Metals

17 pages, 4752 KB

Open AccessArticle

Mechanism of Vanadium–Titanium Slag in Regulating the Performance and Hydration of Metallurgical Slag-Based Cementitious Materials

by Bo Su, Siqi Zhang, Xingyang Xu, Tong Zhao, Huifen Yang and Junyao Liu

Metals 2026, 16(4), 442; https://doi.org/10.3390/met16040442 (registering DOI) - 18 Apr 2026

Abstract

To achieve the large-scale, high-value utilization of vanadium–titanium slag (VTS) in the metallurgical industry, this study replaces blast furnace slag (BFS) with VTS to construct a quaternary all-solid-waste cementitious system composed of VTS, BFS, steel slag (SS), and desulfurization gypsum (DG). It systematically [...] Read more.

To achieve the large-scale, high-value utilization of vanadium–titanium slag (VTS) in the metallurgical industry, this study replaces blast furnace slag (BFS) with VTS to construct a quaternary all-solid-waste cementitious system composed of VTS, BFS, steel slag (SS), and desulfurization gypsum (DG). It systematically investigates the effects of VTS content (0–60%) on the mechanical properties, leaching toxicity, and hydration heat behavior of the system. XRD, TG–DSC, and SEM–EDS techniques are employed to explore the influence of VTS on hydration behavior and microstructural evolution. The results show that when VTS replaces 30% of the BFS (A3, VTS:BFS:SS:DG = 3:3:3:1), the 28-day compressive strength reaches 31.33 MPa. The leaching concentrations of heavy metals in all specimens are far below the standards for drinking water quality. Hydration heat analysis reveals that the incorporation of VTS advances the acceleration period of hydration. The A3 specimen maintains a relatively high heat release rate in the middle and later stages (after 72 h), and its cumulative heat release is significantly higher than that of the system without VTS, revealing the “slow hydration” mechanism of VTS at later stages. The [SiO₄]–[AlO₄] bonds in VTS undergo a depolymerization–repolymerization process. In addition, an appropriate amount of VTS promotes the deposition of hydration products such as ettringite (AFt), C–S–H, and C–A–S–H gels through micro-filling effects and heterogeneous nucleation, thereby improving the microstructure of the system. However, excessive VTS (≥45%) significantly inhibits the hydration reaction and reduces gel formation due to the decrease in highly reactive BFS components and the increased TiO₂ content. This study provides new insights into the resource utilization of VTS in multi-solid-waste cementitious materials. In addition, VTS-based cementitious materials are suitable for practical scenarios with low early strength requirements, such as goaf backfilling. Therefore, future studies should further investigate the long-term sulfate resistance and carbonation resistance of these materials under real application conditions. Full article

(This article belongs to the Special Issue Recent Developments in Ironmaking)

► Show Figures

Figure 1

19 pages, 7794 KB

Open AccessArticle

Effect of Solution Temperature on the Microstructure and Mechanical Properties of Fe-Ni-Cr-Mo-Al-Ti High-Strength Stainless Steel

by Mutian Niu, Jiahao Chen, Zhenbao Liu, Jiarui Hu, Zhiyong Yang, Yonghua Duan and Xiaohui Wang

Metals 2026, 16(4), 441; https://doi.org/10.3390/met16040441 (registering DOI) - 18 Apr 2026

Abstract

High-strength stainless steels are essential materials for critical load-bearing aerospace components, and solution treatment serves as a core process governing their strength–toughness balance. However, in novel multi-element alloy systems, the complex dissolution behavior of precipitates and its underlying mechanisms affecting matrix phase transformations [...] Read more.

High-strength stainless steels are essential materials for critical load-bearing aerospace components, and solution treatment serves as a core process governing their strength–toughness balance. However, in novel multi-element alloy systems, the complex dissolution behavior of precipitates and its underlying mechanisms affecting matrix phase transformations require further investigation. This study systematically explores the thermodynamic evolution and microstructural response of a novel Fe-Ni-Cr-Mo-Al-Ti ultra-high-strength stainless steel during solution treatment. The research highlights how solution temperature drives Laves phase dissolution, controls prior austenite grain growth, redistributes local chemical elements, and dictates retained austenite stability. By establishing the relationship between microstructural features and macroscopic properties, this study aims to provide crucial theoretical guidance for optimizing heat treatment protocols to achieve superior comprehensive mechanical properties in advanced high-strength stainless steels. Full article

