Metals

15 pages, 5886 KiB

Open AccessArticle

Low-Temperature Tempering to Tailor Microstructure, Mechanical and Contact Fatigue Performance in the Carburized Layer of an Alloy Steel for Heavy-Duty Gears

by Qingliang Li, Jian Wang, Gang Cheng and Qing Tao

Metals 2025, 15(9), 934; https://doi.org/10.3390/met15090934 - 22 Aug 2025

Abstract

Taking a typical carburized alloy steel for heavy-duty gears as the research object, this work regulates carburizing–quenching and tempering processes to conduct a layer-by-layer analysis of gradient-distributed microstructures and mechanical properties in the carburized layer. The effects of tempering temperature on martensite evolution, [...] Read more.

Taking a typical carburized alloy steel for heavy-duty gears as the research object, this work regulates carburizing–quenching and tempering processes to conduct a layer-by-layer analysis of gradient-distributed microstructures and mechanical properties in the carburized layer. The effects of tempering temperature on martensite evolution, mechanical properties, and wear resistance were specifically investigated. Results demonstrate that carburizing–quenching followed by cryogenic treatment generates high-carbon martensite at the surface, progressively transitioning to lath martensite towards the core. Low-temperature tempering promotes fine carbide precipitation, while elevated temperatures cause carbide coarsening. Specimens tempered at 175 °C achieve surface hardness of 800 HV and near-surface compressive yield strength of 2940 MPa. These samples exhibit 13% lower wear mass loss compared to 240 °C tempered counterparts, demonstrating superior wear resistance characterized by relatively flat wear surfaces, uniform contact stress distribution, and reduced cross-sectional plastic deformation zones. Key strengthening mechanisms at lower tempering temperatures involve solution strengthening, dislocation strengthening, and partial precipitation strengthening from carbides. Coherent carbides formed under these conditions impede fatigue dislocation motion via shearing mechanisms to suppress plastic deformation and fatigue crack initiation under contact fatigue stress, thereby enhancing wear performance. Full article

(This article belongs to the Special Issue Recent Advances in Fatigue and Corrosion Properties of Steels)

12 pages, 3903 KiB

Open AccessArticle

Fatigue Crack Initiation and Small Crack Propagation Behaviors of Simulated Specimens in a Ni-Based Superalloy

by Zuopeng Zhao, Xuteng Hu and Zhiwei Guo

Metals 2025, 15(9), 933; https://doi.org/10.3390/met15090933 - 22 Aug 2025

Abstract

The role of notch geometry and stress levels on fatigue crack initiation and small crack propagation behavior in the FGH96 superalloy was investigated using groove and bolt hole simulated specimens at 500 °C. The findings indicate that the fatigue crack initiation mechanisms and [...] Read more.

The role of notch geometry and stress levels on fatigue crack initiation and small crack propagation behavior in the FGH96 superalloy was investigated using groove and bolt hole simulated specimens at 500 °C. The findings indicate that the fatigue crack initiation mechanisms and the number of cracks are significantly affected by stress levels. The fatigue crack initiation life and its contribution to the total fatigue lives were analyzed for both specimen types. Notch geometry was found to have a more pronounced effect on crack propagation life than on initiation life under high applied stress. The smaller notch root radius could accelerate the occurrence of crack coalescence, thereby shortening the propagation life. These results are valuable for optimizing the fatigue damage tolerance design of FGH96 turbine discs. Full article

(This article belongs to the Special Issue Structural Integrity of Lightweight Alloys)

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46 pages, 2799 KiB

Open AccessArticle

A Simulation-Based Comparative Analysis of Physics and Data-Driven Models for Temperature Prediction in Steel Coil Annealing

by Ján Kačur, Patrik Flegner, Milan Durdán and Marek Laciak

Metals 2025, 15(9), 932; https://doi.org/10.3390/met15090932 - 22 Aug 2025

Abstract

Annealing of steel coils in bell-type furnaces is a critical process in steel production, requiring precise temperature control to ensure desired mechanical properties and microstructure. However, direct measurement of inner coil temperatures is impractical in industrial conditions, necessitating model-based estimation. This study presents [...] Read more.

