Metals

20 pages, 3861 KB

Open AccessArticle

Picolinoyl N4-Phenylthiosemicarbazide-Modified ZnAl and ZnAlCe Layered Double Hydroxide Conversion Films on Hot-Dip Galvanized Steel for Enhancing Corrosion Protection in Saline Solution

by Thu Thuy Pham, Anh Son Nguyen, Chien Thang Pham, Hong Nhung Nguyen, Maurice Gonon, Lisa Dangreau, Xavier Noirfalise, Thuy Duong Nguyen, Thi Xuan Hang To and Marie-Georges Olivier

Metals 2026, 16(1), 115; https://doi.org/10.3390/met16010115 - 19 Jan 2026

Abstract

ZnAl and ZnAlCe layered double hydroxide (LDH) conversion layers modified with picolinoyl N4-phenylthiosemicarbazide (HL) are fabricated on hot-dip galvanized steel (HDG) to improve corrosion protection. X-ray diffraction (XRD) confirms that HL molecules are not intercalated within the LDH interlayers, whereas Fourier [...] Read more.

ZnAl and ZnAlCe layered double hydroxide (LDH) conversion layers modified with picolinoyl N4-phenylthiosemicarbazide (HL) are fabricated on hot-dip galvanized steel (HDG) to improve corrosion protection. X-ray diffraction (XRD) confirms that HL molecules are not intercalated within the LDH interlayers, whereas Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analyses reveal their surface adsorption. Moreover, scanning electron microscopy (FE-SEM) observations reveal that HL modification induces changes in surface morphology. After 168 h in 0.1 M NaCl, the LDH structure remains intact, and N and S signals are still detected, confirming the persistence of both the LDH layer and adsorbed HL molecules under corrosive conditions. During 168 h immersion in NaCl, electrochemical measurements indicate that the modified LDH layers exhibit higher corrosion resistance than the unmodified ones, with the ZnAlCe LDH/HL coating providing the most effective protection. Full article

(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials)

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18 pages, 8125 KB

Open AccessArticle

EERZ-Based Kinetic Modeling of Ladle Furnace Refining Pathways for Producing Weathering Steels Using CALPHAD TCOX Databases

by Reda Archa, Zakaria Sahir, Ilham Benaouda, Amine Lyass, Ahmed Jibou, Hamza Azzaoui, Sanae Baki Senhaji, Youssef Samih and Johan Jacquemin

Metals 2026, 16(1), 114; https://doi.org/10.3390/met16010114 - 19 Jan 2026

Abstract

The design of ladle furnace (LF) refining pathways for weathering steels requires precise control of multi-component steel/slag reactions governed simultaneously by thermodynamics and interfacial mass transfer kinetics. An EERZ-based kinetic modeling strategy was employed using the Thermo-Calc^® (version 2022a) Process Metallurgy Module [...] Read more.

The design of ladle furnace (LF) refining pathways for weathering steels requires precise control of multi-component steel/slag reactions governed simultaneously by thermodynamics and interfacial mass transfer kinetics. An EERZ-based kinetic modeling strategy was employed using the Thermo-Calc^® (version 2022a) Process Metallurgy Module and the CALPHAD TCOX11 database to develop LF refining schedules capable of upgrading conventional S355J2R steel to weathering steel grades: S355J2W and S355J2WP. First, the sensitivity of predicted compositions to key kinetic inputs was quantified. The validated model was then used to simulate deoxidation and desulfurization sequences, predicting the evolution of liquid–steel and slag compositions, slag basicity, and FeO activity throughout the LF cycle. Subsequently, Cr- and P-ferroalloys were introduced to design tap-to-tap schedules that meet the EN 10025-5 chemical specifications for S355J2W and S355J2WP. To correlate simulation outcomes with material performance, plates produced following the modeled schedules were evaluated through a 1000 h accelerated salt spray test. Steel density and steel phase mass transfer coefficients were found to produce the highest prediction sensitivity (up to 7.5 wt.% variation in C and S), whereas slag phase parameters exhibited a lower impact. The predicted steel compositions showed strong agreement with industrial values obtained during plant trials. SEM-EDS analyses confirmed the development of a Cr-enriched protective patina and validated model-based alloying strategies. Full article

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4 pages, 148 KB

Open AccessEditorial

Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes

by Ilhwan Park and Sanghee Jeon

Metals 2026, 16(1), 113; https://doi.org/10.3390/met16010113 - 19 Jan 2026

Abstract

The global commitment to achieving a carbon-neutral society has accelerated the transition toward renewable energy, electric mobility, and advanced electronic systems [...] Full article

