Metals

17 pages, 3022 KB

Open AccessArticle

A Comparative Evaluation of Microbiologically Induced Corrosion Behaviors of 316L Austenitic and 2205 Duplex Stainless Steels Inoculated in Desulfovibrio vulgaris

by Zhong Li, Yuzhou Chen, Qiang Guo, Xiaohu Zhang, Xiaolong Li, Yong Li, Jiaxing Cai, Yi Fan and Jike Yang

Metals 2025, 15(9), 1040; https://doi.org/10.3390/met15091040 (registering DOI) - 19 Sep 2025

Abstract

Selecting appropriate materials is crucial for mitigating the severe economic and safety challenges posed by microbiologically induced corrosion (MIC) in marine and industrial settings. This study focuses on the MIC behavior of 316L austenitic stainless steel and 2205 duplex stainless steel that is [...] Read more.

Selecting appropriate materials is crucial for mitigating the severe economic and safety challenges posed by microbiologically induced corrosion (MIC) in marine and industrial settings. This study focuses on the MIC behavior of 316L austenitic stainless steel and 2205 duplex stainless steel that is caused by the metabolic activities of D. vulgaris during a life span of 7 days. Cell counts, weight loss, electrochemical measurements, and surface characterization were employed to evaluate the materials’ resistance to MIC. Specifically, 2205 DSS exhibited a 60% lower weight loss (0.02 vs. 0.05 mg/cm²), a 42% lower maximum pit depth (2.11 vs. 3.64 μm), and an orders-of-magnitude lower corrosion current density (0.094 vs. 2.0 μA cm⁻²) compared to 316L SS, demonstrating its superior resistance to D. vulgaris MIC. XRD and XPS analyses revealed that although FeS formed on both materials, FeS₂—a thermodynamically stable deep-sulfidation product—was only present on 316L, indicating a more advanced corrosion stage. The absence of FeS₂ on 2205 suggests limited sulfide corrosion progression. These findings confirm the advantage of duplex stainless steel in mitigating D. vulgaris-induced corrosion and provide insights into the selection of materials for MIC-prone environments. Full article

(This article belongs to the Section Corrosion and Protection)

► Show Figures

Figure 1

20 pages, 7089 KB

Open AccessArticle

Recovery of Cu and Fe from a Sphalerite Concentrate by the MnO₂–KI Leaching Oxidation System

by Aleksandar Jovanović, Dimitrije Anđić, Mladen Bugarčić, Ivana Jelić, Nela Vujović, Corby Anderson and Miroslav Sokić

Metals 2025, 15(9), 1039; https://doi.org/10.3390/met15091039 (registering DOI) - 19 Sep 2025

Abstract

This study examined the leaching behavior of copper and iron from a sphalerite concentrate in sulfuric acid utilizing an ensemble MnO₂–KI oxidizing system. The temperature was shown to significantly influence the leaching kinetics, with the efficiency notably improving between 40 °C [...] Read more.

This study examined the leaching behavior of copper and iron from a sphalerite concentrate in sulfuric acid utilizing an ensemble MnO₂–KI oxidizing system. The temperature was shown to significantly influence the leaching kinetics, with the efficiency notably improving between 40 °C and 80 °C. The introduction of KI affected the balance between sulfur passivation and oxidant availability, facilitating increased leaching efficiencies. At 3 wt% KI, maximum recoveries of 82.1% Cu and 85.3% Fe were achieved, which indicates a notable decrease in surface passivation. Kinetic study analysis revealed low activation energies of 28.90 kJ mol⁻¹ for copper and 18.94 kJ mol⁻¹ for iron, indicating that both processes proceed readily at moderate temperature regimes. Despite being diffusion-controlled, the mechanisms of dissolution are different: iron leaching is more complicated, involving pyrite oxidation, sulfur layer formation, transformation to marcasite, and ultimately iron (III) release, whereas copper leaching involves direct interaction of chalcopyrite with the oxidants, similar to the behavior of sphalerite. Full article

(This article belongs to the Special Issue Advances in Mineral Processing and Hydrometallurgy—3rd Edition)

► Show Figures

Figure 1

12 pages, 647 KB

Open AccessArticle

ISE of Precious Metals: Au, Ag, Pd, and Pt

by Lenka Girmanová, Jozef Petrík, Marek Šolc, Peter Blaško, Alena Pribulová and Peter Futáš

Metals 2025, 15(9), 1038; https://doi.org/10.3390/met15091038 - 19 Sep 2025

Abstract

Precious metals play an important role in various fields, from industry to jewelry and finance. In the industrial field, it is often necessary to know their mechanical properties. Micro-hardness measurement is a suitable test. In this type of test, the results are usually [...] Read more.

