Metals

21 pages, 5434 KB

Open AccessArticle

Statistical Evaluation of the Mechanical Properties of Welded and Unwelded ASTM A706 Reinforcing Steel Bars of Different Commercial Brands

by Lenin Abatta-Jacome, Daniel Rosero-Pazmiño, Jeison Rosero-Vivas, Bryan Fernando Chávez-Guerrero and Germán Omar Barrionuevo

Metals 2025, 15(12), 1307; https://doi.org/10.3390/met15121307 - 27 Nov 2025

Abstract

The future of reinforcing steel bars (rebar) is being shaped by technological advancements, sustainability initiatives, and evolving construction practices. Welding of rebar has a significant and evolving influence on construction practices, particularly with trends emphasizing speed, precision, and prefabrication. On the other hand, [...] Read more.

The future of reinforcing steel bars (rebar) is being shaped by technological advancements, sustainability initiatives, and evolving construction practices. Welding of rebar has a significant and evolving influence on construction practices, particularly with trends emphasizing speed, precision, and prefabrication. On the other hand, the variability in mechanical response depends not only on the chemical composition but also on the manufacturing and welding process. This study analyzed five commercial brands of ASTM A706 reinforcing steel rods available in the Ecuadorian market with different diameters (12, 14, 16, and 18 mm) subjected to tensile and bending tests. A total of 228 specimens were analyzed, and 114 samples were welded by shielded metal arc welding process using an E8018-C3 electrode, preparing the joint with a simple V-bevel at 45°. The tensile tests results allow for a comparison between the welded and unwelded steel bars, where it is identified that the welding process generates a slight decrease in the mechanical properties and increases the variability in the results, although it is emphasized that these variations do not affect compliance with the standards, since all the samples meet the mechanical strength requirements by being within the limits established by the ASTM A706/A706M standard. Full article

(This article belongs to the Special Issue Failure Analysis and Evaluation of Metallic Materials)

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17 pages, 2489 KB

Open AccessArticle

Temperature Based Fatigue Damage Entropy for Assessment of High-Cycle Fatigue in Laser-Welded Joints

by Yang Liu, Yang Sun and Xinhua Yang

Metals 2025, 15(12), 1306; https://doi.org/10.3390/met15121306 - 27 Nov 2025

Abstract

To quickly predict the fatigue strength of welded joints in high-cycle fatigue tests and fit the S-N curve, this paper proposes a new model based on infrared thermal imaging technology. High-cycle fatigue tests were conducted on laser-welded joints of weathering steel Q450NQR1 and [...] Read more.

To quickly predict the fatigue strength of welded joints in high-cycle fatigue tests and fit the S-N curve, this paper proposes a new model based on infrared thermal imaging technology. High-cycle fatigue tests were conducted on laser-welded joints of weathering steel Q450NQR1 and separately, on joints made of stainless steel T4003, while local temperature variations in the joints were monitored. Based on the experimentally observed temperature drop behavior, a novel Temperature-Drop-Curve-Based Fatigue Damage Entropy (TDC-FDE) model was developed to rapidly estimate the fatigue life and fatigue limit of welded joints. The model quantifies the entropy generated during fatigue damage evolution based on the temperature-decrease slope and establishes a direct relationship between entropy and the fatigue performance of the joint using this slope as the linking parameter. Experimental results indicate that a material’s specific heat capacity, density, elastic modulus, and applied stress level directly influence fatigue damage entropy generation. The entropy increase associated with purely elastic deformation does not contribute to fatigue damage in high-cycle fatigue; therefore, this portion should be excluded from the fatigue damage entropy calculation. The fatigue damage entropy of a given weld joint tends to remain nearly constant under different stress levels and loading frequencies. Finally, traditional fatigue tests demonstrated that the maximum deviation between the fatigue strength predicted by the proposed model and the experimentally measured values does not exceed 3.4%, thereby verifying the model’s accuracy and effectiveness in evaluating fatigue performance. Full article

18 pages, 2971 KB

Open AccessArticle

Numerical Investigation of Dual Vertical Water Jets Impinging on High-Temperature Steel

by Jianhui Shi, Zhao Zhang, Xiangfei Ji, Jinwen You and Feng Han

Metals 2025, 15(12), 1305; https://doi.org/10.3390/met15121305 - 27 Nov 2025

Abstract

The flow dynamics and heat transfer of dual vertical water jets impinging a high-temperature steel plate were numerically investigated using a three-dimensional model. A systematic parametric investigation was conducted by varying key operating conditions: including the jet velocity at the nozzle exit ( [...] Read more.

