Metals

11 pages, 8503 KB

Open AccessArticle

Effect of Heat Treatment Temperature on the Microstructure and Mechanical Properties of Fe-18Mn-0.6C-xAl

by Li Xiao, Yuqi Zhang, Huan Huang, Bochao Zhang, Ningning Ji, Shuang Li and Jun Chen

Metals 2025, 15(8), 927; https://doi.org/10.3390/met15080927 - 21 Aug 2025

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High-Mn steels are commonly fabricated by hot rolling and on-line cooling for cryogenic applications, because there exists an aging embrittlement zone in most high-Mn steels, and this shortcoming makes it difficult to optimize their mechanical properties by heat treatments. Hence, 0.6C-18Mn-0/3/5Al (in wt.%) [...] Read more.

High-Mn steels are commonly fabricated by hot rolling and on-line cooling for cryogenic applications, because there exists an aging embrittlement zone in most high-Mn steels, and this shortcoming makes it difficult to optimize their mechanical properties by heat treatments. Hence, 0.6C-18Mn-0/3/5Al (in wt.%) steels were designed to investigate the effects of Al on their strength and toughness. The addition of 5 wt.% Al can increase yield strength from 357 to 461 MPa and the Charpy impact absorbed energy from 56 to 119 J. Although there is still a cryogenic aging embrittlement zone in each steel, we found that the addition of Al can narrow this brittle zone. Moreover, the absorbed energy is lowered by around 89%, 48%, and 40% for the 0Al, 3Al, and 5Al steels at −196 °C, respectively. Additionally, impact plastic deformation mechanisms were also revealed in the steels with a heat-treating temperature of 600 °C, revealing that the main deformation mechanism shifts from numerous partial dislocation slip to twinning plus strong planar slip as the addition of Al increases. Full article

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14 pages, 11112 KB

Open AccessArticle

Effect of Mo on Microstructure and Mechanical Properties of Corrosion-Resistant Tank Steel

by Jun Hong, Yongqi Yang and Qingfeng Wang

Metals 2025, 15(8), 926; https://doi.org/10.3390/met15080926 - 21 Aug 2025

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Abstract

To enhance the safe service performance of corrosion-resistant tank steel, it is of significant importance to develop novel materials characterized by both high strength-toughness and a low yield ratio. In this study, four experimental steels with a gradient of Mo content (0, 0.15 [...] Read more.

To enhance the safe service performance of corrosion-resistant tank steel, it is of significant importance to develop novel materials characterized by both high strength-toughness and a low yield ratio. In this study, four experimental steels with a gradient of Mo content (0, 0.15 wt%, 0.30 wt%, and 0.60 wt% Mo) were prepared via thermomechanical controlled processing. The influence of Mo on the microstructural evolution and mechanical properties of the base metal was systematically investigated. The results revealed that when the Mo content was ≤0.15 wt%, the primary constituents of the matrix microstructure were polygonal ferrite, acicular ferrite, and granular bainitic ferrite. As the Mo content increased to 0.30 wt% and beyond, lath bainitic ferrite (LBF) emerged within the microstructure, and the size of the hard martensite/austenite constituents exhibited a refinement trend with increasing Mo content. Elevated Mo content enhanced the strength of the base metal, while the impact toughness initially increased and subsequently decreased. The equivalent grain size defined by misorientation tolerance angles of 2–6° contributed most significantly to the yield strength, as evidenced by its higher Hall–Petch fitting coefficient. The improvement in impact toughness was primarily attributed to the refinement of M/A constituents, which reduced crack initiation susceptibility, and the high density of high-angle grain boundaries (HAGBs) provided by the acicular ferrite. Conversely, the degradation in toughness was directly correlated with the coarsening of HAGB size and the reduction in HAGB density induced by the formation of LBF. Full article

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9 pages, 3245 KB

Open AccessCommunication

Effect of HfC Content on the Elevated-Temperature Ablation Behavior of W-HfC Composites

by Boyuan Zheng, Chaoqian Song, Yidong Wu, Zhong Du, Liye Du, Baohong Zhang and Xidong Hui

Metals 2025, 15(8), 925; https://doi.org/10.3390/met15080925 - 21 Aug 2025

Viewed by 463

Abstract

The effects of HfC content on the ablation resistance of W-HfC composites were systematically studied. The oxy-acetylene flame ablation test was conducted at 2800 °C. Post-ablation samples were characterized via XRD, section morphology, and EDS. W-10HfC showed the best ablation resistance, with a [...] Read more.

The effects of HfC content on the ablation resistance of W-HfC composites were systematically studied. The oxy-acetylene flame ablation test was conducted at 2800 °C. Post-ablation samples were characterized via XRD, section morphology, and EDS. W-10HfC showed the best ablation resistance, with a linear ablation rate of just 0.0175 mm/s. This enhanced performance is attributed to the formation of a dense HfW₂O₈ oxide layer with negative thermal expansion properties, reinforced by uniformly dispersed blocky HfO₂ particles. However, excessive HfC content induces a stratified oxide structure. The thermal expansion coefficient mismatch between HfW₂O₈ and HfO₂ causes microcrack formation, ultimately degrading ablation resistance. These findings establish critical guidelines for HfC content optimization in W-HfC composite design. Full article

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16 pages, 30287 KB

Open AccessArticle

Converting Iron-Bearing Tailings from Recycling of Urban Steel Scrap to Direct Reduced Iron via Magnetic Separation Followed by Hydrogen Reduction Under Microwave Irradiation

by Tianle Yin, Zhiwei Peng, Weiguang Tian, Wanlong Fan and Huimin Tang

Metals 2025, 15(8), 924; https://doi.org/10.3390/met15080924 - 21 Aug 2025

Viewed by 595

Abstract

In this study, the feasibility of converting iron-bearing tailings from urban steel scrap recycling to value-added direct reduced iron (DRI) via magnetic separation followed by hydrogen reduction under microwave irradiation was investigated, with an emphasis on the effect of reduction temperature. The experimental [...] Read more.

In this study, the feasibility of converting iron-bearing tailings from urban steel scrap recycling to value-added direct reduced iron (DRI) via magnetic separation followed by hydrogen reduction under microwave irradiation was investigated, with an emphasis on the effect of reduction temperature. The experimental results showed that by magnetic separation, the tailings sample with an iron content of 15.42 wt% could transit to a high-grade magnetic concentrate with an iron content of 60.04 wt% and good microwave absorption capability, as revealed by its short microwave penetration depth (D_p). After hydrogen reduction under microwave irradiation, the main iron-bearing phases, including magnetite, hematite, limonite, and martite, had stepwise deoxidation into metallic iron. As the reduction temperature increased from 750 °C to 1050 °C, the total iron content (TFe), reduction degree and iron metallization degree of the product increased rapidly and then became stable due to difficult reduction of FeO. As the reduction process proceeded, the dispersed iron particles gradually aggregated. At the optimum temperature of 950 °C, the reduction degree and iron metallization degree reached 90.10% and 88.71%, respectively. Meanwhile, the pore size, microporous volume, and specific surface area of the product were 1.943 nm, 1.767 × 10⁻⁵ cm³/g, and 0.3961 m²/g, respectively. The saturation magnetization (M_S) and coercivity (H_C) of the product remained 170.94 emu/g and 46.25 Oe, respectively. The product can act as a potential feedstock for electric arc furnace (EAF) steelmaking. Full article