Precious metals play an important role in various fields, from industry to jewelry and finance. In the industrial field, it is often necessary to know their mechanical properties. Micro-hardness measurement is a suitable test. In this type of test, the results are usually influenced by the Indentation Size Effect (ISE). The paper addresses the problem of micro-hardness measurement and the subsequent interpretation of the measured values using Meyer’s index n, the PSR method, and the Hays–Kendall approach in order to determine the true, test-load-independent micro-hardness values of gold, silver, palladium, and platinum. The tester Hanemann (manufactured by Carl Zeiss, Jena, Germany) was used to measure micro-hardness. The loads applied during the micro-hardness test were between 0.09807 N and 0.9807 N. Investment precious metals with a declared purity of at least 99.95% were used for the measurements. Palladium and silver have a Meyer index close to the validity of Kick’s law, with neutral ISE. Gold and platinum show a slightly “normal” ISE. This may be the influence of the previous deformation of the sample. Full article

► Show Figures

Graphical abstract

17 pages, 8633 KB

Open AccessArticle

Microstructural Evolution and Tensile Deformation Behavior of FeCoNiCrTi_0.2 High-Entropy Alloys Regulated by Cold Rolling and Annealing

by Peng Zhang, Dehao Liu, Linfu Zhang, Kang Liu, Jie Zhang, Yuxiao Si, Gang Chen and Qiang Zhu

Metals 2025, 15(9), 1037; https://doi.org/10.3390/met15091037 - 19 Sep 2025

Abstract

Novel structural materials, high-entropy alloys (HEAs), have attracted considerable interest owing to their tunable microstructural designs and adjustable mechanical properties. In the present work, the microstructural evolution and tensile deformation behavior of FeCoNiCrTi_0.2 HEA are comprehensively examined through cold rolling (with 80% [...] Read more.

Novel structural materials, high-entropy alloys (HEAs), have attracted considerable interest owing to their tunable microstructural designs and adjustable mechanical properties. In the present work, the microstructural evolution and tensile deformation behavior of FeCoNiCrTi_0.2 HEA are comprehensively examined through cold rolling (with 80% thickness reduction) followed by annealing, combined with multiscale characterization techniques (EBSD/TEM) and mechanical tests. The results reveal that the as-rolled microstructure was characterized by the presence of strong Brass, Goss/Brass, and S textures, along with the formation of high-density dislocation walls (DDWs) and dislocation cells (DCs). As the annealing temperature increased, recrystallized grains preferentially nucleated at grain boundaries with higher stress concentrations and dislocation densities. The grain size decreased from 120.33 μm in the as-rolled state to 10.26 μm after annealing at 1000 °C. Low-angle grain boundaries (LAGBs) progressively transformed into high-angle grain boundaries (HAGBs), while the fraction of Σ3 twin boundaries initially decreased and subsequently increased, reaching a maximum of 43.7% after annealing at 1000 °C. At annealing temperatures exceeding 800 °C, deformed grains became equiaxed, with partial retention of primary texture components observed. After annealing at 1000 °C, the yield strength and tensile strength decreased compared to the as-rolled state, while the elongation significantly increased from 17.2% to 69.8% Simultaneously, the yield ratio decreased by 53%, and the strain-hardening capacity was enhanced. Ultimately, a constitutive model integrating the influences of dislocation mean free path and twin boundary obstruction was developed, providing microscopic explanations for the inverse relationship between strength and recrystallization fraction. Full article

(This article belongs to the Special Issue Sheet Metal Forming Processes)

► Show Figures

Figure 1

20 pages, 11452 KB

Open AccessArticle

Study on the Influence of Isotropic Simplification in Flexible Multi-Point Stretch-Bending Forming with Roller Dies

by Songyue Yang, Yu Wen, Ce Liang and Yi Li

Metals 2025, 15(9), 1036; https://doi.org/10.3390/met15091036 - 19 Sep 2025

Abstract

For the flexible multi-point stretch-bending forming process, which involves complex forming procedures, finite element (FE) modeling can significantly reduce trial-and-error costs and provide a convenient means for determining process parameters in actual production. During the creation of FE models, simplifying the material model [...] Read more.