The flow dynamics and heat transfer of dual vertical water jets impinging a high-temperature steel plate were numerically investigated using a three-dimensional model. A systematic parametric investigation was conducted by varying key operating conditions: including the jet velocity at the nozzle exit (V = 5 m/s, 7.5 m/s, 10 m/s), the non-dimensional nozzle-to-plate distance (H = h/d = 3.3, 5.8, 8.3, 10.8), and the non-dimensional spacing between twin nozzles (W = w/d = 5, 7.5, 10). Upon impingement, multiple wall-jet flows formed on the steel plate surface, with their radial spread distance increasing along the plate’s surface. A wall-jet interaction zone developed between the two jets, accompanied by a linear fountain upwash flow. To depict the thermal and hydrodynamic characteristics, the distributions of the local Nusselt number and flow velocity vectors were examined. Findings suggest that fluctuations in W have little impact on the mean Nusselt number. Nevertheless, a growth in H brings about a concurrent increase in the Nusselt number of the stagnation point on the plate’s surface. Furthermore, the results indicate that W is a primary factor controlling the heat transfer rate within the interaction zone of the opposing wall jets. Full article

34 pages, 17271 KB

Open AccessReview

Advances in Microstructural Evolution and Mechanical Properties of Magnesium Alloys Under Shear Deformation

by Yaqing Liu, Yong Xue and Zhaoming Yan

Metals 2025, 15(12), 1304; https://doi.org/10.3390/met15121304 - 27 Nov 2025

Abstract

Magnesium (Mg) alloys are the lightest metals used in engineering structures, making them highly valuable for lightweight designs in aerospace, automotives, and related industries. Their low density offers clear advantages for reducing product weight and improving energy efficiency–key priorities in modern manufacturing. However, [...] Read more.

Magnesium (Mg) alloys are the lightest metals used in engineering structures, making them highly valuable for lightweight designs in aerospace, automotives, and related industries. Their low density offers clear advantages for reducing product weight and improving energy efficiency–key priorities in modern manufacturing. However, their unique crystal structure leads to notable drawbacks: low plasticity at room temperature, uneven performance across different directions, and inconsistent strength under tension versus compression. These issues have severely limited their broader application beyond specialized use cases. Shear deformation methods address this challenge by creating high strain variations and complex stress conditions. This approach provides an effective way to regulate the internal structure of Mg alloys and enhance their overall performance, overcoming the inherent limitations of their crystal structure. This paper systematically summarizes current research on using shear deformation to process Mg alloys. It focuses on analyzing key structural changes induced by shear, including the formation and evolution of shear–related features, real–time grain reorganization, crystal twinning processes, the distribution of additional material phases, and reduced directional performance bias. The review also clarifies how these structural changes improve critical mechanical traits: strength, plasticity, formability, and the balance between tensile and compressive strength. Additionally, the paper introduces advanced shear–based processes and their derivative technologies, such as equal–channel angular extrusion, continuous shear extrusion, and ultrasonic vibration–assisted shearing. It also discusses strategies for constructing materials with gradient or mixed internal structures, which further expand the performance potential of Mg alloys. Finally, the review outlines future development directions to advance this field: developing shear processes that combine multiple physical fields, conducting real–time studies of microscale mechanisms, designing tailored shear paths for high–performance Mg alloys, and evaluating long–term service performance. These efforts aim to promote both theoretical innovation and industrial application of shear deformation technology for Mg alloys. Full article

(This article belongs to the Special Issue Novel Insights into Wrought Magnesium Alloys)

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21 pages, 7394 KB

Open AccessArticle

A New Microcrack Characterisation Method for Quench Cracking in Induction-Hardened Steels

by A. Aysu Catal-Isik, Lizeth J. Sanchez, Mangesh Pantawane, Vikram Bedekar and Enrique I. Galindo-Nava

Metals 2025, 15(12), 1303; https://doi.org/10.3390/met15121303 - 27 Nov 2025

Abstract

High-performance induction-hardened bearing steels are prone to quench cracking during manufacturing, causing significant material and energy waste. Understanding the physics behind microcracking is essential to the design of alloys and processes with reduced cracking behaviour. However, conventional quench crack analysis methods provide information [...] Read more.

High-performance induction-hardened bearing steels are prone to quench cracking during manufacturing, causing significant material and energy waste. Understanding the physics behind microcracking is essential to the design of alloys and processes with reduced cracking behaviour. However, conventional quench crack analysis methods provide information only on crack severity and neither link martensite microstructure to microcrack formation or provide meaningful insights on the origins of microcracking. Therefore, this work introduces a new crack quantification method that assesses various crack features, including crack length, location within a martensite plate, crack angle to the plate midrib, and the distance from the induction-hardened surface. It is found that microcrack severity changes with the distance from the induction-hardened surface, peaking at ∼1 mm in depth, with a maximum density of approximately 1000 cracks per mm². In addition, microcracks are mostly seen in the martensite plates rather than at the austenite–martensite interface, with the majority lying perpendicular to the midrib. Approximately 50% of the interfacial cracks are oriented at an angle less than 10 °C to the martensite midrib and are mainly located around the midpoint of the interface. Martensite plates having interfacial cracks are mostly 10–20 μm long, whereas martensite plates with internal cracks are mostly 20–30 μm long. The new method helps build quantitative links between microcracking and martensite morphology to study the mechanisms of cracking and the role of the initial microstructure in more detail. Full article