(This article belongs to the Special Issue Metal Recovery and Separation from Scraps and Wastes)

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19 pages, 8293 KB

Open AccessArticle

Influence of Mn in Balancing the Tensile and Electrical Conductivity Properties of Al-Mg-Si Alloy

by Jiaxing He, Jiangbo Wang, Jian Ding, Yao Wang and Wenshu Qi

Metals 2025, 15(8), 923; https://doi.org/10.3390/met15080923 - 21 Aug 2025

Viewed by 563

Abstract

This study investigated the influence of manganese (Mn) on microstructure evolution and property optimization in Al-0.6Mg-0.58Si-0.24Fe-xMn alloys under both as-cast and hot-extruded conditions. The balance mechanisms of Mn in tensile properties and electrical conductivity of Al-Mg-Si alloy were elucidated, achieving synergistic optimization of [...] Read more.

This study investigated the influence of manganese (Mn) on microstructure evolution and property optimization in Al-0.6Mg-0.58Si-0.24Fe-xMn alloys under both as-cast and hot-extruded conditions. The balance mechanisms of Mn in tensile properties and electrical conductivity of Al-Mg-Si alloy were elucidated, achieving synergistic optimization of strength-elongation-conductivity. For non-equilibrium solidified as-cast alloys, JMatPro simulations coupled with Fe-rich phase size statistics reveal an inhibitory effect of Mn on β-Al₅FeSi phase formation. Matthiessen’s rule analysis quantitatively clarifies Mn-induced resistivity variations through solid solution and phase morphology modifications. In hot-extruded alloys, TEM characterization was used to analyze the structure of Al-Fe-Mn-Si quaternary compounds and clarify their combined effects with typical Mg₂Si phases on dislocation and subgrain configurations. The as-cast Al-0.6Mg-0.58Si-0.24Fe-0.18Mn alloy demonstrate comprehensive properties with ultimate tensile strength, elongation and electrical conductivity. The contributions of dislocations, grain boundaries and precipitates to resistivity are relatively minor, so the main source of resistivity in hot-extruded alloys is still Mn. The hot-extruded alloy containing 0.18 wt.% Mn still has better properties, with a tensile strength of 176 MPa, elongation of 24% and conductivity of 48.07 %IACS. Full article

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14 pages, 5842 KB

Open AccessArticle

Investigating the Effect of Calcium Addition on the Microstructural and Mechanical Properties of a Zn-Al-Cu-Mg Alloy via Squeeze Casting

by Thiyagesan Gopalakrishnan, Sankara Raman Sankaranarayanan and Subramanian Palani Kumaresh Babu

Metals 2025, 15(8), 922; https://doi.org/10.3390/met15080922 - 20 Aug 2025

Viewed by 553

Abstract

This study investigates on Zn-Al alloy microstructural characteristics and mechanical properties of a Zn-Al alloy with calcium (Ca) additions ranging from 0.5 to 1.5 wt.%. The base alloy composition is 94.95 wt.% Zn, 4.0 wt.% Al, 1.0 wt.% Cu, and 0.05 wt.% Mg, [...] Read more.

This study investigates on Zn-Al alloy microstructural characteristics and mechanical properties of a Zn-Al alloy with calcium (Ca) additions ranging from 0.5 to 1.5 wt.%. The base alloy composition is 94.95 wt.% Zn, 4.0 wt.% Al, 1.0 wt.% Cu, and 0.05 wt.% Mg, and it is utilized in various engineering applications, including domestic and automotive. The alloys were fabricated under controlled atmospheric conditions using the traditional squeeze casting technique. The squeeze-cast Zn-Al alloys with varying Ca content were characterized through chemical analysis, optical microscopy (OM), scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray diffraction (XRD) analysis. The microstructure of the Zn-Al alloy with Ca reinforcement comprises the intermetallic phase CaZn₁₃, which is distributed within the Zn-Al solid solution. The CaZn₁₃ phase within the Zn matrix exhibited a synergistic effect on grain refinement, resulting in a 96% reduction in grain size, as confirmed by SEM analysis. The mechanical properties of the Zn-Al alloy reinforced with calcium significantly enhanced microhardness and tensile strength. The results indicated that calcium additions up to 1.5 wt.% increased both microhardness and tensile strength, with the 1.0 wt.% calcium addition yielding the highest hardness value of 141 HV0.1 and a tensile strength of 359 MPa compared to the base alloy. These findings suggest that adding calcium enhances the grain refinement and mechanical properties of Zn-Al alloys. Full article

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24 pages, 19879 KB

Open AccessArticle

Residual Stress Field Effect on Fatigue Crack Growth Direction

by Peter Zobec and Jernej Klemenc

Metals 2025, 15(8), 921; https://doi.org/10.3390/met15080921 - 20 Aug 2025

Viewed by 549

Abstract

This study presents a novel approach to understanding fatigue and crack growth phenomena by benchmarking experimental observations with numerical simulations. We introduced controlled residual stress fields away from notch-induced crack nucleation sites and analyzed their interaction with crack nucleation and growth. Surprisingly, our [...] Read more.

This study presents a novel approach to understanding fatigue and crack growth phenomena by benchmarking experimental observations with numerical simulations. We introduced controlled residual stress fields away from notch-induced crack nucleation sites and analyzed their interaction with crack nucleation and growth. Surprisingly, our findings revealed that the introduction of generally beneficial compressive residual stresses had a counter-intuitive negative impact on product fatigue life. Despite daunting challenges in applying classical fatigue principles to describe crack nucleation and growth, our numerical simulations provided valuable insights, capturing the trend of observed crack paths, albeit not their velocity. This research sheds light on the complex interplay between residual stresses and crack propagation, offering important considerations for fatigue analysis and product design. Full article

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

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14 pages, 3808 KB

Open AccessArticle

A Method for Determining Twins and Corresponding Schmid Factors Based on Electron Diffraction

by Zhirui Li, Renlong Xin, Xin Wen and Jian Wang

Metals 2025, 15(8), 920; https://doi.org/10.3390/met15080920 - 20 Aug 2025

Viewed by 605

Abstract

Determining orientation relationships between different grains or phases via electron diffraction typically requires coincident zone axes, but it is difficult to achieve in most cases due to tilting angle limitations. To address this challenge, a straightforward method for determining the twinning relationship and [...] Read more.

