Metals

25 pages, 19715 KiB

Open AccessArticle

Microstructure, Mechanical Properties, and Magnetic Properties of 430 Stainless Steel: Effect of Critical Cold Working Rate and Heat Treatment Atmosphere

by Che-Wei Lu, Fei-Yi Hung and Tsung-Wei Chang

Metals 2025, 15(8), 868; https://doi.org/10.3390/met15080868 (registering DOI) - 2 Aug 2025

Abstract

430 stainless steel exhibits soft magnetic properties, excellent formability, and corrosion resistance, making it widely used in industrial applications. This study investigates the effects of different cold working rates on the properties of 430 stainless steel subjected to various magnetic annealing atmospheres (F-1.5Si, [...] Read more.

430 stainless steel exhibits soft magnetic properties, excellent formability, and corrosion resistance, making it widely used in industrial applications. This study investigates the effects of different cold working rates on the properties of 430 stainless steel subjected to various magnetic annealing atmospheres (F-1.5Si, F-1.5Si-10%, F-1.5Si-40%, F-1.5Si-10% (MA), F-1.5Si-40% (MA), F-1.5Si-10% (H₂), and F-1.5Si-40% (H₂)). The results indicate that increasing the cold working rate improves the material’s mechanical properties; however, it negatively impacts its magnetic and corrosion resistance properties. Additionally, the magnetic annealing process improves the mechanical properties, while atmospheric magnetic annealing optimizes the overall magnetic performance. In contrast, magnetic annealing in a hydrogen atmosphere does not enhance the magnetic properties as effectively as atmospheric magnetic annealing. Still, it promotes the formation of a protective layer, preserving the mechanical properties and providing better corrosion resistance. Furthermore, regardless of whether magnetic annealing is conducted in an atmospheric or hydrogen environment, materials with 10% cold work rate (F-1.5Si-10% (MA) and F-1.5Si-10% (H₂)) exhibit the lowest coercive force (286 and 293 A/m in the 10 Hz test condition), making them ideal for electromagnetic applications. Full article

(This article belongs to the Special Issue Heat Treatment and Mechanical Behavior of Steels and Alloys)

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19 pages, 5488 KiB

Open AccessArticle

Treatment of Recycled Metallurgical By-Products for the Recovery of Fe and Zn Through a Plasma Reactor and RecoDust

by Wolfgang Reiter, Loredana Di Sante, Vincenzo Pepe, Marta Guzzon and Klaus Doschek-Held

Metals 2025, 15(8), 867; https://doi.org/10.3390/met15080867 (registering DOI) - 1 Aug 2025

Abstract

The 1.9 billion metric tons of steel globally manufactured in 2023 justify the steel industry’s pivotal role in modern society’s growth. Considering the rapid development of countries that have not fully taken part in the global market, such as Africa, steel production is [...] Read more.

The 1.9 billion metric tons of steel globally manufactured in 2023 justify the steel industry’s pivotal role in modern society’s growth. Considering the rapid development of countries that have not fully taken part in the global market, such as Africa, steel production is expected to increase in the next decade. However, the environmental burden associated with steel manufacturing must be mitigated to achieve sustainable production, which would align with the European Green Deal pathway. Such a burden is associated both with the GHG emissions and with the solid residues arising from steel manufacturing, considering both the integrated and electrical routes. The valorisation of the main steel residues from the electrical steelmaking is the central theme of this work, referring to the steel electric manufacturing in the Dalmine case study. The investigation was carried out from two different points of view, comprising the action of a plasma electric reactor and a RecoDust unit to optimize the recovery of iron and zinc, respectively, being the two main technologies envisioned in the EU-funded research project ReMFra. This work focuses on those preliminary steps required to detect the optimal recipes to consider for such industrial units, such as thermodynamic modelling, testing the mechanical properties of the briquettes produced, and the smelting trials carried out at pilot scale. However, tests for the usability of the dusty feedstock for RecoDust are carried out, and, with the results, some recommendations for pretreatment can be made. The outcomes show the high potential of these streams for metal and mineral recovery. Full article

(This article belongs to the Special Issue Recent Advances in the Recycling and Reuse of Metallurgical Wastes and By-Products)

