBSiC) powders were coated onto 316L stainless steel substrates using the atmospheric plasma spraying (APS) method and subjected to isothermal oxidation (5–100 h) and hot corrosion (55% V₂O₅ + 45% Na₂SO₄, 1–5 h) tests. Although the coatings exhibited a laminar microstructure and some pores, cracks, and oxide-containing regions, they did not show any flaking or structural integrity deformations during the tests. Microstructural changes, oxide layer morphology, and the phases formed were examined in detail. The findings demonstrate that these coating systems not only provide chemical and structural stability against existing high-temperature environments, but also meet the requirements of next-generation thermal protection needs. In this regard, the study provides directly applicable information for the coating design and performance optimization for turbine blades, energy production equipment, and similar industrial components exposed to high-temperature oxidation and hot corrosion. Full article

(This article belongs to the Special Issue Processing, Microstructure and Properties of Cemented Carbide)

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23 pages, 18943 KB

Open AccessArticle

Influence of Tramp Elements on Phase Transformations, Microstructure and Hardness of a 0.3 wt.%C Low-Alloyed Steel

by Marek Gocnik, Lukas Hatzenbichler, Michael Meindlhumer, Phillip Haslberger, Matthew Galler, Andreas Stark, Claes-Olof A. Olsson, Jozef Keckes and Ronald Schnitzer

Metals 2025, 15(9), 1053; https://doi.org/10.3390/met15091053 - 20 Sep 2025

Viewed by 282

Abstract

Decarbonizing the steel industry relies on a transition from carbon-intensive blast furnace technology to scrap-based secondary steelmaking using electric arc furnaces. This transition introduces tramp elements and leads to their gradual accumulation, which can significantly influence the functional properties of chemically sensitive steel [...] Read more.

Decarbonizing the steel industry relies on a transition from carbon-intensive blast furnace technology to scrap-based secondary steelmaking using electric arc furnaces. This transition introduces tramp elements and leads to their gradual accumulation, which can significantly influence the functional properties of chemically sensitive steel grades. In this study, the combined impact of several tramp element contents on the phase transformations, microstructure and mechanical properties of a 0.3 wt.% C low-alloyed steel was investigated. To achieve this, a reference alloy was produced using the conventional blast furnace production route. It was then compared with two trial alloys, which contained intentionally elevated levels of tramp elements and were produced through an experimental melting route designed to simulate scrap-based electric arc furnace production. The experimental characterization included light optical and electron microscopy, electron back-scatter diffraction, in situ synchrotron high-energy X-ray diffraction coupled with dilatometry, and Vickers hardness testing. The results revealed the formation of displacive transformation products such as martensite and showed that austenite was retained in the tramp element-enriched trial alloys. The combination of solid solution strengthening and martensitic transformation led to a gradual increase in hardness. These findings underscore the critical role of tramp elements in determining the microstructural and mechanical response of steels produced from scrap-based feedstock. Full article

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18 pages, 18240 KB

Open AccessArticle

High-Temperature Corrosion Behavior of 12Cr18Ni10Ti Grade Austenitic Stainless Steel Under Chlorination Conditions

by Yuliya Baklanova, Yerzhan Sapatayev and Kuanysh Samarkhanov

Metals 2025, 15(9), 1052; https://doi.org/10.3390/met15091052 - 20 Sep 2025

Viewed by 264

Abstract

Ensuring the long-term integrity of structural materials in extreme environments is a critical challenge in the design of equipment for nuclear fuel cycle operations. In particular, the durability of materials exposed to high temperatures and chemically aggressive environments during the processing of irradiated [...] Read more.

Ensuring the long-term integrity of structural materials in extreme environments is a critical challenge in the design of equipment for nuclear fuel cycle operations. In particular, the durability of materials exposed to high temperatures and chemically aggressive environments during the processing of irradiated reactor components remains a key concern. This study investigates the high-temperature corrosion behavior of 12Cr18Ni10Ti austenitic stainless steel in the reaction chamber of a beryllium chlorination plant developed for recycling irradiated beryllium reflectors from the JMTR (Japan Materials Testing Reactor). The chlorination process was conducted at temperatures ranging from 500 °C to 1000 °C in a chlorine-rich atmosphere. Post-operation analysis of steel samples extracted from the chamber revealed that uniform wall thinning was the predominant degradation mechanism. However, in high-temperature regions near the heating element, localized forms of damage, specifically pitting and intergranular corrosion, were detected, indicating that thermal stresses exacerbated localized attack. These findings contribute to the assessment of the service life of structural components under extreme conditions and offer practical guidance for material selection and design optimization in high-temperature chlorination systems used in nuclear applications. Full article

(This article belongs to the Section Corrosion and Protection)

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13 pages, 3522 KB

Open AccessArticle

High-Purity Tungsten Oxide Production from Low-Grade Scheelite Concentrates at Pilot Plant Scale

by Javier Nieto, Lourdes Yurramendi, Javier Antoñanzas and Jose Luis Aldana

Metals 2025, 15(9), 1051; https://doi.org/10.3390/met15091051 - 20 Sep 2025

Viewed by 208

Abstract

Tungsten is a critical raw material with increasingly important industrial applications. It is primarily found in minerals such as scheelite and wolframite (0.5% W), which are extracted and processed at the mine site to produce a high-grade scheelite concentrate (60% W). This process [...] Read more.