Determining orientation relationships between different grains or phases via electron diffraction typically requires coincident zone axes, but it is difficult to achieve in most cases due to tilting angle limitations. To address this challenge, a straightforward method for determining the twinning relationship and twin variant in deformed metals is developed by interpreting the selected area electron diffraction (SAED) patterns and corresponding tilt angles in the transmission electron microscope (TEM). The transformation matrix from the sample coordinate system (SCS) to the crystal coordinate system (CCS) is derived to describe the orientation matrix of the observed target. This method is demonstrated by characterizing twins and corresponding Schmid factors in deformed Ti−15Mo alloy even when the zone axes are not coaxial. This method significantly facilitates the determination of multiple orientation relationships and the quantitative analysis of plastic deformation mechanisms in TEM. Full article

(This article belongs to the Section Crystallography and Applications of Metallic Materials)

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14 pages, 3359 KB

Open AccessArticle

Effects of Boron Addition on Microstructure and Mechanical Properties of B₄C/Al Composites Fabricated by Pressureless Infiltration

by Yao Liu, Jianle Xie, Hao Peng, Chunli Liu, Donglin Ma and Yongxiang Leng

Metals 2025, 15(8), 919; https://doi.org/10.3390/met15080919 - 19 Aug 2025

Viewed by 542

Abstract

Boron (B) is widely used as a neutron-absorbing nuclide and has significant applications in the nuclear industry. B₄C/Al composites combine the high hardness of B₄C with the ductility of Al, making them commonly used neutron-absorbing materials. Under current preparation [...] Read more.

Boron (B) is widely used as a neutron-absorbing nuclide and has significant applications in the nuclear industry. B₄C/Al composites combine the high hardness of B₄C with the ductility of Al, making them commonly used neutron-absorbing materials. Under current preparation methods, the poor wettability and low reactivity of B₄C with molten Al limit its effective incorporation into the matrix, and the addition of B₄C in B₄C/Al composites has reached its threshold limit, making it difficult to achieve breakthrough improvements in neutron absorption performance. However, incorporating additional B elements into the B₄C/Al composite can break this limit, effectively enhancing the material’s neutron absorption performance. Nevertheless, research on the impact of this addition on the mechanical properties of the composite remains unclear. The requirements for B₄C/Al composites as spent fuel storage and transportation devices include high mechanical strength and certain machinability. This study fabricated B₄C/Al composites with varying B contents (5 wt.%, 10 wt.%, and 15 wt.%), and the influence of B addition on the microstructure and mechanical properties of B₄C/Al composites was investigated. The results demonstrate that the composites exhibit a density of approximately 99% with well-established interfacial bonds. Increasing B content leads to a higher quantity of interfacial reaction products Al₃BC and AlB₂, enhancing the Vickers hardness to 370.93 HV. The bending strength and fracture toughness of composites with 5 wt.% and 15 wt.% B addition decreased, whereas those with 10 wt.% B exhibited excellent resistance to crack growth and high-temperature plastic deformation due to a high content of ductile phase. Full article

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20 pages, 4741 KB

Open AccessArticle

Electrochemical Characterization of CO₂ Corrosion Inhibition of API X100 by a Gemini Surfactant Under Static and Dynamic Conditions

by Andres Carmona-Hernandez, Rolando Abraham Sánchez-Garrido, Eduardo Palacios-González, Elizabeth America Flores-Frías, Aldo Emelio Landa-Gómez, Edgar Mejía-Sánchez, Araceli Espinoza-Vázquez, Ricardo Orozco-Cruz and Ricardo Galván-Martínez

Metals 2025, 15(8), 918; https://doi.org/10.3390/met15080918 - 19 Aug 2025

Viewed by 603

Abstract

In this research work, the electrochemical evaluation of a non-ionic gemini surfactant as a green corrosion inhibitor for X100 pipeline steel in CO₂-saturated brine solution was carried out by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves (PPC). The corrosion inhibition [...] Read more.

In this research work, the electrochemical evaluation of a non-ionic gemini surfactant as a green corrosion inhibitor for X100 pipeline steel in CO₂-saturated brine solution was carried out by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves (PPC). The corrosion inhibition performance of the gemini surfactant was studied in static and hydrodynamic conditions at room temperature and 60 °C. Electrochemical measurements showed that the inhibitor’s performance was enhanced with increasing inhibitor concentration and with increasing exposure time at room temperature, reaching the highest inhibition efficiency (η) at 100 ppm. With increasing temperature, the inhibitor efficiency decreased, with similar behavior at all concentrations. The analysis of the cathodic polarization curves at different rotation speeds showed the strong influence of mass transport on the cathodic process in the absence and the presence of the inhibitor. Under hydrodynamic conditions, PPC and EIS results indicated that the best inhibitor performance was with a concentration of 50 ppm, achieving a maximum inhibition efficiency of 91%. The adsorption of the inhibitor molecules on the surface obeyed the Langmuir isotherm, and the type of adsorption was mixed in all the study conditions. Surface characterization by scanning electron microscopy (SEM) revealed the formation of a protective corrosion inhibitor film. Full article

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

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22 pages, 6027 KB

Open AccessArticle

Study on the Process Characteristics of Picosecond Laser Trepan Cutting Hole Manufacturing for Heat-Resistant Steel

by Liang Wang, Long Xu, Changjian Wu, Yefei Rong and Kaibo Xia

Metals 2025, 15(8), 917; https://doi.org/10.3390/met15080917 - 19 Aug 2025

Viewed by 472

Abstract

Picosecond laser drilling offers high precision and quality, and compared to femtosecond lasers, it also balances processing efficiency, making it widely used across various fields. However, existing drilling processes still face issues such as roundness and taper. Therefore, further research into the processing [...] Read more.

Picosecond laser drilling offers high precision and quality, and compared to femtosecond lasers, it also balances processing efficiency, making it widely used across various fields. However, existing drilling processes still face issues such as roundness and taper. Therefore, further research into the processing characteristics of picosecond laser technology is needed to improve processing quality. This paper uses ANSYS software to conduct numerical simulations of picosecond laser ring-cutting drilling, analyzing the temperature field of microholes under ring-cutting scanning paths as parameters change. Experimental studies were conducted using AISI 310S heat-resistant stainless steel as the base material. This material exhibits excellent high-temperature oxidation resistance and strength retention, making it suitable for laser thermal processing. Using a single-factor method, the study investigated the influence of equidistant concentric circular paths and inner-dense-outer-sparse concentric circular paths on microhole morphology characteristics. The results show that the laser energy distribution is different under different paths. The entrance aperture of the equidistant concentric circle path is larger than that of the inner dense and outer sparse concentric circle path, while the exit aperture is smaller than the latter. Moreover, the roundness is also better than that of the inner dense and outer sparse concentric circle path. The taper of the inner dense and outer sparse concentric circle path is better than that of the equidistant concentric circle path. This study can provide a reference for the optimization of different processing paths in the future. Full article

(This article belongs to the Special Issue High-Energy Beam Machining of Metals)

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12 pages, 5636 KB

Open AccessArticle

CTOD Evaluation of High-Nitrogen Steels for Low-Temperature Welded Structures

by Min-Suk Oh, Young-Gon Kim and Sung-Min Joo

Metals 2025, 15(8), 916; https://doi.org/10.3390/met15080916 - 19 Aug 2025

Viewed by 552

Abstract

Welded structures, such as offshore platforms, require robust toughness in their heat-affected zones (HAZ) to withstand low-temperature environments. The coarse-grained HAZ (CGHAZ) adjacent to the fusion boundary often exhibits reduced toughness due to grain coarsening, particularly under high heat input welding conditions aimed [...] Read more.