25 pages, 7708 KiB

Open AccessReview

A Review of Heat Transfer and Numerical Modeling for Scrap Melting in Steelmaking Converters

by Mohammed B. A. Hassan, Florian Charruault, Bapin Rout, Frank N. H. Schrama, Johannes A. M. Kuipers and Yongxiang Yang

Metals 2025, 15(8), 866; https://doi.org/10.3390/met15080866 (registering DOI) - 1 Aug 2025

Abstract

Steel is an important product in many engineering sectors; however, steelmaking remains one of the largest

{CO}_{2}

emitters. Therefore, new governmental policies drive the steelmaking industry toward a cleaner and more sustainable operation such as the gas-based direct reduction–electric arc furnace process. [...] Read more.

Steel is an important product in many engineering sectors; however, steelmaking remains one of the largest

{CO}_{2}

emitters. Therefore, new governmental policies drive the steelmaking industry toward a cleaner and more sustainable operation such as the gas-based direct reduction–electric arc furnace process. To become carbon neutral, utilizing more scrap is one of the feasible solutions to achieve this goal. Addressing knowledge gaps regarding scrap heterogeneity (size, shape, and composition) is essential to evaluate the effects of increased scrap ratios in basic oxygen furnace (BOF) operations. This review systematically examines heat and mass transfer correlations relevant to scrap melting in BOF steelmaking, with a focus on low Prandtl number fluids (thick thermal boundary layer) and dense particulate systems. Notably, a majority of these correlations are designed for fluids with high Prandtl numbers. Even for the ones tailored for low Prandtl, they lack the introduction of the porosity effect which alters the melting behavior in such high temperature systems. The review is divided into two parts. First, it surveys heat transfer correlations for single elements (rods, spheres, and prisms) under natural and forced convection, emphasizing their role in predicting melting rates and estimating maximum shell size. Second, it introduces three numerical modeling approaches, highlighting that the computational fluid dynamics–discrete element method (CFD–DEM) offers flexibility in modeling diverse scrap geometries and contact interactions while being computationally less demanding than particle-resolved direct numerical simulation (PR-DNS). Nevertheless, the review identifies a critical gap: no current CFD–DEM framework simultaneously captures shell formation (particle growth) and non-isotropic scrap melting (particle shrinkage), underscoring the need for improved multiphase models to enhance BOF operation. Full article

(This article belongs to the Special Issue Advanced Simulation and Modeling Technologies of Metallurgical Processes—2nd Edition)

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11 pages, 5112 KiB

Open AccessArticle

Fabrication of a Porous TiNi₃ Intermetallic Compound to Enhance Anti-Corrosion Performance in 1 M KOH

by Zhenli He, Yue Qiu, Yuehui He, Qian Zhao, Zhonghe Wang and Yao Jiang

Metals 2025, 15(8), 865; https://doi.org/10.3390/met15080865 (registering DOI) - 1 Aug 2025

Abstract

Porous intermetallic compounds have the properties of porous materials as well as a combination of covalent and metallic bonds, and they exhibit high porosity, structural stability, and corrosion resistance. In this work, a porous TiNi₃ intermetallic compound was fabricated through reactive synthesis [...] Read more.

Porous intermetallic compounds have the properties of porous materials as well as a combination of covalent and metallic bonds, and they exhibit high porosity, structural stability, and corrosion resistance. In this work, a porous TiNi₃ intermetallic compound was fabricated through reactive synthesis of elemental powders. Next, detailed studies of its phase composition and pore structure characteristics at different sintering temperatures, as well as its corrosion behavior against an alkaline environment, were carried out. The results show that the as-prepared porous TiNi₃ intermetallic compound has abundant pore structures, with an open porosity of 56.5%, which can be attributed to a combination of the bridging effects of initial powder particles and the Kirkendall effect occurring during the sintering process. In 1 M KOH solution, a higher positive corrosion potential (−0.979 V_SCE) and a lower corrosion current density (1.18 × 10⁻⁴ A∙cm⁻²) were exhibited by the porous TiNi₃ intermetallic compound, compared to the porous Ni, reducing the thermodynamic corrosion tendency and the corrosion rate. The corresponding corrosion process is controlled by the charge transfer process, and the increased charge transfer resistance value (713.9 Ω⋅cm²) of TiNi₃ makes it more difficult to charge-transfer than porous Ni (204.5 Ω⋅cm²), thus decreasing the rate of electrode reaction. The formation of a more stable passive film with the incorporation of Ti contributes to this improved corrosion resistance performance. Full article