Tungsten is a critical raw material with increasingly important industrial applications. It is primarily found in minerals such as scheelite and wolframite (0.5% W), which are extracted and processed at the mine site to produce a high-grade scheelite concentrate (60% W). This process results in significant tungsten losses in the form of tailings, currently not utilized at the EU level. Deep eutectic solvents and imidazolium-based ionic liquids have been shown to possess excellent utility for recovering tungsten from low-grade concentrates, achieving tungsten oxide (96% purity) at high global yields (80%). In this study, an optimized ionic liquid-based process (involving leaching, solvent extraction, crystallization, and calcination) was developed at the laboratory scale. Important issues such as solvent flammability or the commercial availability of ionic liquids were addressed to ensure the safety and industrial feasibility of the process. Furthermore, a pilot plant was designed, constructed, and operated for a significant period (3 days). Tungsten oxide was produced with improved purity (>99%) and global yield (91.6%) in continuous operation. Full article

(This article belongs to the Special Issue Separation, Purification and Extraction of Metals from Primary and Secondary Resources)

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19 pages, 8320 KB

Open AccessArticle

Insights into Optimizing Heat Treatment for Hot Isostatic Pressing of Ti-48Al-3Nb-1.5Ta Alloy Powder

by Zhenbo Zuo, Rui Hu, Shaoqiang Li, Chengpeng Liu, Qingxiang Wang, Xiangyu Gao, Yunjin Lai, Xian Luo, Cheng Luo, Zonghong Qu and Lu Kang

Metals 2025, 15(9), 1050; https://doi.org/10.3390/met15091050 - 20 Sep 2025

Viewed by 158

Abstract

In this study, various characterization techniques were utilized to investigate the effects of heat treatments on the microstructure and mechanical properties of Ti-48Al-3Nb-1.5Ta (at. %) alloy prepared by the supreme-speed plasma rotating electrode process and hot isostatic pressing. By comparing the microstructures of [...] Read more.

In this study, various characterization techniques were utilized to investigate the effects of heat treatments on the microstructure and mechanical properties of Ti-48Al-3Nb-1.5Ta (at. %) alloy prepared by the supreme-speed plasma rotating electrode process and hot isostatic pressing. By comparing the microstructures of the alloy under different heat treatments conditions, it was found that the nearly lamellar structure with a size of about 145 μm is formed by a simple heat treatment (1400 °C/10 min, FC to 1300 °C, AC, 850 °C/3 h/FC). Under this heat treatment condition, the alloy exhibited satisfied mechanical properties, with a tensile fracture strain of 1.2% at room temperature and a tensile fracture strain of 7.5% at 750 °C. No fracture occurred after 225 h when creeping at 750 °C/250 MPa. Ta inhibited the growth of lamellae and the expansion of pores, thereby improving creep performance. In summary, the TiAl alloy with satisfied performance was obtained through a simple heat treatment process, which provides a significant idea for engineering application. Full article

(This article belongs to the Special Issue Microstructure, Tensile Properties and Creep Behavior of Metallic Materials)

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17 pages, 14013 KB

Open AccessArticle

The Effect of Welding Parameters on the Morphology and Mechanical Properties of AA6061-T6/CF-PPS Friction Stir Lap Welding Joints

by Wenhao Xu, Yongyong Lin, Qiaobo Feng, Yangjun Wang, Jie Wang, Sizhe Niu and Ming Lou

Metals 2025, 15(9), 1049; https://doi.org/10.3390/met15091049 - 20 Sep 2025

Viewed by 255

Abstract

The application of lightweight materials in the automotive industry can effectively achieve further weight reduction while maintaining overall structural strength, thereby reducing energy consumption. Currently, friction stir spot welding (FSSW) is the primary method for joining carbon fiber-reinforced polyphenylene sulfide (CF-PPS) with aluminum [...] Read more.

The application of lightweight materials in the automotive industry can effectively achieve further weight reduction while maintaining overall structural strength, thereby reducing energy consumption. Currently, friction stir spot welding (FSSW) is the primary method for joining carbon fiber-reinforced polyphenylene sulfide (CF-PPS) with aluminum alloys. This study successfully achieved the connection between 6061-T6 aluminum alloy and CF-PPS using the more operationally convenient friction stir lap welding (FSLW) technique. The primary objective of this study was to explore the potential of expanding the welding technologies available for successfully joining these two dissimilar materials. The joint morphology and strength were analyzed through metallographic observation and tensile testing, and the effects of different welding parameters on the microstructure and mechanical properties of dissimilar joints were studied. The study demonstrated that the successful connection between AA6061-T6 and CF-PPS was primarily attributable to the combined effects of mechanical interlocking and mixture bonding. The joint strength demonstrated a maximum value of 9.41 MPa when the following parameters were set: a rotation speed of 1800 rpm, a welding speed of 40 mm/min, and a plunge depth of 0.2 mm. Although low rotation speed and low welding speed cannot form an effective mechanical interlocking structure for the joint, the failed joints have different causes. When the rotation and welding speeds are fixed, changing the plunge depth cannot change the interlocking structure of the joint. A larger plunge depth will thin the weld and greatly reduce the joint strength. Full article

(This article belongs to the Special Issue New Welding Materials and Green Joint Technology—2nd Edition)

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22 pages, 4461 KB

Open AccessArticle

Numerical Investigation of Burden Distribution in Oxygen Blast Furnace Ironmaking

by Lulu Jiao, Xinyang Shu and Aibing Yu

Metals 2025, 15(9), 1048; https://doi.org/10.3390/met15091048 - 19 Sep 2025

Viewed by 332

Abstract

The oxygen blast furnace (OBF) is a promising technology for ironmaking, and its burden distribution pattern plays a key role in optimizing performance. This study investigates the impact of the peripheral opening extent (POE), which reflects the coke distribution adjacent to the furnace [...] Read more.