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

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12 pages, 3431 KB

Open AccessArticle

Temperature-Correlated Characterization of EoL Lithium Cobalt Oxide Batteries with Microwave-Based Pyrometallurgical Recovery

by Emma Pitacco, Marco Ragazzini, Caterina Bernardini, Mehran Ghadimi, Mirko Pigato, Michele Forzan and Katya Brunelli

Metals 2025, 15(12), 1302; https://doi.org/10.3390/met15121302 - 26 Nov 2025

Abstract

With the increasing volumes of spent lithium-ion batteries from electric vehicles and the concurrent increase in raw materials cost for cathode production, finding effective methods for recycling battery materials has become critically important. This study investigated a pyrometallurgical approach using microwave irradiation to [...] Read more.

With the increasing volumes of spent lithium-ion batteries from electric vehicles and the concurrent increase in raw materials cost for cathode production, finding effective methods for recycling battery materials has become critically important. This study investigated a pyrometallurgical approach using microwave irradiation to achieve carbothermal reduction of LiCoO₂. FactSage thermodynamic calculations were performed for process simulation and an infrared thermal camera was employed for temperature measurements, allowing the authors to optimize the process parameters to obtain metallic cobalt. Specifically, the research included microwave experiments on mixed black mass samples of anode and cathode materials in different proportions, treated at varying power levels and exposure times under air atmosphere. The effect of the process parameters and therefore of the temperature on microstructure was studied with SEM-EDS and XRD analysis. The feasibility of a wet magnetic separation method between cobalt and lithium compounds formed during the reaction was also evaluated. The results obtained from the final separation process indicated that individual compounds can be obtained at the end of the cycle; moreover, the optimization of time, temperature, and graphite additions during the tests allowed the authors to obtain promising results. Full article

(This article belongs to the Special Issue Current Trends in Non-Ferrous Metals Extraction, Separation, and Refining)

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13 pages, 4531 KB

Open AccessArticle

Enhancing Automotive Valve Guide Tribomechanical Performance Through Alloy Optimization in Powder Metallurgy

by Fujian Guo, Zhongyuan Yan, Guangyi Lu, Wenle Liu, Pan Zhang and Gengzhe Shen

Metals 2025, 15(12), 1301; https://doi.org/10.3390/met15121301 - 26 Nov 2025

Abstract

Given the critical role of valve guides in the performance and lifespan of automotive engines, it is crucial to understand and improve their wear resistance. This study focuses on the wear resistance of powder metallurgy valve guides, aiming to systematically analyze the intrinsic [...] Read more.

Given the critical role of valve guides in the performance and lifespan of automotive engines, it is crucial to understand and improve their wear resistance. This study focuses on the wear resistance of powder metallurgy valve guides, aiming to systematically analyze the intrinsic relationship between their composition, microstructure, and properties. Three powder metallurgy valve guide samples with different compositions—specifically, a high-MoS₂ Fe-C-Mo-Cu-S alloy (1.5 wt.% C, 1.9 wt.% Mo, 1.5 wt.% Cu, 1.4 wt.% S), a low-MoS₂ Fe-C-Mo-Cu-S alloy (1.2 wt.% C, 0.3 wt.% Mo, 0.8 wt.% Cu, 0.2 wt.% S), and a Mo-free high-C-Cu Fe-C alloy (1.8 wt.% C, 5 wt.% Cu, 0 wt.% Mo, 0.01 wt.% S)—were studied using field emission scanning electron microscopy, metallographic microscopy, a reciprocating friction testing machine, and a 3D optical profilometer. The results show that the friction coefficient of the high-MoS₂ Fe-C-Mo-Cu-S alloy is the highest at 0.5, the low-MoS₂ Fe-C-Mo-Cu-S alloy is 0.25, and the Mo-free high-C-Cu Fe-C alloy is the lowest at 0.22. Since the minor wear amount cannot be accurately measured by the gravimetric method, the concave area of the wear-induced average roughness curve is employed to qualitatively indicate the magnitude of material loss: the area of the high-MoS₂ Fe-C-Mo-Cu-S alloy is 2964 μm², the low-MoS₂ Fe-C-Mo-Cu-S alloy is 1580 μm², and the Mo-free high-C-Cu Fe-C alloy is 1502 μm². The hardness results of the material show that the high-MoS₂ Fe-C-Mo-Cu-S alloy reaches 154 HB, the low-MoS₂ Fe-C-Mo-Cu-S alloy is 134 HB, and the Mo-free high-C-Cu Fe-C alloy is 145 HB. The porosity results show a difference of about 2% among the three alloys. Based on the microstructure characterization results, it can be concluded that the Mo-free high-C-Cu Fe-C alloy—with high carbon (C) and copper (Cu) content and fine pearlite layers—exhibits excellent wear resistance: high C can improve the hardness of the matrix, while Cu can act as a lubricating phase to enhance the material’s wear resistance. In contrast, although the addition of MoS₂ is intended to improve wear resistance, the irregular pearlite generated by MoS₂ reduces the wear resistance of the high-MoS₂ and low-MoS₂ Fe-C-Mo-Cu-S alloys; among them, the high-MoS₂ Fe-C-Mo-Cu-S alloy contains a higher amount of MoS₂, and large chunks appearing in the tissue easily cause abrasive wear and aggravate material wear during friction. This study provides solid theoretical and practical support for the material selection and performance optimization of powder metallurgy engine valve guides: the identified intrinsic relationship between alloy composition (MoS₂, C, and Cu contents), microstructure (pearlite morphology and second-phase distribution), and tribological performance establishes a clear theoretical basis for regulating the wear resistance of such components. Full article