Welded structures, such as offshore platforms, require robust toughness in their heat-affected zones (HAZ) to withstand low-temperature environments. The coarse-grained HAZ (CGHAZ) adjacent to the fusion boundary often exhibits reduced toughness due to grain coarsening, particularly under high heat input welding conditions aimed at enhancing productivity. To address this, high-nitrogen steels containing TiN particles were developed to suppress austenite grain growth by leveraging the thermal stability of TiN precipitates. Three high-nitrogen steels with varying carbon contents (0.09%, 0.11%, and 0.15%) were fabricated and subjected to crack tip opening displacement (CTOD) testing at −20 °C and −40 °C to evaluate low-temperature HAZ toughness. Results indicate that high-nitrogen TiN steels exhibit superior CTOD values (1.38–2.73 mm) compared to conventional 490-MPa class steels, with no significant reduction in toughness despite increased carbon content. This is attributed to the presence of stable TiN particles, which restrict austenite grain growth during welding thermal cycles, and the formation of fine ferrite–pearlite microstructures in the HAZ. These findings highlight the efficacy of high-nitrogen TiN steels in enhancing low-temperature fracture resistance for welded structures. Full article

(This article belongs to the Special Issue Advances in Welding Processes of Metallic Materials)

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19 pages, 5923 KB

Open AccessArticle

Microstructure and Properties of Bi-Sn, Bi-Sn-Sb, and Bi-Sn-Ag Solder Alloys for Electronic Applications

by Andrei-Alexandru Ilie, Florentina Niculescu, Gheorghe Iacob, Ion Pencea, Florin Miculescu, Robert Bololoi, Dumitru-Valentin Drăguț, Alexandru-Cristian Matei, Mihai Ghiţă, Adrian Priceputu and Constantin Ungureanu

Metals 2025, 15(8), 915; https://doi.org/10.3390/met15080915 - 18 Aug 2025

Viewed by 708

Abstract

The Bi-Sn, Bi-Sn-Ag, and Bi-Sn-Sb solder alloy systems represent lead-free, environmentally friendly alternatives for reliable electronic assembly. These alloys comply with increasingly strict environmental and health regulations, while offering low melting points suitable for soldering temperature-sensitive components. Microstructural analysis revealed distinct phase segregation [...] Read more.

The Bi-Sn, Bi-Sn-Ag, and Bi-Sn-Sb solder alloy systems represent lead-free, environmentally friendly alternatives for reliable electronic assembly. These alloys comply with increasingly strict environmental and health regulations, while offering low melting points suitable for soldering temperature-sensitive components. Microstructural analysis revealed distinct phase segregation in all alloys, with Sb promoting coarse Sn₂Sb₃ intermetallic compounds and Ag inducing fine needle-like Ag₃Sn precipitates. Eutectic refinement and compositional contrast were confirmed by SEM-BSE and EDS mapping. Vickers microhardness measurements revealed increased hardness in Sb- and Ag-modified Bi–Sn alloys, with Ag₃Sn dispersion yielding the highest strengthening effect, indicating enhanced mechanical potential. This study also reports the thermal and electrical conductivities of Bi60Sn40, Bi60Sn35Ag5, and Bi60Sn35Sb5 alloys over the 25–140 °C range. Bi60Sn40 showed an increase in thermal conductivity across the full temperature range from 16.93 to 26.93 W/m·K, while Bi60Sn35Ag5 reached 18.28 W/m·K at 25 °C, and Bi60Sn35Sb5 exhibited 13.90 W/m·K. These findings underline the critical influence of alloying elements on microstructure, phase stability, and thermophysical behavior, supporting their application in low-temperature soldering technologies. Full article

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32 pages, 1553 KB

Open AccessReview

Hydrometallurgical Treatment of EAF By-Products for Metal Recovery: Opportunities and Challenges

by Ewa Rudnik

Metals 2025, 15(8), 914; https://doi.org/10.3390/met15080914 - 17 Aug 2025

Viewed by 1437

Abstract

The electric arc furnace (EAF) is a key technology in the steel production industry, particularly for recycling scrap iron. It plays a crucial role in the shift to low-carbon metallurgy, responding to the growing demand for more sustainable production methods. Alongside its environmental [...] Read more.

The electric arc furnace (EAF) is a key technology in the steel production industry, particularly for recycling scrap iron. It plays a crucial role in the shift to low-carbon metallurgy, responding to the growing demand for more sustainable production methods. Alongside its environmental and energy benefits, the EAF process generates significant amounts of solid by-products, including dust (EAFD) and slag (EAFS). These wastes are not only rich in base metals but also contain critical elements, which have attracted increasing scientific and industrial interest. Depending on the waste type, key metals such as zinc (from EAFD) and chromium, vanadium, and titanium (from EAFS) are targeted for recovery. This review examines the chemical and phase compositions of these wastes, various leaching techniques (often combined with pretreatment stages), and methods for final metal recovery, either in their pure form or as compounds. Key challenges in hydrometallurgical routes include chloride contamination, the dissolution of refractory zinc ferrite, and impurity management. Despite current limited industrial adoption, hydrometallurgical approaches show significant promise as efficient and environmentally friendly solutions for resource recycling, offering high-purity metal recovery. Full article

(This article belongs to the Special Issue Recent Progress in Metal Extraction and Recycling)

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10 pages, 1814 KB

Open AccessArticle

Impact of Surface Preparation on the Quantification of Diffusible Hydrogen Content in Aluminum Alloys

by Mehrdad Hoseinpoor, Nikola Macháčková, Terezie Košová Altnerová, Sandrine Zanna, Darja Rudomilova and Tomáš Prošek

Metals 2025, 15(8), 913; https://doi.org/10.3390/met15080913 - 17 Aug 2025

Viewed by 685

Abstract

The impact of final surface preparation immediately prior to hydrogen content measurements in aluminum alloy samples was investigated using thermal desorption analysis (TDA). Samples ground in water showed an apparent hydrogen signal. Glow-discharge optical emission spectroscopy (GDOES) confirmed that the analyzed hydrogen originated [...] Read more.

The impact of final surface preparation immediately prior to hydrogen content measurements in aluminum alloy samples was investigated using thermal desorption analysis (TDA). Samples ground in water showed an apparent hydrogen signal. Glow-discharge optical emission spectroscopy (GDOES) confirmed that the analyzed hydrogen originated from the subsurface layer. X-ray photoelectron spectroscopy (XPS) revealed the presence of a thin aluminum oxide/hydroxide layer on the surface. Formation of these compounds indicates that hydrogen was introduced into the material by the reaction of oxide-free aluminum with water molecules during the grinding, followed by its entrapment at near-surface interstitial lattice sites. Chemical pickling in concentrated nitric acid and combined grinding, chemical pickling, and electrochemical polishing approaches are proposed as proper surface-preparation techniques for samples without and with adherent corrosion products, respectively. Full article

(This article belongs to the Special Issue Light Alloy and Its Application (2nd Edition))

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16 pages, 8293 KB

Open AccessArticle

Thermodynamic Modeling of Microstructural Design of Lightweight Ferritic Steels

by Tamiru Hailu Kori, Adam Skowronek, Jarosław Opara, Ana Paula Domingos Cardoso and Adam Grajcar

Metals 2025, 15(8), 912; https://doi.org/10.3390/met15080912 - 16 Aug 2025

Viewed by 565

Abstract

Ferritic lightweight steels are an emerging class of low-density steels (LDSs) with promising mechanical properties. The study aimed to develop two ferritic lightweight steels with different Mn concentrations. Al was incorporated to achieve the lightweighting effect due to its relatively low atomic mass [...] Read more.