The oxygen blast furnace (OBF) is a promising technology for ironmaking, and its burden distribution pattern plays a key role in optimizing performance. This study investigates the impact of the peripheral opening extent (POE), which reflects the coke distribution adjacent to the furnace wall, on OBF performance using a computational fluid dynamics (CFD) process model. A 380 m³ OBF is simulated, incorporating reducing gas injection through both the hearth tuyeres and shaft tuyeres. By analyzing the inner states, the global performance is evaluated. The results show that the optimal POE value is 20°, which minimizes the fuel rate, maximizes productivity, and achieves the highest top gas utilization factor. As POE increases, chemical reaction carbon consumption decreases. The combustion heat in front of the tuyeres initially decreases and then increases, leading to a corresponding decrease and subsequent increase in carbon consumption in the tuyeres. The combined effects of these factors cause the fuel rate to first decrease and then increase. Additionally, this study quantifies the relationship between shaft injection rate and burden distribution. It is found that shaft injection improves the furnace’s thermal state and enhances the reducing atmosphere, leading to a reduced fuel rate. Notably, the optimal POE value remains constant at 20°, regardless of the shaft injection rate, suggesting that POE selection is independent of the injection rate. Overall, appropriate peripheral openings contribute to improving OBF global performance. These findings should be helpful to the industrial OBF operation. Full article

(This article belongs to the Special Issue Sustainable Ironmaking and Steelmaking: Challenges and Opportunities)

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19 pages, 3960 KB

Open AccessArticle

Optimization of Hot Stamping Parameters for Aluminum Alloy Crash Beams Using Neural Networks and Genetic Algorithms

by Ruijia Qu, Zhiqiang Zhang, Mingwen Ren, Hongjie Jia and Tongxin Lv

Metals 2025, 15(9), 1047; https://doi.org/10.3390/met15091047 - 19 Sep 2025

Viewed by 1518

Abstract

The hot stamping process of aluminum alloys involves multiple parameters, including blank holder force, stamping speed, die temperature, and friction coefficient. Traditional methods often fail to capture the nonlinear interactions among these parameters. This study proposes an optimization framework that integrates BP neural [...] Read more.

The hot stamping process of aluminum alloys involves multiple parameters, including blank holder force, stamping speed, die temperature, and friction coefficient. Traditional methods often fail to capture the nonlinear interactions among these parameters. This study proposes an optimization framework that integrates BP neural networks with genetic algorithms (GA), while six bio-inspired algorithms—Grey Wolf Optimization (GWO), Sparrow Search Algorithm (SSA), Crested Porcupine Optimizer (CPO), Grey lag Goose Optimization (GOOSE), Dung Beetle Optimizer (DBO), and Parrot Optimizer (PO)—were employed to optimize the network hyperparameters. Comparative results show that all optimized models outperformed the baseline BP model (R² = 0.702, RMSE = 0.106, MAPE = 20.8%). The PO-BP achieved the best performance, raising R² by 27.3% and reducing MAPE by 27.1%. Furthermore, combining GA with the PO-BP model yielded optimized process parameters, reducing the maximum thinning rate to 17.0% with only a 1.16% error compared with experiments. Overall, the proposed framework significantly improves prediction accuracy and forming quality, offering an efficient solution for rapid process optimization in intelligent manufacturing of aluminum alloy automotive parts. Full article

(This article belongs to the Special Issue Forming and Processing Technologies of Lightweight Metal Materials)

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20 pages, 4394 KB

Open AccessArticle

Optimization of Multilayer Metal Bellow Hydroforming Process with Response Surface Method and Genetic Algorithm

by Jing Liu, Liang Li, Jian Liu and Lanyun Li

Metals 2025, 15(9), 1046; https://doi.org/10.3390/met15091046 - 19 Sep 2025

Viewed by 247

Abstract

In this paper, an optimization strategy for the hydroforming process of bellows is proposed, based on finite element analysis, design of experiments, response surface methodology, and genetic algorithms. A numerical model of the bellows hydroforming process is developed using the finite element simulation [...] Read more.

In this paper, an optimization strategy for the hydroforming process of bellows is proposed, based on finite element analysis, design of experiments, response surface methodology, and genetic algorithms. A numerical model of the bellows hydroforming process is developed using the finite element simulation code ABAQUS and validated experimentally. A combination of experimental design, numerical simulations, and regression analysis is employed to establish the mathematical models relating the objectives to the design variables. An analysis of variance (ANOVA) is conducted to evaluate the significance of each individual factor on the response variable. The main and interaction effects of the process parameters on the outer diameter and convolution pitch are illustrated and discussed. Furthermore, the response surface methodology and a Pareto-based multi-objective genetic algorithm (MOGA) are applied to determine optimal solutions within the given optimization criteria. The optimized results show good agreement with the experimental data, demonstrating that the optimization methodology is reliable. Full article

(This article belongs to the Special Issue Advanced Plastic Forming Processes: Theory, Experiments and Numerical Simulations)

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12 pages, 479 KB

Open AccessArticle

Quantifying Latent Heat in AlSi5Cu Alloys (with 1, 2, and 4% of Cu by Mass) via DSC, Thermal Analysis, and Commercial Software

by Mile Djurdjevic, Vladimir Jovanovic and Srecko Stopic

Metals 2025, 15(9), 1045; https://doi.org/10.3390/met15091045 - 19 Sep 2025

Viewed by 138

Abstract

This study comprehensively evaluates the latent heat of hypoeutectic AlSi5Cu alloys with 1, 2, and 4% of Cu by mass, investigating their solidification behavior under controlled cooling conditions. Latent heat, a critical thermophysical property, significantly influences solidification and microstructural formation in casting processes. [...] Read more.

This study comprehensively evaluates the latent heat of hypoeutectic AlSi5Cu alloys with 1, 2, and 4% of Cu by mass, investigating their solidification behavior under controlled cooling conditions. Latent heat, a critical thermophysical property, significantly influences solidification and microstructural formation in casting processes. The evaluation employed an integrated approach, combining experimental measurements from Differential Scanning Calorimetry (DSC) and thermal analysis (TA-Newtonian method) with computational assessments performed using JMatPro and Thermo-Calc software packages. The findings reveal a reasonable agreement between the measured and calculated latent heat values, suggesting that methods beyond DSC, such as commercial software and thermal analysis techniques, offer acceptable and viable alternatives for determining latent heat in AlSiCu alloys. While DSC served as the experimental reference, providing particularly consistent lowest values for AlSi5Cu1 and AlSi5Cu2, relative error analysis indicated that JMatPro generally yielded results closest to DSC, especially for AlSi5Cu2 (0.245% relative error), and the TA-Newtonian method also showed strong agreement, particularly for AlSi5Cu1 (0.356% relative error) and AlSi5Cu4 (0.787% relative error). Maximum deviation was observed with Thermo-Calc for AlSi5Cu1 (7.474%). These discrepancies are primarily attributed to inherent differences in the underlying thermodynamic databases for computational tools and the sensitivity of experimental techniques to specific material properties and solidification behaviors. Full article