(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)

17 pages, 1285 KB

Open AccessArticle

Surface Modification of Inconel 625 in Nitrate Environment

by Mieczysław Scendo

Metals 2026, 16(1), 112; https://doi.org/10.3390/met16010112 - 19 Jan 2026

Abstract

The influence of nitrate (NO₃⁻) concentration on the corrosion resistance of the Inconel 625 (superalloy) was investigated. The surface of Inconel 625 was chemically modified by oxidation in an alkaline sodium nitrate(V) solution. The surface and microstructure of specimens were [...] Read more.

The influence of nitrate (NO₃⁻) concentration on the corrosion resistance of the Inconel 625 (superalloy) was investigated. The surface of Inconel 625 was chemically modified by oxidation in an alkaline sodium nitrate(V) solution. The surface and microstructure of specimens were observed by a scanning electron microscope (SEM). The mechanical properties of Inconel 625 were characterized by microhardness (HV) measurements. The corrosion tests of materials were carried out by using the electrochemical method in the acidic chloride solution. The adsorption of the (Me_mO_n)_ads layer effectively separates the Inconel 625 surface from contact with the aggressive corrosive environment. The microhardness (HV10) value increased (about 13%) with the increase in nitrate concentration. A more-than-five-times-lower corrosion rate (CW) value was obtained for the Inconel 625 sample, whose surface was modified in an alkaline solution with the highest NO₃⁻ concentration. Chemical modification improves the structure and surface topography of the superalloy. After exposing Inconel 625 to an oxidizing environment (1.00 M NO₃⁻), the surface coverage degree (SC) was 80%. Full article

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19 pages, 4052 KB

Open AccessArticle

Microstructure and Wear Resistance of (Mg₂Si + SiC_p)/Al Composites

by Dekun Zhou, Xiaobo Liu and Miao Yang

Metals 2026, 16(1), 111; https://doi.org/10.3390/met16010111 - 18 Jan 2026

Abstract

The microstructure and wear behaviors of Mg₂Si/Al composites with 0 wt.%, 5 wt.%, and 10 wt.% SiC particles were studied using XRD, OM observation, SEM observation, EDS analysis, an extraction experiment, a hardness test, and the dry sliding wear test. It [...] Read more.

The microstructure and wear behaviors of Mg₂Si/Al composites with 0 wt.%, 5 wt.%, and 10 wt.% SiC particles were studied using XRD, OM observation, SEM observation, EDS analysis, an extraction experiment, a hardness test, and the dry sliding wear test. It is shown by the results that after the addition of 10 wt.% SiC particles, the population of primary Mg₂Si particles increased, while the mean size of these particles reduced from 40 ± 10 μm (in the SiC-free composite) to 25 ± 8 μm. Both the matrix and the eutectic structure were refined. The tetrakaidecahedral morphologies of Mg₂Si crystals were confirmed by the results of extraction tests. The wear test results with GCr15 steel as the friction pair show that the Mg₂Si/Al composite with 10 wt.% SiC particles displayed more favorable wear resistance than the specimens with 0 wt.% and 5 wt.% SiC particle additions under both constant load and constant sliding velocity conditions. Under applied loads of 10 N, 20 N, and 30 N at a fixed sliding speed of 300 r/min, the wear rate of the Mg₂Si-Al composites reinforced with 10 wt.% SiC particles was 36.01%, 48.29%, and 23.32% lower than that of the SiC-free composites, respectively. When the sliding speed was set to 300 r/min, 550 r/min, 750 r/min, and 1000 r/min under a constant applied load of 20 N, the wear rate of the 10 wt.% SiC-reinforced Mg₂Si-Al composites was reduced by 40.37%, 40.87%, 26.20%, and 25.78%, respectively, compared with the SiC-free counterparts. The wear failure mechanisms of (Mg₂Si + SiC_P)/Al composites were mainly adhesive wear and abrasive wear, but the proportion of oxidation wear increased after the addition of the SiC particles. Full article

(This article belongs to the Special Issue Recent Advances in Forming Processes of Lightweight Metals)

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18 pages, 4148 KB

Open AccessArticle

Optimizing S20C Steel and SUS201 Steel Welding Using Stainless Steel Filler and MIG Method

by Van Huong Hoang, Thanh Tan Nguyen, Minh Tri Ho, Pham Tran Minh Trung, Nguyen Van Sung, Van-Thuc Nguyen and Van Thanh Tien Nguyen

Metals 2026, 16(1), 110; https://doi.org/10.3390/met16010110 - 18 Jan 2026

Abstract

The reliable joining of dissimilar stainless steel and carbon steel remains a critical challenge in Metal Inert Gas (MIG) welding due to complex thermal–metallurgical interactions and the formation of brittle phases at the weld interface. In this study, a Taguchi-based design of experiments [...] Read more.

