Metals

2 pages, 109 KiB

Open AccessEditorial

Advanced Applications of Artificial Intelligence in Metallic Materials Processing

by Panorios Benardos

Metals 2025, 15(2), 153; https://doi.org/10.3390/met15020153 - 1 Feb 2025

As the name of this Special Issue indicates, its aim was to highlight advanced applications of Artificial Intelligence (AI) in metallic materials processing, containing a final total of 12 published papers [...] Full article

(This article belongs to the Special Issue Advanced Applications of Artificial Intelligence in Metallic Materials Processing)

29 pages, 5792 KiB

Open AccessArticle

Probabilistic Modelling of Fatigue Behaviour of 51CrV4 Steel for Railway Parabolic Leaf Springs

by Vítor M. G. Gomes, Felipe K. Fiorentin, Rita Dantas, Filipe G. A. Silva, José A. F. O. Correia and Abílio M. P. de Jesus

Metals 2025, 15(2), 152; https://doi.org/10.3390/met15020152 - 1 Feb 2025

Abstract

The longevity of railway vehicles is an important factor in their mechanical and structural design. Fatigue is a major issue that affects the durability of railway components, and therefore, knowledge of the fatigue resistance characteristics of critical components, such as the leaf springs, [...] Read more.

The longevity of railway vehicles is an important factor in their mechanical and structural design. Fatigue is a major issue that affects the durability of railway components, and therefore, knowledge of the fatigue resistance characteristics of critical components, such as the leaf springs, must be extensively investigated. This research covers the fatigue resistance of chromium–vanadium alloy steel, usually designated as 51CrV4, from the high-cycle regime (HCF) (

10^{3}

–

10^{4}

) up to very high-cycle fatigue (VHCF) (

10^{9}

) under the bending loading conditions typical of leaf springs and under uniaxial tension/compression loading, respectively, for a stress ratio,

R_{σ}

, of −1. Different test frequencies were considered (23, 150, and 20,000 Hz) despite the material not exhibiting a relatively significant frequency effect. In order to create a new fatigue prediction model, two prediction models, the Basquin SN linear regression model and the Castillo–Fernandez–Cantelli (CFC) model, were evaluated. According to the analysis carried out, the CFC model provided a better prediction of the fatigue failures than the SN model, especially when outlier failure data were considered. The investigation also examined the failure modes, observing multiple cracks for higher loads and single cracks that initiated on the surface or from internal inclusions at lower loading. The present investigation aims to provide a fatigue resistance prediction model encompassing the HCF and VHCF regions for the fatigue design of railway wagon leaf springs, or even for other components made of 51CrV4 with a tempered martensitic microstructure. Full article

(This article belongs to the Special Issue Fracture Mechanics of Metals (2nd Edition))

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19 pages, 14656 KiB

Open AccessArticle

Research Progress on Development of PVP-Ag-Doped LaMnO₃ Composites for Methyl Orange Degradation

by Adina Căta, Madalina-Gabriela Ivanovici, Paula Svera, Ioana Maria Carmen Ienașcu and Paula Sfirloaga

Metals 2025, 15(2), 151; https://doi.org/10.3390/met15020151 - 1 Feb 2025

Abstract

Water pollution caused by emerging contaminants is increasing due to rising urbanization, industrialization, and agriculture production; therefore, new materials with high efficiency for wastewater decontamination are needed. A perovskite material based on 1% Ag-doped LaMnO₃ synthesized through a sol–gel technique was combined [...] Read more.

Water pollution caused by emerging contaminants is increasing due to rising urbanization, industrialization, and agriculture production; therefore, new materials with high efficiency for wastewater decontamination are needed. A perovskite material based on 1% Ag-doped LaMnO₃ synthesized through a sol–gel technique was combined with PVP in a 1:10 (w/w) ratio and subjected to different temperature and microwave conditions at various time intervals. The composite materials were obtained as thin films (S1, S2) or powders (S3) and were analyzed by modern techniques. The SEM analysis showed strongly agglomerated, asymmetric formations for the S1, S2 materials; as for the S3 composite, irregularly shaped grains of perovskite were deposited on the polymer surface. Small, round formations across the surface, mainly organized as clusters with conic/square-shaped particles and observed asperity on top, were highlighted by AFM images. The XRD spectra confirmed the presence of both the perovskite and PVP phases, and the crystallite size of the materials was determined to be in the range of 33–43 nm. The structural analyses, FT-IR, and Raman spectroscopy proved the interactions between the perovskite and the polymer, which led to novel composite materials. The different methods used for the synthesis of the new materials influenced their features and behavior. Moreover, the composites were successfully tested for methyl orange (MO) elimination from an acidic aqueous solution in dark conditions, with fast and complete (>95%) MO degradation at pH = 2. Full article