(This article belongs to the Special Issue Recent Advances in High-Performance Steel (2nd Edition))

► Show Figures

Graphical abstract

23 pages, 2890 KB

Open AccessReview

Fatigue Crack Growth Models Applied to Additively Manufactured Electron Beam Melted Ti6Al4V: A Review

by Nicole Atmadja and Mamidala Ramulu

Metals 2026, 16(4), 440; https://doi.org/10.3390/met16040440 - 17 Apr 2026

Abstract

This article comprehensively reviews the fatigue crack growth (FCG) models applied to Ti6Al4V alloy manufactured by electron beam melting (EBM) powder bed fusion (PBF). The current progress in FCG analytical and numerical models and their application to EBM Ti6Al4V are reviewed. Much experimental [...] Read more.

This article comprehensively reviews the fatigue crack growth (FCG) models applied to Ti6Al4V alloy manufactured by electron beam melting (EBM) powder bed fusion (PBF). The current progress in FCG analytical and numerical models and their application to EBM Ti6Al4V are reviewed. Much experimental data for the creation of historical FCG models was based on conventionally manufactured (CM) aluminum alloys and various steels. With the growth of additive manufacturing (AM), recent studies have applied traditional models and modified new models to EBM Ti6Al4V and validated their use as accurate predictive models for the da/dN-ΔK curve and ΔK_th. Due to pores and surface roughness inherent in AM and the unique anisotropic microstructure developed from the EBM process, classical models may require modifications to accurately predict FCG of EBM Ti6Al4V. Full article

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

► Show Figures

Graphical abstract

15 pages, 25895 KB

Open AccessArticle

High-Temperature Oxidation Behavior of Al_xCoCr_0.5NiPt_0.1 (x = 0.5, 1.0) Multi-Principal Element Alloys at 1100 °C

by Olga Samoilova, Svetlana Pratskova, Polina Plotnikova, Nataliya Shaburova, Mariappan Anandkumar and Evgeny Trofimov

Metals 2026, 16(4), 439; https://doi.org/10.3390/met16040439 - 17 Apr 2026

Abstract

The microstructure, phase composition, and high-temperature oxidation behavior of Al_0.5CoCr_0.5NiPt_0.1 and AlCoCr_0.5NiPt_0.1 multi-principal element alloys (MPEAs) at 1100 °C in air were investigated. Depending on the content of aluminum, the microstructure of as-cast samples contains [...] Read more.

The microstructure, phase composition, and high-temperature oxidation behavior of Al_0.5CoCr_0.5NiPt_0.1 and AlCoCr_0.5NiPt_0.1 multi-principal element alloys (MPEAs) at 1100 °C in air were investigated. Depending on the content of aluminum, the microstructure of as-cast samples contains FCC and BCC solid solutions. Similarly, the ratio of two solid solutions varies depending on the aluminum content in the alloy. When the content of aluminum is x = 0.5, the microstructure is dominated by the FCC solid solution, while a BCC solid solution is dominated when the concentration of aluminum is increased to x = 1.0. Moreover, in both MPEAs, platinum exists as a part of solid solutions rather than a separate phase. High-temperature oxidation was carried out in a Plavka.Pro PM-1 SmartKiln muffle furnace under isothermal conditions at 1100 °C for 100 h exposure in air, and weighing was performed every 10 h. The maximum specific weight gain for the Al_0.5CoCr_0.5NiPt_0.1 alloy was 0.965 mg/cm², and 0.675 mg/cm² for the AlCoCr_0.5NiPt_0.1 alloy. Based on the high-temperature oxidation experiment results, it was established that AlCoCr_0.5NiPt_0.1 MPEA exhibits greater resistance towards high-temperature dry air corrosion with the formation of an exclusive Al₂O₃ scale on the surface with 3–5 μm thickness; the parabolic oxidation rate constant for this alloy is k_p = 20.2 × 10^–13 (g²/cm⁴s). Introduction of platinum into the composition of the Fe-free AlCoCr_0.5Ni alloy reduces the value of the parabolic oxidation rate constant by half. Full article

(This article belongs to the Section Entropic Alloys and Meta-Metals)

► Show Figures

Figure 1

26 pages, 6077 KB

Open AccessArticle

Knowledge Transfer Between Machines in Laser Powder Bed Fusion—Transfer Learning with Small Training Datasets

by Florian Funcke, Sebastian Brummer, Marinus Kolbinger and Peter Mayr

Metals 2026, 16(4), 438; https://doi.org/10.3390/met16040438 - 17 Apr 2026

Abstract

Laser Powder Bed Fusion (PBF-LB) is currently one of the most versatile and adopted additive manufacturing technologies for printing metals. To take new PBF-LB machines into service, a thorough characterization and calibration is often necessary to get the desired output. This is commonly [...] Read more.