For the flexible multi-point stretch-bending forming process, which involves complex forming procedures, finite element (FE) modeling can significantly reduce trial-and-error costs and provide a convenient means for determining process parameters in actual production. During the creation of FE models, simplifying the material model is crucial: insufficient simplification greatly increases computation time, while excessive simplification reduces model accuracy. This study establishes user material subroutines in the FE simulation software Abaqus to introduce anisotropic yield models, specifically Hill’s 48 and Yld2004-18p models. Multi-point stretch-bending experiments were repeated and compared with simulations using the traditional isotropic Von Mises yield model to analyze the impact of isotropic simplification on the accuracy of forming results. The applicability of isotropic simplification under different degrees of deformation is investigated, and the fundamental causes of errors are analyzed. Ultimately, the error response of the material simplified model is obtained. This provides an error reduction scheme for subsequent research using the isotropic simplified model. Full article

► Show Figures

Figure 1

25 pages, 2357 KB

Open AccessArticle

Gradient-Based Calibration of a Precipitation Hardening Model for 6xxx Series Aluminium Alloys

by Amir Alizadeh, Maaouia Souissi, Mian Zhou and Hamid Assadi

Metals 2025, 15(9), 1035; https://doi.org/10.3390/met15091035 - 19 Sep 2025

Abstract

Precipitation hardening is the primary mechanism for strengthening 6xxx series aluminium alloys. The characteristics of the precipitates play a crucial role in determining the mechanical properties. In particular, predicting yield strength (YS) based on microstructure is experimentally complex and costly because its key [...] Read more.

Precipitation hardening is the primary mechanism for strengthening 6xxx series aluminium alloys. The characteristics of the precipitates play a crucial role in determining the mechanical properties. In particular, predicting yield strength (YS) based on microstructure is experimentally complex and costly because its key variables, such as precipitate radius, spacing, and volume fraction (VF), are difficult to measure. Physics-based models have emerged to tackle these complications utilising advancements in simulation environments. Nevertheless, pure physics-based models require numerous free parameters and ongoing debates over governing equations. Conversely, purely data-driven models struggle with insufficient datasets and physical interpretability. Moreover, the complex dynamics between internal model variables has led both approaches to adopt heuristic optimisation methods, such as the Powell or Nelder–Mead methods, which fail to exploit valuable gradient information. To overcome these issues, we propose a gradient-based optimisation for the Kampmann–Wagner Numerical (KWN) model, incorporating CALPHAD (CALculation of PHAse Diagrams) and a strength model. Our modifications include facilitating differentiability via smoothed approximations of conditional logic, optimising non-linear combinations of free parameters, and reducing computational complexity through a single size-class assumption. Model calibration is guided by a mean squared error (MSE) loss function that aligns the YS predictions with interpolated experimental data using L2 regularisation for penalising deviations from a purely physics-based modelling structure. A comparison shows that the gradient-based adaptive moment estimation (ADAM) outperforms the gradient-free Powell and Nelder–Mead methods by converging faster, requiring fewer evaluations, and yielding more physically plausible parameters, highlighting the importance of calibration techniques in the modelling of 6xxx series precipitation hardening. Full article

(This article belongs to the Special Issue Modeling Thermodynamic Systems and Optimizing Metallurgical Processes)

► Show Figures

Figure 1

23 pages, 4917 KB

Open AccessArticle

Kinetics of the Reduction of Iron Ore Pellets with Hydrogen: A Parametric Experimental and Modeling Study

by Antoine Marsigny, Jean-Baptiste Letz, Olivier Mirgaux and Fabrice Patisson

Metals 2025, 15(9), 1034; https://doi.org/10.3390/met15091034 - 18 Sep 2025

Abstract

The direct reduction of iron ore by hydrogen is a serious candidate for reducing greenhouse gas emissions in the iron and steelmaking industry by replacing traditional blast furnace technology. The reduction kinetics are key to this process. The present paper reports an extensive [...] Read more.

The direct reduction of iron ore by hydrogen is a serious candidate for reducing greenhouse gas emissions in the iron and steelmaking industry by replacing traditional blast furnace technology. The reduction kinetics are key to this process. The present paper reports an extensive parametric study of the reduction of iron ore pellets with hydrogen that combines both experiments and modeling. A new model (modified grainy pellet model) was developed on the basis of the grainy pellet concept, the law of additive reaction times and the evolution of gas composition. The chemical kinetic constants of the three-step reduction reaction were determined from isothermal thermogravimetry experiments in the 600–900 °C temperature range. The model was then validated against laboratory-scale fixed-bed experimental results. A comparison with the experimental thermogravimetry results for a broad range of operating parameters shows the robustness of the model. The effects of temperature, gas dilution, gas flow rate, water content, pellet size, pressure, porosity, tortuosity, and specific surface area were investigated. The temperature, pellet size, pressure, gas composition and, particularly, the water content and gas flow rate have major influences on the reaction rate, in contrast to the initial porosity and specific surface area. Full article