(This article belongs to the Special Issue Synthesis, Microstructure, and Properties of Lightweight Metal Matrix Composite Materials)

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10 pages, 2840 KiB

Open AccessArticle

The Effect of Final Cooling Temperature on Nano Cu Precipitation in a Cu-Bearing High-Strength Low-Alloy Steel

by Haitao Cui, Haicheng Liang, Xinglong Sun, Yonghua Li, Zhanjie Gao and Jinsong Liu

Metals 2025, 15(2), 150; https://doi.org/10.3390/met15020150 - 1 Feb 2025

Abstract

Nano Cu precipitation plays a crucial role in significantly improving the performance of the Cu-bearing high-strength low-alloy steel. The final cooling temperature effects the transformation products of austenite during the continuous cooling process, as well as the nano precipitations of steel. This study [...] Read more.

Nano Cu precipitation plays a crucial role in significantly improving the performance of the Cu-bearing high-strength low-alloy steel. The final cooling temperature effects the transformation products of austenite during the continuous cooling process, as well as the nano precipitations of steel. This study investigated the microstructure and hardness at different final cooling temperatures (750, 700, 650, 600, 550, and 500 °C) using the MMS-300 thermal simulation experimental machine (Northeastern University, Shenyang, China) and Vickers hardness tester. The changes in microstructure and the phase transformation law of austenite were determined during continuous cooling and then analyzed. The precipitation reaction of nano Cu precipitation during continuous cooling was studied using transmission electron microscopy (TEM), revealing the precipitation state under different final cooling temperature conditions. The results showed that the precipitations led to an increase and then a decrease in the microhardness, and the microhardness reaches its peak at 550 °C. The precipitations changed from spherical to elliptical, and the size gradually increased when the final cooling temperature increased. Full article

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

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16 pages, 15712 KiB

Open AccessArticle

Anisotropic Hardening of HC420 Steel Sheet: Experiments and Analytical Modeling

by Thamer Sami Alhalaybeh, Hammad Akhtar, Ashiq Iqbal Chowdhury and Yanshan Lou

Metals 2025, 15(2), 149; https://doi.org/10.3390/met15020149 - 1 Feb 2025

Abstract

Choosing the appropriate yield function is essential to precisely predicting the anisotropic hardening behavior of steel metals considering general loading directions. This research investigates the anisotropic hardening behavior of HC420 steel sheet by combining experimental and analytical modeling. Experiments are conducted for uniaxial [...] Read more.

Choosing the appropriate yield function is essential to precisely predicting the anisotropic hardening behavior of steel metals considering general loading directions. This research investigates the anisotropic hardening behavior of HC420 steel sheet by combining experimental and analytical modeling. Experiments are conducted for uniaxial tensile tests according to the three different directions and bulging tests to obtain hardening data. The experimental findings show that the loading direction affects the anisotropic behavior of HC420 steel’s strength and plastic deformation. The Chen-coupled quadratic and non-quadratic (Chen-CQN) approach is used to ensure the convexity of the HC420 steel. By comparing the Chen-CQN approach with the Yld2000-2d and Stoughton-Yoon’2009 yield functions, the Chen-CQN approach shows superiority in predicting the hardening behavior of the HC420 sheet, exhibiting a more straightforward numerical implementation and enhanced accuracy in yield stress predictions under different loading directions. Results from experimental hardening tests reveal that the Chen-CQN function precisely and flexibly characterizes the yield surface of HC420 steel, with a constant variation of within 2% from its predictions. Full article

(This article belongs to the Special Issue Metal Plastic Deformation and Forming)

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40 pages, 2946 KiB

Open AccessArticle

An Approach to Evaluate the Fatigue Life of the Material of Liquefied Gases’ Vessels Based on the Time Dependence of Acoustic Emission Parameters: Part 1

by Oleg G. Perveitalov and Viktor V. Nosov

Metals 2025, 15(2), 148; https://doi.org/10.3390/met15020148 - 31 Jan 2025

Abstract

In the first part of this article devoted to the assessment of the fatigue life of structural steels at low temperatures, a study was conducted on the effect of pre-cycling in a low-cycle fatigue mode on the time dependences of acoustic emission parameters. [...] Read more.