The reliable joining of dissimilar stainless steel and carbon steel remains a critical challenge in Metal Inert Gas (MIG) welding due to complex thermal–metallurgical interactions and the formation of brittle phases at the weld interface. In this study, a Taguchi-based design of experiments was employed to systematically optimize MIG welding parameters for SUS201/S20C dissimilar joints using a SUS201 filler wire, with particular attention to the welding current, voltage, travel speed, and electrode stick-out. The welding process was performed using an automatic welding robot. Tensile specimens were tested on a universal testing machine. Microstructural analysis was performed using a metallurgical microscope. The microstructure reveals that the development of the carbon side’s large ferrite and the stainless steel side’s δ-ferrite both significantly degrade joint quality. Among all process parameters, electrode stick-out is identified as the most influential parameter governing both tensile and bending performance, highlighting a critical process sensitivity that has received limited attention in prior studies. Optimized parameter combinations are required to maximize tensile and flexural responses. The highest tensile strength is 450.96 MPa. These findings advance the understanding of parameter–microstructure–property relationships in dissimilar MIG welding. Future work applying numerical welding simulations and advanced evaluation techniques is recommended. Full article

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18 pages, 10356 KB

Open AccessArticle

Chlorella vulgaris Powder as an Eco-Friendly and Low-Cost Corrosion Inhibitor Against Carbon Steel Corrosion by HCl

by Zhong Li, Xiaolong Li, Jianfeng Lai, Shaohua Cao, Guoqiang Liu, Xiaowan Wang, Yan Lyu, Junlei Wang and Jike Yang

Metals 2026, 16(1), 109; https://doi.org/10.3390/met16010109 - 18 Jan 2026

Abstract

In this study, dried biomass of the alga Chlorella vulgaris was ground into a powder as an eco-friendly, low-cost inhibitor to mitigate the corrosion of carbon steel in acidic solutions. Electrochemical and weight loss measurements, surface morphology observations, adsorption isotherms, activation energy, and [...] Read more.

In this study, dried biomass of the alga Chlorella vulgaris was ground into a powder as an eco-friendly, low-cost inhibitor to mitigate the corrosion of carbon steel in acidic solutions. Electrochemical and weight loss measurements, surface morphology observations, adsorption isotherms, activation energy, and potential of zero charge calculations were applied to evaluate the inhibition performance. Electrochemical results indicate that C. vulgaris powder can simultaneously inhibit both the anodic and cathodic corrosion processes of carbon steel, demonstrating good inhibition performance and classifying it as a mixed-type inhibitor with both anodic and cathodic characteristics. Weight loss data further confirm that at a concentration of 300 mg/L, the corrosion inhibition efficiency reaches 88%. The fitted adsorption isotherm reveals that the adsorption of Chlorella vulgaris powder on the carbon steel surface follows the Langmuir model. Density functional theory (DFT) and molecular dynamics simulations indicate that the excellent inhibition performance is attributed to the combined effects of physisorption and chemisorption of constituents such as amino acids and cellulose present in C. vulgaris. Full article

(This article belongs to the Special Issue Advances in Microbiological Corrosion of Metals, Alloys, and Metallic Compounds)

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24 pages, 12498 KB

Open AccessArticle

Study on Surface Properties and Microstructural Evolution of LA103Z Mg-Li Alloy by Friction Stir Processing

by Jiqiang Zhai, Kai Hu, Zihan Kong and Xinzhen Fang

Metals 2026, 16(1), 108; https://doi.org/10.3390/met16010108 - 18 Jan 2026

Abstract

Magnesium–lithium alloys are the lightest structural metals and offer high specific strength, good damping capacity, and excellent thermal conductivity; however, their limited room-temperature strength restricts wider engineering applications. In this study, friction stir processing (FSP) was applied to LA103Z magnesium–lithium alloy to modify [...] Read more.