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

► Show Figures

Graphical abstract

19 pages, 30585 KB

Open AccessArticle

Microstructure and Mechanical Properties of Ti35421 Alloy: A Comparison Between Laser Directed Energy Deposition (L-DED) and Rolling

by Zulei Liang, Bin Li, Jie Jiang, Hai Gu, Zhonggang Sun and Xianxiang Lu

Metals 2025, 15(9), 1033; https://doi.org/10.3390/met15091033 - 18 Sep 2025

Abstract

In this study, the newly developed Ti35421 (Ti3Al5Mo4Cr2Zr1Fe wt.%) alloy was prepared by laser directed energy deposition (L-DED) because it contains several major elements that can refine grains, which is expected to enable the transformation from columnar to equiaxed grains. The results show [...] Read more.

In this study, the newly developed Ti35421 (Ti3Al5Mo4Cr2Zr1Fe wt.%) alloy was prepared by laser directed energy deposition (L-DED) because it contains several major elements that can refine grains, which is expected to enable the transformation from columnar to equiaxed grains. The results show that the L-DED Ti35421 alloy is predominantly composed of equiaxed grains and features various α-phase morphologies, including grain boundary α, lath α, and acicular α′ structures. These microstructural features are attributed to the rapid cooling conditions during processing. Such a microstructure enhances the alloy’s tensile strength (1446 MPa) while leading to limited ductility (1.7%). Following the solution and aging treatment, the grain boundary α phase undergoes coarsening, while the matrix β phase transforms into numerous fine lamellar α phases. This leads to a reduction in strength but an improvement in ductility. Therefore, the optimal heat treatment process for the L-DED Ti35421 alloy is determined to be a two-stage procedure: first, heating at 780 °C for 2 h followed by air cooling, and subsequently heating at 575 °C for 8 h with air cooling. Under this treatment, the alloy exhibits excellent mechanical properties, including a tensile strength of 1196 MPa, a yield strength of 1162 MPa, an elongation of 6.8%, and a reduction in area of 16.7%. Since there are no continuous grain boundaries in α, the rolled Ti35421 alloy exhibits better ductility than the L-DED Ti35421 alloy. This article is a revised and expanded version of a poster presentation entitled “Microstructure and mechanical properties of Ti-3Al-5Mo-4Cr-2Zr-1Fe alloy fabricated by laser deposition manufacturing”, which was accepted and presented at the 15th World Conference on Titanium (Ti-2023), Edinburgh, UK, 12–16 June 2023. Full article

(This article belongs to the Special Issue Additive Manufactured Metal Structural Materials)

► Show Figures

Figure 1

16 pages, 13876 KB

Open AccessArticle

Effect of Electrochemical Hydrogen Charging on the Notch Tensile Properties of Natural Gas Transportation Pipeline Steel with Electroless-Plated Coatings and Their Adhesiveness Characterization

by Ladislav Falat, Lucia Čiripová, Viktor Puchý, Ivan Petrišinec and Róbert Džunda

Metals 2025, 15(9), 1032; https://doi.org/10.3390/met15091032 - 18 Sep 2025

Abstract

Traditional natural gas transportation pipeline steels, such as API 5L X42 grade and the higher grades, are currently receiving a lot of attention in terms of their potential implementation in hydrogen transmission infrastructure. However, the microstructural constitution of steels with a ferrite phase [...] Read more.

Traditional natural gas transportation pipeline steels, such as API 5L X42 grade and the higher grades, are currently receiving a lot of attention in terms of their potential implementation in hydrogen transmission infrastructure. However, the microstructural constitution of steels with a ferrite phase and the presence of welds, with their non-polyhedral “sharp” microstructures acting as structural notches, make these steels prone to hydrogen embrittlement (HE). In this work, the notch tensile properties of copper- or nickel–phosphorus-coated API 5L X42 grade pipeline steel were studied in both the non-hydrogenated and electrochemically hydrogen-charged conditions in order to estimate anticipated protective effects of the coatings against HE. Both the Cu and Ni–P coatings were produced using conventional coating solutions for electroless plating. To study the material systems’ HE sensitivity, electrochemical hydrogenation of cylindrical, circumferentially V-notched tensile specimens was performed in a solution of hydrochloric acid with the addition of hydrazine sulfate. Notch tensile tests were carried out for the uncoated steel, Cu-coated steel, and Ni–P-coated steel at room temperature. The HE resistance was evaluated by determination of the hydrogen embrittlement index (HEI) in terms of relative changes in notch tensile properties related to the non-hydrogenated and hydrogen-charged material conditions. The results showed that pure electroless deposition of both coatings induced some degree of HE, likely due to the presence of hydrogen ions in the coating solutions used and the lower surface quality of the coatings. However, after the electrochemical hydrogen charging, the coated systems showed improved HE resistance (lower HEI_RA values) compared with the uncoated material. This behavior was accompanied by the hydrogen-induced coatings’ deterioration, including the occurrence of superficial defects, such as bubbling, flocks, and spallation. Thus, further continuing research is needed to improve the coatings’ surface quality and long-term durability, including examination of their performance under pressurized hydrogen gas charging conditions. Full article