(This article belongs to the Special Issue Solidification and Casting of Metals and Alloys (2nd Edition))

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22 pages, 7700 KB

Open AccessArticle

Towards a Global Constitutive Formulation for Modeling the Hot Working Behavior of Low-Carbon Steels

by Unai Mayo, Sergio Fernandez-Sanchez, Isabel Gutierrez, Denis Jorge-Badiola and Amaia Iza-Mendia

Metals 2025, 15(9), 1044; https://doi.org/10.3390/met15091044 - 19 Sep 2025

Viewed by 248

Abstract

The current study explores the applicability of a single constitutive equation, based on the Arrhenius hyperbolic sine model, to a wide range of chemical compositions and test conditions by using a unique approximation. To address this challenge, a mixed model is proposed, integrating [...] Read more.

The current study explores the applicability of a single constitutive equation, based on the Arrhenius hyperbolic sine model, to a wide range of chemical compositions and test conditions by using a unique approximation. To address this challenge, a mixed model is proposed, integrating a physical model with phenomenological expressions to capture the strain and strain rate hardening, forming temperature, dynamic recovery (DRV) and dynamic recrystallization (DRX). The investigation combines high-temperature mechanical testing with modeling in order to understand the hot deformation mechanisms. Hot torsion tests were conducted on ten different low-carbon steels with distinct microalloying additions to capture their responses under diverse initial austenite grain sizes, deformation temperatures and strain rate conditions (d₀ = 22–850 µm, T = 800–1200 °C and

\dot{ε}

= 0.1–10 s⁻¹). The developed constitutive equation has resulted in a robust expression that effectively simulates the hot behavior of various alloys across a wide range of conditions. The application of an optimization tool has significantly reduced the need for adjustments across different alloys, temperatures and strain rates, showcasing its versatility and effectiveness in predicting the flow behavior in a variety of scenarios with excellent accuracy. Moreover, the model has been validated with experimental torsion data from the literature, enhancing the applicability of the developed expression to a broader spectrum of chemical compositions. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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20 pages, 15388 KB

Open AccessArticle

Internal SEN Design and Its Influence on Fluid Dynamics in Slab Molds: A Combined Numerical and Experimental Analysis

by Edith Ramos-Cardona, Ismael Calderon-Ramos, Rodolfo Morales Dávila, Rumualdo Servín-Castañeda, Alejandro Pérez-Alvarado, Sixtos A. Arreola-Villa, Alma R. Méndez-Gordillo and Saúl García-Hernández

Metals 2025, 15(9), 1043; https://doi.org/10.3390/met15091043 - 19 Sep 2025

Viewed by 148

Abstract

The optimization of submerged entry nozzle (SEN) designs plays a pivotal role in achieving stable flow conditions and high-quality steel production during continuous casting. This study presents a comparative analysis of two SEN geometries under identical operational parameters using a combined approach of [...] Read more.

The optimization of submerged entry nozzle (SEN) designs plays a pivotal role in achieving stable flow conditions and high-quality steel production during continuous casting. This study presents a comparative analysis of two SEN geometries under identical operational parameters using a combined approach of numerical simulation and physical modeling. A full-scale water model and a validated CFD framework based on the realizable k-

ε

and VOF models were employed to evaluate velocity distribution, turbulence intensity, free surface behavior, and flow symmetry. Results reveal that the SEN-2 design enhances flow stability near the meniscus region, promotes a consistent double-roll flow pattern (DRF), and reduces surface oscillations and sub-meniscus velocities, thereby minimizing the risk of mold flux entrapment. The proposed dimensionless KE number effectively quantifies the energy dissipation behavior of both designs, highlighting SEN-2’s superior hydraulic performance. This integrated methodology offers a robust evaluation framework for future nozzle development aimed at improving product quality without compromising productivity. Full article

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

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16 pages, 9544 KB

Open AccessArticle

Solid-State Recycling of AA6063 Aluminum Chips via Accumulative Roll Bonding: A Green Pathway to High-Performance Materials

by Mauro Carta, Noomane Ben Khalifa, Pasquale Buonadonna, Francesco Aymerich and Mohamad El Mehtedi

Metals 2025, 15(9), 1042; https://doi.org/10.3390/met15091042 - 19 Sep 2025

Viewed by 209

Abstract

Accumulative Roll Bonding (ARB) is a severe plastic deformation process typically used to produce ultra-fine-grained structures. This study investigates the feasibility of using the ARB process to recycle aluminum chips from an Al-Mg-Si alloy (AA6063). The chips were first compacted under a 200 [...] Read more.

Accumulative Roll Bonding (ARB) is a severe plastic deformation process typically used to produce ultra-fine-grained structures. This study investigates the feasibility of using the ARB process to recycle aluminum chips from an Al-Mg-Si alloy (AA6063). The chips were first compacted under a 200 kN hydraulic press and then directly hot-rolled at 550 °C without prior heat treatment to a final sheet thickness of 1.5 mm. Subsequent ARB cycles were then applied to achieve full consolidation. Mechanical properties were evaluated through tensile testing and microhardness measurements, while microstructure was characterized using Optical Microscopy and SEM-EBSD. These analyses revealed significant grain refinement and improved homogeneity with increasing ARB cycles. Mechanical testing showed that the ARB process substantially enhanced both tensile strength and hardness of the recycled AA6063 chips while maintaining good ductility. The best results were obtained after two ARB cycles, yielding an ultimate tensile strength (UTS) of 170 MPa and an elongation at rupture of 15.7%. The study conclusively demonstrates that the ARB process represents a viable and effective method for recycling aluminum chips. This approach not only significantly improves mechanical properties and microstructural characteristics but also offers environmental benefits by eliminating the energy-intensive melting stage. Full article

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16 pages, 4370 KB

Open AccessArticle

Influence of Pre-Corrosion in NaCl Solution on Cavitation Resistance of Steel Samples (42CrMo4)

by Stanica Nedović, Ana Alil, Sanja Martinović, Stefan Dikić and Tatjana Volkov-Husović

Metals 2025, 15(9), 1041; https://doi.org/10.3390/met15091041 - 19 Sep 2025

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Abstract

Marine applications often involve metallic materials, including steel, that must endure harsh conditions such as cavitation erosion (CE). This study investigates the CE behavior of 42CrMo4 steel, both in its original state and after pre-corrosion in a 3.5% NaCl solution for 120 days, [...] Read more.

