Metals

20 pages, 7274 KiB

Open AccessArticle

Influence of Hot Deformation Temperature on Grain Size and γ’ Phase in U720Li Alloy After Sub-Solvus Heat Treatment

by Junyi Cheng, Jiangying Xiong, Anping Long, Lei Xiao, Xiangdong Ma, Ganjiang Feng and Jianzheng Guo

Metals 2025, 15(4), 409; https://doi.org/10.3390/met15040409 (registering DOI) - 4 Apr 2025

Abstract

Precise control of forging and heat treatment parameters is essential to achieve microstructural homogeneity in turbine disks, ensuring optimal mechanical performance for aerospace applications. This study examines the influence of the hot deformation temperatures on the grain size and γ’ phase characteristics of [...] Read more.

Precise control of forging and heat treatment parameters is essential to achieve microstructural homogeneity in turbine disks, ensuring optimal mechanical performance for aerospace applications. This study examines the influence of the hot deformation temperatures on the grain size and γ’ phase characteristics of U720Li alloy following subsequent heat treatments. Samples extracted from a hot-extruded U720Li billet were subjected to isothermal compression within the temperature range of 1100–1130 °C, followed by holding at 1100 °C and 1120 °C for 4 h and air cooling. The results demonstrate that increasing the deformation temperature from 1100 °C to 1120 °C reduces the γ’ phase volume fraction at grain boundaries from 13% to 5%, weakens pinning effects, promotes grain growth during deformation, elevates grain boundary energy, and diminishes stored deformation energy, despite maintaining an equivalent degree of dynamic recrystallization. When the sub-solvus heat treatment temperature was 20 °C below the effective deformation temperature, Ostwald ripening dominated, resulting in a multimodal γ’ phase distribution after cooling. Conversely, when the sub-solvus heat treatment temperature 20 °C exceeded the effective deformation temperature, a significant portion of the intergranular γ’ phase dissolved, leaving a bimodal distribution comprising both large- and small-sized particles. Full article

(This article belongs to the Special Issue Characterization, Microstructure and Mechanical Properties of Nickel-Based Superalloys)

42 pages, 3224 KiB

Open AccessReview

Application of Artificial Intelligence to Support Design and Analysis of Steel Structures

by Sina Sarfarazi, Ida Mascolo, Mariano Modano and Federico Guarracino

Metals 2025, 15(4), 408; https://doi.org/10.3390/met15040408 (registering DOI) - 4 Apr 2025

Abstract

In steel structural engineering, artificial intelligence (AI) and machine learning (ML) are improving accuracy, efficiency, and automation. This review explores AI-driven approaches, emphasizing how AI models improve predictive capabilities, optimize performance, and reduce computational costs compared to traditional methods. Inverse Machine Learning (IML) [...] Read more.

In steel structural engineering, artificial intelligence (AI) and machine learning (ML) are improving accuracy, efficiency, and automation. This review explores AI-driven approaches, emphasizing how AI models improve predictive capabilities, optimize performance, and reduce computational costs compared to traditional methods. Inverse Machine Learning (IML) is a major focus since it helps engineers to minimize reliance on iterative trial-and-error by allowing them to identify ideal material properties and geometric configurations depending on predefined performance targets. Unlike conventional ML models that focus mostly on forward predictions, IML helps data-driven design generation, enabling more adaptive engineering solutions. Furthermore, underlined is Explainable Artificial Intelligence (XAI), which enhances model transparency, interpretability, and trust of AI. The paper categorizes AI applications in steel construction based on their impact on design automation, structural health monitoring, failure prediction and performance evaluation throughout research from 1990 to 2025. The review explores challenges such as data limitations, model generalization, engineering reliability, and the need for physics-informed learning while examining AI’s role in bridging research and real-world structural applications. By integrating AI into structural engineering, this work supports the adoption of ML, IML, and XAI in structural analysis and design, paving the way for more reliable and interpretable engineering practices. Full article

(This article belongs to the Special Issue Simulation and Optimization Methods in Machining and Structure/Material Design)

12 pages, 11039 KiB

Open AccessArticle

Microwave Dielectric Behavior of CoTiTa₂O₈-MgNb₂O₆ Composite Ceramics: A Focus on Temperature Stability and Compositional Effects

by Jun Zuo, Haodong Wang, Xiuli Fu and Zhijian Peng

Metals 2025, 15(4), 407; https://doi.org/10.3390/met15040407 (registering DOI) - 4 Apr 2025

Abstract

Microwave dielectric (1 − x)CoTiTa₂O₈-xMgNb₂O₆ composite ceramics (x = 0.625–0.725) were fabricated through a two-step method and sintering techniques. The applied CoTiTa₂O₈ and MgNb₂O₆ powders were both synthesized by calcining [...] Read more.