(This article belongs to the Special Issue Advanced Ti-Based Alloys and Ti-Based Materials)

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14 pages, 6773 KiB

Open AccessArticle

MoTiCo Conversion Coating on 7075 Aluminium Alloy Surface: Preparation, Corrosion Resistance Analysis, and Application in Outdoor Sports Equipment Trekking Poles

by Yiqun Wang, Feng Huang and Xuzheng Qian

Metals 2025, 15(8), 864; https://doi.org/10.3390/met15080864 (registering DOI) - 1 Aug 2025

Abstract

The problem of protecting 7075 Al alloy trekking poles from corrosion in complex outdoor environments was addressed using a composite conversion coating system. This system comprised Na₂MoO₄, NaF, CoSO₄·7H₂O, ethylenediaminetetraacetic acid-2Na, and H₂(TiF [...] Read more.

The problem of protecting 7075 Al alloy trekking poles from corrosion in complex outdoor environments was addressed using a composite conversion coating system. This system comprised Na₂MoO₄, NaF, CoSO₄·7H₂O, ethylenediaminetetraacetic acid-2Na, and H₂(TiF₆). The influences of this system on the properties of the coating layer were systematically studied by adjusting the pH of the coating solution. The conversion temperature and pH were the pivotal parameters influencing the formation of the conversion coating. The pH substantially influenced the compactness of the coating layer, acting as a regulatory agent of the coating kinetics. When the conversion temperature and pH were set to 40 °C and 3.8, respectively, the prepared coating layer displayed optimal performance in terms of compactness and protective properties. Therefore, this parameter combination favours the synthesis of high-performance conversion coatings. Microscopy confirmed the formation of a continuous, dense composite oxide film structure under these conditions, effectively blocking erosion in corrosive media. Furthermore, the optimised process led to substantial enhancements in the environmental adaptabilities and service lives of the components of trekking poles, thus establishing a theoretical foundation and technical reference for use in the surface protection of outdoor equipment. Full article

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20 pages, 15301 KiB

Open AccessArticle

Application of CH241 Stainless Steel with High Concentration of Mn and Mo: Microstructure, Mechanical Properties, and Tensile Fatigue Life

by Ping-Yu Hsieh, Bo-Ding Wu and Fei-Yi Hung

Metals 2025, 15(8), 863; https://doi.org/10.3390/met15080863 (registering DOI) - 1 Aug 2025

Abstract

A novel stainless steel with high Mn and Mo content (much higher than traditional stainless steel), designated CH241SS, was developed as a potential replacement for Cr-Mo-V alloy steel in the cold forging applications of precision industry. Through carbon reduction in an environmentally friendly [...] Read more.

A novel stainless steel with high Mn and Mo content (much higher than traditional stainless steel), designated CH241SS, was developed as a potential replacement for Cr-Mo-V alloy steel in the cold forging applications of precision industry. Through carbon reduction in an environmentally friendly manner and a two-stage heat treatment process, the hardness of as-cast CH241 was tailored from HRC 37 to HRC 29, thereby meeting the industrial specifications of cold-forged steel (≤HRC 30). X-ray diffraction analysis of the as-cast microstructure revealed the presence of a small amount of ferrite, martensite, austenite, and alloy carbides. After heat treatment, CH241 exhibited a dual-phase microstructure consisting of ferrite and martensite with dispersed Cr(Ni-Mo) alloy carbides. The CH241 alloy demonstrated excellent high-temperature stability. No noticeable softening occurred after 72 h for the second-stage heat treatment. Based on the mechanical and room-temperature tensile fatigue properties of CH241-F (forging material) and CH241-ST (soft-tough heat treatment), it was demonstrated that the CH241 stainless steel was superior to the traditional stainless steel 4xx in terms of strength and fatigue life. Therefore, CH241 stainless steel can be introduced into cold forging and can be used in precision fatigue application. The relevant data include composition design and heat treatment properties. This study is an important milestone in assisting the upgrading of the vehicle and aerospace industries. Full article

(This article belongs to the Special Issue Advanced High Strength Steels: Properties and Applications)