Marine applications often involve metallic materials, including steel, that must endure harsh conditions such as cavitation erosion (CE). This study investigates the CE behavior of 42CrMo4 steel, both in its original state and after pre-corrosion in a 3.5% NaCl solution for 120 days, simulating a simplified marine environment. Cavitation testing was conducted using an ultrasonic vibratory setup with a stationary sample, at intervals of 10 and 30 min, with a total testing time of 150 min. Mass loss (ML), mass loss rate (MLR), mean depth of erosion (MDE), and level of degradation (LoD) were calculated, while surface roughness (Rz) was measured using a TR200 tester. Surface changes were analyzed through field emission scanning electron microscopy (FESEM) and image analysis techniques. Morphological parameters such as the number of pits, average diameter, and total pit area were used to quantify surface damage. Results showed that pre-corroded samples exhibited a significantly higher erosion rate than non-corroded ones. Pre-corrosion introduced microcracks and surface defects that served as initiation sites for cavitation damage. These imperfections increased surface roughness and created favorable conditions for pit formation, leading to faster and deeper material loss. Image and FESEM analyses confirmed the presence of larger and deeper pits in pre-corroded samples compared to the smaller and shallower pits in non-corroded specimens. This study highlights the impact of pre-corrosion on the cavitation resistance of 42CrMo4 steel and demonstrates the effectiveness of combining mass loss data with morphological and surface analyses for evaluating cavitation damage under marine-like conditions. Full article

(This article belongs to the Special Issue Corrosion and Oxidation of Metals: Mechanisms, Kinetics, and Protection)

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17 pages, 3022 KB

Open AccessArticle

A Comparative Evaluation of Microbiologically Induced Corrosion Behaviors of 316L Austenitic and 2205 Duplex Stainless Steels Inoculated in Desulfovibrio vulgaris

by Zhong Li, Yuzhou Chen, Qiang Guo, Xiaohu Zhang, Xiaolong Li, Yong Li, Jiaxing Cai, Yi Fan and Jike Yang

Metals 2025, 15(9), 1040; https://doi.org/10.3390/met15091040 - 19 Sep 2025

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Abstract

Selecting appropriate materials is crucial for mitigating the severe economic and safety challenges posed by microbiologically induced corrosion (MIC) in marine and industrial settings. This study focuses on the MIC behavior of 316L austenitic stainless steel and 2205 duplex stainless steel that is [...] Read more.

Selecting appropriate materials is crucial for mitigating the severe economic and safety challenges posed by microbiologically induced corrosion (MIC) in marine and industrial settings. This study focuses on the MIC behavior of 316L austenitic stainless steel and 2205 duplex stainless steel that is caused by the metabolic activities of D. vulgaris during a life span of 7 days. Cell counts, weight loss, electrochemical measurements, and surface characterization were employed to evaluate the materials’ resistance to MIC. Specifically, 2205 DSS exhibited a 60% lower weight loss (0.02 vs. 0.05 mg/cm²), a 42% lower maximum pit depth (2.11 vs. 3.64 μm), and an orders-of-magnitude lower corrosion current density (0.094 vs. 2.0 μA cm⁻²) compared to 316L SS, demonstrating its superior resistance to D. vulgaris MIC. XRD and XPS analyses revealed that although FeS formed on both materials, FeS₂—a thermodynamically stable deep-sulfidation product—was only present on 316L, indicating a more advanced corrosion stage. The absence of FeS₂ on 2205 suggests limited sulfide corrosion progression. These findings confirm the advantage of duplex stainless steel in mitigating D. vulgaris-induced corrosion and provide insights into the selection of materials for MIC-prone environments. Full article

(This article belongs to the Section Corrosion and Protection)

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20 pages, 7089 KB

Open AccessArticle

Recovery of Cu and Fe from a Sphalerite Concentrate by the MnO₂–KI Leaching Oxidation System

by Aleksandar Jovanović, Dimitrije Anđić, Mladen Bugarčić, Ivana Jelić, Nela Vujović, Corby Anderson and Miroslav Sokić

Metals 2025, 15(9), 1039; https://doi.org/10.3390/met15091039 - 19 Sep 2025

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Abstract

This study examined the leaching behavior of copper and iron from a sphalerite concentrate in sulfuric acid utilizing an ensemble MnO₂–KI oxidizing system. The temperature was shown to significantly influence the leaching kinetics, with the efficiency notably improving between 40 °C [...] Read more.