Ferritic lightweight steels are an emerging class of low-density steels (LDSs) with promising mechanical properties. The study aimed to develop two ferritic lightweight steels with different Mn concentrations. Al was incorporated to achieve the lightweighting effect due to its relatively low atomic mass of substitutional solutions. The C concentration was kept at a minimum level to avoid the precipitation of carbides and the Mn addition was intended to increase solid solution strengthening. Thermodynamic calculations (Thermo-Calc) were employed to design the composition, analyze the phase constituents, and predict the phase transformation behavior. Microstructural investigation and hardness tests were conducted to experimentally verify the calculations. Both produced alloys exhibited a fully ferritic microstructure. Compared to industrially produced DP980 steel, a density reduction of about 7.2% and 8.3% was attained for the Fe-0.04C-5.5Al-1.6Mn-0.075Nb and Fe-0.04C-5.6Al-5.5Mn-0.08Nb steels, respectively. The steel with the higher Mn content showed increased hardness attributed to its solution strengthening effect. An increase in the hardness values was also measured with the progress in hot-rolling thickness reductions for both alloys. The alloying elements influenced the microstructural characteristics, phase transformation behavior, density, and hardness of the newly designed lightweight steels. Full article

(This article belongs to the Special Issue Thermodynamic Modeling of Phase Equilibrium in Metallic Materials)

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16 pages, 3863 KB

Open AccessArticle

Die-Casting Conditions for Pure Aluminum Heat Sink with Thin Fins

by Hiroshi Fuse and Toshio Haga

Metals 2025, 15(8), 911; https://doi.org/10.3390/met15080911 - 16 Aug 2025

Cited by 1 | Viewed by 593

Abstract

Heat sinks with thin and tall fins made from pure aluminum using die casting are in demand due to the higher thermal conductivity of pure aluminum compared to aluminum alloys. However, die casting of thin and tall fins using pure aluminum is considered [...] Read more.

Heat sinks with thin and tall fins made from pure aluminum using die casting are in demand due to the higher thermal conductivity of pure aluminum compared to aluminum alloys. However, die casting of thin and tall fins using pure aluminum is considered difficult because of the poor castability of pure aluminum. Casting conditions suitable for pure aluminum heat sinks with tall and thin fins were identified from flow length tests using a narrow-gap spiral die. Based on these findings, casting of pure aluminum heat sinks with thin and tall fins was attempted. The casting conditions that extended the flow length of pure aluminum were different from the conventional theoretical conditions for aluminum alloy die casting. Discovery of this unique result was very useful for the production of pure aluminum heat sinks using die casting. Specifically, using the appropriate plunger speed and die temperature to extend the flow length was effective for filling the thin fins with molten metal. As a result, it was clarified that pure aluminum heat sinks with thin and tall fins, having a height of 50 mm, a draft angle of 0.5°, and a fin top thickness of 0.5 mm, could be successfully produced using die casting. The heat dissipation properties of the pure aluminum heat sink with thin and tall fins were also evaluated. Full article

(This article belongs to the Special Issue Casting Alloy Design and Characterization—2nd Edition)

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19 pages, 11294 KB

Open AccessArticle

Study of Microstructure, Mechanical, and Corrosion Properties of K-TIG Welded Joints of 2205/316L Dissimilar Stainless Steel

by Shuwan Cui, Hongchen Li, Baoyan Zhang, Xiaozhen Liu and Ganli Mo

Metals 2025, 15(8), 910; https://doi.org/10.3390/met15080910 - 16 Aug 2025

Viewed by 619

Abstract

Stainless steel welding plays a critical role in industrial manufacturing due to its superior corrosion resistance and structural reliability. The keyhole tungsten inert gas (K-TIG) welding, renowned for its high efficiency, high precision, and cost-effectiveness, demonstrates particular advantages in medium-to-thick plate joining. In [...] Read more.

Stainless steel welding plays a critical role in industrial manufacturing due to its superior corrosion resistance and structural reliability. The keyhole tungsten inert gas (K-TIG) welding, renowned for its high efficiency, high precision, and cost-effectiveness, demonstrates particular advantages in medium-to-thick plate joining. In order to synergistically leverage the properties of 2205 duplex stainless steel (DSS) and 316L austenitic stainless steel (ASS), we have implemented K-TIG welding with a single variable under control: a constant current and voltage travelling speeds spanning 280–360 mm/min. Defect-free dissimilar joints were consistently achieved within the 280–320 mm/min speed window. The effects of welding speed on microstructural characteristics, mechanical properties, and corrosion behavior of the weld seams were systematically investigated. The percentage of austenite in the weld zone decreases from 84.7% to 59.9% as the welding speed increases. At a welding speed of 280 mm/min, the microstructural features in the regions near the weld seam and fusion zone were investigated. All obtained joints exhibited excellent tensile properties, with their tensile strengths surpassing those of the 316L base metal. The optimal impact toughness of 142 J was achieved at a welding speed of 320 mm/min. The obtained joints exceeded the hardness of TIG joints by 19%. Notably, the grain refinement in the weld zone not only enhanced the hardness of the welded joint but also improved its corrosion resistance. This study provides valuable process references in dissimilar stainless steel K-TIG welding applications. Full article

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11 pages, 2484 KB

Open AccessArticle

Effect of Aging Treatment on the Mechanical Properties and Impact Abrasive Wear Property of High-Manganese Steel

by Xiya Qiao, Ling Yan, Xiao Han, Xiangyu Qi, Xin Yang and Yu Xin

Metals 2025, 15(8), 909; https://doi.org/10.3390/met15080909 - 16 Aug 2025

Viewed by 565

Abstract

High manganese steel can improve its microstructure after aging treatment, which is beneficial for enhancing strength, toughness, and wear resistance. This study aims to explore the effect of aging treatment on mechanical properties and wear resistance of high manganese steel (containing 25% Mn, [...] Read more.