(This article belongs to the Special Issue Hydrogen Embrittlement of Metals: Behaviors and Mechanisms)

► Show Figures

Figure 1

2 pages, 416 KB

Open AccessCorrection

Correction: Ou et al. Manufacturing and Characterization of NiTi Alloy with Functional Properties by Selective Laser Melting. Metals 2018, 8, 342

by Shih-Fu Ou, Bou-Yue Peng, Yi-Cheng Chen and Meng-Hsiu Tsai

Metals 2025, 15(9), 1031; https://doi.org/10.3390/met15091031 - 18 Sep 2025

Abstract

In the original publication [...] Full article

► Show Figures

Figure 4

13 pages, 2169 KB

Open AccessArticle

Controlled Formation of Nanoislands During Microwave Annealing of Au Thin Films

by Ali Ghanim Gatea Al-Rubaye, Alaa Alasadi, Khalid Rmaydh Muhammed and Catalin-Daniel Constantinescu

Metals 2025, 15(9), 1030; https://doi.org/10.3390/met15091030 - 18 Sep 2025

Abstract

We present a systematic study on the fabrication of gold nanoislands by microwave-assisted annealing, a rapid and energy-efficient alternative to conventional thermal treatments. Gold thin films with nominal thicknesses of 4, 5, 6, 8, and 10 nm are deposited by thermal evaporation directly [...] Read more.

We present a systematic study on the fabrication of gold nanoislands by microwave-assisted annealing, a rapid and energy-efficient alternative to conventional thermal treatments. Gold thin films with nominal thicknesses of 4, 5, 6, 8, and 10 nm are deposited by thermal evaporation directly onto BK7 glass substrates, with and without a 3 nm chromium adhesion layer. The samples are subsequently annealed in a microwave kiln, where microwave irradiation is absorbed and converted to heat within the graphite-coated cavity (kiln), allowing the substrate temperature to exceed 550 °C, the threshold required for film dewetting. This process induces a controlled morphological evolution from continuous thin films to well-defined nanoislands, with the final size distribution strongly dependent on the initial film thickness. Compared with oven-based annealing, microwave treatment promotes faster and more uniform heating, which enhances atomic diffusion and accelerates dewetting while reducing the risk of substrate deformation or excessive coalescence. The resulting nanoislands exhibit tailored size-dependent plasmonic properties, with clear correlations between film thickness, crystallite size, and optical absorption features. Importantly, the method is cost-efficient, requiring shorter processing times and lower energy input, while enabling reproducible fabrication of high-quality plasmonic nanostructures on inexpensive glass substrates, suitable for applications in sensing, photonics, and nanophotonics. Full article

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

► Show Figures

Graphical abstract

22 pages, 15695 KB

Open AccessArticle

Microstructure Evolution of Keyhole Repair Using Refilling Friction Stir Spot Welding of 6082 Aluminum Alloys

by Liangliang Zhang and Guijie Yue

Metals 2025, 15(9), 1029; https://doi.org/10.3390/met15091029 - 17 Sep 2025

Abstract

The keyhole defect located at the termination of the friction stir welding (FSW) seam of 6082 aluminum alloys was repaired utilizing the refilling friction stir spot technique. This study examined the impact of the plunge depths on the microstructure of the welding spot. [...] Read more.