This study examined the leaching behavior of copper and iron from a sphalerite concentrate in sulfuric acid utilizing an ensemble MnO₂–KI oxidizing system. The temperature was shown to significantly influence the leaching kinetics, with the efficiency notably improving between 40 °C and 80 °C. The introduction of KI affected the balance between sulfur passivation and oxidant availability, facilitating increased leaching efficiencies. At 3 wt% KI, maximum recoveries of 82.1% Cu and 85.3% Fe were achieved, which indicates a notable decrease in surface passivation. Kinetic study analysis revealed low activation energies of 28.90 kJ mol⁻¹ for copper and 18.94 kJ mol⁻¹ for iron, indicating that both processes proceed readily at moderate temperature regimes. Despite being diffusion-controlled, the mechanisms of dissolution are different: iron leaching is more complicated, involving pyrite oxidation, sulfur layer formation, transformation to marcasite, and ultimately iron (III) release, whereas copper leaching involves direct interaction of chalcopyrite with the oxidants, similar to the behavior of sphalerite. Full article

(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy—3rd Edition)

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12 pages, 647 KB

Open AccessArticle

ISE of Precious Metals: Au, Ag, Pd, and Pt

by Lenka Girmanová, Jozef Petrík, Marek Šolc, Peter Blaško, Alena Pribulová and Peter Futáš

Metals 2025, 15(9), 1038; https://doi.org/10.3390/met15091038 - 19 Sep 2025

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Abstract

Precious metals play an important role in various fields, from industry to jewelry and finance. In the industrial field, it is often necessary to know their mechanical properties. Micro-hardness measurement is a suitable test. In this type of test, the results are usually [...] Read more.

Precious metals play an important role in various fields, from industry to jewelry and finance. In the industrial field, it is often necessary to know their mechanical properties. Micro-hardness measurement is a suitable test. In this type of test, the results are usually influenced by the Indentation Size Effect (ISE). The paper addresses the problem of micro-hardness measurement and the subsequent interpretation of the measured values using Meyer’s index n, the PSR method, and the Hays–Kendall approach in order to determine the true, test-load-independent micro-hardness values of gold, silver, palladium, and platinum. The tester Hanemann (manufactured by Carl Zeiss, Jena, Germany) was used to measure micro-hardness. The loads applied during the micro-hardness test were between 0.09807 N and 0.9807 N. Investment precious metals with a declared purity of at least 99.95% were used for the measurements. Palladium and silver have a Meyer index close to the validity of Kick’s law, with neutral ISE. Gold and platinum show a slightly “normal” ISE. This may be the influence of the previous deformation of the sample. Full article

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17 pages, 8633 KB

Open AccessArticle

Microstructural Evolution and Tensile Deformation Behavior of FeCoNiCrTi_0.2 High-Entropy Alloys Regulated by Cold Rolling and Annealing

by Peng Zhang, Dehao Liu, Linfu Zhang, Kang Liu, Jie Zhang, Yuxiao Si, Gang Chen and Qiang Zhu

Metals 2025, 15(9), 1037; https://doi.org/10.3390/met15091037 - 19 Sep 2025

Viewed by 177

Abstract

Novel structural materials, high-entropy alloys (HEAs), have attracted considerable interest owing to their tunable microstructural designs and adjustable mechanical properties. In the present work, the microstructural evolution and tensile deformation behavior of FeCoNiCrTi_0.2 HEA are comprehensively examined through cold rolling (with 80% [...] Read more.

Novel structural materials, high-entropy alloys (HEAs), have attracted considerable interest owing to their tunable microstructural designs and adjustable mechanical properties. In the present work, the microstructural evolution and tensile deformation behavior of FeCoNiCrTi_0.2 HEA are comprehensively examined through cold rolling (with 80% thickness reduction) followed by annealing, combined with multiscale characterization techniques (EBSD/TEM) and mechanical tests. The results reveal that the as-rolled microstructure was characterized by the presence of strong Brass, Goss/Brass, and S textures, along with the formation of high-density dislocation walls (DDWs) and dislocation cells (DCs). As the annealing temperature increased, recrystallized grains preferentially nucleated at grain boundaries with higher stress concentrations and dislocation densities. The grain size decreased from 120.33 μm in the as-rolled state to 10.26 μm after annealing at 1000 °C. Low-angle grain boundaries (LAGBs) progressively transformed into high-angle grain boundaries (HAGBs), while the fraction of Σ3 twin boundaries initially decreased and subsequently increased, reaching a maximum of 43.7% after annealing at 1000 °C. At annealing temperatures exceeding 800 °C, deformed grains became equiaxed, with partial retention of primary texture components observed. After annealing at 1000 °C, the yield strength and tensile strength decreased compared to the as-rolled state, while the elongation significantly increased from 17.2% to 69.8% Simultaneously, the yield ratio decreased by 53%, and the strain-hardening capacity was enhanced. Ultimately, a constitutive model integrating the influences of dislocation mean free path and twin boundary obstruction was developed, providing microscopic explanations for the inverse relationship between strength and recrystallization fraction. Full article

(This article belongs to the Special Issue Sheet Metal Forming Processes)

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20 pages, 11452 KB

Open AccessArticle

Study on the Influence of Isotropic Simplification in Flexible Multi-Point Stretch-Bending Forming with Roller Dies

by Songyue Yang, Yu Wen, Ce Liang and Yi Li

Metals 2025, 15(9), 1036; https://doi.org/10.3390/met15091036 - 19 Sep 2025

Viewed by 217

Abstract

For the flexible multi-point stretch-bending forming process, which involves complex forming procedures, finite element (FE) modeling can significantly reduce trial-and-error costs and provide a convenient means for determining process parameters in actual production. During the creation of FE models, simplifying the material model [...] Read more.

For the flexible multi-point stretch-bending forming process, which involves complex forming procedures, finite element (FE) modeling can significantly reduce trial-and-error costs and provide a convenient means for determining process parameters in actual production. During the creation of FE models, simplifying the material model is crucial: insufficient simplification greatly increases computation time, while excessive simplification reduces model accuracy. This study establishes user material subroutines in the FE simulation software Abaqus to introduce anisotropic yield models, specifically Hill’s 48 and Yld2004-18p models. Multi-point stretch-bending experiments were repeated and compared with simulations using the traditional isotropic Von Mises yield model to analyze the impact of isotropic simplification on the accuracy of forming results. The applicability of isotropic simplification under different degrees of deformation is investigated, and the fundamental causes of errors are analyzed. Ultimately, the error response of the material simplified model is obtained. This provides an error reduction scheme for subsequent research using the isotropic simplified model. Full article

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25 pages, 2357 KB

Open AccessArticle

Gradient-Based Calibration of a Precipitation Hardening Model for 6xxx Series Aluminium Alloys

by Amir Alizadeh, Maaouia Souissi, Mian Zhou and Hamid Assadi

Metals 2025, 15(9), 1035; https://doi.org/10.3390/met15091035 - 19 Sep 2025

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Abstract

Precipitation hardening is the primary mechanism for strengthening 6xxx series aluminium alloys. The characteristics of the precipitates play a crucial role in determining the mechanical properties. In particular, predicting yield strength (YS) based on microstructure is experimentally complex and costly because its key [...] Read more.