Annealing of steel coils in bell-type furnaces is a critical process in steel production, requiring precise temperature control to ensure desired mechanical properties and microstructure. However, direct measurement of inner coil temperatures is impractical in industrial conditions, necessitating model-based estimation. This study presents a comparative analysis of physics-based and machine learning (ML) approaches for predicting internal temperatures during annealing. A finite difference method (FDM) was developed as a physics-based model and validated against experimental data from both laboratory and industrial annealing cycles. Furthermore, several ML models, including support vector regression (SVR), neural networks (NN), multivariate adaptive regression splines (MARS), k-nearest neighbors (k-NN), and random forests (RFs), were trained on surface temperature measurements to predict inner temperatures. The results demonstrate that the MARS, k-NN, and RF models achieved high prediction accuracy with performance index (PI) values below 1.0 on unseen data, demonstrating excellent generalization capabilities. In contrast, SVR with polynomial kernels and NN exhibited poor performance in specific configurations, highlighting their sensitivity to overfitting and data variability. The findings suggest that combining physics-based models with data-driven techniques offers a robust framework for soft-sensing in annealing operations, enabling improved process monitoring and control. Full article

(This article belongs to the Special Issue Characterization and Modeling of Microstructure Evolution During Metallic Material Processing)

19 pages, 4812 KiB

Open AccessArticle

Bainitic Transformation in 100Cr6 Steel for Bearing Balls: Effect on Fatigue Endurance

by Paolo Matteis and Raffaella Sesana

Metals 2025, 15(9), 931; https://doi.org/10.3390/met15090931 - 22 Aug 2025

Abstract

A set of bearing balls, fabricated with grade 100Cr6 bearing steel, was subjected either to ordinary quenching and tempering final heat treatment (leading to a mainly tempered martensitic microstructure) or to an alternative heat treatment (leading to a mainly bainitic microstructure). In order [...] Read more.

A set of bearing balls, fabricated with grade 100Cr6 bearing steel, was subjected either to ordinary quenching and tempering final heat treatment (leading to a mainly tempered martensitic microstructure) or to an alternative heat treatment (leading to a mainly bainitic microstructure). In order to compare their final properties and service performance, the balls were then subjected to rolling contact fatigue tests, as well as to other metallurgical and mechanical characterizations. Further mechanical tests, including tensile tests and rotating bending fatigue tests, were also performed on test specimens made with the same material and subjected to the same final heat treatments. The bainitic material, compared to the tempered martensitic one, exhibited a slightly better performance in the rotating bending fatigue tests, but not in the rolling contact fatigue tests. Full article

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

14 pages, 7282 KiB

Open AccessArticle

Effects of Sintering Pressure and Co Content on the Microstructure and Mechanical Performance of WC–Co Cemented Carbides

by Jinhu Ju, Dan Huang, Haitao Xu, Duo Dong, Jiangpeng Lou, Yuan Xu, Jiao Shi and Liu Zhu

Metals 2025, 15(9), 930; https://doi.org/10.3390/met15090930 - 22 Aug 2025

Abstract

The fabrication of WC-based cemented carbides faced challenges including inhomogeneous composition and grain coarsening. To solve these problems, WC–Co cemented carbides were fabricated via spark plasma sintering (SPS) using core–shell WC–Co powders prepared by an electroless plating method. The effects of sintering pressure [...] Read more.

The fabrication of WC-based cemented carbides faced challenges including inhomogeneous composition and grain coarsening. To solve these problems, WC–Co cemented carbides were fabricated via spark plasma sintering (SPS) using core–shell WC–Co powders prepared by an electroless plating method. The effects of sintering pressure and Co content on the microstructure and mechanical properties of the cemented carbides were investigated. The results showed that, with increasing sintering pressure, the relative density of the sintered samples was improved (98.4–99.6%) while the grains were coarsened (0.94–1.07 μm). The optimal properties (fracture toughness 11.11 MPa·m^1/2, and hardness 2100.3 HV30) were obtained when sintered with a pressure of 20 MPa. Grain coarsening at higher pressure (30 MPa) reduced the toughness of the cemented carbides. When the Co content was increased from 3 wt.% to 8 wt.%, fracture toughness was improved while the hardness of the cemented carbides was reduced, attributed to the intrinsic high toughness and low hardness of the Co phase. The WC–8 wt.% Co cemented carbides exhibited optimized synergic mechanical performance (hardness of 1874.2 HV30 and fracture toughness of 13.77 MPa·m^1/2). This work elucidated the relationship between the key sintering parameters (pressure and Co content) and the microstructure and mechanical properties of the cemented carbides. The achievements obtained provide a theoretical foundation for high-quality fabrication of the WC–Co cemented carbides. Full article