The keyhole defect located at the termination of the friction stir welding (FSW) seam of 6082 aluminum alloys was repaired utilizing the refilling friction stir spot technique. This study examined the impact of the plunge depths on the microstructure of the welding spot. The results show that under the action of shear stress introduced by the pin, the (111)[1

\bar{1}

0] shear texture and (112)[11

\bar{1}

] Copper texture were formed. The formation of (001)[100] Cube and (001)[310] Cube_ND textures was due to the occurrence of discontinuous dynamic recrystallization. When the plunge depth of the sleeve was 1.0 mm, the volume fraction of deformed grains in the welding spot reached 45%, and the tensile strength of the welding spots was 184 MPa. When the plunge depth of the sleeve was 1.5 mm, the tensile strength of the repaired spot welding was 210 MPa, which was basically equal to the strength of the FSW seam. Full article

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

► Show Figures

Figure 1

15 pages, 9972 KB

Open AccessArticle

Austenite Grain Growth Behavior and Dynamic Model of ADB790E Hydropower Steel

by Yuxuan Liu, Hongmei Zhang, Zhongxiang Yu and Zhengyi Jiang

Metals 2025, 15(9), 1028; https://doi.org/10.3390/met15091028 - 17 Sep 2025

Abstract

The growth behavior of austenite grains in ADB790E hydropower steel under the synergistic effects of heating temperature and holding time was studied using in situ quenching and an in situ high-temperature confocal laser scanning microscope (HT-CLSM) system. The experimental results indicate that the [...] Read more.

The growth behavior of austenite grains in ADB790E hydropower steel under the synergistic effects of heating temperature and holding time was studied using in situ quenching and an in situ high-temperature confocal laser scanning microscope (HT-CLSM) system. The experimental results indicate that the size of the austenite grains exhibits a significant coarsening trend as the heating temperature increases and the holding time extends. Based on the experimental data, the Beck’s model and Sellars’ model for austenite grain growth were constructed and compared and analyzed. The predicted grain size values obtained by the models have a strong correlation with the experimental measured values. To verify the accuracy of the model, the predicted values of the model were compared with the in situ observations of HT-CLSM. The results were highly consistent, effectively revealing the growth law of austenite grains of this steel grade during the thermal cycling process. Full article

► Show Figures

Figure 1

21 pages, 2630 KB

Open AccessArticle

Optimization of L-PBF Process Parameters: A Multi-Objective Framework for Variance Reduction and Mechanical Strength Enhancement Using Linear Programming and Multi-Objective Methods

by Alexander I. Khaimovich, Vitaliy G. Smelov, Viktoriya V. Kokareva and Vyacheslav P. Alekseev

Metals 2025, 15(9), 1027; https://doi.org/10.3390/met15091027 - 17 Sep 2025

Abstract

A new approach to the multi-criteria optimization of L-PBF process parameters in the face of high variability is proposed, based on the application of the reward function (RF), which is essentially the inverse of the Taguchi quality loss function (QLF [...] Read more.

A new approach to the multi-criteria optimization of L-PBF process parameters in the face of high variability is proposed, based on the application of the reward function (RF), which is essentially the inverse of the Taguchi quality loss function (QLF). The RF is defined as the logarithm of the ratio of the design parameter value to the minimum target parameter value. For values below 1, the RF becomes sharply negative. Logarithmic additivity enables the optimization of the target function to be defined as a sum of reward functions for the optimization criteria, each with a corresponding weight coefficient. This makes it possible to formulate the optimization problem in terms of linear programming. This approach was tested in the optimization of the L-PBF technological modes of AISI 321 powder, leading to a 6.7% increase in productivity. The mechanical properties of the samples obtained were not inferior to those of the alloyed samples using the previously recommended process parameters in terms of ultimate strength, and they exceeded the latter by 5% in terms of conditional yield strength. Process variability significantly decreased; the RMS of ultimate strength decreased nine-fold, conditional yield strength decreased ten-fold, and relative elongation decreased two-fold. Full article

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

► Show Figures

Figure 1

38 pages, 2245 KB

Open AccessReview

Nanoparticle Architecture Governing Antibacterial and Osteoinductive Responses in Bone-Integrating Implants

by Juliana Gaviria, Veronica Gaviria, Kamilla V. R. A. Silva, Ana Alcudia, Eduardo Padrón-Hernández and Yadir Torres

Metals 2025, 15(9), 1026; https://doi.org/10.3390/met15091026 - 16 Sep 2025

Abstract

Metallic nanoparticles (MNPs) have emerged as leading candidates in biomedical applications owing to their unique physicochemical properties and dual functionality, combining potent bactericidal and osteoinductive effects. These bioactivities are intricately governed by structural parameters such as size, shape, crystallinity, and chemical composition, which [...] Read more.