Microwave dielectric (1 − x)CoTiTa₂O₈-xMgNb₂O₆ composite ceramics (x = 0.625–0.725) were fabricated through a two-step method and sintering techniques. The applied CoTiTa₂O₈ and MgNb₂O₆ powders were both synthesized by calcining stoichiometric mixtures of their respective metal oxides at 1000 °C for 3 h. The optimal sintering parameters were determined using visual high-temperature deformation analysis. The influence of the MgNb₂O₆ content on the phase composition, microstructure, and microwave dielectric properties of the obtained composite ceramics was comprehensively investigated. It was observed that an increase in the MgNb₂O₆ content resulted in a reduction in the dielectric constant (ε_r) and a significant enhancement in the quality factor (Q × f). The ceramics with a compositional value of x = 0.675, sintered at 1193 °C for 4.5 h, demonstrated a near-zero temperature coefficient of the resonant frequency (τ_f), exhibiting optimal microwave dielectric properties: ε_r = 28.4, Q × f = 33,055 GHz, and τ_f = −3.1 ppm/°C. These findings underscore the potential of the present CoTiTa₂O₈-MgNb₂O₆ composite ceramics for advanced microwave applications. Full article

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28 pages, 2422 KiB

Open AccessArticle

Multi-Parameter Optimization and Corrosion Behavior of FeCoNiCrAl HEA Coatings via Laser Cladding

by Rang Chen, ChuanBo Zheng, Han Ma, Guo Yi, Dianchun Ju, Jiming Zhang, Xianjun Hu and Jincheng Wang

Metals 2025, 15(4), 406; https://doi.org/10.3390/met15040406 (registering DOI) - 4 Apr 2025

Abstract

In this study, FeCoNiCrAl high-entropy alloy (HEA) coatings were fabricated on Q235 steel surfaces using laser cladding (LC) to enhance corrosion resistance in harsh environments. The laser processing parameters (laser power, defocus distance, and scanning speed) were optimized using response surface methodology (RSM), [...] Read more.

In this study, FeCoNiCrAl high-entropy alloy (HEA) coatings were fabricated on Q235 steel surfaces using laser cladding (LC) to enhance corrosion resistance in harsh environments. The laser processing parameters (laser power, defocus distance, and scanning speed) were optimized using response surface methodology (RSM), establishing a mathematical model to guide the process. The optimized coatings demonstrated strong metallurgical bonding to the substrate, with a microstructure comprising Al-Ni-rich B2 phases and Cr-Fe-rich BCC phases. Elemental segregation was effectively mitigated as energy density decreased, leading to significant improvements in corrosion resistance. Electrochemical tests in 3.5 wt.% NaCl and 0.5 mol/L H₂SO₄ solutions showed that the optimized coating (laser power: 800 W, scanning speed: 450 mm/min, defocus: −15 mm) exhibited exceptionally low corrosion current densities of 1.78 × 10⁻⁷ A/cm² and 1.07 × 10⁻⁵ A/cm², respectively. The passive film on the optimized coating surface consisted of stable oxides, with low oxygen vacancy densities of 1.937 × 10²³ cm⁻³ in NaCl and 4.967 × 10²¹ cm⁻³ in H₂SO₄, significantly enhancing its resistance to localized and uniform corrosion. These results demonstrate the effectiveness of RSM-based optimization in producing HEA coatings with superior corrosion resistance suitable for applications in highly corrosive environments. Full article

(This article belongs to the Special Issue Advances in Corrosion and Protection of Materials (Third Edition))

22 pages, 24375 KiB

Open AccessArticle

Effect of Heat Treatment on Microstructure and Residual Stress of a Nickel-Cobalt-Based Superalloy Produced by Laser Powder Bed Fusion

by Chengjun Wang, Renren Zheng, Xiaolong Liu, Meijuan Li and Dongfeng Chen

Metals 2025, 15(4), 405; https://doi.org/10.3390/met15040405 (registering DOI) - 4 Apr 2025

Abstract

This study comprehensively evaluates a non-weldable nickel-cobalt-based superalloy fabricated using laser powder bed fusion (LPBF) technology. The investigation systematically examined the impact of heat treatment, specifically solution treatment and solution treatment followed by aging treatment, on the microstructural characteristics and the evolution of [...] Read more.