Precipitation hardening is the primary mechanism for strengthening 6xxx series aluminium alloys. The characteristics of the precipitates play a crucial role in determining the mechanical properties. In particular, predicting yield strength (YS) based on microstructure is experimentally complex and costly because its key variables, such as precipitate radius, spacing, and volume fraction (VF), are difficult to measure. Physics-based models have emerged to tackle these complications utilising advancements in simulation environments. Nevertheless, pure physics-based models require numerous free parameters and ongoing debates over governing equations. Conversely, purely data-driven models struggle with insufficient datasets and physical interpretability. Moreover, the complex dynamics between internal model variables has led both approaches to adopt heuristic optimisation methods, such as the Powell or Nelder–Mead methods, which fail to exploit valuable gradient information. To overcome these issues, we propose a gradient-based optimisation for the Kampmann–Wagner Numerical (KWN) model, incorporating CALPHAD (CALculation of PHAse Diagrams) and a strength model. Our modifications include facilitating differentiability via smoothed approximations of conditional logic, optimising non-linear combinations of free parameters, and reducing computational complexity through a single size-class assumption. Model calibration is guided by a mean squared error (MSE) loss function that aligns the YS predictions with interpolated experimental data using L2 regularisation for penalising deviations from a purely physics-based modelling structure. A comparison shows that the gradient-based adaptive moment estimation (ADAM) outperforms the gradient-free Powell and Nelder–Mead methods by converging faster, requiring fewer evaluations, and yielding more physically plausible parameters, highlighting the importance of calibration techniques in the modelling of 6xxx series precipitation hardening. Full article

(This article belongs to the Special Issue Modeling Thermodynamic Systems and Optimizing Metallurgical Processes)

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23 pages, 4917 KB

Open AccessArticle

Kinetics of the Reduction of Iron Ore Pellets with Hydrogen: A Parametric Experimental and Modeling Study

by Antoine Marsigny, Jean-Baptiste Letz, Olivier Mirgaux and Fabrice Patisson

Metals 2025, 15(9), 1034; https://doi.org/10.3390/met15091034 - 18 Sep 2025

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Abstract

The direct reduction of iron ore by hydrogen is a serious candidate for reducing greenhouse gas emissions in the iron and steelmaking industry by replacing traditional blast furnace technology. The reduction kinetics are key to this process. The present paper reports an extensive [...] Read more.

The direct reduction of iron ore by hydrogen is a serious candidate for reducing greenhouse gas emissions in the iron and steelmaking industry by replacing traditional blast furnace technology. The reduction kinetics are key to this process. The present paper reports an extensive parametric study of the reduction of iron ore pellets with hydrogen that combines both experiments and modeling. A new model (modified grainy pellet model) was developed on the basis of the grainy pellet concept, the law of additive reaction times and the evolution of gas composition. The chemical kinetic constants of the three-step reduction reaction were determined from isothermal thermogravimetry experiments in the 600–900 °C temperature range. The model was then validated against laboratory-scale fixed-bed experimental results. A comparison with the experimental thermogravimetry results for a broad range of operating parameters shows the robustness of the model. The effects of temperature, gas dilution, gas flow rate, water content, pellet size, pressure, porosity, tortuosity, and specific surface area were investigated. The temperature, pellet size, pressure, gas composition and, particularly, the water content and gas flow rate have major influences on the reaction rate, in contrast to the initial porosity and specific surface area. Full article

(This article belongs to the Special Issue Recent Developments and Research on Ironmaking and Steelmaking)

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19 pages, 30585 KB

Open AccessArticle

Microstructure and Mechanical Properties of Ti35421 Alloy: A Comparison Between Laser Directed Energy Deposition (L-DED) and Rolling

by Zulei Liang, Bin Li, Jie Jiang, Hai Gu, Zhonggang Sun and Xianxiang Lu

Metals 2025, 15(9), 1033; https://doi.org/10.3390/met15091033 - 18 Sep 2025

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Abstract

In this study, the newly developed Ti35421 (Ti3Al5Mo4Cr2Zr1Fe wt.%) alloy was prepared by laser directed energy deposition (L-DED) because it contains several major elements that can refine grains, which is expected to enable the transformation from columnar to equiaxed grains. The results show [...] Read more.

In this study, the newly developed Ti35421 (Ti3Al5Mo4Cr2Zr1Fe wt.%) alloy was prepared by laser directed energy deposition (L-DED) because it contains several major elements that can refine grains, which is expected to enable the transformation from columnar to equiaxed grains. The results show that the L-DED Ti35421 alloy is predominantly composed of equiaxed grains and features various α-phase morphologies, including grain boundary α, lath α, and acicular α′ structures. These microstructural features are attributed to the rapid cooling conditions during processing. Such a microstructure enhances the alloy’s tensile strength (1446 MPa) while leading to limited ductility (1.7%). Following the solution and aging treatment, the grain boundary α phase undergoes coarsening, while the matrix β phase transforms into numerous fine lamellar α phases. This leads to a reduction in strength but an improvement in ductility. Therefore, the optimal heat treatment process for the L-DED Ti35421 alloy is determined to be a two-stage procedure: first, heating at 780 °C for 2 h followed by air cooling, and subsequently heating at 575 °C for 8 h with air cooling. Under this treatment, the alloy exhibits excellent mechanical properties, including a tensile strength of 1196 MPa, a yield strength of 1162 MPa, an elongation of 6.8%, and a reduction in area of 16.7%. Since there are no continuous grain boundaries in α, the rolled Ti35421 alloy exhibits better ductility than the L-DED Ti35421 alloy. This article is a revised and expanded version of a poster presentation entitled “Microstructure and mechanical properties of Ti-3Al-5Mo-4Cr-2Zr-1Fe alloy fabricated by laser deposition manufacturing”, which was accepted and presented at the 15th World Conference on Titanium (Ti-2023), Edinburgh, UK, 12–16 June 2023. Full article