In the first part of this article devoted to the assessment of the fatigue life of structural steels at low temperatures, a study was conducted on the effect of pre-cycling in a low-cycle fatigue mode on the time dependences of acoustic emission parameters. Commonly used St-3 steel was tested at −60 °C with varying durabilities, after which it was fractured once during static tests. The multilevel acoustic model used made it possible to estimate the structural parameter at the stage of elastoplastic deformation. The stage of active development of microcracks and their coalescence corresponds to a homogeneous fracture with stable acoustic emission characteristics (signal duration, amplitude variation coefficient, etc.). It was shown that regardless of the maximum voltage (460, 480, and 500 MPa) in the cycle and the operating times of up to 0.3, 0.5, and 0.7, the structural parameter remains within the known limits. The parameters of the Weibull law distribution and the logarithmically normal distribution for the coefficient γ were obtained, theoretical and calculated fatigue curves were plotted, and a method was proposed for evaluating the number of cycles before fracture under irregular loading conditions in the real operation of pressure vessels based on the “rainflow” cycles counting method. Full article

(This article belongs to the Special Issue Fatigue Assessment of Metals)

18 pages, 1632 KiB

Open AccessArticle

Material Characterization and Technological Properties of Biocompatible Ti-12Al-42Nb Spherical Powder Alloy for Additive Manufacturing of Personal Medical Implants

by Alexander Anokhin, Andrey Kirsankin, Elena Kukueva, Alexander Luk’yanov, Maria Chuvikina, Elena Ermakova, Svetlana Strelnikova and Stepan Kupreenko

Metals 2025, 15(2), 147; https://doi.org/10.3390/met15020147 - 31 Jan 2025

Abstract

The paper focuses on material characterization and technology properties of a new Ti-12Al-42Nb spherical powder alloy for additive manufacturing of personal medical implants. The electrode induction melting inert gas atomization (EIGA) method was used to produce the powder alloy. The powder sphericity coefficient [...] Read more.

The paper focuses on material characterization and technology properties of a new Ti-12Al-42Nb spherical powder alloy for additive manufacturing of personal medical implants. The electrode induction melting inert gas atomization (EIGA) method was used to produce the powder alloy. The powder sphericity coefficient (PSC) was 1.02. Image J software was used to calculate the spherical degree by processing images sets from scanning electron microscopy (SEM) and optical microscopy (OM). SEM of particles cross-sections indicated internal thermal-induced porosity (TIP) with a 2.3 μm pore diameter. Particle size distribution was in the range from 15.72 μm (d10) to 64.48 μm (d100) as measured by laser particle analyzer. It was indicated that flowability and powder bulk density were 196 sec and 2.79 g/cm³, respectively. XRD analysis confirmed the beta phase of the powder alloy with no additional phases. X-ray fluorescence spectrometry confirmed the alloyed composition. Reducing and oxidative melting methods of analysis showed a slight amount of impurities: oxygen (0.0087 wt.%), nitrogen (0.03 wt.%), hydrogen (0.0012 wt.%), sulfur (0.0016 wt.%), and carbon (0.022 wt.%). Simultaneous thermal analysis (STA) was performed to indicate weight growth and losses and thermal effects in argon, nitrogen, and air as well as the oxidation of Al₂O₃, TiO₂, and Nb₂O₅ on the surface layer of Ti-12Al-42Nb powder alloy particles. Different phase transformations of γAl₂O₃ θAl₂O₃ αAl₂O₃ and TiO₂ rutile TiO₂ anatase phase transformation were detected by STA in the oxidative layer. Full article

23 pages, 6599 KiB

Open AccessArticle

Enhancement of Corrosion Resistance of MAO/Polydopamine/Polylactic Acid-Coated AZ31 Magnesium Alloy for Biomedical Applications

by Annalisa Acquesta, Fulvia Desiderio, Pietro Russo, Giulia Stornelli, Andrea Di Schino and Tullio Monetta

Metals 2025, 15(2), 146; https://doi.org/10.3390/met15020146 - 31 Jan 2025

Abstract

This paper aimed to investigate the enhancement of the corrosion resistance of a protective system applied on the AZ31 magnesium alloy to be used as an orthopedic biomedical device, composed of three different superimposed layers: (a) magnesium-based oxide, (b) polydopamine, and (c) polylactic [...] Read more.