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19 pages, 2806 KiB

Open AccessArticle

Operating Solutions to Improve the Direct Reduction of Iron Ore by Hydrogen in a Shaft Furnace

by Antoine Marsigny, Olivier Mirgaux and Fabrice Patisson

Metals 2025, 15(8), 862; https://doi.org/10.3390/met15080862 (registering DOI) - 1 Aug 2025

Abstract

The production of iron and steel plays a significant role in the anthropogenic carbon footprint, accounting for 7% of global GHG emissions. In the context of CO₂ mitigation, the steelmaking industry is looking to potentially replace traditional carbon-based ironmaking processes with hydrogen-based [...] Read more.

The production of iron and steel plays a significant role in the anthropogenic carbon footprint, accounting for 7% of global GHG emissions. In the context of CO₂ mitigation, the steelmaking industry is looking to potentially replace traditional carbon-based ironmaking processes with hydrogen-based direct reduction of iron ore in shaft furnaces. Before industrialization, detailed modeling and parametric studies were needed to determine the proper operating parameters of this promising technology. The modeling approach selected here was to complement REDUCTOR, a detailed finite-volume model of the shaft furnace, which can simulate the gas and solid flows, heat transfers and reaction kinetics throughout the reactor, with an extension that describes the whole gas circuit of the direct reduction plant, including the top gas recycling set up and the fresh hydrogen production. Innovative strategies (such as the redirection of part of the bustle gas to a cooling inlet, the use of high nitrogen content in the gas, and the introduction of a hot solid burden) were investigated, and their effects on furnace operation (gas utilization degree and total energy consumption) were studied with a constant metallization target of 94%. It has also been demonstrated that complete metallization can be achieved at little expense. These strategies can improve the thermochemical state of the furnace and lead to different energy requirements. Full article

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

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3 pages, 146 KiB

Open AccessEditorial

Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods

by Stefano Ubaldini

Metals 2025, 15(8), 861; https://doi.org/10.3390/met15080861 (registering DOI) - 1 Aug 2025

Abstract

Raw materials (RMs) are crucial to the world economy [...] Full article

(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)

12 pages, 3212 KiB

Open AccessArticle

Microstructure and Properties of Dissoluble LA141-0.5Cu Magnesium Alloy Wires Applied to Oil and Gas Resource Exploitation

by Qiang Sun, Jianjun Xue, Yang Shi, Dingwei Weng, Shaolin Zhang, Ran Wei, Zheng Tong and Jie Qian

Metals 2025, 15(8), 860; https://doi.org/10.3390/met15080860 (registering DOI) - 31 Jul 2025

Abstract

Mg-Li-based dissoluble metal is a promising material for preparing dissoluble magnesium alloy wires. However, there are few reports on the development of Mg-Li dissoluble magnesium alloy wires so far. In this paper, the mechanical properties and dissoluble properties of as-drawn and annealed LA141-0.5Cu [...] Read more.

Mg-Li-based dissoluble metal is a promising material for preparing dissoluble magnesium alloy wires. However, there are few reports on the development of Mg-Li dissoluble magnesium alloy wires so far. In this paper, the mechanical properties and dissoluble properties of as-drawn and annealed LA141-0.5Cu wires were investigated in detail. It was found that the tensile strength of the LA141-0.5Cu wires decreased from 160 MPa to 127 MPa and the elongation increased from 17% to 22% after annealing. The difference in corrosion rates (93 °C/3% KCl solution) between the as-drawn wires and annealed wires is not significant, with values of 5.1 mg·cm⁻²·h⁻¹ and 4.5 mg·cm⁻²·h⁻¹, respectively. This can be explained as follows: after annealing, the number of dislocations in the wire decreases, the strength decreases, and the plasticity increases. The reason why the wires have a significant corrosion rate is that there is a large potential difference between the Cu-containing second phase and the magnesium matrix, which forms galvanic corrosion. The decrease in dislocation density after annealing leads to a slight reduction in the corrosion rate of the wires. This work provides a qualified material for fabricating temporary blocking knots for the exploitation of unconventional oil and gas resources. Full article

19 pages, 9155 KiB

Open AccessArticle

Microstructure Evolution in Homogenization Heat Treatment of Inconel 718 Manufactured by Laser Powder Bed Fusion

by Fang Zhang, Yifu Shen and Haiou Yang

Metals 2025, 15(8), 859; https://doi.org/10.3390/met15080859 (registering DOI) - 31 Jul 2025

Abstract

This study systematically investigates the homogenization-induced Laves phase dissolution kinetics and recrystallization mechanisms in laser powder bed fusion (L-PBF) processed IN718 superalloy. The as-built material exhibits a characteristic fine dendritic microstructure with interdendritic Laves phase segregation and high dislocation density, featuring directional sub-grain [...] Read more.