(This article belongs to the Special Issue Additive Manufactured Metal Structural Materials)

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16 pages, 13876 KB

Open AccessArticle

Effect of Electrochemical Hydrogen Charging on the Notch Tensile Properties of Natural Gas Transportation Pipeline Steel with Electroless-Plated Coatings and Their Adhesiveness Characterization

by Ladislav Falat, Lucia Čiripová, Viktor Puchý, Ivan Petrišinec and Róbert Džunda

Metals 2025, 15(9), 1032; https://doi.org/10.3390/met15091032 - 18 Sep 2025

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Abstract

Traditional natural gas transportation pipeline steels, such as API 5L X42 grade and the higher grades, are currently receiving a lot of attention in terms of their potential implementation in hydrogen transmission infrastructure. However, the microstructural constitution of steels with a ferrite phase [...] Read more.

Traditional natural gas transportation pipeline steels, such as API 5L X42 grade and the higher grades, are currently receiving a lot of attention in terms of their potential implementation in hydrogen transmission infrastructure. However, the microstructural constitution of steels with a ferrite phase and the presence of welds, with their non-polyhedral “sharp” microstructures acting as structural notches, make these steels prone to hydrogen embrittlement (HE). In this work, the notch tensile properties of copper- or nickel–phosphorus-coated API 5L X42 grade pipeline steel were studied in both the non-hydrogenated and electrochemically hydrogen-charged conditions in order to estimate anticipated protective effects of the coatings against HE. Both the Cu and Ni–P coatings were produced using conventional coating solutions for electroless plating. To study the material systems’ HE sensitivity, electrochemical hydrogenation of cylindrical, circumferentially V-notched tensile specimens was performed in a solution of hydrochloric acid with the addition of hydrazine sulfate. Notch tensile tests were carried out for the uncoated steel, Cu-coated steel, and Ni–P-coated steel at room temperature. The HE resistance was evaluated by determination of the hydrogen embrittlement index (HEI) in terms of relative changes in notch tensile properties related to the non-hydrogenated and hydrogen-charged material conditions. The results showed that pure electroless deposition of both coatings induced some degree of HE, likely due to the presence of hydrogen ions in the coating solutions used and the lower surface quality of the coatings. However, after the electrochemical hydrogen charging, the coated systems showed improved HE resistance (lower HEI_RA values) compared with the uncoated material. This behavior was accompanied by the hydrogen-induced coatings’ deterioration, including the occurrence of superficial defects, such as bubbling, flocks, and spallation. Thus, further continuing research is needed to improve the coatings’ surface quality and long-term durability, including examination of their performance under pressurized hydrogen gas charging conditions. Full article

(This article belongs to the Special Issue Hydrogen Embrittlement of Metals: Behaviors and Mechanisms)

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2 pages, 416 KB

Open AccessCorrection

Correction: Ou et al. Manufacturing and Characterization of NiTi Alloy with Functional Properties by Selective Laser Melting. Metals 2018, 8, 342

by Shih-Fu Ou, Bou-Yue Peng, Yi-Cheng Chen and Meng-Hsiu Tsai

Metals 2025, 15(9), 1031; https://doi.org/10.3390/met15091031 - 18 Sep 2025

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Abstract

In the original publication [...] Full article

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13 pages, 2169 KB

Open AccessArticle

Controlled Formation of Nanoislands During Microwave Annealing of Au Thin Films

by Ali Ghanim Gatea Al-Rubaye, Alaa Alasadi, Khalid Rmaydh Muhammed and Catalin-Daniel Constantinescu

Metals 2025, 15(9), 1030; https://doi.org/10.3390/met15091030 - 18 Sep 2025

Viewed by 328

Abstract

We present a systematic study on the fabrication of gold nanoislands by microwave-assisted annealing, a rapid and energy-efficient alternative to conventional thermal treatments. Gold thin films with nominal thicknesses of 4, 5, 6, 8, and 10 nm are deposited by thermal evaporation directly [...] Read more.

We present a systematic study on the fabrication of gold nanoislands by microwave-assisted annealing, a rapid and energy-efficient alternative to conventional thermal treatments. Gold thin films with nominal thicknesses of 4, 5, 6, 8, and 10 nm are deposited by thermal evaporation directly onto BK7 glass substrates, with and without a 3 nm chromium adhesion layer. The samples are subsequently annealed in a microwave kiln, where microwave irradiation is absorbed and converted to heat within the graphite-coated cavity (kiln), allowing the substrate temperature to exceed 550 °C, the threshold required for film dewetting. This process induces a controlled morphological evolution from continuous thin films to well-defined nanoislands, with the final size distribution strongly dependent on the initial film thickness. Compared with oven-based annealing, microwave treatment promotes faster and more uniform heating, which enhances atomic diffusion and accelerates dewetting while reducing the risk of substrate deformation or excessive coalescence. The resulting nanoislands exhibit tailored size-dependent plasmonic properties, with clear correlations between film thickness, crystallite size, and optical absorption features. Importantly, the method is cost-efficient, requiring shorter processing times and lower energy input, while enabling reproducible fabrication of high-quality plasmonic nanostructures on inexpensive glass substrates, suitable for applications in sensing, photonics, and nanophotonics. Full article

(This article belongs to the Special Issue Metallic Nanostructured Materials and Thin Films)

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Metals, Volume 15, Issue 9 (September 2025) – 132 articles

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