This study comprehensively evaluates a non-weldable nickel-cobalt-based superalloy fabricated using laser powder bed fusion (LPBF) technology. The investigation systematically examined the impact of heat treatment, specifically solution treatment and solution treatment followed by aging treatment, on the microstructural characteristics and the evolution of residual stress within the alloy. The findings indicated that the as-built Ni-Co-based superalloy predominantly consists of equiaxed crystals and epitaxial columnar crystals, with no formation of the γ′ phase observed. After the solution treatment, the alloy experienced equiaxed columnar crystallization, recrystallization, and grain refinement. Additionally, a significant quantity of γ′ phases within the alloy exhibited a specific arrangement and precipitation. Following the aging treatment, there was an observed increase in the average dimensions of both the γ′ phase and the grains within the alloy. The evolution of residual stress distribution perpendicular to the construction direction in the alloy, both before and following heat treatment, was assessed using the contour method. The results showed that heat treatment progressively diminished the residual stress levels within the alloy. Furthermore, this study discusses the interrelationship between residual stress and the microstructural evolutions of nickel-cobalt-based superalloys throughout the heat treatment process. Full article

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41 pages, 5695 KiB

Open AccessReview

Intermetallic Phase Control in Cast Aluminum Alloys by Utilizing Heterogeneous Nucleation on Oxides

by Gábor Gyarmati and János Erdélyi

Metals 2025, 15(4), 404; https://doi.org/10.3390/met15040404 (registering DOI) - 4 Apr 2025

Abstract

With the increasing demand for premium-quality aluminum alloy castings that can be used as safety-critical structural components, as well as the rising urge to utilize sustainable materials during the manufacturing process, novel technologies need to be developed and implemented during the treatment of [...] Read more.

With the increasing demand for premium-quality aluminum alloy castings that can be used as safety-critical structural components, as well as the rising urge to utilize sustainable materials during the manufacturing process, novel technologies need to be developed and implemented during the treatment of liquid alloys. Impurity and alloying elements accumulate in recycled aluminum alloys, which frequently results in the formation of coarse intermetallic compound (IMC) particles in the microstructure that have a detrimental effect on the ductility of cast products. One successful approach to alleviate this negative effect relies on affecting the phase selection and refinement of IMC phases. A growing body of literature has shown that the crystallization process of IMCs is affected by the native oxide phases present in the liquid alloys. It has also been demonstrated that by appropriate technologies, harmful oxide inclusion (like oxide bifilms) can be transformed into small-sized oxide particles that can be dispersed throughout the liquid alloy to serve as heterogeneous nucleation sites for different phases. In this way, the adverse effects of oxide inclusions and IMCs are simultaneously mitigated. This contribution aims to review the recent progress of experimental and theoretical work related to intermetallic particle refinement by oxide phases. Emerging technological solutions capable of refining intermetallics through transforming harmful oxide inclusions into numerous, well-dispersed heterogeneous nucleation sites are comprehensively reviewed. Besides analyzing the current state of these techniques, this discussion evaluates their future implications and the potential challenges that may arise in their application and development. Full article

(This article belongs to the Special Issue Advanced Metal Casting Processes: Latest Research, Insights, and Challenges)

43 pages, 8525 KiB

Open AccessArticle

Enhanced Corrosion Protection as a Sustainable Approach for Nickel Using Novel FeL Salen Complex: Electrochemical Investigation and DFT Insights

by Hoda Abd El-Shafy Shilkamy, Mohamed Salaheldeen, Arcady Zhukov, R. A. El-Kasaby, Mehran Feizi-Dehnayebi, Mona M. A. Alharas, Hala M. Abo-Dief, Rafat M. El-Khatib and Ahmed M. Abu-Dief

Metals 2025, 15(4), 403; https://doi.org/10.3390/met15040403 (registering DOI) - 3 Apr 2025

Abstract

A novel tera-dentate salen ligand and its Fe(III) complex was synthesized and characterized via several spectroscopic and physicochemical techniques. The corrosion rate inhibition of nickel and its alloys inspired the utilization of the L ligand and its FeL complex as vital and eco-friendly [...] Read more.