Laser Powder Bed Fusion (PBF-LB) is currently one of the most versatile and adopted additive manufacturing technologies for printing metals. To take new PBF-LB machines into service, a thorough characterization and calibration is often necessary to get the desired output. This is commonly achieved empirically; however, data-driven methods have become more and more available over the last few years. This research explores the use of transfer learning (TL) to transfer process knowledge from an already-established source machine (Nikon SLM 500) to a target machine (Trumpf TruPrint 5000) with different hardware specifications. To predict the tensile properties of AlSi10Mg0.5 utilizing a minimal data set of merely 25 training samples, eight TL model variants, determined by their degrees of training freedom, were investigated. The results showed that TL is effective in transferring machine learning (ML)-based process models. High prediction accuracy was achieved on the target machine, with coefficient of determination (

R^{2}

) values reaching 75.5% for yield strength, 82.1% for ultimate tensile strength, and up to 92.0% for elongation at break in testing. Additionally, a weighted mean model ensemble of all eight single models was developed, including all eight TL variants, to enable higher prediction robustness. Validation trials for three different use cases confirmed the capability of the approach to optimize processing conditions, like increasing hatch scan speed by 167% to 292% while maintaining high mechanical performance. Additional microstructure analysis was given to support the findings. The results demonstrate a time- and resource-efficient approach for rapid industrialization of PBF-LB machines, combining ML-based process modeling with machine-specific data. Full article

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

21 pages, 2669 KB

Open AccessArticle

Investigation of Al-Si-Mn Alloy Smelting Based on Thermodynamic Analysis of Phase Diagrams

by Gauhar Yerekeyeva, Bauyrzhan Kelamanov, Vera Tolokonnikova and Assylbek Abdirashit

Metals 2026, 16(4), 437; https://doi.org/10.3390/met16040437 - 17 Apr 2026

Abstract

This study investigates the phase formation and smelting process of a complex Al-Si-Mn alloy based on thermodynamic diagram analysis (TDA). The Fe-Si-Mn-Al system was analyzed considering binary and ternary subsystems, and the standard Gibbs free energy of formation of selected ternary compounds was [...] Read more.

This study investigates the phase formation and smelting process of a complex Al-Si-Mn alloy based on thermodynamic diagram analysis (TDA). The Fe-Si-Mn-Al system was analyzed considering binary and ternary subsystems, and the standard Gibbs free energy of formation of selected ternary compounds was calculated using the additive method. Based on these results, phase equilibrium diagrams were constructed, and the system was tetrahedralized, leading to the identification of 15 thermodynamically stable tetrahedra. It was established that compositions of industrial interest are predominantly localized within tetrahedra enriched in silicide and aluminosilicide phases, particularly FeSi-Fe₂Al₂Si-Fe₃Al₁₁Si₆-Mn₅Si₃. Experimental verification was carried out in a 250 kVA ore-thermal furnace using manganese ore, high-ash coal, and quartzite. The smelting process was conducted under slag-free conditions with stable electrical operation. The obtained alloy had the following composition (wt.%): Fe ~ 12.1, Si ~ 44.7, Mn ~ 34.5, and Al ~ 5.1, with low impurity levels (C < 0.5%, S < 0.02%, p < 0.09%). Microstructural analysis using SEM-EDS confirmed the formation of silicide (FeSi, Mn₅Si₃) and aluminosilicide phases, which ensure the structural stability of the alloy. It is shown that the localization of alloy compositions within specific tetrahedra of the Fe-Si-Mn-Al system prevents self-disintegration. The results demonstrate that TDA is an effective tool for predicting phase composition and optimizing the production technology of complex ferroalloys. Full article

► Show Figures

Figure 1

18 pages, 2791 KB

Open AccessArticle

Phase Formation Features in the Metallothermal Reduction of Natural Coltan

by Kirill V. Pikulin, Stanislav N. Tyushnyakov, Roza I. Gulyaeva, Sofya A. Petrova, Andrey N. Dmitriev and Galina Yu. Vitkina

Metals 2026, 16(4), 436; https://doi.org/10.3390/met16040436 - 17 Apr 2026

Abstract

Phase formation characteristics during the thermochemical reduction of metals from natural coltan using aluminum and calcium–aluminum alloy at 1400–1450 °C were investigated to develop methods for extracting niobium and tantalum from rare metal raw materials. The studied coltan sample consists of a columbite–tantalite [...] Read more.