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29 pages, 6014 KB

Open AccessArticle

Probabilistic Modeling of Fatigue Life Prediction of Notched Specimens Combining Highly Stressed Volume and Theory of Critical Distance Approach

by Bin Li, Peng Liu, Yuan Cheng, Xiaodi Wang and Xuechong Ren

Metals 2025, 15(12), 1300; https://doi.org/10.3390/met15121300 - 26 Nov 2025

Abstract

Notch and size effects significantly influence the fatigue performance of engineering components, which is crucial for ensuring structural integrity. A novel probabilistic fatigue life prediction Kt-V-L model considering both the size and the notch effect, based on the theory of critical distance L [...] Read more.

Notch and size effects significantly influence the fatigue performance of engineering components, which is crucial for ensuring structural integrity. A novel probabilistic fatigue life prediction Kt-V-L model considering both the size and the notch effect, based on the theory of critical distance L (TCD) and the improved highly stressed volume V (HSV) method, is proposed in this study. The new definition more accurately characterizes fatigue damage and accumulation, overcoming the underestimation issues of traditional HSV methods under high-stress or low cycle fatigue (LCF) conditions. Specifically, the Weibull distribution is also proposed to characterize the material fatigue failure probability. The experimental data of 26Cr2Ni4MoV, En3B, and TC4 materials with varying notched sizes are utilized for the model validation and comparison. In addition, the predictive ability of the point method (Kt-V-L-PM) and line method (Kt-V-L-LM) under the novel proposed model was explored and evaluated. The predicted lives of 26Cr2Ni4MoV specimens fall within the ±2 scatter band of the Kt-V-L-LM, while the Kt-V-L-PM shows increasing deviation with larger notches due to its limited ability to capture stress gradients. For En3B and TC4, the predicted lives are within ± 2 life factors, verifying the model’s reliability and accuracy. Furthermore, fracture morphology analysis reveals the influence of notches on fatigue performance and elucidates the fracture failure mechanisms. Full article

(This article belongs to the Special Issue Fatigue, Fracture, and Multiaxial Integrity of Metallic Structure Materials: From Microstructure to Data-Driven Assessment)

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15 pages, 3469 KB

Open AccessArticle

An Ultrasonic Vibration-Assisted Superplastic Forming Method for Zr-Based Bulk Amorphous Alloys: Experiment and Simulation

by Hui Li, Jinfu Liu, Chenpu Shen and Canhua Li

Metals 2025, 15(12), 1299; https://doi.org/10.3390/met15121299 - 26 Nov 2025

Abstract

The processing of bulk amorphous alloys is typically realized through superplastic deformation in the supercooled liquid region, and current research efforts predominantly focus on enhancing formability by optimizing processing parameters such as temperature and duration. However, excessive temperatures or prolonged exposure times can [...] Read more.

The processing of bulk amorphous alloys is typically realized through superplastic deformation in the supercooled liquid region, and current research efforts predominantly focus on enhancing formability by optimizing processing parameters such as temperature and duration. However, excessive temperatures or prolonged exposure times can induce crystallization, which severely compromises the mechanical and functional properties of the alloy. This study presents the design of an ultrasonic vibration (UV)-assisted metal hot-forming apparatus that integrates an ultrasonic vibration field into the superplastic flow deformation of amorphous alloys. High-temperature compression experiments were conducted on Zr₅₅Cu₃₀Al₁₀Ni₅ amorphous alloy, and finite element simulations were performed to model the experimental process. Results show that ultrasonic vibration reduces the flow stress of the amorphous alloy, thereby enhancing its superplastic deformation capability. Simulation analysis reveals that surface effects arise from periodic interface separation between the pressure plate and the specimen caused by ultrasonic vibration, leading to a cyclic disappearance of friction forces, which manifest macroscopically as a reduction in effective friction. On the other hand, vibration introduces additional strain rates. Since the undercooled liquid of amorphous alloys exhibits non-Newtonian fluid behavior characterized by shear-thinning, ultrasonic vibration assistance can effectively reduce the apparent viscosity, thereby improving their filling capacity. Full article

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

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18 pages, 4958 KB

Open AccessArticle

Quenching Internal Stress Evolution and Shape Control in Gigapascal Ultra-High-Strength Martensitic Steel

by Zigang Chen, Yan Peng, Xinjun Shen, Xiaonan Wang and Hongyan Liu

Metals 2025, 15(12), 1298; https://doi.org/10.3390/met15121298 - 26 Nov 2025

Abstract

Gigapascal ultra-high-strength steel holds significant applications in the energy and military sectors. Such steel is typically produced through quenching and tempering processes. However, during quenching, issues such as excessive internal stress often lead to significant deviations in flatness, thereby reducing product precision. This [...] Read more.