Magnesium–lithium alloys are the lightest structural metals and offer high specific strength, good damping capacity, and excellent thermal conductivity; however, their limited room-temperature strength restricts wider engineering applications. In this study, friction stir processing (FSP) was applied to LA103Z magnesium–lithium alloy to modify its surface microstructure and mechanical properties. The effects of tool rotational speed and travelling speed on dynamic recrystallization behavior, grain refinement, and phase evolution in the stirred zone (SZ) and thermomechanically affected zone (TMAZ) were systematically investigated. FSP induced significant grain refinement accompanied by the precipitation of a reticular α-Mg phase along β-Li grain boundaries, as well as Li₃Mg₇ and Li₂MgAl phases within the stirred zone, leading to pronounced strengthening. Under optimized processing conditions, substantial improvements in hardness and tensile properties were achieved compared with the base material. The optimal condition was obtained at 600 rpm and 100 mm/min, yielding an average hardness of 79.17 HV_0.2, a tensile strength of 243.6 MPa, and an elongation of 17.9%, corresponding to increases of 47.5% in hardness and 53.3% in tensile strength. Quantitative relationships between heat input, grain size, and mechanical properties further demonstrate that heat input governs microstructural evolution and strengthening behavior during FSP of LA103Z alloy. Full article

(This article belongs to the Special Issue Surface Modification and Characterization of Metals and Alloys)

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17 pages, 10848 KB

Open AccessArticle

Creep Deformation Estimation of Single Crystal Ni-Based Superalloy by Optimized Geometrically Necessary Dislocation Density Evaluation

by Cristina Motta, Francesco Mastromatteo, Niccolò Baldi, Elisabetta Gariboldi and Luca Bernardini

Metals 2026, 16(1), 107; https://doi.org/10.3390/met16010107 - 17 Jan 2026

Abstract

In the framework of high temperature components, the need to evaluate the accumulated creep damage during service life is fundamental to extend the life of components which are currently deemed as scrap as per design intent. Thus, the life assessment of Ni-based superalloys [...] Read more.

In the framework of high temperature components, the need to evaluate the accumulated creep damage during service life is fundamental to extend the life of components which are currently deemed as scrap as per design intent. Thus, the life assessment of Ni-based superalloys could be performed in relation to the accumulated creep deformation which represents the limiting factor for serviced components. Despite the different microstructural changes that occur in service life, this work focuses on the possibility to evaluate the material strain by means of electron backscattered diffraction (EBSD). The key point is the identification of the correlation between geometrically necessary dislocation (GND) density derived from EBSD analyses and the reached creep strain for a single crystal Ni-based superalloy. However, the results of GND density are affected by the settings’ parameters adopted to perform the analysis by the magnification level and the step size. These two parameters have been optimized by analyzing specimens from interrupted creep tests at strain levels between 0.5% and 10%, in the temperature range between 850 °C and 1000 °C. Full article

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16 pages, 7668 KB

Open AccessArticle

Heterogeneity of Microstructure and Mechanical Response in Steel–Titanium Multilayer Wires Subjected to Severe Plastic Deformation

by Bartłomiej Pabich, Paulina Lisiecka-Graca, Marcin Kwiecień and Janusz Majta

Metals 2026, 16(1), 106; https://doi.org/10.3390/met16010106 - 17 Jan 2026

Abstract

This study addresses the fundamental problem of representing the rheological properties of heterostructured materials composed of metals that differ significantly in their crystal structure, stacking fault energy, and related characteristics. The necessity of accounting for essential strengthening mechanisms is highlighted. The study is [...] Read more.

This study addresses the fundamental problem of representing the rheological properties of heterostructured materials composed of metals that differ significantly in their crystal structure, stacking fault energy, and related characteristics. The necessity of accounting for essential strengthening mechanisms is highlighted. The study is based on experimental results related to the fabrication of a multilayer, heterogeneous system via multistage wire drawing, supported by microstructural analysis, microhardness measurements, and numerical simulations employing various flow-stress models. A discussion is presented regarding the effectiveness of these models in representing the deformation behavior of the investigated materials. The primary materials examined were a multilayer system composed of microalloyed steel and titanium. The obtained results indicate that, in addition to incorporating strengthening mechanisms, it is necessary to consider significant microstructural changes affecting microstructure evolution—particularly grain refinement induced by continuous recrystallization and the effects of strain hardening. Moreover, the findings point to the potential intensification of strengthening associated with pile-up mechanisms, linked to the development of dislocation substructures and the possible fragmentation of the hard phase in the vicinity of the more ductile microalloyed steel phase. In conclusion, the discussion integrates measurements of rheological properties obtained through tensile tests, supported by microstructural analysis, digital image correlation (DIC), and microhardness measurements, which collectively demonstrate the effectiveness of the adopted analytical approach. Full article