Phase formation characteristics during the thermochemical reduction of metals from natural coltan using aluminum and calcium–aluminum alloy at 1400–1450 °C were investigated to develop methods for extracting niobium and tantalum from rare metal raw materials. The studied coltan sample consists of a columbite–tantalite solid solution with the composition (Mn,Fe)(Nb,Ta)₂O₆, cassiterite Sn_0.9O₂, tapiolite (Ta,Nb)₂(Mn,Fe)O₆, and calcioolivine Ca₂SiO₄. This study established that the choice of reducing agent determines the sequence of oxide phase transformations. During the aluminothermic process, orthorhombic columbite–tantalite is completely reduced, while tetragonal tapiolite persists even at 1400 °C. The use of a calcium–aluminum alloy containing 69.4 wt.% Ca results in a reversal of this trend: tapiolite is reduced at the early stages (800–1250 °C) through an intermediate (Ta,Nb)O₂ phase, whereas the columbite–tantalite solid solution remains up to 1250 °C. Calcium, having a high affinity for oxygen, forms intermediate perovskite-type oxide phases that act as diffusion barriers, limiting the access of the reducing agent to residual mineral inclusions (mainly Nb-Ta minerals of the orthorhombic crystal system). A temperature rise to 1450 °C initiates the redistribution of oxide components: the content of CaNbO₃ decreases, the Ca₂(Nb,Ta)AlO₆ phase disappears, and its components are involved in the formation of Ca(Nb,Ta)_0.25MnO_2.74 and Ca₄Nb₂O₉. Diffusion constraints are reduced, and the residual columbite–tantalite solid solution is reduced, as confirmed by its complete absence in the products at 1450 °C. In the metallic phase, solid solutions of tantalum and niobium, Ta-Nb-Sn intermetallic compounds (Ta,Nb)₃Sn, titanium aluminide, and ferroalloys with an increased (Ta,Nb)/(Fe,Mn) ratio are formed. The phase transformations elucidated during metallothermic reduction of coltan using different reducing agents, together with the formation of metallic and intermetallic phases, establish a scientific foundation for the development of advanced rare metal extraction processes. Full article

► Show Figures

Figure 1

26 pages, 7789 KB

Open AccessArticle

Mg₂(Co_1/3Fe_1/3Ni_1/3) Processed by Ball-Milling/Annealing and High-Pressure Torsion for Hydrogen Storage, a Hydriding/Dehydriding Cycling Stability Testing

by Karina Suárez-Alcántara, Nidia Libia Torres-García, Paula del Carmen Cintron-Núñez, Joaquín Eduardo González-Hernández, Jorge Mauricio Cubero-Sesin, Espiridión Martínez-Aguilar and Rigoberto López-Juárez

Metals 2026, 16(4), 435; https://doi.org/10.3390/met16040435 - 17 Apr 2026

Abstract

A mandatory prerequisite for a good hydrogen storage material is long-term stability in hydriding/dehydriding reactions, in a suitable temperature interval (250–350 °C for magnesium intermetallics). A 50-cycle hydriding/dehydriding stability test of two Mg₂(Co_1/3Fe_1/3Ni_1/3) materials is [...] Read more.