Gigapascal ultra-high-strength steel holds significant applications in the energy and military sectors. Such steel is typically produced through quenching and tempering processes. However, during quenching, issues such as excessive internal stress often lead to significant deviations in flatness, thereby reducing product precision. This study adopts an approach integrating theoretical and practical methods to develop a control technology for achieving high flatness in gigapascal ultra-high-strength martensitic steel. Firstly, finite element simulation was employed to establish a temperature-phase transformation-stress coupling model for the quenching process of gigapascal martensitic steel. The study investigated the deformation behavior of steel plates under unilateral cooling, the influence of dynamic martensitic transformation on internal stress, and the effects of plate thickness and water ratio. This revealed how quenching process parameters affect the internal stress and deformation of steel plates. Based on theoretical calculations and considering on-site equipment conditions, industrial production line commissioning was conducted, which significantly reduced the quenching internal stress of gigapascal ultra-high-strength martensitic steel and greatly improved the flatness of the steel plates. The results surpassed those of international companies such as Sweden’s SSAB and other domestic enterprises, achieving an internationally leading level. Full article

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16 pages, 5989 KB

Open AccessArticle

Exploring Complex Patterns: How Cold Work Modulates Defect Evolution and Radiation Resistance in CLF-1 Steels Under Multi-Beam Ion Irradiations

by Zhihao Xu, Sizhe Diao, Hongtai Luo, Hongbin Liao, Guoping Yang, Fangqian Zhao, Shang Xu, Yiheng Chen, Yaqi Wu, Chenxu Wang, Liping Guo, Yong Zhang and Qian Zhan

Metals 2025, 15(12), 1297; https://doi.org/10.3390/met15121297 - 25 Nov 2025

Abstract

China Low-Activation Ferrite (CLF-1) steel, renowned for its excellent thermomechanical properties and irradiation resistance, plays a key role in the development of the R&D of the Chinese Helium-Cooled Ceramic Breeding Test Blanket Module. Cold-worked CLF-1 steels were irradiated with sequential dual ion beams [...] Read more.

China Low-Activation Ferrite (CLF-1) steel, renowned for its excellent thermomechanical properties and irradiation resistance, plays a key role in the development of the R&D of the Chinese Helium-Cooled Ceramic Breeding Test Blanket Module. Cold-worked CLF-1 steels were irradiated with sequential dual ion beams of (Fe²⁺ and H⁺), followed by single He⁺ irradiation at 723 K, with a dose rate of 1.09 dpa/h, to explore the complex relationship between cold work, defect evolution, and irradiation hardening. Samples with cold-working deformations of 0%, 10%, and 50% (denoted as CW 0%, CW 10%, and CW 50%, respectively) were examined. The results based on nanoindentation, TEM, and EBSD reveal that moderate cold work (10%) introduces dense dislocations, acting as effective sinks to suppress irradiation-induced defect accumulation and hardening, while excessive cold work (50%) triggers partial recrystallization under relatively long-time multi-beam irradiation, reducing dislocation density, which leads to the comparable hardening with CW 10%. In contrast, non-deformed samples (0% cold work) exhibit severe irradiation hardening (38.46%). He bubbles and dislocation loops follow non-monotonic trends in number density (CW 50% < CW 0% < CW 10%) and size (CW 50% > CW 0% > CW 10%), governed by the interplay of sink efficiency, thermal diffusion, and recrystallization. These findings highlight that a moderate level of cold-working deformation contributes to enhancing the sink strength, thereby offering a viable approach for designing radiation-tolerant RAFM steels. Full article

22 pages, 9034 KB

Open AccessArticle

Laser Beam Welding of IN625 Alloy with Equiaxed Grains: Influence of Process Parameters

by Giuliano Angella, Fabio Bergamini, Francesco Cognini, Alessandra Fava, Paolo Ferro, Alessandra Palombi, Maria Richetta and Alessandra Varone

Metals 2025, 15(12), 1296; https://doi.org/10.3390/met15121296 - 25 Nov 2025

Abstract

Ni-based superalloys, known for their excellent mechanical strength and corrosion resistance at high temperature, are widely used in aeronautic, aerospace, and energy industries. Since both the materials and manufacturing processes required to produce high-performance components made of these alloys are expensive, the welding [...] Read more.