(This article belongs to the Special Issue Advances in the Forming and Processing of Metallic Materials)

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15 pages, 5606 KB

Open AccessArticle

Effect of Deposition Angle and Arc Current on the Structure and Optical Properties of Ti Coatings Deposited by Cathodic Arc Evaporation

by Iulian Pana, Anca C. Parau, Mihaela Dinu, Adrian E. Kiss, Lidia R. Constantin, Nicolae C. Zoita, Alina Vladescu (Dragomir) and Catalin Vitelaru

Metals 2026, 16(1), 105; https://doi.org/10.3390/met16010105 - 17 Jan 2026

Abstract

This study investigates the effects of deposition angle and arc current on the surface morphology and optical response of Ti coatings obtained by unfiltered cathodic arc evaporation for spectrally selective solar-thermal applications. 100 nm-thick Ti films were deposited at normal (0°) and oblique [...] Read more.

This study investigates the effects of deposition angle and arc current on the surface morphology and optical response of Ti coatings obtained by unfiltered cathodic arc evaporation for spectrally selective solar-thermal applications. 100 nm-thick Ti films were deposited at normal (0°) and oblique (80°) angles of incidence, with arc currents of 65 A and 90 A, respectively. The SEM measurements revealed the characteristic arc-generated microdroplet population. At normal incidence (0°), droplets are predominantly spherical and relatively uniformly distributed, whereas at 80° incidence, many droplets exhibit elongated footprints aligned with the incoming flux from the Ti cathode. This behavior is consistent with oblique-angle deposition (OAD), where the arrival geometry can promote self-shadowing and transient droplet spreading before solidification. AFM confirms an increase in nanoscale roughness, whereas GIXRD indicates nanocrystalline α-Ti and cubic TiO, with maximum crystallinity for 0°/65 A. Contact-angle measurements demonstrate a transition from hydrophobic 316L (~103°) to moderately hydrophilic Ti-coated surfaces (~68–72°), with only minor dependence on deposition geometry. Optical reflectance in the 400–800 nm range is significantly lower for Ti-coated glass and is further reduced for OAD films, indicating enhanced solar absorptance. Full article

(This article belongs to the Special Issue Metallic Coatings Synthesized by Magnetron Sputtering)

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14 pages, 3394 KB

Open AccessArticle

Softening and Melting Behavior of Lead Blast Furnace Slags

by Josué López-Rodríguez, Cancio Jiménez-Lugos, Manuel Flores-Favela, Aurelio Hernández-Ramírez, Alejandro Cruz-Ramírez, Carmen Martínez-Morales, Miguel Pérez-Labra and Antonio Romero-Serrano

Metals 2026, 16(1), 104; https://doi.org/10.3390/met16010104 - 16 Jan 2026

Abstract

In this work, the characteristic temperatures (solidus and liquidus) of selected lead blast furnace slags were investigated using in situ high-temperature optical microscopy. The effects of the basicity of the slag (CaO/SiO₂), the Fe/SiO₂ ratio, and the Zn content were [...] Read more.

In this work, the characteristic temperatures (solidus and liquidus) of selected lead blast furnace slags were investigated using in situ high-temperature optical microscopy. The effects of the basicity of the slag (CaO/SiO₂), the Fe/SiO₂ ratio, and the Zn content were investigated. The deformation temperature associated with the rounding of the sample edges and the temperature at which 75% of the sample height decreases were experimentally considered as the solidus and liquidus temperatures, respectively. The pseudoternary phase diagrams CaO-SiO₂-Fe_0.63Zn_0.37O and FeO-Ca_0.54Si_0.46O_1.46-ZnO were calculated, along with the crystallization curves, using the thermodynamic software FactSage to estimate the characteristic temperatures and phase evolution during the cooling of the slag. The difference between the calculated and experimental solidus and liquidus temperatures was about 70 °C. The results of XRD, SEM, and DSC analysis at high temperatures showed that spinel (ZnFe₂O₄), melilite (Ca₂ZnSi₂O₇), and andradite (Ca₃Fe₂Si₃O₁₂) were the base crystals for all slag samples. The liquidus temperature increases with decreasing slag basicity (CaO/SiO₂), while the liquidus temperature increases with increasing Fe/SiO₂ ratio or Zn content. Full article