This paper aimed to investigate the enhancement of the corrosion resistance of a protective system applied on the AZ31 magnesium alloy to be used as an orthopedic biomedical device, composed of three different superimposed layers: (a) magnesium-based oxide, (b) polydopamine, and (c) polylactic acid. Specifically, morphological and chemical analyses, crystallographic, roughness, and micro-hardness were carried out. The electrochemical measurements were performed in Hanks’ Balanced Salt solution at 37 °C. The micro arc oxidation (MAO) treatment involved the classic pancake structure of the oxide with a consequent high extension of the real area.The sealing ofits pores via the polydopamine was well highlighted through the surface roughness analysis. As expected, the magnesium oxide layer reduced the degradation rate.The presence of polydopamine on the oxide layer improved the corrosion resistance of the alloy, showing a pseudo-passivity range in the potentiodynamic polarization curve, due to the filling of oxide pores.The highest impedance modulus in the electrochemical impedance spectroscopy analysis during the temporal observation of 168 h was observed when all coatings were applied on magnesium substrate, due to a synergetic action. Thus, the multilayers should represent a protective system to control the degradation process. Full article

(This article belongs to the Topic Microstructure and Properties in Metals and Alloys, 3rd Volume)

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25 pages, 5349 KiB

Open AccessArticle

Analysis of Nonuniform Deformation in Aluminum Wires Under Varying Torsional Loads Using EBSD Measurement and Multiscale Crystal Plasticity

by Mohammad Javad Rezaei, Fernando Warchomicka, Maria Cecilia Poletti, Mojtaba Pourbashiri and Mohammad Sedighi

Metals 2025, 15(2), 145; https://doi.org/10.3390/met15020145 - 30 Jan 2025

Abstract

Computational crystal plasticity (CP) models are widely utilized in the literature to analyze the deformation responses of materials at the microstructural level under macroscopic loading conditions. The challenge of connecting changes in texture with macroscopic loading can be effectively addressed through a multiscale [...] Read more.

Computational crystal plasticity (CP) models are widely utilized in the literature to analyze the deformation responses of materials at the microstructural level under macroscopic loading conditions. The challenge of connecting changes in texture with macroscopic loading can be effectively addressed through a multiscale CPFE approach. This research focuses on bridging changes in texture and macroscopic loading in pure aluminum wire under torsional loading through the innovative use of the multiscale CP finite element simulation approach and integration with experimental data. The study deals with the effects of the initial average grain size, strain rate, and strains on microstructural evolution at room temperature and mechanical properties. An inhomogeneous initial texture for an as-received specimen was extracted using EBSD measurements and assigned to a CP code to solve the multiscale CPFEM simulations. Changes in texture obtained from pole figures indicated that the and () [] components had the highest frequencies among the torsional tests. The analysis of the resulting texture through the Taylor factor (TF) revealed that the average TF distribution increased from 2.65 to 3.04 when the local strain increased from 0.5 to 2.5 revolutions. Furthermore, an increase in the number of rotations from 0.5 to 2.5 resulted in an 11% increase in average hardness near the outer surface of specimens with an average grain size of 55 µm. Full article

(This article belongs to the Special Issue Plasticity and Metal Forming)

15 pages, 11415 KiB

Open AccessArticle

In Situ Synthesis of MoSi₂-SiC Composites by Two-Step Spark Plasma Sintering

by Yue-Yao Wang and Guo-Hua Zhang

Metals 2025, 15(2), 144; https://doi.org/10.3390/met15020144 - 30 Jan 2025

Abstract

The effect of different SiC doping content on the properties of MoSi₂-based composites was analyzed in this study. The MoSi₂-SiC composites were fabricated in situ by the SPS technique, utilizing self-synthesized carbon-containing Mo powder and Si powder as raw [...] Read more.

The effect of different SiC doping content on the properties of MoSi₂-based composites was analyzed in this study. The MoSi₂-SiC composites were fabricated in situ by the SPS technique, utilizing self-synthesized carbon-containing Mo powder and Si powder as raw materials. A two-step sintering process was employed to ensure the formation of a uniform and dense composite structure. The microstructures and mechanical properties of these composites with various compositions were characterized. The results show that the composites were primarily composed of MoSi₂, SiC, and a minor proportion of MoSiC phase. The introduction of SiC as a second phase was found to considerably enhance the mechanical properties of the MoSi₂ matrix material. In particular, the MoSi₂-26mol.%SiC sample exhibited Vickers hardness, fracture toughness, and flexural strength values of 16.1 GPa, 6.7 MPa·m^1/2, and 496 MPa, respectively, corresponding to increases of 33%, 24%, and 28% compared to the pure MoSi₂ material. Full article