Ni-based superalloys, known for their excellent mechanical strength and corrosion resistance at high temperature, are widely used in aeronautic, aerospace, and energy industries. Since both the materials and manufacturing processes required to produce high-performance components made of these alloys are expensive, the welding repair of damaged components plays a crucial role in industrial applications. High energy density welding techniques, such as laser beam welding (LBW) and electron beam welding (EBW), are the most promising to achieve high-quality welds. Nevertheless, welding processes significantly affect the microstructure and mechanical properties of both the melted zone (MZ) and the heat-affected zone (HAZ). This may result in alloying element segregation, precipitation of undesired secondary phases, and the presence of residual stresses that can lead to crack formation. Therefore, a comprehensive investigation of the effects of process parameters on weld seam properties is essential to maintain high performance standards. In this work, LBW was employed to join 2.5 mm thick plates of equiaxed IN625 superalloy. The seams were produced by varying three parameters: the two characteristic parameters of LBW, i.e., laser power (P = 1700, 2000, 2300 W) and welding speed (v = 15, 20, 25 mm/s), alongside power modulation (Γ = P_min/P_max = 0.6, 0.8, 1). The scope of this work is to evaluate the effect of the combined variation of all these welding parameters on the final characteristics of welded seams. The resulting microstructures were characterized by using digital radiography, Light Microscopy (LM), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). Vickers microhardness measurements were performed across the weld seams to evaluate the mechanical properties in the MZ and HAZ. The optimal set of welding parameters, producing defect-free seams without cracks and pores, was identified as P = 2000 W, v = 25 mm/s, and Γ = 0.6. Full article

(This article belongs to the Special Issue Weldability and Reparability of Nickel-Base Alloys)

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14 pages, 5287 KB

Open AccessArticle

Determining Residual Stress in Copper by Nanoindentation in Compressive and Tensile Stress States

by Guanna Li, Jianyuan Mei, Haidong Qi and Xiping Song

Metals 2025, 15(12), 1295; https://doi.org/10.3390/met15121295 - 25 Nov 2025

Abstract

In this study, nanoindentation was employed to determine residual stresses in copper after compression and tension deformations with different deformation levels. Rectangular and cylindrical compression specimens were prepared in order to produce residual stresses parallel or perpendicular to the stress direction. For the [...] Read more.

In this study, nanoindentation was employed to determine residual stresses in copper after compression and tension deformations with different deformation levels. Rectangular and cylindrical compression specimens were prepared in order to produce residual stresses parallel or perpendicular to the stress direction. For the compression deformation, with the increase in compressive strain, the residual compression stress parallel to the compression direction increased and exhibited a linear relationship with the compressive strain,

σ_{c o m p r e s s i o n r e s}^{p a r a l l e l} = - 1.56 ε_{rectangle compression}

, while the residual compression stress perpendicular to the compression direction were as follows:

σ_{c o m p r e s s i o n r e s}^{p e r p e n d i c u l a r} = - 0.20 ε_{cylinder compression}

. For the tension deformation, with the increase in tensile strains, the residual tension stress parallel to the tension direction increased and exhibited a linear relationship with the tensile strain,

σ_{t e n s i o n r e s}^{p a r a l l e l} = 1.03 ε_{p l a t e t e n s i o n}

, while the residual tension stress perpendicular to the tension direction were as follows:

σ_{t a n s i o n r e s}^{p e r p e n d i c u l a r} = 0.65 ε_{c y l i n d e r t e n s i o n}

. The residual stresses parallel to the stress direction exhibited significant anisotropic characteristics, while the residual stresses perpendicular to the stress direction exhibited significant isotropic characteristics. Based on the above results, the relationship between strains and residual stress were successfully determined, providing valuable data reference for engineering applications. Full article

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19 pages, 6268 KB

Open AccessArticle

Research on Arc Characteristics and Microstructure of 6061 Aluminum Alloy Multi-Pulse Composite Arc Welding

by Guangshun Zhang, Xin Ye, Fang Li, Yonggang Du, Guangcai Chang and Peng Xia

Metals 2025, 15(12), 1294; https://doi.org/10.3390/met15121294 - 25 Nov 2025

Abstract

To mitigate welding defects and optimize the microstructure of aluminum alloys, this study introduces a multi-pulse hybrid arc welding process. A comparative investigation was carried out between this novel process (AC/DC composite 1 kHz pulsed welding) and conventional methods (AC pulsed, AC/DC pulsed) [...] Read more.