High manganese steel can improve its microstructure after aging treatment, which is beneficial for enhancing strength, toughness, and wear resistance. This study aims to explore the effect of aging treatment on mechanical properties and wear resistance of high manganese steel (containing 25% Mn, called Mn25 steel) by designing different aging temperatures (450 °C, 500 °C, and 550 °C) with the same aging time (1 h). The results indicated that with the increase in aging treatment temperature, the surface hardness of Mn25 steel first increased and then decreased, but was still higher than that of untreated Mn25 steel. In addition, the impact toughness of steel decreased first and then increased with the increase in aging temperature, with the optimal hardness and impact toughness exhibited at 550 °C. The impact abrasive wear test results showed that the weight loss of Mn25 steel decreased with the increase in aging treatment temperature. After aging treatment at 550 °C, the weight loss is the lowest, which shows the optimal wear resistance performance. Under a high-impact load of 5.0 J, the hardness increased by nearly 49.96% after impact abrasive wear, and the effective hardening layer of the steel was the thickest, about 3800 μm. This is mainly related to the best match between the hardness and impact toughness of high manganese steel after aging treatment. The wear morphology is often caused by various wear mechanisms working together to cause the wear loss of Mn25 steel during the impact wear process. The wear morphologies of the Mn25 steel were mainly characterized by press-in particles, furrow, spalling, and strain fatigue. Through experimental analysis, a suitable aging treatment process has been determined, providing a theoretical basis for the practical application of high manganese steel. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Metal Casting, Forming and Heat Treatment)

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23 pages, 12765 KB

Open AccessArticle

Optimization of Eleven Cross-Roll Straightening Process for 20CrMnTi Bars Based on Combined Hardening Model

by Shangwu Jia, Longyi Bao, Shijie Wang, Qingdang Meng, Jun Zhao and Ruixue Zhai

Metals 2025, 15(8), 908; https://doi.org/10.3390/met15080908 - 15 Aug 2025

Viewed by 558

Abstract

Straightness is one of the important indices to measure the quality of bars; multi-roll straightening is an essential process in bar production. Materials undergo multiple cycles of alternating tensile and compressive loading during multi-roll straightening, subject to the influence of the Bauschinger effect. [...] Read more.

Straightness is one of the important indices to measure the quality of bars; multi-roll straightening is an essential process in bar production. Materials undergo multiple cycles of alternating tensile and compressive loading during multi-roll straightening, subject to the influence of the Bauschinger effect. However, most existing studies have failed to adequately account for the Bauschinger effect, leading to insufficient prediction accuracy of the process. This study establishes an eleven-roll straightening finite element model (FEM) for bars based on the nonlinear combined hardening model. The orthogonal experimental design method is employed to optimize the process parameters. Straightening experiments of 20CrMnTi bars using an eleven-roll straightener were conducted. Based on the FEM, the influence patterns of different process parameters on the straightening results were investigated. The results indicate excellent agreement between the eleven-roll straightening finite element simulation results and the experimental results. Using the optimized parameters, both the simulated and experimental straightness after straightening were within 1‰, with a relative error between them below 8%. The findings of this study can improve the prediction accuracy of the eleven-roll bar straightening process and provide reliable theoretical support and technical reference for the optimization of straightening process parameters. Full article

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

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14 pages, 3164 KB

Open AccessArticle

Size Effect on Tensile Properties and Fracture Mechanism of Micro-Rolled Ultra-Thin Cu/Al Composite Sheet

by Pengkun Zhang, Hongmei Zhang, Guoao Yu and Zhengyi Jiang

Metals 2025, 15(8), 907; https://doi.org/10.3390/met15080907 - 15 Aug 2025

Viewed by 454

Abstract

In this study, a laboratory-precision four-high micro-rolling mill was employed to investigate the influence of grain size on the deformation behavior and fracture mechanism of a micro-rolled Cu/Al composite ultra-thin sheet. Analytical testing techniques including scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM+EDS), [...] Read more.

In this study, a laboratory-precision four-high micro-rolling mill was employed to investigate the influence of grain size on the deformation behavior and fracture mechanism of a micro-rolled Cu/Al composite ultra-thin sheet. Analytical testing techniques including scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM+EDS), X-ray diffraction (XRD), and unidirectional tensile experiments were utilized. The experimental results indicate that the grain size of the Cu/Al composite ultra-thin sheet increases with increasing annealing temperature and extended holding time while undergoing the first and second micro-rolling processes. Under identical annealing conditions, secondary micro-rolling leads to an increase in the grain size of Cu, while the growth rate of Al grains is reduced. Tensile tests and fracture surface observations reveal that as the annealing temperature increases, the grain size of the once-micro-rolled Cu/Al composite ultra-thin sheet also increases. When annealing at 400 °C for 40 min, the elongation reaches a maximum of 25.6%, with a tensile strength of 106.3 MPa. For the second micro-rolled samples, a maximum tensile strength of 114.8 MPa is achieved after annealing at a temperature of 360 °C for an 80 min holding time, although the elongation is significantly lower at 3.4%. This indicates that the fracture mode of the once-micro-rolled ultra-thin Cu/Al composite sheet is ductile fracture, whereas that of the second micro-rolled sample is brittle fracture. Full article

(This article belongs to the Special Issue Numerical Simulation and Experimental Research of Metal Rolling)

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15 pages, 10642 KB

Open AccessArticle

Effect of La/Zn on Microstructural Evolution and Mechanical Properties of Extruded Mg-9Gd-3Y Alloy

by Xiang Zhang, Yuyang Gao, Ang Zhang, Jing Zhao, Yan Song, Tian Li and Bin Jiang

Metals 2025, 15(8), 906; https://doi.org/10.3390/met15080906 - 15 Aug 2025

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Abstract

This study investigated the impact of La and Zn additions on the microstructure and mechanical properties (at room and high temperatures) of extruded Mg-9Gd-3Y (GW93) alloy. The incorporation of La and Zn induced the precipitation of granular second phases and LPSO phases, increasing [...] Read more.

This study investigated the impact of La and Zn additions on the microstructure and mechanical properties (at room and high temperatures) of extruded Mg-9Gd-3Y (GW93) alloy. The incorporation of La and Zn induced the precipitation of granular second phases and LPSO phases, increasing the second-phase area fraction in the Mg-9Gd-3Y-0.6La-1Zn (3GW93) alloy to 14.6%. Within the 3GW93 alloy, the Mg₁₂La phase exhibited the following crystallographic orientation relationship with the α-Mg matrix: (020)_Mg12La//(01

\bar{1}

0)_α-Mg and [10

\bar{1}

]_Mg12La//[

\bar{2}

110]_α-Mg. The 3GW93 alloy containing both La and Zn demonstrated the highest strength under both room- and high-temperature conditions. At room temperature, its yield strength (YS) and ultimate tensile strength (UTS) were 284 MPa and 354 MPa, respectively. This represents an increase of 83 MPa in YS and 70 MPa in UTS compared to the GW93 alloy (YS: 201 MPa, UTS: 284 MPa). Similarly, at 300 °C, the 3GW93 alloy (YS: 249 MPa, UTS: 285 MPa) exceeded the GW93 alloy (YS: 182 MPa, UTS: 244 MPa) by 67 MPa in YS and 41 MPa in UTS. The enhanced mechanical properties of the 3GW93 alloy are attributed to synergistic grain refinement and dispersion strengthening effects originating from the LPSO, Mg₅RE, and Mg₁₂La phases. Full article

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15 pages, 12102 KB

Open AccessArticle

Multi-Model Collaborative Optimization of Inconel 690 Deposited Geometry in Laser-Directed Energy Deposition: Machine Learning Prediction and NSGA-II Decision Framework

by Chen Liu, Junxiao Liu, Xiuyuan Yin, Xiaoyu Zhang, Shuo Shang and Changsheng Liu

Metals 2025, 15(8), 905; https://doi.org/10.3390/met15080905 - 14 Aug 2025

Viewed by 510

Abstract

The critical challenge of achieving precise geometric control in laser directed energy deposition (L-DED) of Inconel 690 for nuclear applications is addressed by this study. We established a data-driven optimization framework that reduces time-consuming trial-and-error experiments. A comprehensive process-geometry dataset was generated through [...] Read more.