This study systematically investigates the homogenization-induced Laves phase dissolution kinetics and recrystallization mechanisms in laser powder bed fusion (L-PBF) processed IN718 superalloy. The as-built material exhibits a characteristic fine dendritic microstructure with interdendritic Laves phase segregation and high dislocation density, featuring directional sub-grain boundaries aligned with the build direction. Laves phase dissolution demonstrates dual-stage kinetics: initial rapid dissolution (0–15 min) governed by bulk atomic diffusion, followed by interface reaction-controlled deceleration (15–60 min) after 1 h at 1150 °C. Complete dissolution of the Laves phase is achieved after 3.7 h at 1150 °C. Recrystallization initiates preferentially at serrated grain boundaries through boundary bulging mechanisms, driven by localized orientation gradients and stored energy differentials. Grain growth kinetics obey a fourth-power time dependence, confirming Ostwald ripening-controlled boundary migration via grain boundary diffusion. Such a study is expected to be helpful in understanding the microstructural development of L-PBF-built IN718 under heat treatments. Full article

(This article belongs to the Section Additive Manufacturing)

16 pages, 4530 KiB

Open AccessArticle

A Novel Selective Oxygen Pressure Leaching for Zinc Extraction from Hemimorphite in Acid-Free Solutions

by Tong Wang, Yubo Zeng, Shuang Zhang, Chen Chen, Yang Li, Wenhui Ma and Hongwei Ni

Metals 2025, 15(8), 858; https://doi.org/10.3390/met15080858 (registering DOI) - 31 Jul 2025

Abstract

A novel acid-free oxygen pressure leaching for the extraction of zinc from hemimorphite was proposed in this study. Green vitriol (FeSO₄·7H₂O), as one of the important industrial by-products, was used as the leaching reagent to separate zinc from silicon [...] Read more.

A novel acid-free oxygen pressure leaching for the extraction of zinc from hemimorphite was proposed in this study. Green vitriol (FeSO₄·7H₂O), as one of the important industrial by-products, was used as the leaching reagent to separate zinc from silicon and iron. The effect of leaching conditions, including Fe/Zn molar ratio, leaching temperature, pressure, and reaction time, on the leaching efficiency of zinc, Fe, and Si was investigated systematically. The results showed that the molar ratio of Fe/Zn and leaching temperature play a pivotal role in determining the leaching efficiency rate of Zn. Under the optimized leaching conditions (Fe/Zn molar ratio = 6:1, 150 °C, 1.8 × 10⁶ Pa, and leaching time of 2 h), the leaching efficiency of Zn reached 98.80% and the leaching efficiencies of Fe and Si were 0.76% and 16.80%, respectively. In addition, the shrinking core model was established to represent the relationship between the rate control step and the leaching conditions. The leaching process was controlled by chemical reaction and diffusion, and the activation energy of the leaching process is 97.14 kJ/mol. Full article

(This article belongs to the Special Issue Separation, Reduction, and Metal Recovery in Slag Metallurgy)

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15 pages, 6090 KiB

Open AccessArticle

Vacuum Brazing of 6061 Aluminum Using Al-Si-Ge Filler Metals with Different Si Contents

by Sen Huang, Jiguo Shan, Jian Qin, Yuanxun Shen, Chao Jiang and Peiyao Jing

Metals 2025, 15(8), 857; https://doi.org/10.3390/met15080857 (registering DOI) - 31 Jul 2025

Abstract

Al-xSi-35Ge (x = 4, 6, 8, 10, 12, wt.%) filler metals were prepared to vacuum braze 6061 aluminum alloy. The wettability of filler metals was studied. A thermodynamics model of the Al-Si-Ge ternary alloy was established to analyze the mechanism and impact of [...] Read more.