(This article belongs to the Special Issue Design and Development of Metal Matrix Composites)

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27 pages, 41979 KiB

Open AccessArticle

Integrating Temperature History into Inherent Strain Methodology for Improved Distortion Prediction in Laser Powder Bed Fusion

by Iñaki Setien, Michele Chiumenti, Maria San Sebastian, Carlos A. Moreira and Manuel A. Caicedo

Metals 2025, 15(2), 143; https://doi.org/10.3390/met15020143 - 30 Jan 2025

Abstract

Powder bed fusion–laser beam (PBF-LB) additive manufacturing enables the production of intricate, lightweight metal components aligned with Industry 4.0 and sustainable principles. However, residual stresses and distortions challenge the dimensional accuracy and reliability of parts. Inherent strain methods (ISMs) provide a computationally efficient [...] Read more.

Powder bed fusion–laser beam (PBF-LB) additive manufacturing enables the production of intricate, lightweight metal components aligned with Industry 4.0 and sustainable principles. However, residual stresses and distortions challenge the dimensional accuracy and reliability of parts. Inherent strain methods (ISMs) provide a computationally efficient approach to predicting these issues but often overlook transient thermal histories, limiting their accuracy. This paper introduces an enhanced inherent strain method (EISM) for PBF-LB, integrating macro-scale temperature histories into the inherent strain framework. By incorporating temperature-dependent adjustments to the precomputed inherent strain tensor, EISM improves the prediction of residual stresses and distortions, addressing the limitations of the original ISM. Validation was conducted on two Ti-6Al-4V geometries—a non-symmetric bridge and a complex structure (steady blowing actuator)—through comparisons with experimental measurements of temperature, distortion, and residual stress. Results demonstrate improved accuracy, particularly in capturing localized thermal and mechanical effects. Sensitivity analyses emphasize the need for adaptive layer lumping and mesh refinement in regions with abrupt stiffness changes, such as shrink lines. While EISM slightly increases computational cost, it remains feasible for industrial-scale applications. This work bridges the gap between simplified inherent strain models and high-fidelity simulations, offering a robust tool for simulation-driven optimisation. Full article

(This article belongs to the Special Issue Advances in 3D Printing Technologies of Metals—2nd Edition)

14 pages, 1197 KiB

Open AccessArticle

Molecular Dynamics Investigation on Grain Size-Dependent Superelastic Behavior of CuZr Shape Memory Alloys

by Mixun Zhu, Kai Wang, Hongtao Zhong, Huahuai Shen, Yong Zhang, Xiaoling Fu and Yuanzheng Yang

Metals 2025, 15(2), 142; https://doi.org/10.3390/met15020142 - 29 Jan 2025

Abstract

The superelasticity of CuZr shape memory alloys (SMAs) originates from stress-induced transformations between the B2 (austenite) and B19’ (martensite) phases. Grain size is a key parameter affecting the superelasticity of shape memory alloys. Previous studies on NiTi, Fe-based, and Cu-based SMAs confirm that [...] Read more.

The superelasticity of CuZr shape memory alloys (SMAs) originates from stress-induced transformations between the B2 (austenite) and B19’ (martensite) phases. Grain size is a key parameter affecting the superelasticity of shape memory alloys. Previous studies on NiTi, Fe-based, and Cu-based SMAs confirm that altering grain size effectively regulates superelasticity. Current research on the influence of grain size on the superelasticity of CuZr shape memory alloys (SMAs) is relatively sparse. This study employs molecular dynamics simulations to evaluate the effect of grain size on the superelasticity of CuZr SMAs through uniaxial loading–unloading tests. Polycrystalline samples with grain sizes of 6.59 nm, 5 nm, and 4 nm were analyzed. The results indicate that reducing grain size can decrease the irrecoverable strain, thereby enhancing superelasticity. The improvement in superelasticity is attributed to a higher recovery rate of the martensite-to-austenite transformation, allowing more plastic deformation within the grain interior to recover during unloading, and thereby reducing the irrecoverable strain. The recovery rate of the martensite-to-austenite transformation is closely related to the elastic strain energy accumulated within the grain interior during loading. Full article

20 pages, 16570 KiB

Open AccessArticle

Effect of Al-5Ti-1B-xCe Refiner on Microstructure and Mechanical Properties of Cast Al-5Mg-3Zn-1Cu Alloys

by Shenshen Cui, Qiang Lu, Qudong Wang, Dezhi Li and Chuan Lei

Metals 2025, 15(2), 141; https://doi.org/10.3390/met15020141 - 29 Jan 2025

Abstract

The effects of Ce content on the microstructure and phase composition of the Al-5Ti-1B refiner and the refining effect of the Al-5Ti-1B-xCe (x = 0, 1, 5, 10 wt.%) refiner on the grain size, microstructure, and mechanical properties of Al-5Mg-3Zn-1Cu alloys were studied. [...] Read more.