(This article belongs to the Section Extractive Metallurgy)

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19 pages, 5077 KB

Open AccessArticle

The Influence of Microstructure on Decisions Regarding Repurposing Natural Gas Pipelines for Hydrogen Service

by Jonathan Parker, Mike Gagliano and Eeva Griscom

Metals 2026, 16(1), 103; https://doi.org/10.3390/met16010103 - 16 Jan 2026

Abstract

Empirical approaches alone have significant limitations for accurate estimation of the fracture toughness of welds in gas line pipes being considered for repurposing to hydrogen service. These problems arise because most samples machined from ex-service welds contain a range of microstructures. The different [...] Read more.

Empirical approaches alone have significant limitations for accurate estimation of the fracture toughness of welds in gas line pipes being considered for repurposing to hydrogen service. These problems arise because most samples machined from ex-service welds contain a range of microstructures. The different microstructural zones have different properties and even when compact tension samples with side grooves are utilized, it is unlikely that plane strain conditions are achieved during laboratory testing. Thus, the measured toughness may not be directly relevant to assessing in-service performance. The present research has been undertaken as part of an integrated series of projects seeking to define a robust protocol for assessing the damage tolerance of piping used for the transmission of hydrogen, especially when considering repurposing existing infrastructure. The key work described in this paper involved establishing heat treatments which produced microstructures relevant to the constituents found in ex-service welds of X46 type steel. Following comprehensive microstructural characterization, these heat treatments were applied to steel sections which allowed for the fabrication of standard compact tension specimens, which were subsequently tested in hydrogen to measure fracture toughness. The results obtained showed that the fracture behavior varied for different microstructures. To identify the influence that hydrogen gas has on the performance of pipeline steels, it is important to assess microstructures relevant to the welds present, as testing only on base metal may not provide conservative information. However, the results from well-planned and carefully executed programs can be used to identify the relative performance in hydrogen. The data can also be used as critical input to models which form part of an integrated approach to structural integrity assessment. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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15 pages, 1199 KB

Open AccessArticle

Roller Joining of AA1050 and AA6061 Aluminum Foam Immediately After Heating Process

by Yoshihiko Hangai, Shingo Nagatake, Ryosuke Suzuki, Kenji Amagai and Nobuhiro Yoshikawa

Metals 2026, 16(1), 102; https://doi.org/10.3390/met16010102 - 16 Jan 2026

Abstract

Aluminum foam is attracting attention as a multifunctional, ultra-lightweight material. To apply this aluminum foam to actual industrial materials, aluminum foam plates are required. In addition, it is expected that a multi-layer aluminum foam composed of dissimilar aluminum alloy foam layers can further [...] Read more.

Aluminum foam is attracting attention as a multifunctional, ultra-lightweight material. To apply this aluminum foam to actual industrial materials, aluminum foam plates are required. In addition, it is expected that a multi-layer aluminum foam composed of dissimilar aluminum alloy foam layers can further enhance its functionality. In this study, we attempted to fabricate a three-layer aluminum foam composed of commercially pure aluminum AA1050 and Al-Mg-Si aluminum alloy AA6061 by heating and foaming a total of three pieces of AA1050 precursor and AA6061 precursor arranged alternately, followed by immediate roller joining. It was found that, by traversing a roller immediately after foaming the AA1050 and AA6061 precursors, the aluminum foam could be joined while forming it into a flat plate. In addition, X-ray CT images of the fabricated samples revealed that material flow induced by roller traversing ruptured the surface skin layer. Numerous pores were observed within the sample, indicating pores were maintained during the roller traversing and no significant differences in porosities were identified between AA1050 aluminum foam and AA6061 aluminum foam. Furthermore, from the four-point bending test and the observation of samples after bending test, although quantitative mechanical properties were not obtained due to the as-joined samples were used for the bending test, pores were observed at the fracture surfaces, confirming that roller joining achieved seamless joining. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

27 pages, 4055 KB

Open AccessArticle

Additive Manufacturing of Layered Nb-Al₂O₃ Composite Granules Based on Paste Extrusion

by Tilo Zienert, Dinesh Kumar Gunasekar, Dirk Endler, Christina Faßauer and Christos G. Aneziris

Metals 2026, 16(1), 101; https://doi.org/10.3390/met16010101 - 16 Jan 2026

Abstract

How would it be possible to functionalize ceramic aggregates for use in refractories? In this work, we demonstrate how paste extrusion can be used to fabricate layered and porous Nb-Al₂O₃-based composite refractories for adjusting thermal and electrical conductivity. Additive [...] Read more.