Al-xSi-35Ge (x = 4, 6, 8, 10, 12, wt.%) filler metals were prepared to vacuum braze 6061 aluminum alloy. The wettability of filler metals was studied. A thermodynamics model of the Al-Si-Ge ternary alloy was established to analyze the mechanism and impact of Si in the microstructure of the brazed joint. The findings indicated that Si addition had a slight effect on the melting point of Al-xSi-35Ge filler metals. Great molten temperature region of fillers was responsible for the loss of Ge during the wetting process, making residual filler metal difficult to melt. The microstructure of the joint was characterized by a multilayer structure that was primarily composed of three zones: two transition regions (Zone I) and a filler residual region (Zone II). There was liquidation of filler metal for Al-Si-35Ge filler metals during brazing, resulting in holes and cracks in joints. Increasing the Si content in fillers could alleviate the liquidation of filler metal, owing to diminishing difference of chemical potential of Ge (μ_Ge) in fillers and 6061 substrates, hindering the diffusion of Ge from filler metal to substrates. Full article

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22 pages, 15066 KiB

Open AccessArticle

Influence of Shot Peening on Selected Properties of the Surface and Subsurface Regions of Additively Manufactured 316L and AlSi10Mg

by Ali Al-Zuhairi, Patrick Lehner, Bastian Blinn, Marek Smaga, Jonas Flatter, Tilmann Beck and Roman Teutsch

Metals 2025, 15(8), 856; https://doi.org/10.3390/met15080856 - 30 Jul 2025

Abstract

Due to the high potential of shot peening to improve the surface quality of additively manufactured components, in this work, the influence on surface morphology and, thus, the surface topography and selected properties of the surface and subsurface regions of additively manufactured parts [...] Read more.

Due to the high potential of shot peening to improve the surface quality of additively manufactured components, in this work, the influence on surface morphology and, thus, the surface topography and selected properties of the surface and subsurface regions of additively manufactured parts is analysed. For this, cubic specimens made of stainless steel 316L and AlSi10Mg were manufactured via powder bed fusion laser beam metal (PBF-LB/M), and subsequently, their “as-built” surfaces were shot peened. Shot peening was conducted with stainless steel or ceramic beads using pressures of 3 and 5 bar. The resulting morphologies were analysed regarding topography, microstructure and mechanical properties (hardness and cyclic deformation behaviour) in the subsurface region and the residual stresses. The results demonstrate a strong plastic deformation due to shot peening, resulting in a decreased surface roughness as well as an increased hardness and compressive residual stresses near the surface. These effects were generally more pronounced after using higher peening pressure and/or ceramic beads. Note that two sets of PBF-LB/M parameters were used to produce the AlSi10Mg specimens. The investigation of these specimens reveals an interrelation between the parameters used in shot peening and PBF-LB/M on the resulting surface morphology. Full article

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21 pages, 6163 KiB

Open AccessArticle

Residual Stress and Corrosion Performance in L-PBF Ti6Al4V: Unveiling the Optimum Stress Relieving Temperature via Microcapillary Electrochemical Characterisation

by Lorenzo D’Ambrosi, Katya Brunelli, Francesco Cammelli, Reynier I. Revilla and Arshad Yazdanpanah

Metals 2025, 15(8), 855; https://doi.org/10.3390/met15080855 - 30 Jul 2025

Abstract

This study aims to determine the optimal low-temperature stress relieving heat treatment that minimizes residual stresses while preserving corrosion resistance in Laser Powder Bed Fusion (L-PBF) processed Ti6Al4V alloy. Specifically, it investigates the effects of stress relieving at 400 °C, 600 °C, and [...] Read more.