(This article belongs to the Special Issue Powder Metallurgy of Metals and Composites)

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17 pages, 1990 KiB

Open AccessArticle

Selective Separation of Antimony and Preparation of Sodium Antimonate by Sodium Salt Leaching-Synergistic Oxidation from High Arsenic Antimony Residue

by Yanliang Zeng, Jun Jin, Chunfa Liao and Fupeng Liu

Metals 2025, 15(9), 929; https://doi.org/10.3390/met15090929 - 22 Aug 2025

Abstract

In this study, the catalytic air oxidation method was used to selectively form sodium antimonate from an antimony residue Na₂S-NaOH leaching solution of a high arsenic copper anode slime. In the first stage, the leaching process with Na₂S and [...] Read more.

In this study, the catalytic air oxidation method was used to selectively form sodium antimonate from an antimony residue Na₂S-NaOH leaching solution of a high arsenic copper anode slime. In the first stage, the leaching process with Na₂S and NaOH media resulted in more than 98% leaching of antimony. The synergistic oxidation method was used to selectively separate antimony in the second stage. In this study, the oxidation rate of antimony was greater than 98% at the NaOH concentration of 50 g·L⁻¹ and a combined oxidation concentration of 0.75 g·L⁻¹ catechol + 0.75 g·L⁻¹ KMnO₄, under the air flow rates of 1.415 m³·min⁻¹ at 75 °C for 8 h. The pH of the crude sodium antimonate product was adjusted; subsequently, it was redissolved and precipitated to prepare refined sodium antimonate that meets the secondary product standard of China’s non-ferrous metal industry, which recommends an antimony recovery rate of >95.60%. After neutralisation, the liquid contains [As] < 0.10 g·L⁻¹, [Sb] = 0.16–0.38 g·L⁻¹, which can be reused in the composite leaching process. The apparent activation energy (Ea) of the catalytic oxidation reaction was 6.47 kJ·mol⁻¹; the results suggested that the reaction process was diffusion controlled.

- \frac{d [S b]}{d t} = 8.86 \times 10^{- 5} \times e^{\frac{- 778.44}{T}} \times {[S b]}^{0.4906} \times {[N a O H]}^{1.190}

. Full article

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13 pages, 2300 KiB

Open AccessArticle

Arc Quenching Effects on the Groove Shapes of Carbon Steel Tubes

by Tran Minh The Uyen, Van-Thuc Nguyen, Pham Quan Anh, Pham Son Minh and Nguyen Ho

Metals 2025, 15(9), 928; https://doi.org/10.3390/met15090928 - 22 Aug 2025

Abstract

This study investigates the impact of arc-hardening parameters on a groove-shaped S45C steel tube, with a focus on surface hardness and microstructure. According to the findings, when arc quenching occurs, the tube’s surface hardness increases significantly compared to its original hardness. The surface [...] Read more.

This study investigates the impact of arc-hardening parameters on a groove-shaped S45C steel tube, with a focus on surface hardness and microstructure. According to the findings, when arc quenching occurs, the tube’s surface hardness increases significantly compared to its original hardness. The surface layer hardness can increase to 50.3 HRC, which is 3.4 times greater than the untreated surface. Changing arc quenching parameters such as current intensity, gas flow rate, arc length, scan speed, heating angle, and cooling angle causes a variation in surface hardness due to the balance of heat input and cooling value. Moreover, the microhardness distribution is divided into three zones: the hardened zone (with a high hardness value), the heat-affected zone (HAZ), which has rapidly declining hardness, and the base metal (with a low hardness value). The hardened zone could have a hardness with a load of 0.3 N of 440 HV and a case depth of about 900 μm. The next zone is the HAZ, where the hardness with a load of 0.3 N drops significantly. The hardness in the base metal zone recovers to its original value of 152 HV. Interestingly, the microstructure, under the hardness distribution, illustrates the relationship between the hardness value and its phases. The hardened zone consists of martensite and residual austenite phases, resulting in a high hardness value. The bainite phase constitutes the HAZ, which correlates to the zone of rapid hardness reduction. Finally, the base metal zone has ferrite and pearlite microstructures, indicating the softest zone. The investigation’s findings may increase our understanding of the arc-hardening process and widen its industrial applications. Full article

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11 pages, 8503 KiB

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

Abstract

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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 KiB

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

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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