A novel tera-dentate salen ligand and its Fe(III) complex was synthesized and characterized via several spectroscopic and physicochemical techniques. The corrosion rate inhibition of nickel and its alloys inspired the utilization of the L ligand and its FeL complex as vital and eco-friendly inhibitors. To assess their effectiveness, both Tafel plot analysis and electrochemical impedance spectroscopy were employed to examine the electrochemical properties of L and the FeL complex. The results show that corrosion current density (I_corr) steadily drops when the additive concentration is increased, but the inhibition efficiency increases. It has been observed that the efficiency of inhibition rises with temperature, particularly at high temperatures (55 °C) when 1 × 10⁻³ M of L and FeL are present as additives, with η = 90.5% and 92.7%, respectively. Additionally, the findings propose that the adsorption mechanism of both L and FeL additive reptiles follows the Langmuir design isotherm. Electrochemical impedance spectroscopy has also verified these findings. DFT calculations were employed to prove the structure of the investigated FeL complex and its activity as a corrosion inhibitor. Full article

(This article belongs to the Special Issue Corrosion and Sustainability: Challenges, Innovations and Future Perspectives in Green Energy)

12 pages, 811 KiB

Open AccessArticle

Numerical Analysis of the Laser Forming Process of Cylindrical Surfaces

by Daniel Cabezas, Diego J. Celentano, Marcela A. Cruchaga, Claudio García-Herrera and Alberto Monsalve

Metals 2025, 15(4), 402; https://doi.org/10.3390/met15040402 (registering DOI) - 3 Apr 2025

Abstract

This research reports on numerical simulations of the multi-pass laser forming process aimed at obtaining cylindrical surfaces from planar AISI 304 stainless-steel sheets. The effect of laser power, scanning speed, and distance between irradiation lines on the thermomechanical material response is assessed, with [...] Read more.

This research reports on numerical simulations of the multi-pass laser forming process aimed at obtaining cylindrical surfaces from planar AISI 304 stainless-steel sheets. The effect of laser power, scanning speed, and distance between irradiation lines on the thermomechanical material response is assessed, with particular emphasis on the final curvature radius, maximum temperature, and final plastic deformation. To this end, a coupled thermomechanical finite element formulation is applied to the analysis of different experimental tests reported in the literature. The predictive capabilities of this model are demonstrated in the analysis of bent parts exhibiting a wide range of curvature radii, whose values were found in this work to inversely correlate with the total line energy input to the workpiece. In such situations, it was found that both the thermal response and the effective plastic strain values obtained in each test correlate directly with the line energy value. Furthermore, the distance between irradiation lines was identified as a key parameter in the formation of cylindrical surfaces, as it significantly influences the displacement and induced deformation. However, no significant impact of this parameter on the effective plastic strain was observed. Full article

(This article belongs to the Special Issue Numerical Modelling of Metal-Forming Processes)

13 pages, 3274 KiB

Open AccessArticle

In-Situ Synthesis of Multiscale Al₂O₃ and AlSi₃Ti₂ Reinforced Al Matrix Composites Based on Al12Si-TiO₂ System

by Pengcheng Yao, Peng Gao, Zunyan Xu, Xianxian Deng and Caiju Li

Metals 2025, 15(4), 401; https://doi.org/10.3390/met15040401 (registering DOI) - 3 Apr 2025

Abstract

In situ particle reinforced aluminum matrix composites have become an important development in the field of materials science due to their unique reinforced structure design and excellent mechanical properties. In this paper, in situ Al₂O₃ and AlSi₃Ti₂ [...] Read more.

In situ particle reinforced aluminum matrix composites have become an important development in the field of materials science due to their unique reinforced structure design and excellent mechanical properties. In this paper, in situ Al₂O₃ and AlSi₃Ti₂ particle reinforced Al12Si matrix composites were prepared via powder metallurgy. The microstructure and mechanical properties of the composites were analyzed systematically. With the increase in TiO₂ content, the grain size of the composites was refined, resulting in the composites exhibiting higher strength. The in situ generated AlSi₃Ti₂ phase has a higher Young’s modulus of elasticity compared to the Si phase. The in situ formed nano-Al₂O₃ and micrometer AlSi₃Ti₂ formed a strong interfacial bonding with the matrix, which ensured a good reinforcement effect. At the same time, the introduction of reinforced particles also changed the texture characteristics of extruded Al12Si, from <001>∥ED of Al12Si to <111>∥ED of composite. As a result, the strength of the Al12Si–7TiO₂ composite was 330 MPa, which is a 120% enhancement compared with that of the matrix. The hardness reached 107 HV, an increase of 80% compared to the matrix. This study can provide a reference value for the design of new multi-particle hybrid reinforced composites to enhance the material properties. Full article

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17 pages, 8882 KiB

Open AccessArticle

Microstructures and Deep-Drawing Properties of Copper–Steel Bimetallic Sheets Fabricated Using an Arc Spray-Rolling Short Process

by Tairan Yao, Jinbiao Bai, Dehao Kong, Ruixiong Zhai, Yuwei Liang, Taihong Huang, Qing Li and Peng Song

Metals 2025, 15(4), 400; https://doi.org/10.3390/met15040400 - 3 Apr 2025

Abstract

Annealing and rolling play critical roles in improving the mechanical properties of arc spraying coatings. In this work, we successfully fabricated copper–steel bimetallic sheets (CSBSs) using an arc spray-rolling short process and achieved excellent internal bonding of the copper coating and improved deep-drawing [...] Read more.