How would it be possible to functionalize ceramic aggregates for use in refractories? In this work, we demonstrate how paste extrusion can be used to fabricate layered and porous Nb-Al₂O₃-based composite refractories for adjusting thermal and electrical conductivity. Additive manufacturing is used to generate a specific sequence of alumina and composite layers. After drying, the samples were sintered at 1600 °C, crushed, and sieved into particle sizes up to 3150 µm. The rheology of the paste revealed the intended shear-thinning behavior with microcrack formation between the yield and flow strain. The sintered material showed promising thermal-shock characteristics reaching plateau values after the third cycle without signs of further structural damage up to the fifth thermal shock. The layered microstructure was retained after crushing the composites, establishing functionalization of the refractory granules for all particle sizes. Full article

(This article belongs to the Special Issue Mechanical and Functional Properties of Metal–Ceramic Composites for Harsh Environments)

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18 pages, 5767 KB

Open AccessArticle

From √A to Elliptical Defects: Refining Murakami’s Model for Fatigue Prediction in Sintered Steels

by S. Otero, G. Álvarez, J. Sicre, C. Soto and C. Rodríguez

Metals 2026, 16(1), 100; https://doi.org/10.3390/met16010100 - 16 Jan 2026

Abstract

The use of powder metallurgy in the manufacturing of automotive components requires understanding the influence of porosity on fatigue behaviour. The most widely accepted explanation for the impact of porosity on the fatigue limit is Murakami’s “√Area = √A” theory. However, the presence [...] Read more.

The use of powder metallurgy in the manufacturing of automotive components requires understanding the influence of porosity on fatigue behaviour. The most widely accepted explanation for the impact of porosity on the fatigue limit is Murakami’s “√Area = √A” theory. However, the presence of elongated or irregular pores in sintered steels challenges this simplification. This study analyses the fatigue behaviour of three sintered steels and performs a statistical and geometrical assessment of porosity. Results demonstrate that replacing the √A parameter with the ellipse-fitted major axis (d_max) reduces the average prediction error from nearly 50% to below 6%, markedly improving the predictive accuracy of defect-based fatigue models. Full article

(This article belongs to the Special Issue Innovative Fabrication and Characterization Techniques for Metal Powder Composites)

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19 pages, 6581 KB

Open AccessArticle

Data-Driven Design of HPDC Aluminum Alloys Using Machine Learning and Inverse Design

by Seunghyeok Choi, Sungjin Kim, Junho Lee, Jeonghoo Choi, MiYoung Lee, JaeHwang Kim, Jae-Gil Jung and Seok-Jae Lee

Metals 2026, 16(1), 99; https://doi.org/10.3390/met16010099 - 16 Jan 2026

Abstract

This work proposes a data-driven design framework for high-pressure die-cast (HPDC) aluminum alloys that integrates robust data refinement, machine learning (ML) modeling, explainability, and inverse design. A total of 1237 tensile-test records from T5-aged HPDC alloys were aggregated into a curated dataset of [...] Read more.

This work proposes a data-driven design framework for high-pressure die-cast (HPDC) aluminum alloys that integrates robust data refinement, machine learning (ML) modeling, explainability, and inverse design. A total of 1237 tensile-test records from T5-aged HPDC alloys were aggregated into a curated dataset of 382 unique composition–heat-treatment combinations. Four regression models—Ridge regression, Random Forest (RF), XGBoost (XGB), and a multilayer perceptron (MLP)—were trained to predict yield strength (YS), ultimate tensile strength (UTS), and elongation (EL). Tree-based ensemble models (XGB and RF) achieved the highest accuracy and stability, capturing nonlinear interactions inherent to industrial HPDC data. In particular, the XGB model exhibited the best predictive performance, achieving test R² values of 0.819 for UTS and 0.936 for EL, with corresponding RMSE values of 15.23 MPa and 1.112%, respectively. Feature-importance and SHapley Additive exPlanations (SHAP) analyses identified Mn, Si, Mg, Zn, and T5 aging temperature as the most influential variables, consistent with metallurgical considerations such as microstructural stabilization and precipitation strengthening. Finally, RF-based inverse design suggested new composition–process candidates satisfying UTS > 300 MPa and EL > 8%, a region scarcely represented in the experimental dataset. These results illustrate how interpretable ML can expand the feasible design space of HPDC aluminum alloys and support composition–process optimization in industrial applications. Full article