Metallic nanoparticles (MNPs) have emerged as leading candidates in biomedical applications owing to their unique physicochemical properties and dual functionality, combining potent bactericidal and osteoinductive effects. These bioactivities are intricately governed by structural parameters such as size, shape, crystallinity, and chemical composition, which collectively dictate their interactions with biological systems. These interactions affect key mechanisms including oxidative stress induction, membrane disruption, and modulation of cellular signaling pathways. Despite considerable progress, a comprehensive understanding of the structure property–activity-specific structural relationship in MNPs remains incomplete, hindering the rational design of optimized nanomaterials. This review critically examines recent advances in elucidating the bactericidal and osteoinductive mechanisms of MNPs, with a particular focus on the role of structural determinants. Furthermore, current challenges and future directions for tailoring nanoparticle architecture to enhance clinical performance are discussed. To address this, we conducted a systematic review of the literature published between 2005 and 2024 using Web and Web of Science direct and Scopus databases. Our analysis is structured around a structure →mechanism→outcome perspective, linking nanoparticle features to biological responses. Key insights include the following: (i) nanoparticles below ~20 nm generally enhance bacterial efficiency through enhanced membrane disruption; (ii) surface hydroxyl density above critical thresholds promotes osteogenic signaling; and (iii) safe concentration windows remain narrow, highlighting the importance of dose optimization. We conclude by discussing the translational challenges and future directions for tailoring nanoparticle architectures to advance clinical applications. Full article

(This article belongs to the Special Issue Study on the Preparation and Properties of Metal Functional Materials)

► Show Figures

Graphical abstract

19 pages, 25476 KB

Open AccessArticle

The Effect of Mo on the Microstructure and Mechanical Properties of High-Manganese Railway Frog Steel Produced with the Thermal Mechanical Control Process

by Junke Lin, Genhao Shi, Xiangyao Fu, Tiebing Tang, Qingfeng Wang and Ping Wang

Metals 2025, 15(9), 1025; https://doi.org/10.3390/met15091025 - 16 Sep 2025

Abstract

The aim of this study is to investigate the influence of Mo on the microstructure and mechanical properties of railway frog steel. To address the challenges of a coarse microstructure and alloy element segregation caused by the current casting method of railway frog [...] Read more.

The aim of this study is to investigate the influence of Mo on the microstructure and mechanical properties of railway frog steel. To address the challenges of a coarse microstructure and alloy element segregation caused by the current casting method of railway frog steel, the application of thermal mechanical control process (TMCP) technology can achieve a uniform and refined microstructure and stable mechanical properties, which is progress for the development of high-manganese railway frog steel. The TMCP of four experimental steels with varying Mo contents of 0.02~1.01 wt.% was simulated using a Gleeble 3500. The mechanical properties were tested, and the microstructure of each sample was characterized. A single austenite formed in each Mo-containing steel. With the increased Mo content, the grain boundary carbides decreased due to the formation of carbides within the grains, and the austenite and twin sizes were refined. Moreover, grain boundary strengthening and dislocation strengthening increased, while solid solution strengthening and precipitation strengthening had little effect, leading to an increase in the final yield strength. The contribution of dislocation strengthening to the yield strength was 51~56%, indicating that dislocation strengthening was the most significant strengthening method in the high-manganese railway frog steel produced using the TMCP. The impact energy showed a trend of first increasing and then decreasing, and the impact energy reached the highest point when the Mo content was 0.30 wt.%. In addition, the mechanisms governing the effect of increased Si in controlling the final microstructure and mechanical properties are discussed. Full article

► Show Figures

Figure 1

19 pages, 4493 KB

Open AccessArticle

Optimization Study of Laser-Drilling Processes in Stainless Steel Under Two Scanning Path Strategies

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

Metals 2025, 15(9), 1024; https://doi.org/10.3390/met15091024 - 15 Sep 2025

Abstract

To optimize the quality of picosecond laser drilling in stainless steel, this study systematically investigates the key influencing factors and optimization strategies of the laser-drilling process through experimental methods. In the experimental section, a single-factor comparison experiment was conducted to evaluate two picosecond [...] Read more.

To optimize the quality of picosecond laser drilling in stainless steel, this study systematically investigates the key influencing factors and optimization strategies of the laser-drilling process through experimental methods. In the experimental section, a single-factor comparison experiment was conducted to evaluate two picosecond laser-drilling paths. The results show that the holes produced using the equidistant concentric circle path exhibited superior overall quality. Based on this finding, further orthogonal experiments were carried out using the equidistant concentric circle path to optimize the process parameters. The orthogonal experimental results indicate that the number of scans has the most significant effect on the inlet hole diameter and roundness; the pulse energy greatly influences the outlet hole diameter, outlet roundness, and hole taper; and the scanning speed has the second-most significant effect on all hole parameters. By applying a comprehensive balancing method to the orthogonal experimental results, the optimal process parameters were determined: pulse energy at 90% (total power 30 W), 35 scans, and a scanning speed of 20 mm/s. This combination effectively reduced the hole taper, increased the roundness, and minimized the hole diameter, significantly improving the overall hole quality. Full article