Annealing and rolling play critical roles in improving the mechanical properties of arc spraying coatings. In this work, we successfully fabricated copper–steel bimetallic sheets (CSBSs) using an arc spray-rolling short process and achieved excellent internal bonding of the copper coating and improved deep-drawing of the CSBSs via annealing and rolling synergistic treatment. The results indicate that the microstructure of the copper coating became dense, and the porosity effectively reduced after annealing–rolling–annealing (ARA) treatment. Tight bonding was also observed between the copper coating and steel substrate. The copper coating had a porosity of less than 0.2%, an average grain size of 3.8 μm, and a micro-hardness of 55 HV_0.05. After tensile testing, the As-sprayed coating generated brittle fractures and delamination. The A-R-A coating also displayed elongated dimples, with the majority oriented along the TD direction, and bonded well with the steel substrate. In addition, the As-sprayed coating fell off directly after deep drawing. In contrast, the A-R-A coating did not exhibit cracks and fall off. The fracture mechanism gradually changed from falling off and cracking, to toughness deformation due to the reduced porosity and tighter grain boundaries, and finally to cooperative deformation due to the metallurgical bonding of the sprayed particles and good interface bonding properties. These findings provide guidance and reference for the practical application of thermal spray additive manufacturing. Full article

(This article belongs to the Special Issue Casting Process, Processing Deformation and Microstructure Optimization of Advanced Metallic Materials)

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27 pages, 7550 KiB

Open AccessArticle

Effect of Nano TiO₂ Flux on Depth of Penetration and Mechanical Properties of TIG-Welded SA516 Grade 70 Steel Joints—An Experimental Investigation

by Rakesh Narayanan, Krishnaswamy Rameshkumar, Arangot Sumesh, Balakrishnan Shankar and Dinu Thomas Thekkuden

Metals 2025, 15(4), 399; https://doi.org/10.3390/met15040399 - 3 Apr 2025

Abstract

This research investigates the application of activated tungsten inert gas (A-TIG) welding on boiler grade SA516 Grade 70 carbon steel using nano titanium dioxide (TiO₂) nano flux to enhance weld penetration depth, microstructure, and mechanical properties. A unique flux application technique [...] Read more.

This research investigates the application of activated tungsten inert gas (A-TIG) welding on boiler grade SA516 Grade 70 carbon steel using nano titanium dioxide (TiO₂) nano flux to enhance weld penetration depth, microstructure, and mechanical properties. A unique flux application technique was devised and experiments were carried out. Response Surface Methodology (RSM) was utilized to optimize weld parameters, namely arc length, welding current, and travel speed.The selection between A-TIG and TIG welding significantly influences penetration depth, as A-TIG benefits from arc constriction and elevated current density. The welding speed is crucial for controlling heat input, whereas current and arc length enhance penetration by influencing arc force and energy distribution. Optimizing all three parameters guarantees optimal penetration and weld quality. Microstructural research revealed enhanced mechanical properties in A-TIG weldments, distinguished by acicular ferrite in the fusion zone, which augmented toughness and tensile strength (520 MPa) compared to TIG weldments (470 MPa) and the base metal (480 MPa). Although A-TIG welds exhibited reduced impact toughness (68 J) relative to the base metal (128 J), A-TIG joints had superior ductility. The findings of this research clearly demonstrate the A-TIG welding process improved the depth of penetration and mechanical strength of the weld joints. Full article

(This article belongs to the Section Welding and Joining)

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10 pages, 3169 KiB

Open AccessArticle

Two-Fold Enhancement of Curie Temperature in Monolayer CrI₃ by High Pressure

by Wenxia Su, Dunhui Wang, Dong Wei and Zhenhong Dai

Metals 2025, 15(4), 398; https://doi.org/10.3390/met15040398 - 2 Apr 2025

Abstract

In recent years, the discovery of the two-dimensional (2D) intrinsically ferromagnetic monolayer CrI₃ has opened up promising avenues for the advancement of spintronic devices. Nevertheless, the relatively low Curie temperature poses a significant challenge for practical applications. Herein, we determine changes in [...] Read more.