(This article belongs to the Special Issue Solidification and Casting of Light Alloys)

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13 pages, 5889 KB

Open AccessArticle

Metallic Structures and Tribological Properties of Ti-15mass%Nb Alloy After Gas Nitriding and Quenching Process

by Yoshikazu Mantani, Riho Takahashi, Tomoyuki Homma and Eri Akada

Metals 2026, 16(1), 98; https://doi.org/10.3390/met16010098 - 16 Jan 2026

Abstract

This study aimed to experimentally investigate the differences in metallic structures owing to the gas nitriding and quenching process (GNQP) temperature of the Ti-15mass%Nb alloy and differences in the tribological properties of the surface layer. The GNQP heating temperature was 1023 K or [...] Read more.

This study aimed to experimentally investigate the differences in metallic structures owing to the gas nitriding and quenching process (GNQP) temperature of the Ti-15mass%Nb alloy and differences in the tribological properties of the surface layer. The GNQP heating temperature was 1023 K or 1223 K, and the holding time was set to 1 h. In the X-ray diffraction profiles, the diffraction peak of the (10

\bar{1}

1) plane of the hexagonal close-packed phase exhibited a shift toward lower angles, following the sequence AN:α, AQ:α′, and GNQP:α-TiN_0.3. In both the 1023 K and 1223 K GNQP specimens, the α″ phase exhibited lower values than the α′ phase; nonetheless, it still exhibited larger values than the annealed α phase. Based on transmission electron microscopy observations, the high core hardness of the 1223 K GNQP specimen was attributed to solid-solution strengthening caused by nitrogen diffusion or to strain hardening associated with the diffusion and was not attributed to the influence of precipitation phases, such as the ω phase. In the friction and wear tests, both the 1023 K and 1223 K GNQP specimens exhibited narrower wear track widths, clearly demonstrating that the GNQP enhanced the wear resistance. Moreover, the TiO₂ layer was effective in maintaining a low coefficient of friction. Full article

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

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18 pages, 4040 KB

Open AccessArticle

Non-Uniform Microstructural Evolution Rules and Mechanisms of Ti₂AlNb-Based Alloy Stiffened Panels Subjected to Electrically Assisted Press Bending

by Xiao-Li Zhang, Si-Liang Yan, Zi-Long Liu, Yu-Hong Gong and Miao Meng

Metals 2026, 16(1), 97; https://doi.org/10.3390/met16010097 - 15 Jan 2026

Abstract

A knowledge of the process–structure–property correlation and underlying deformation mechanisms of material under a coupled electro-thermal–mechanical field is crucial for developing novel electrically assisted forming techniques. In this work, numerical simulation and experimental analyses were carried out to study the non-uniform deformation behaviors [...] Read more.

A knowledge of the process–structure–property correlation and underlying deformation mechanisms of material under a coupled electro-thermal–mechanical field is crucial for developing novel electrically assisted forming techniques. In this work, numerical simulation and experimental analyses were carried out to study the non-uniform deformation behaviors and microstructure evolution of Ti₂AlNb-based alloy stiffened panels in different characteristic deformation regions during electrically assisted press bending (EAPB). The quantitative relationships between electro-thermal–mechanical routes, microstructural features, and mechanical properties of EAPBed stiffened panels were initially established, and the underlying mechanisms of electrically induced phase transformation and morphological transformation were unveiled. Results show that the temperature of the panel first increases then deceases with forming time in most regions, but it increases monotonically and reaches its peak value of 720.1 °C in the web region close to the central transverse rib. The higher accumulated strain and precipitation of the acicular O phase at mild temperature leads to strengthening of the longitudinal ribs at near blank holder regions, resulting in an ideal microstructure of 3~4% blocky α₂ phase + a dual-scale O structure in a B2 matrix with a maximal hardness of 389.4 ± 7.2 HV_0.3. While the dissolution of the α₂ phase and the spheroidization and coarsening of the O phase bring about softening (up to 9.29%) of the lateral ribs and web near the center region, the differentiated evolution of microstructure and the mechanical property in EAPB results in better deformation coordination and resistance to wrinkling and thickness variation in the rib–web structure. The present work will provide valuable references for achieving shape-performance coordinated manufacturing of Ti₂AlNb-based stiffened panels. Full article

(This article belongs to the Special Issue Thermomechanical Performance of Metallic Alloys)

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