► Show Figures

Figure 1

16 pages, 13804 KB

Open AccessArticle

The Effect of Cobalt Incorporation on the Microstructure and Properties of Cu(Co) Alloys for Use in Hybrid Bonding

by Sarabjot Singh and Kathleen Dunn

Metals 2025, 15(9), 1023; https://doi.org/10.3390/met15091023 - 15 Sep 2025

Abstract

In this study, the properties of Cu(Co) alloy films were investigated to assess their utility as an alternative material for interconnections in hybrid bonding applications. Thin films of Cu(Co) were deposited using electrochemical deposition in a standard sulfate-based electrolyte. X-ray photoelectron spectroscopy (XPS) [...] Read more.

In this study, the properties of Cu(Co) alloy films were investigated to assess their utility as an alternative material for interconnections in hybrid bonding applications. Thin films of Cu(Co) were deposited using electrochemical deposition in a standard sulfate-based electrolyte. X-ray photoelectron spectroscopy (XPS) of the films revealed that an increasing current density during deposition resulted in an increase in cobalt concentration. Bright-field scanning transmission electron microscopy (STEM) coupled with energy-dispersive x-ray spectroscopy (EDS) was used to visualize the fine-grained microstructure and confirmed grain boundary segregation of cobalt in the films. X-ray diffraction with a heated stage determined that the coefficient of thermal expansion (CTE) increased linearly with increasing cobalt content, from 17.5 ppm/K for pure copper to a maximum of 27.5 ppm/K for a film containing 24 at.% Co. Nanoindentation experiments found that the mechanical properties depended non-linearly on composition, with hardness increasing from 3.5 GPa for a 0% cobalt film to a maximum of 4.5 GPa (24 at.% Co) and the Young’s modulus increasing from 118 GPa to 214 GPa, respectively. Four-point probe electrical measurements confirmed the expected linear increase in resistivity as Co content increased. Since electrical and mechanical properties have differing dependences on the film composition, an optimal alloy composition that balances an acceptable increase in resistance with improved mechanical properties could enable more reliable, low-temperature bonding solutions in advanced microelectronic devices. Full article

(This article belongs to the Special Issue Solidification and Microstructure of Metallic Alloys)

► Show Figures

Figure 1

22 pages, 7835 KB

Open AccessArticle

Anodizing 3D-Printed AlSi10Mg Alloy and Its Fatigue Properties

by Hirotaka Kurita, Shinya Tako, Chika Tanaka, Kenji Hara, Kazunori Matsushima, Koji Satsukawa, Keita Watanabe and Hideki Kyogoku

Metals 2025, 15(9), 1022; https://doi.org/10.3390/met15091022 - 15 Sep 2025

Abstract

Two ways of anodizing 3D-printed AlSi10Mg alloy were characterized, and then their fatigue properties were evaluated. Test specimens were fabricated via a laser-powder bed fusion (L-PBF) process followed by machining. Normal and hard anodizing were both conducted in a sulfuric acid bath. The [...] Read more.

Two ways of anodizing 3D-printed AlSi10Mg alloy were characterized, and then their fatigue properties were evaluated. Test specimens were fabricated via a laser-powder bed fusion (L-PBF) process followed by machining. Normal and hard anodizing were both conducted in a sulfuric acid bath. The anodized layer was observed using FE-SEM/EDS. Fine Si particles dispersed in the matrix showing web-like patterns were incorporated in the anodized layer. By etching the Si particles away with Keller’s reagent, a characteristic maze-like 3D structure of anodized Al was observed. Then, rotating bending fatigue tests were carried out to evaluate the fatigue strength at 10⁷ cycles. The fatigue strength of the as-machined, normal-anodized and hard-anodized specimens was 106, 100 and 95 MPa, respectively. The fatigue limits were proportional to the surface roughness with higher linearity. By reducing the surface roughness, the fatigue strength of the hard-anodized specimen was improved. This result demonstrates the possibility of improving the fatigue properties of anodized components by reducing their surface roughness. Lastly, a CASS (copper-accelerated acetic acid salt spray) test was conducted, and superior corrosion resistance of the normal- and hard-anodized layers was verified. Full article

(This article belongs to the Section Additive Manufacturing)

► Show Figures

Figure 1

Journal Description

Metals

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Further Information

Guidelines

MDPI Initiatives

Follow MDPI