In recent years, the discovery of the two-dimensional (2D) intrinsically ferromagnetic monolayer CrI₃ has opened up promising avenues for the advancement of spintronic devices. Nevertheless, the relatively low Curie temperature poses a significant challenge for practical applications. Herein, we determine changes in the superexchange interaction of ferromagnetic coupling caused under pressure by using first-principles calculations and Monte Carlo simulations. Based on the superexchange interaction of ferromagnetic coupling, the effect of applying high pressure on the Curie temperature of monolayer CrI₃ is investigated. With a pressure coefficient of 2.0%, the Curie temperature is enhanced to 97.3 K, which is nearly double that of the monolayer CrI₃ without pressure. In addition, the direction of the easy magnetization axis changes from the out-of-plane to the in-plane one when the pressure coefficient is 1.2%. Meanwhile, the band gap of monolayer CrI₃ can be transformed from indirect to direct by applying high pressure. Our work enriches the process of modulating the magnetic and electronic properties of 2D monolayer materials. Full article

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17 pages, 10131 KiB

Open AccessArticle

The Effect of Ti and Mo Microalloying on Hydrogen Embrittlement Resistance of Ultra-High Strength Medium Mn Steel

by Pujunhuan Zhang, Yang Zhao, Jianglong Pan, Weizhuo Hao, Shuyi Wang and Minghui Cai

Metals 2025, 15(4), 397; https://doi.org/10.3390/met15040397 - 1 Apr 2025

Abstract

This study elucidated the effect of Ti–Mo microalloying on the hydrogen embrittlement (HE) resistance and fracture behavior of warm-rolled Fe-5.6Mn-0.16C-1Al (wt%) steel. After intercritical annealing, both steels, i.e., without and with Ti–Mo microalloying, showed ultrafine ferrite (α) and austenite (γ [...] Read more.

This study elucidated the effect of Ti–Mo microalloying on the hydrogen embrittlement (HE) resistance and fracture behavior of warm-rolled Fe-5.6Mn-0.16C-1Al (wt%) steel. After intercritical annealing, both steels, i.e., without and with Ti–Mo microalloying, showed ultrafine ferrite (α) and austenite (γ_R) duplex microstructure. The addition of Ti–Mo to 5.6Mn steel reduces the volume fraction of γ_R, facilitating the formation of (Ti, Mo)C carbides in α phase and further refining the final microstructure. The product of ultimate tensile strength (UTS) and total elongation (TEL) of 5.6MnTiMo can be as high as 35 GPa·% with an ultra-high yield strength of above 1.2 GPa. Furthermore, the addition of Ti–Mo also had a significant effect on the resistance to HE of medium Mn steels. Firstly, the limited (Ti, Mo)C carbides precipitated in γ_R could act as irreversibly trap sites to capture a considerable amount of H, effectively increasing the C_H (Diffusible Hydrogen Content). Additionally, 5.6MnTiMo displayed higher γ_R stability, resulting in a reduced susceptibility to HE. The H-assisted microcracks mainly formed inside γ(α′) and extended along γ(α′) grain boundaries, leading to intergranular cracking and premature fracture. Full article

(This article belongs to the Special Issue Recent Advances in High-Performance Steel)

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19 pages, 5617 KiB

Open AccessArticle

Effect of Leaching on Particle Migration and Pore Structure of Ionic Rare Earth Ores with Different Fine Particle Contents

by Yunzhang Rao, Jiazheng Wan, Shujun Tan, Zhihua Yang, Guozhu Rao, Qiang Huang, Yangjun Xie and Qiande Lai

Metals 2025, 15(4), 396; https://doi.org/10.3390/met15040396 - 1 Apr 2025

Abstract

In in situ leaching, fine particles can be stripped and transported with the leach solution, significantly altering the particle size distribution and pore structure of each layer of the rare earth ore body. In this study, water and magnesium sulfate were used as [...] Read more.

In in situ leaching, fine particles can be stripped and transported with the leach solution, significantly altering the particle size distribution and pore structure of each layer of the rare earth ore body. In this study, water and magnesium sulfate were used as leaching agents. Based on indoor column leaching experiments, particle gradation experiments, and pore structure tests, this study investigates and analyzes the patterns of particle migration and changes in pore structure in rare earth ores with varying fine particle contents under leaching conditions. The results indicate that during the leaching process, the degree of change in particle gradation follows the order of upper layer > middle layer > lower layer. As the depth increases, the soil becomes denser, leading to reduced permeability, a slower seepage rate of the leaching solution, and a higher fine particle content, making the effect more pronounced. During magnesium sulfate leaching, the overall trend of porosity in the rare earth ore structure initially increases and then decreases. Additionally, a higher fine particle content corresponds to higher porosity. In the early and late stages of leaching, pore size changes involve the transformation of larger pores into smaller ones, followed by the conversion of smaller pores into larger ones. Moreover, the higher the fine particle content, the greater the degree of transformation between the pore sizes. Full article