The effects of Ce content on the microstructure and phase composition of the Al-5Ti-1B refiner and the refining effect of the Al-5Ti-1B-xCe (x = 0, 1, 5, 10 wt.%) refiner on the grain size, microstructure, and mechanical properties of Al-5Mg-3Zn-1Cu alloys were studied. The results show that the addition of 1.0 wt.% Ce in the Al-5Ti-1B refiner changes the TiAl₃ phase from block to strip, and the massive Ti₂Al₂₀Ce phase is formed. When the Ce content of the Al-5Ti-1B refiner increases to 5.0 wt.%, the plate-like TiAl₃ phase is surrounded by the Ti₂Al₂₀Ce phase, and the reticulate Al₄Ce phase is formed. With the Ce content of the Al-5Ti-1B refiner further increasing to 10.0 wt.%, a lot of network distribution Al₄Ce phase is formed. The volume of the Mg₃₂(AlCuZn)₄₉ phase of the as-cast Al-5Mg-3Zn-1Cu alloys is reduced after refining with the Al-5Ti-1B-xCe refiner. The Al-5Ti-1B-1Ce refiner has the best refining effect on as-cast Al-5Mg-3Zn-1Cu alloys, and the grain size of as-cast Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B-1Ce refiner is reduced by 43% compared with as-cast Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B refiner. Compared to the aged Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B refiner, the yield strength, ultimate tensile strength, and fracture elongation of aged Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B-5Ce refiner are improved by 4.0%, 4.6%, and 25.6%, respectively. Therefore, it can be seen that Al-5Ti-1B-1Ce refiner and Al-5Ti-1B-5Ce refiner have broad application prospects. Full article

(This article belongs to the Special Issue Microstructure, Crystallography, and Mechanical Properties of Metallic Materials)

19 pages, 1324 KiB

Open AccessReview

Enrichment Methods for Metal Recovery from Waste from Electrical and Electronic Equipment: A Brief Review

by Ernesto Chicardi, Antonio Lopez-Paneque, Victoria Humildad Gallardo García-Orta, Ranier Enrique Sepúlveda-Ferrer and Jose Maria Gallardo

Metals 2025, 15(2), 140; https://doi.org/10.3390/met15020140 - 29 Jan 2025

Abstract

The growing global demand for minerals and metals, coupled with fluctuations in pricing and market disruptions, has emphasised the critical role of these resources in sustaining the global economy. Waste from Electrical and Electronic Equipment (WEEE) has emerged as a promising source of [...] Read more.

The growing global demand for minerals and metals, coupled with fluctuations in pricing and market disruptions, has emphasised the critical role of these resources in sustaining the global economy. Waste from Electrical and Electronic Equipment (WEEE) has emerged as a promising source of raw materials, particularly for metal recycling and the valorisation of plastic fractions. In 2022, approximately 62 million metric tons of e-waste were generated worldwide, with projections indicating a rise to 74 million metric tons by 2030. Despite the significant volume of WEEE, only 17.4% was collected and recycled, which reveals a considerable opportunity for resource recovery. This review highlights the composition of metals in WEEE, which includes valuable precious metals, such as gold, silver, and palladium, alongside base metals, such as copper and aluminium. The review also discusses current methodologies for metal recovery and focuses on mechanical size-reduction techniques and various physical separation methods, including a shaking table, magnetic, electrostatic, and eddy current separation, flotation, and the use of a hydrocyclone. These technologies play a vital role in enhancing recovery efficiencies, thereby contributing to sustainable practices in the recycling industry. Thus, the works evaluated in this paper reveal the possibility of recovering more than 90 wt.% of precious (Ag, Au, Pd, Pt) and main metals (Cu, Sn, Al, Fe, Ni) by a combination of these mechanical size-reduction and physical separation methods. Full article

(This article belongs to the Special Issue Trends and Advances in Leaching, Extraction and Flotation for Sustainable Metal Recovery)

13 pages, 11299 KiB

Open AccessArticle

Study on Stress Corrosion Cracking Mechanism of Steel Wires with Different Strength Levels

by Guangze Zhao, Xu Ma and Ke Ma

Metals 2025, 15(2), 139; https://doi.org/10.3390/met15020139 - 29 Jan 2025

Abstract

In civil engineering, stress corrosion cracking (SCC) is a common cause of premature failure in steel wires, and effective solutions are currently limited. Investigating the SCC behavior of steel wires with different strength levels is crucial for understanding its fracture mechanism and developing [...] Read more.