To mitigate welding defects and optimize the microstructure of aluminum alloys, this study introduces a multi-pulse hybrid arc welding process. A comparative investigation was carried out between this novel process (AC/DC composite 1 kHz pulsed welding) and conventional methods (AC pulsed, AC/DC pulsed) during wire-fed overlay welding of 6061 aluminum alloy. Analyses were conducted on electrical signals, arc morphology, joint microstructure, and hardness. The results indicate that the AC/DC hybrid 1 kHz pulsed process combines the characteristics of both AC and DC pulsed signals with full-cross-section frequency pulse superposition, thereby optimizing arc welding process control. The frequency pulses induce a magnetoelectric effect, leading to significant arc constriction, which enhances arc energy density and arc pressure. This intensifies the fluid flow in the molten pool and accelerates cooling, thereby suppressing the growth of columnar grains and promoting the formation of fine equiaxed grains and an increased proportion of high-angle grain boundaries. Meanwhile, this process effectively reduces the number, area fraction, and overall porosity, and facilitates the distribution of a large amount of Al–Si eutectic structure along grain boundaries, enhancing the impediment to dislocation motion. The microstructural optimization significantly improves the hardness at the weld center to 73.1 HV, leading to enhanced mechanical properties. Full article

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

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20 pages, 3077 KB

Open AccessArticle

Recovering Battery-Grade LiOH·H₂O from Spent Lithium-Containing Sagger Crucible by Thermal Dehydration and BaSO₄-Driven Double Decomposition

by Seongbong Heo and Jei-Pil Wang

Metals 2025, 15(12), 1293; https://doi.org/10.3390/met15121293 - 25 Nov 2025

Abstract

This study develops and validates an integrated hydrometallurgical process to recover battery-grade lithium hydroxide monohydrate from spent aluminosilicate sagger crucibles. Lithium was first leached as Li₂SO₄ from the crucibles using sulfuric acid; the Li₂SO₄·H₂O [...] Read more.

This study develops and validates an integrated hydrometallurgical process to recover battery-grade lithium hydroxide monohydrate from spent aluminosilicate sagger crucibles. Lithium was first leached as Li₂SO₄ from the crucibles using sulfuric acid; the Li₂SO₄·H₂O present in the leachate was then thermally decomposed at 300 °C to Li₂SO₄ + H₂O, as confirmed by TGA-guided selection and XRD. Subsequent conversion to LiOH proceeded via double decomposition with Ba(OH)₂. Guided by HSC-based equilibrium simulations and an Eh–pH analysis of the Li–Ba–S–H₂O system, reaction conditions were optimized over 60–80 °C and [OH⁻]/[Li⁺] = 1–3. The optimum was identified at 70 °C and [OH⁻]/[Li⁺] = 1, delivering a conversion efficiency of 98.78% and a Li recovery of 98.86%. Two-end-point acid titration indicated a LiOH content of 90.29 wt.% in solution with minimal Li₂CO₃ formation, consistent with processing under vacuum–Ar to suppress CO₂ uptake. The crystallized product obtained by evaporation at ≥90 °C for 24 h was confirmed as LiOH·H₂O (with LiOH) by XRD, while the solid by-product was single-phase BaSO₄. ICP-OES measured a final LiOH·H₂O purity of 99.8%. Full article

(This article belongs to the Special Issue Metal Leaching and Recovery)

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21 pages, 8623 KB

Open AccessArticle

Direct Energy Deposition of Inconel 718 onto Cu Substrate for Bimetallic Structures with Excellent Comprehensive Properties

by Stefano Felicioni, Josip Vincic, Annalisa Zacco, Alberta Aversa, Paolo Fino and Federica Bondioli

Metals 2025, 15(12), 1292; https://doi.org/10.3390/met15121292 - 25 Nov 2025

Abstract

In the aerospace sector, integrating advanced materials with high mechanical capabilities represents the forefront of material science, especially in the field of rocketry. Bimetallic structures are increasingly used in aerospace applications due to their combination of high strength-to-weight ratio, thermal conductivity, and corrosion [...] Read more.

In the aerospace sector, integrating advanced materials with high mechanical capabilities represents the forefront of material science, especially in the field of rocketry. Bimetallic structures are increasingly used in aerospace applications due to their combination of high strength-to-weight ratio, thermal conductivity, and corrosion resistance. Among these, Inconel-copper (In718-Cu) systems are particularly promising, although large differences in thermophysical and mechanical properties between the two materials can induce residual stresses, cracks, and other interfacial defects, requiring careful process control. This study evaluates the fabrication of In718-Cu structures through Direct Energy Deposition (DED), in which In718 was deposited onto a copper substrate using an innovative deposition strategy. Interface quality and microstructure were characterized by SEM/EDS and X-ray diffraction, whereas the mechanical properties were evaluated by nanoindentation, indentation creep, and tensile testing. The results showed that crack-free samples can be achieved, with strong diffusion bonding at the interface and efficient precipitation strengthening on the copper side already in the as-built condition. A uniform distribution of precipitates and consistent penetration depth were also observed, confirming the effectiveness of the deposition strategy for producing reliable In718-Cu components. Full article

(This article belongs to the Section Additive Manufacturing)

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15 pages, 28719 KB

Open AccessArticle

The Impact of Structural Units on Copper Grain Boundary–Dislocation Interactions

by Ke Wang, Yongsheng Xu, Lingchao Xu, Weigang Zhang and Jinquan Xu

Metals 2025, 15(12), 1291; https://doi.org/10.3390/met15121291 - 25 Nov 2025

Abstract

A molecular dynamics approach was employed to investigate the interaction behavior between tilt-[110] copper grain boundaries (GBs) and dislocations, with particular emphasis on elucidating the role of GB structural unit (SU) types in the mechanisms of dislocation absorption and transmission. The results reveal [...] Read more.