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16 pages, 4993 KiB

Open AccessArticle

Rapid Microwave Irradiation-Enhanced Detoxification and Mineralization of Cr(VI) by FeS₂/ZVI Composites

by Xiaoming Zhang, Haiying Wang, Mengying Si, Qi Liao, Zhihui Yang, Qi Li and Weichun Yang

Metals 2025, 15(4), 395; https://doi.org/10.3390/met15040395 - 1 Apr 2025

Abstract

The rapid detoxification and mineralization of Cr(VI) in aqueous environments hold critical importance for emergency response and resource recovery yet remain technically challenging. Herein, we report the synthesis of FeS₂/ZVI composites through ethanol-assisted wet ball-milling and their application in Cr(VI) removal [...] Read more.

The rapid detoxification and mineralization of Cr(VI) in aqueous environments hold critical importance for emergency response and resource recovery yet remain technically challenging. Herein, we report the synthesis of FeS₂/ZVI composites through ethanol-assisted wet ball-milling and their application in Cr(VI) removal under microwave (MW) irradiation. This study systematically investigates the effects of MW irradiation on the removal efficiency of Cr(VI) using FeS₂/ZVI composites, with particular focus on key parameters including composite dosage, initial pH, MW temperature, and Cr(VI) concentration. Notably, 1 g/L FeS₂/ZVI composites achieved near-complete removal (>99%) of 50 mg/L Cr(VI) within 7 min at a MW irradiation temperature of 333 K, which exhibited 5.9-fold and 13.1-fold superior performance compared to pure pyrite and ZVI, respectively. Additionally, there is a 96.1% reduction in reaction time in comparison to non-MW irradiation system. In real electroplating wastewater samples, Cr(VI) concentration was reduced from 38.93 to 0.42 mg L⁻¹ by MW irradiation-assisted treatment, validating its potential for practical applications in industrial Cr(VI) pollution control. The activation energy determined by fitting the Arrhenius equation showed a 39.7% reduction for the MW-assisted FeS₂/ZVI system (16.0 kJ mol⁻¹) compared to conventional thermal heating (from 25.6 kJ mol⁻¹), indicating that MW irradiation induced catalytic enhancement of FeS₂/ZVI, thereby lowering the energy barrier for Cr(VI) reduction. Moreover, MW irradiation-assisted processes facilitated the mineralization of reduced Cr(III) to stable spinel FeCr₂O₄. These findings collectively establish a synergistic mechanism between MW activation and FeS₂/ZVI composites, offering innovative pathways for efficient Cr(VI) detoxification and resource recovery from high-strength industrial wastewaters. Full article

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26 pages, 6349 KiB

Open AccessArticle

Upset Resistance Welding of a Microcomposite Cu-Nb Conductor for Pulsed Power Applications

by Nikolaj Višniakov, Paulius Beinoras and Oleksandr Kapustynskyi

Metals 2025, 15(4), 394; https://doi.org/10.3390/met15040394 - 1 Apr 2025

Abstract

The present study offers an experimental investigation into the welding of Cu–Nb wire using upset resistance welding. The aim is to examine the structure, as well as the electrical and mechanical properties, of Cu–Nb conductor joints produced by this method, which are intended [...] Read more.

The present study offers an experimental investigation into the welding of Cu–Nb wire using upset resistance welding. The aim is to examine the structure, as well as the electrical and mechanical properties, of Cu–Nb conductor joints produced by this method, which are intended for use in coils in pulsed magnetic systems. Analysis of the joint structure revealed that it was free from welding defects. The welded joint demonstrated a negligible change in electrical resistance while retaining sufficient ultimate strength and plasticity comparable to the base material. The tensile strength of the welded sample was found to be 620 MPa. The heat-affected zone is narrow, and the heating temperature is lower than the melting point of the composite material. Therefore, welding occurs in the solid phase without remelting the Cu–Nb composite wire or destroying its unique microstructure. Thus, upset welding is a promising technology for use in solenoid terminal connections with external electrical circuits that are not directly exposed to the high magnetic or tensile forces generated inside a solenoid of a pulsed magnet system. Full article

(This article belongs to the Section Welding and Joining)

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17 pages, 16960 KiB

Open AccessArticle

Effect of Laser Welding on Performance of the B1500HS/340LA High-Strength Steel

by Heyuan Wang, Yongchuan Duan, Shijun Hao and Yingping Guan

Metals 2025, 15(4), 393; https://doi.org/10.3390/met15040393 - 1 Apr 2025

Abstract

In this study, high-strength steels B1500HS and B340LA were used as base materials, and laser welding experiments were conducted within a parameter range of welding power from 1500 W to 3000 W and welding speed from 15 mm/s to 35 mm/s. Microstructural analysis, [...] Read more.