In civil engineering, stress corrosion cracking (SCC) is a common cause of premature failure in steel wires, and effective solutions are currently limited. Investigating the SCC behavior of steel wires with different strength levels is crucial for understanding its fracture mechanism and developing potential solutions. This study examines the SCC behavior of wire rods with three strength grades (Steel A, B, and C) through stress corrosion experiments. The results show that high-strength wire rods have smaller pearlite interlamellar spacing. Steel C has the highest tensile strength (2303 MPa), while Steel A has the lowest (1830 MPa). Regarding stress corrosion sensitivity, the SCC mechanism of Steel C is dominated by hydrogen embrittlement, while Steels A and B primarily exhibit anodic dissolution as the cracking mechanism. Although Steel C has the smallest pearlite interlamellar spacing and superior corrosion resistance, its SCC failure time is the shortest due to hydrogen embrittlement. In contrast, for the anodic dissolution cracking mechanism, Steel B has a smaller pearlite interlamellar spacing, which enhances its corrosion resistance, and exhibits higher local stress stability due to its higher strength, resulting in the best SCC resistance (failure time: 3.81 h). This study reveals the synergistic effects of microstructure and strength on the SCC behavior of wire rods, offering theoretical guidance for the application of high-strength wire rods. Full article

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17 pages, 8159 KiB

Open AccessArticle

Numerical Study on Continuous-Bending-Under-Tension of 3rd Generation Steel

by João F. A. Pereira, Pedro A. Prates, Marilena C. Butuc and Gabriela Vincze

Metals 2025, 15(2), 138; https://doi.org/10.3390/met15020138 - 29 Jan 2025

Abstract

Sheet metal forming is one of the key processes in the manufacturing of parts for several industries, such as automotive, aerospace and packaging. However, it is often constrained by the onset of plastic instability, which limits uniform deformation. To address this challenge, considerable [...] Read more.

Sheet metal forming is one of the key processes in the manufacturing of parts for several industries, such as automotive, aerospace and packaging. However, it is often constrained by the onset of plastic instability, which limits uniform deformation. To address this challenge, considerable attention has been given to methods that enhance strength, formability, and energy absorption during forming processes. One such method is the continuous-bending-under-tension (CBT) deformation mechanism, which has shown potential in mitigating localized instability during plastic deformation. This study presents a numerical investigation of the CBT process using Abaqus 2017 to evaluate the forces generated in both the CBT equipment and material when processing high-strength materials. The reference material used is the USS CR980XG3™ AHSS, a third-generation, high-strength, high-elongation steel grade with retained austenite (980T/600Y). The study systematically analyzes the effects of key parameters, such as roll diameter, distance between rolls, depth setting, specimen thickness, and the number of deformation cycles, on the evolution of forces during the CBT process. The results demonstrate that both the forces applied by the rolls and those experienced by the specimen are significantly influenced by the distance between rolls, depth setting, and specimen thickness. In contrast, the roll diameters have minimal influence. These findings contribute to the optimization of the CBT process and provide valuable insights for future studies aimed at enhancing the performance and formability of various materials. Full article

(This article belongs to the Special Issue Numerical and Experimental Advances in Metal Processing)

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16 pages, 6886 KiB

Open AccessArticle

Characterization of Microstructure and Localized Corrosion Resistance of Heat-Treated 17-4 PH Stainless Steel Fabricated by Material Extrusion

by Pietro Forcellese, Tommaso Mancia, Michela Simoncini and Tiziano Bellezze

Metals 2025, 15(2), 137; https://doi.org/10.3390/met15020137 - 29 Jan 2025

Abstract

The quality, reproducibility, and reliability of additive manufactured parts strongly depend on optimizing printing parameters and post-processing treatments. This study evaluates the effects on the microstructure and corrosion resistance properties of solution annealing and aging heat treatments performed on 17-4 PH stainless steel [...] Read more.