The critical challenge of achieving precise geometric control in laser directed energy deposition (L-DED) of Inconel 690 for nuclear applications is addressed by this study. We established a data-driven optimization framework that reduces time-consuming trial-and-error experiments. A comprehensive process-geometry dataset was generated through full-factor experiments. Pearson correlation analysis revealed significant correlations: strong positive correlations between laser power and bead width (r = 0.82) and depth (r = 0.85), and between powder feed rate and height (r = 0.70). A hybrid machine learning model was subsequently developed. It used a Backpropagation Neural Network (BPNN) to achieve excellent prediction of width, height, and depth (R² ≤ 0.962). It also generated 100 uniformly distributed Pareto optimal process parameter sets via the Non-dominated Sorting Genetic Algorithm II (NSGA-II). Experimental validation confirmed the model’s high predictive accuracy—relative error ≤ 5% for width/depth, and a maximum relative error of 5.34% for height. This demonstrates the framework’s effectiveness for reliable multi-objective process optimization in high-precision deposition tasks. It also highlights its potential for use in nuclear component repair and other material systems. Full article

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

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15 pages, 11276 KB

Open AccessArticle

Influence of Casting Texture on Local Material Flow During ECAP of Commercially Pure Aluminum

by Nadja Berndt and Martin Franz-Xaver Wagner

Metals 2025, 15(8), 904; https://doi.org/10.3390/met15080904 - 14 Aug 2025

Viewed by 1032

Abstract

The plastic deformation during equal-channel angular pressing (ECAP) can be affected by various material- and processing-related factors. For instance, the initial crystal orientation and grain size play an important role in determining the material flow, which may cause localized deformation in terms of [...] Read more.

The plastic deformation during equal-channel angular pressing (ECAP) can be affected by various material- and processing-related factors. For instance, the initial crystal orientation and grain size play an important role in determining the material flow, which may cause localized deformation in terms of macroscopic deformation banding. In this study, we use a continuous cast AA1080 aluminum alloy with coarse columnar grains to analyze the influence of casting texture on the local material flow during ECAP. Billets are extracted with their columnar grains inclined either in the same direction as the ECAP shear plane or opposite to it. Visio-plastic analysis is performed on split billets. The pass is interrupted halfway through the ECAP tool to accurately capture steady-state deformation conditions. Flow lines at several positions within the billet are identified based on the positions of deformed and undeformed marker points and fitted to a phenomenological model based on a super-ellipse function. For further characterization, hardness measurements, optical and electron microscopy are carried out on the ECAP-deformed samples. Significant differences in terms of local material flow and microstructure evolution regarding the resulting crystal orientation and deformation banding are observed. Our results confirm and emphasize the importance of initial grain size and texture effects for ECAP processing. Full article

(This article belongs to the Special Issue Preparation, Formation and Application of Light Alloys and Their Composites)

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13 pages, 4949 KB

Open AccessArticle

Preparation and Characterization of MnFe₂O₄/Fe Soft Magnetic Composites by Surface Oxidation

by Shigeng Li, Rutie Liu and Xiang Xiong

Metals 2025, 15(8), 903; https://doi.org/10.3390/met15080903 - 14 Aug 2025

Viewed by 600

Abstract

MnFe₂O₄/Fe soft magnetic composites (SMCs) were designed by the surface oxidation method, and the MnFe₂O₄ layer was utilized as the insulation coating. The microstructure of SMCs and the chemical composition of the insulation layer were observed [...] Read more.

MnFe₂O₄/Fe soft magnetic composites (SMCs) were designed by the surface oxidation method, and the MnFe₂O₄ layer was utilized as the insulation coating. The microstructure of SMCs and the chemical composition of the insulation layer were observed using scanning electron microscopy and energy-dispersive spectroscopy. The surface phase composition of SMCs was characterized using X-ray diffraction, X-ray photoelectron spectrometry, and Raman spectroscopy. The effect of annealing temperature on the insulation layer was investigated, and its relationship with the magnetic properties of the MnFe₂O₄/Fe SMCs was explored. The best overall performances were obtained at 50 mT and 100 kHz with saturation magnetization M_s = 205 emu/g, amplitude permeability μ_a = 100, and a core loss of 234.9 W/kg. Therefore, this work can provide a method to develop a novel insulating coating to reduce core loss, which is of great significance to the investigation of other Fe-based soft magnetic composites for applications in high-frequency magnetic fields. Full article

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

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15 pages, 7895 KB

Open AccessArticle

Microstructural Characteristics of WC-Cu Cladding on Mild Steel Substrate Prepared Through Plasma Transferred Arc Welding

by Muhammad Hussain, Bosheng Dong, Zhijun Qiu, Ulf Garbe, Zengxi Pan and Huijun Li

Metals 2025, 15(8), 902; https://doi.org/10.3390/met15080902 - 13 Aug 2025

Viewed by 534

Abstract

This study explores the development of a novel composite coating system combining the high hardness of WC and thermal conductivity of Cu, employing the plasma transfer arc welding method under ambient conditions. Utilizing an advanced welding approach, the work investigates microstructural evolution and [...] Read more.

This study explores the development of a novel composite coating system combining the high hardness of WC and thermal conductivity of Cu, employing the plasma transfer arc welding method under ambient conditions. Utilizing an advanced welding approach, the work investigates microstructural evolution and phase formation in a WC-Cu-based coating applied to a mild steel substrate. Emphasis is placed on understanding the solidification behaviour and its influence on defects, microstructural refinement, and carbide formation. The study provides insights into the interactions between coating constituents and the underlying substrate under controlled thermal conditions. These findings demonstrate the potential for producing functionally graded coatings tailored for demanding wear and heat dissipation applications. The approach offers a pathway for enhancing the durability and performance of steel components in extreme service environments. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metallic Materials: Experiments and Modelling)

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14 pages, 3658 KB

Open AccessArticle

Research on the Vector Coherent Factor Threshold Total Focusing Imaging Method for Austenitic Stainless Steel Based on Material Characteristics

by Tianwei Zhao, Ziyu Liu, Donghui Zhang, Junlong Wang and Guowen Peng

Metals 2025, 15(8), 901; https://doi.org/10.3390/met15080901 - 12 Aug 2025

Viewed by 525

Abstract

The degree of anisotropy and heterogeneity in coarse-grained materials significantly affects ultrasonic propagation behavior and scattering. This paper proposes a vector coherent factor threshold total focusing imaging method (VCF-T-TFM) for austenitic stainless steel, based on material properties, through a combination of simulation and [...] Read more.