This study aims to determine the optimal low-temperature stress relieving heat treatment that minimizes residual stresses while preserving corrosion resistance in Laser Powder Bed Fusion (L-PBF) processed Ti6Al4V alloy. Specifically, it investigates the effects of stress relieving at 400 °C, 600 °C, and 800 °C on microstructure, residual stress, and electrochemical performance. Specimens were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical techniques. A novel microcapillary electrochemical method was employed to precisely assess passive layer stability and corrosion behaviour under simulated oral conditions, including fluoride contamination and tensile loading. Results show that heat treatments up to 600 °C effectively reduce residual stress with minimal impact on corrosion resistance. However, 800 °C treatment leads to a phase transformation from α′ martensite to a dual-phase α + β structure, significantly compromising passive film integrity. The findings establish 600 °C as the optimal stress-relieving temperature for balancing mechanical stability and electrochemical performance in biomedical and aerospace components. Full article

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12 pages, 3886 KiB

Open AccessArticle

Effect of W Contents and Annealing Temperatures on the Microstructure and Mechanical Properties of CoFeNi Medium Entropy Alloys

by Yaqi Cui, Huan Ma, Li Yang, Yang Shao and Renguo Guan

Metals 2025, 15(8), 854; https://doi.org/10.3390/met15080854 - 30 Jul 2025

Abstract

In this work, the W element, with a larger atomic radius compared to Co, Fe, and Ni, was added to modify the microstructure and enhance the yield strength of CoFeNi medium entropy alloy (MEA). A detailed study was conducted to clarify the effects [...] Read more.

In this work, the W element, with a larger atomic radius compared to Co, Fe, and Ni, was added to modify the microstructure and enhance the yield strength of CoFeNi medium entropy alloy (MEA). A detailed study was conducted to clarify the effects of W additions and annealing temperatures on the microstructure evolution and mechanical properties of CoFeNiW_x (x = 0, 0.1, and 0.3) MEAs. CoFeNiW_0.1 retained a single FCC structure without the formation of precipitates in the FCC phase, indicating that W, with a larger atomic radius, can completely dissolve in CoFeNiW_0.1. For CoFeNiW_0.3 MEA, coarse particles with an average diameter of ~2 μm appeared after homogenizing. Nevertheless, when the alloy was annealed at 800 °C and 900 °C, fine particles formed, with the average diameters of approximately 144 nm and 225 nm, respectively. After annealing at 800 °C, the CoFeNiW_0.3 with a partially recrystallized microstructure exhibited better comprehensive mechanical properties. Full article

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24 pages, 6760 KiB

Open AccessArticle

Influence of Microstructure and Heat Treatment on the Corrosion Resistance of Mg-1Zn Alloy Produced by Laser Powder Bed Fusion

by Raúl Reyes-Riverol, Ángel Triviño-Peláez, Federico García-Galván, Marcela Lieblich, José Antonio Jiménez and Santiago Fajardo

Metals 2025, 15(8), 853; https://doi.org/10.3390/met15080853 - 30 Jul 2025

Abstract

The corrosion behavior of an additively manufactured Mg-1Zn alloy was investigated in both the transverse and longitudinal directions relative to the build direction, in the as-built condition and after annealing at 350 °C for 24 h under high vacuum. Microstructural characterization using XRD [...] Read more.

The corrosion behavior of an additively manufactured Mg-1Zn alloy was investigated in both the transverse and longitudinal directions relative to the build direction, in the as-built condition and after annealing at 350 °C for 24 h under high vacuum. Microstructural characterization using XRD and SEM revealed the presence of magnesium oxide (MgO) and the absence of intermetallic second-phase particles. Optical microscopy (OM) images and Electron Backscatter Diffraction (EBSD) maps showed a highly complex grain morphology with anomalous, anisotropic shapes and a heterogeneous grain size distribution. The microstructure includes grains with a pronounced columnar morphology aligned along the build direction and is therefore characterized by a strong crystallographic texture. Electrochemical techniques, including PDP and EIS, along with gravimetric H₂ collection, concluded that the transverse plane exhibited greater corrosion resistance compared to the longitudinal plane. Additionally, an increase in cathodic kinetics was observed when comparing as-built with heat-treated samples. Full article

(This article belongs to the Section Corrosion and Protection)

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14 pages, 7356 KiB

Open AccessArticle

Study on Incremental Sheet Forming Performance of AA2024 Aluminum Alloy Based on Adaptive Fuzzy PID Temperature Control

by Zhengfang Li, Zhengyuan Gao, Kaiguo Qian, Lijia Liu, Jiangpeng Song, Shuang Wu, Li Liu and Xinhao Zhai

Metals 2025, 15(8), 852; https://doi.org/10.3390/met15080852 - 30 Jul 2025

Abstract

The development of technology has driven a rising need for high-accuracy and high-efficiency manufacturing of low-volume products. Incremental forming technology, characterized by die-free flexibility and low production costs, can effectively replace stamping processes for manufacturing customized small-batch products. However, high-performance aluminum alloys generally [...] Read more.