The quality, reproducibility, and reliability of additive manufactured parts strongly depend on optimizing printing parameters and post-processing treatments. This study evaluates the effects on the microstructure and corrosion resistance properties of solution annealing and aging heat treatments performed on 17-4 PH stainless steel samples fabricated with different build-up orientations using a material extrusion technology: the Bound Metal Deposition^TM. The chemical composition and microstructures were determined using X-ray diffraction, chemical etching, optical microscopy, and scanning electron microscopy. The corrosion resistance properties in neutral sodium chloride electrolytes were investigated through cyclic potentiodynamic polarization and open circuit potential monitoring and analysis. The findings demonstrated that the solution annealing heat treatment remarkably enhanced the overall corrosion resistance properties of the samples. The improvement was attributed to the growth of the ferritic phase along the grain boundaries of the martensitic matrix and a finer dispersion of copper precipitates. The aging heat treatment performed after solution annealing enhanced the ferritic phase development, resulting in a further improvement of the localized corrosion resistance properties. Full article

(This article belongs to the Section Corrosion and Protection)

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30 pages, 49858 KiB

Open AccessReview

Research Advances in Additively Manufactured High-Entropy Alloys: Microstructure, Mechanical Properties, and Corrosion Resistance

by Feng Han, Chunyang Li, Jiqiang Huang, Jiacai Wang, Long Xue, Caimei Wang and Yu Zhang

Metals 2025, 15(2), 136; https://doi.org/10.3390/met15020136 - 29 Jan 2025

Abstract

High-entropy alloys have garnered significant attention due to their unique composition and exceptional properties. Additive manufacturing technology, with its distinctive processing methods, offers new options for the fabrication of high-entropy alloys. However, due to the diversity of high-entropy alloys and additive manufacturing technologies, [...] Read more.

High-entropy alloys have garnered significant attention due to their unique composition and exceptional properties. Additive manufacturing technology, with its distinctive processing methods, offers new options for the fabrication of high-entropy alloys. However, due to the diversity of high-entropy alloys and additive manufacturing technologies, it is imperative to provide a comprehensive overview of the high-entropy alloys produced using various additive manufacturing methods. This paper presents a summary of the microstructure, mechanical properties, and corrosion resistance of high-entropy alloys fabricated using different additive manufacturing techniques. This paper initially reviews the impact of various additive manufacturing process parameters and the influence of different elements on the microstructure of additively manufactured high-entropy alloys. Subsequently, it discusses the effects of different additive manufacturing techniques on mechanical properties and summarizes four strengthening mechanisms in additively manufactured high-entropy alloys. Additionally, the corrosion resistance of various additively manufactured high-entropy alloys is summarized. Finally, based on the review of additively manufactured high entropy alloys presented in this paper, the current challenges and future research directions are proposed. Full article

(This article belongs to the Special Issue Additive Manufacturing of Intermetallics: Process, Microstructures and Mechanical Properties)

21 pages, 3472 KiB

Open AccessArticle

Phase Field Simulation of Al-Fe-Mn-Si Quaternary Eutectic Solidification

by Kimiya NouraniNiaki, Murali Uddagiri, Daysianne Isidorio, Oleg Shchyglo and Ingo Steinbach

Metals 2025, 15(2), 135; https://doi.org/10.3390/met15020135 - 29 Jan 2025

Abstract

This study investigates the eutectic equilibrium phases in a multicomponent system through 3-D multi-phase-field simulations. Emphasizing the directional solidification process, the work examines the growth dynamics of intermetallic phase

{Al}_{13} {Fe}_{4}

, a lamellar structure (

FCC

-A1), and a quaternary [...] Read more.

This study investigates the eutectic equilibrium phases in a multicomponent system through 3-D multi-phase-field simulations. Emphasizing the directional solidification process, the work examines the growth dynamics of intermetallic phase

{Al}_{13} {Fe}_{4}

, a lamellar structure (

FCC

-A1), and a quaternary phase beta-AlMnSi from the liquid that is solidified at a specific temperature. The eutectic transformation, described by the four phase reaction

L \to {Al}_{13} {Fe}_{4} + FCC - A 1 + beta - AlMnSi

, is analyzed to develop a microstructure selection map. This map correlates stable growth modes with initial system composition and lamellar spacing. The results provide detailed insights into the segregation behaviour of alloying elements and their influence on transformation kinetics, enhancing the understanding of eutectic microstructure evolution in complex alloy systems. Full article

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

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