In this study, high-strength steels B1500HS and B340LA were used as base materials, and laser welding experiments were conducted within a parameter range of welding power from 1500 W to 3000 W and welding speed from 15 mm/s to 35 mm/s. Microstructural analysis, microhardness testing, and uniaxial tensile tests were performed to systematically investigate the effects of different welding parameters on the weld microstructure and macroscopic mechanical properties, leading to the identification of an optimal welding parameter range that avoids defect-prone regions. The bending formability of tailor-welded blanks (TWBs) was evaluated using hat-shaped bending tests, with finite element simulations employed to analyze the effects of welding parameters on stress distribution and material hardening behavior. Based on the identified high-quality welding parameters, a suitable welding parameter range for reverse bending conditions was determined, effectively improving the bending formability of TWBs and providing theoretical guidance and experimental support for their engineering applications. Full article

(This article belongs to the Section Welding and Joining)

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22 pages, 17592 KiB

Open AccessArticle

Impact of Feature-Selection in a Data-Driven Method for Flow Curve Identification of Sheet Metal

by Quang Ninh Hoang, Hyungbum Park, Dang Giang Lai, Sy-Ngoc Nguyen, Quoc Tuan Pham and Van Duy Dinh

Metals 2025, 15(4), 392; https://doi.org/10.3390/met15040392 - 31 Mar 2025

Abstract

This study presents an innovative data-driven methodology to model the hardening behavior of sheet metals across a broad strain range, crucial for understanding sheet metal mechanics. Conventionally, true stress–strain data from such tests are used to analyze plastic flow within the pre-necking regime, [...] Read more.

This study presents an innovative data-driven methodology to model the hardening behavior of sheet metals across a broad strain range, crucial for understanding sheet metal mechanics. Conventionally, true stress–strain data from such tests are used to analyze plastic flow within the pre-necking regime, often requiring additional experiments to inverse finite element methods, which demand extensive field data for improved accuracy. Although digital image correlation offers precise data, its implementation is costly. To address this, we integrate experimental data from standard tensile tests with a machine-learning approach to estimate the flow curve. Subsequently, we conduct finite element simulations on uniaxial tensile tests, using materials characterized by the Swift constitutive equation to build a comprehensive database. Loading force-gripper displacement curves from these simulations are then transformed into input features for model training. We propose and compare three models—Models A, B, and C—each employing different input feature selections to estimate the flow curve. Experimental validation including uniaxial tensile, plane strain, and simple shear tests on the DP590 and DP780 sheets are then carefully considered. Results demonstrate the effectiveness of our proposed method, with Model C showing the highest efficacy. Full article

(This article belongs to the Special Issue Machine Learning Models in Metals)

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13 pages, 5508 KiB

Open AccessArticle

The Effect of Al Loss on the Microstructural Formation of TiAl Alloys Produced via Direct Laser Deposition

by Xinyu Zhang, Chuanwei Li and Jianfeng Gu

Metals 2025, 15(4), 391; https://doi.org/10.3390/met15040391 - 31 Mar 2025

Abstract

Additive manufacturing is becoming a popular and effective process for lightweight high-temperature TiAl alloys, but there is a lack of understanding regarding the corresponding microstructural formation mechanisms. In this study, various Ti-47Al-2Cr-2Nb alloys were additively manufactured with different laser power values, and the [...] Read more.

Additive manufacturing is becoming a popular and effective process for lightweight high-temperature TiAl alloys, but there is a lack of understanding regarding the corresponding microstructural formation mechanisms. In this study, various Ti-47Al-2Cr-2Nb alloys were additively manufactured with different laser power values, and the related microstructures were carefully characterized. The results show that a convoluted microstructure, a nearly full α₂/γ lamellar structure, and an α₂/β Widmanstatten structure were obtained as the laser power was increased. Moreover, the Al content of the as-deposited specimen decreased from 47 at.% to 40 at.%, which is considered to have strongly affected microstructural formation. As the Al content decreased, the solidified microstructure transformed from hexagonal dendritic α₂ to orthogonal dendritic β and cellular β, successively. Moreover, massive α → γ transformation is more likely when the Al content is high, and α → α₂ transformation tends to occur when the Al content decreases. The microstructure evolution processes are evaluated in the present paper by synthesizing the experimental results with a thermodynamics analysis. Full article

(This article belongs to the Section Additive Manufacturing)

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