The development of technology has driven a rising need for high-accuracy and high-efficiency manufacturing of low-volume products. Incremental forming technology, characterized by die-free flexibility and low production costs, can effectively replace stamping processes for manufacturing customized small-batch products. However, high-performance aluminum alloys generally exhibit poor room-temperature plasticity but excellent high-temperature plasticity, necessitating the integration of thermal-assisted methods for manufacturing such products. However, the temperature of the forming region will excessively rise without temperature control, which will affect the forming performance of the material in hot incremental sheet forming of AA2024-T4 aluminum alloy. This study focuses on AA2024-T4 aluminum alloy and proposes a uniform temperature control method for the electric hot tube-assisted incremental sheet forming process, incorporating an adaptive fuzzy PID algorithm. The temperature difference of the forming region is lower than 6% under the various temperatures. On this basis, the forming limit angle and the microstructure state of the material are analyzed, and the grain feature of the material exhibits significantly refined grains and the uniform fine grain distribution under 180 °C with the temperature control of the adaptive fuzzy PID algorithm. Full article

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

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11 pages, 1053 KiB

Open AccessCommunication

Understanding Room-Temperature Ductility of Bcc Refractory Alloys from Their Atomistic-Level Features

by Jiayi Yan and Cheng Fu

Metals 2025, 15(8), 851; https://doi.org/10.3390/met15080851 - 30 Jul 2025

Abstract

Many bcc refractory alloys show excellent high-temperature mechanical properties, while their fabricability can be limited by brittleness near room temperature. For the purpose of predicting ductile alloys, a number of ductility metrics based on atomic structures and crystal properties, ranging from mechanistic to [...] Read more.

Many bcc refractory alloys show excellent high-temperature mechanical properties, while their fabricability can be limited by brittleness near room temperature. For the purpose of predicting ductile alloys, a number of ductility metrics based on atomic structures and crystal properties, ranging from mechanistic to empirical, have been proposed. In this work, we propose an “average bond stiffness” as a new ductility metric that is also convenient to obtain from first-principles calculations, in addition to using the average magnitude of static displacements of atoms. The usefulness of average bond stiffness is validated by comparing first-principles calculation results to experimental data on the “rhenium effect” in Mo/W-base and V/Nb/Ta-base binary alloys. The average bond stiffness also correlates well with the room-temperature ductility of refractory high-entropy alloys, with a better performance than some ductility metrics previously reported. While in reality the ductility of an alloy can be influenced by many factors, from processing and microstructure, the average magnitude of static displacements and the average bond stiffness are atomistic-level features useful for design of alloy composition towards a desired level of ductility. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Metal Crystal/Polycrystal Plastic Strain Hardening)

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12 pages, 3230 KiB

Open AccessArticle

Cr-Si Alloys with Very Low Impurity Levels Prepared by Optical Floating Zone Technique

by Kilian Sandner, Hung Yen, Jhuo-Lun Lee, Rainer Völkl, An-Chou Yeh and Uwe Glatzel

Metals 2025, 15(8), 850; https://doi.org/10.3390/met15080850 - 29 Jul 2025

Abstract

The optical floating zone technique was utilized to purify chromium and a single-phase chromium–silicon alloy in this work. The impurity content (carbon, nitrogen, and oxygen) can be reduced by decreasing the withdrawal speed of samples during the zone refining process, and the coarsening [...] Read more.

The optical floating zone technique was utilized to purify chromium and a single-phase chromium–silicon alloy in this work. The impurity content (carbon, nitrogen, and oxygen) can be reduced by decreasing the withdrawal speed of samples during the zone refining process, and the coarsening of grains was also observed. The effect of the impurities on mechanical properties was determined by hardness measurements at room temperature, and the hardness of both chromium and the chromium–silicon alloy decreased with lower concentrations of nitrogen and oxygen. In contrast, brittle material behavior is observed in samples prepared by arc melting process with higher concentrations of impurities. To use chromium–silicon alloys for future high-temperature applications, their brittle behavior must be improved, which can be achieved by reducing their carbon, nitrogen, and oxygen concentrations. Full article

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