A molecular dynamics approach was employed to investigate the interaction behavior between tilt-[110] copper grain boundaries (GBs) and dislocations, with particular emphasis on elucidating the role of GB structural unit (SU) types in the mechanisms of dislocation absorption and transmission. The results reveal that singular GBs composed of continuous and uniform B-type or C-type SUs exhibit a pronounced ability to absorb dislocations, whereby incident dislocations are fully absorbed by the GB and prevented from transmitting across it. In contrast, for discrete GBs containing both C SUs and intrinsic stacking fault facets, the dislocation accommodation capacity of the GB is closely related to the number of C SUs within the discrete region. Multiple continuous C SUs can effectively facilitate dislocation absorption and energy dissipation through a synergistic linkage mechanism. This study underscores the critical role of GB SUs in governing GB–dislocation interactions and provides atomic-scale insights into the microstructural regulation mechanisms of GBs during plastic deformation. Full article

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20 pages, 22468 KB

Open AccessArticle

Effect of CMT Welding Heat Input on Microstructure and Mechanical Properties of Different Groove Angles for Al-6061-T6 Alloy Joint

by Guo Xian, Zhen Gao, Yunfeng Fu, Zhao Ding, Xianshu Que and Jingbang Pan

Metals 2025, 15(12), 1290; https://doi.org/10.3390/met15121290 - 25 Nov 2025

Abstract

Air suspension components are critical elements of automotive chassis and are commonly fabricated by welding 6061-T6 aluminum using 4043 filler wire with the cold metal transfer (CMT) process. Variations in vehicle architecture necessitate different groove angles and matching parameter windows. This study aims [...] Read more.

Air suspension components are critical elements of automotive chassis and are commonly fabricated by welding 6061-T6 aluminum using 4043 filler wire with the cold metal transfer (CMT) process. Variations in vehicle architecture necessitate different groove angles and matching parameter windows. This study aims to elucidate how groove angle and heat input govern weld quality to inform process optimization. Two groove angles (120° and 90°) were investigated under distinct heat-input conditions (denoted 120-H and 90-L). Characterization covered chemical composition, macroscopic morphology, porosity, microstructure, hardness, and mechanical properties. The key novelty lies in elucidating the relationship between liquation cracking and metal flow lines, which jointly govern crack propagation. Integrating evidence from porosity measurements, crack characterization, and numerical simulations indicates that the 120-H parameter set requires further optimization. Overall, the results underscore the pivotal roles of groove angle and heat input in CMT welding of 6061-T6 aluminum and provide a basis for process parameter optimization in air suspension manufacturing. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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21 pages, 8710 KB

Open AccessArticle

The Impact of Ce on the Microstructure and Properties of Weld Metal in Corrosion-Resistant Steel

by Yuwei Wang, Jun Qiu, Qiuming Wang and Qingfeng Wang

Metals 2025, 15(12), 1289; https://doi.org/10.3390/met15121289 - 25 Nov 2025

Abstract

In this study, two types of submerged arc welding (SAW) wires were prepared—one without cerium (Ce) and another containing 0.14 wt.% Ce. Deposition experiments were carried out on corrosion-resistant crude oil storage tank steel plates using a multi-layer, multi-pass welding process. Through a [...] Read more.

In this study, two types of submerged arc welding (SAW) wires were prepared—one without cerium (Ce) and another containing 0.14 wt.% Ce. Deposition experiments were carried out on corrosion-resistant crude oil storage tank steel plates using a multi-layer, multi-pass welding process. Through a combination of microstructural characterization techniques, including optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), along with mechanical property testing, a systematic investigation was conducted to evaluate the influence of Ce on the weld metal microstructure and its impact toughness at −20 °C. The results reveal that Ce introduced via the welding wire into the weld seam refines and disperses inclusions, leading to the formation of composite inclusions primarily composed of Ce₂O₃, Ce₂O₂S, and CeS. These Ce-enriched inclusions serve as heterogeneous nucleation sites, increasing the area fraction of acicular ferrite (AF) within the weld columnar grain region from 52% to 83%, and within the heat-affected zone from 20% to 37%. Correspondingly, the proportions of blocky and polygonal ferrite decrease, while the size of martensite/austenite (M/A) constituents is reduced. The addition of Ce thus diminishes the size of hard phase inclusions and M/A constituents in the weld metal, enhancing the critical fracture stress and increasing the energy required for crack initiation. Meanwhile, the higher proportion of AF elevates the density of high-angle grain boundaries, thereby improving crack propagation resistance. These combined effects raise the −20 °C impact energy of the weld metal from 117 J to 197 J. Full article

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