The degree of anisotropy and heterogeneity in coarse-grained materials significantly affects ultrasonic propagation behavior and scattering. This paper proposes a vector coherent factor threshold total focusing imaging method (VCF-T-TFM) for austenitic stainless steel, based on material properties, through a combination of simulation and experimentation. Three types of austenitic stainless steel weld test blocks with varying degrees of heterogeneity were selected containing multiple side-drilled hole defects, each with a diameter of 2 mm. Full-matrix data were collected using a 32-element phased array probe with a center frequency of 5 MHz. The grain size and orientation of the material were quantitatively observed via electron backscatter diffraction (EBSD). By combining the instantaneous phase distribution of the TFM image, the coarse-grained material coherence compensation value (C_A) and probability threshold (P_T) were optimized for different heterogeneous regions, and the vector coherence imaging threshold (γ) was adjusted. The defect imaging results of homogeneous material (carbon steel) and three austenitic stainless steels with different levels of heterogeneity were compared, and the influence of coarse-grained, anisotropic heterogeneous structures on the imaging signal-to-noise ratio was analyzed. The results show that the VCF-T-TFM, which considers the influence of material properties on phase coherence, can suppress structural noise. Compared to compensation results that did not account for material properties, the signal-to-noise ratio was improved by 97.3%. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Metallic Materials)

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11 pages, 5053 KB

Open AccessArticle

The Influence of Microcracks Generated During Forging on Crack Propagation in Steel Forgings

by Marek Grega and Janette Brezinová

Metals 2025, 15(8), 900; https://doi.org/10.3390/met15080900 - 12 Aug 2025

Viewed by 546

Abstract

This article investigates the formation of solidification cracks in steel forgings used for bearing rings in gear reducers of robotic arms. The forging and heat treatment processes, conducted under consistent technological conditions, revealed the occurrence of high-temperature annealing cracks caused by plasticity depletion [...] Read more.

This article investigates the formation of solidification cracks in steel forgings used for bearing rings in gear reducers of robotic arms. The forging and heat treatment processes, conducted under consistent technological conditions, revealed the occurrence of high-temperature annealing cracks caused by plasticity depletion during stress relaxation. Additionally, solidification cracks were analyzed, with chemical compositions and hardness measurements indicating susceptibility due to elevated carbon and chromium content, as well as a high cracking parameter. Die tool wear and damage during forging were identified as key contributors to crack formation, transferring surface defects, inclusions, and creating cracks that propagate during subsequent processing. The findings underscore the influence of the tooling conditions, material properties, and process parameters on the quality and reliability of steel forgings. Full article

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15 pages, 3120 KB

Open AccessArticle

Effect of Cu and Ag Content on the Electrochemical Performance of Fe40Al Intermetallic Alloy in Artificial Saliva

by Jesus Porcayo-Calderon, Roberto Ademar Rodriguez-Diaz, Jonathan de la Vega Olivas, Cinthya Dinorah Arrieta-Gonzalez, Jose Gonzalo Gonzalez-Rodriguez, Jose Guadalupe Chacón-Nava and José Luis Reyes-Barragan

Metals 2025, 15(8), 899; https://doi.org/10.3390/met15080899 - 11 Aug 2025

Viewed by 575

Abstract

This study investigates the effect of copper (Cu) and silver (Ag) additions on the electrochemical behavior of the Fe40Al intermetallic alloy in artificial saliva, aiming to evaluate its potential for biomedical applications such as dental implants. Alloys with varying concentrations of Ag (0.5, [...] Read more.

This study investigates the effect of copper (Cu) and silver (Ag) additions on the electrochemical behavior of the Fe40Al intermetallic alloy in artificial saliva, aiming to evaluate its potential for biomedical applications such as dental implants. Alloys with varying concentrations of Ag (0.5, 1.0, and 3.0 wt%) and Cu (1.0, 3.0, and 5.0 wt%) were synthesized and exposed to a biomimetic electrolyte simulating oral conditions. Electrochemical techniques, including open circuit potential (OCP), linear polarization resistance (LPR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS), were employed to assess corrosion performance. Results show that unmodified Fe40Al exhibits good corrosion resistance, attributed to the formation of a stable passive oxide layer. The addition of Cu, particularly at 3.0 wt%, significantly improved corrosion resistance, yielding lower corrosion current densities and higher polarization resistance and charge transfer resistance values, surpassing even 316L stainless steel in some metrics. Conversely, Ag additions led to a degradation of corrosion resistance, especially at 3.0 wt%, due to microstructural changes and the formation of metallic Ag precipitates, AgSCN, and galvanic cells, which promoted localized corrosion. EIS results revealed that Cu- and Ag-modified alloys developed less homogeneous and less protective passive layers over time, as indicated by increased double-layer capacitance (C_dl) and reduced constant phase element exponent (n_dl) values. Overall, the Fe40Al alloy shows intrinsic corrosion resistance in simulated physiological environments, and Cu additions can enhance this performance under controlled conditions. However, Ag additions negatively affect the protective behavior of the passive layer. These findings offer critical insight into the design of Fe-Al-based biomaterials for dental or biomedical applications where corrosion resistance and electrochemical stability are paramount. Full article

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

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22 pages, 6453 KB

Open AccessArticle

Experimental Study on the Microscale Milling Process of DD5 Nickel-Based Single-Crystal Superalloy

by Ying Li, Yadong Gong, Yang Liu, Zhiheng Wang, Junhe Zhao, Zhike Wang and Zelin Xu

Metals 2025, 15(8), 898; https://doi.org/10.3390/met15080898 - 11 Aug 2025

Viewed by 448

Abstract

Technological advances have expanded the use of single-crystal in microscale applications—particularly in infrared optics, electronics, and aerospace. Conducting research on the surface quality of micro-milling processes for single-crystal superalloys has become a key factor in expanding their applications. In this paper, the nickel-based [...] Read more.

Technological advances have expanded the use of single-crystal in microscale applications—particularly in infrared optics, electronics, and aerospace. Conducting research on the surface quality of micro-milling processes for single-crystal superalloys has become a key factor in expanding their applications. In this paper, the nickel-based single-crystal superalloy DD5 is selected as the test object, and the finite element analysis software ABAQUS 2022 version is used to conduct a simulation study on its micro-scale milling process with reasonable milling parameters. A three-factor five-level L₂₅(5³) slot milling orthogonal experiment is conducted to investigate the effects of milling speed, milling depth, and feed rate on its milling force and surface quality, respectively. The results show that the milling depth has the greatest impact on the milling force during the micro-milling process, while the milling speed has the greatest influence on the surface quality. Finally, based on the experimental data, the optimal parameter combination for micro-milling nickel-based single-crystal superalloy DD5 parts is found—when the milling speed is 1318.8 mm/s; the milling depth is 12 µm; the feed rate is 20 µm/s; and the surface roughness value is at its minimum, indicating the best surface quality—which has certain guiding significance for practical machining. Full article

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