A mandatory prerequisite for a good hydrogen storage material is long-term stability in hydriding/dehydriding reactions, in a suitable temperature interval (250–350 °C for magnesium intermetallics). A 50-cycle hydriding/dehydriding stability test of two Mg₂(Co_1/3Fe_1/3Ni_1/3) materials is presented. Mg₂(Co_1/3Fe_1/3Ni_1/3) was processed progressively by ball milling and annealing, followed by high-pressure torsion. A comparison of the effects of the processing on the cycling test is presented. X-ray diffraction, scanning and transmission electron microscopy, and infrared characterization indicate the morphological and structural changes in the materials after production and cycling. The highest hydrogen storage was 3.55 wt.% and 3.25 wt.% for the ball-milled and annealed Mg₂(Co_1/3Fe_1/3Ni_1/3) and high-pressure torsion processed Mg₂(Co_1/3Fe_1/3Ni_1/3), respectively, at 15 bar and 300 °C. After 50 cycles of hydriding/dehydriding reactions, the hydriding onset temperature is 69 °C and 50 °C for the ball-milled and annealed Mg₂(Co_1/3Fe_1/3Ni_1/3) and high-pressure torsion processed Mg₂(Co_1/3Fe_1/3Ni_1/3), respectively. Meanwhile, the dehydriding onset temperatures are 257 °C and 223 °C, with hydrogen storage losses of 16% and 7.4% for the ball-milled and annealed Mg₂(Co_1/3Fe_1/3Ni_1/3) and the high-pressure torsion processed Mg₂(Co_1/3Fe_1/3Ni_1/3), respectively. Overall, the ball-milled and annealed Mg₂(Co_1/3Fe_1/3Ni_1/3) material presented better performance. Full article

(This article belongs to the Special Issue Hydrogen Storage Alloys: State of the Art)

► Show Figures

Figure 1

23 pages, 7594 KB

Open AccessArticle

Hydrogen Reduction Behavior and Kinetic Modeling of a High-Barium Manganese Ore: Effect of Calcination

by Alok Sarkar, Elias Trondsen Dahl and Jafar Safarian

Metals 2026, 16(4), 434; https://doi.org/10.3390/met16040434 - 17 Apr 2026

Abstract

Hydrogen-based reduction of manganese ores has attracted increasing attention as a promising route for low-carbon manganese production. In this study, the reduction behavior, microstructural evolution, and kinetics of a high-barium-rich manganese ore were investigated in both dried and calcined states under isothermal hydrogen [...] Read more.

Hydrogen-based reduction of manganese ores has attracted increasing attention as a promising route for low-carbon manganese production. In this study, the reduction behavior, microstructural evolution, and kinetics of a high-barium-rich manganese ore were investigated in both dried and calcined states under isothermal hydrogen atmospheres at 600–800 °C. The ore was characterized using XRF, XRD, optical microscopy, SEM-EDS, and porosity measurements to evaluate mineralogical and structural changes during calcination and reduction. Calcination at 900 °C transformed MnO₂ into Mn₂O₃/Mn₃O₄, removed volatile components, and generated micro-porosity that improved gas accessibility. Isothermal reduction experiments revealed a rapid initial reduction stage followed by a slower reaction regime, with increasing temperature significantly accelerating the reduction rate. Despite isothermal furnace conditions, a temporary rise in sample temperature was observed due to the exothermic nature of manganese oxide reduction by hydrogen. XRD analysis confirmed that manganese oxides were predominantly reduced to MnO, while iron oxides were converted to metallic Fe. Porosity measurements showed significant pore development during reduction at moderate temperatures due to oxygen removal and gas evolution; however, at higher temperatures, partial sintering led to pore coalescence and densification, reducing the overall porosity. Kinetic analysis showed that the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model effectively describes the reduction behavior. The apparent activation energies were 21.92 kJ.mol⁻¹ for dried ore and 17.40 kJ.mol⁻¹ for calcined ore, indicating diffusion-influenced kinetics. The results demonstrate that calcination enhances hydrogen reducibility by improving gas accessibility and reducing kinetic resistance, highlighting its importance for hydrogen-based manganese pre-reduction processes. Full article

(This article belongs to the Special Issue Green Technologies in Metal Recovery)

► Show Figures

Figure 1

32 pages, 5925 KB

Open AccessReview

Addressing the Hydrogen Embrittlement Challenge in Future Hydrogen Pipelines: A Multiscale Review from Mechanisms to Material Design

by Zongneng Zheng, Di Liu, Xinming Sun, Yinghu Wang, Yanhui Zhao and Jianyan Xu

Metals 2026, 16(4), 433; https://doi.org/10.3390/met16040433 - 17 Apr 2026

Abstract

To mitigate fossil fuel dependency and facilitate the transition towards a green economy, utilization of hydrogen energy has emerged as a paramount objective. Nevertheless, during transportation, this goal introduces novel challenges pertaining to material integrity, notably hydrogen embrittlement. This review systematically examines contemporary [...] Read more.

To mitigate fossil fuel dependency and facilitate the transition towards a green economy, utilization of hydrogen energy has emerged as a paramount objective. Nevertheless, during transportation, this goal introduces novel challenges pertaining to material integrity, notably hydrogen embrittlement. This review systematically examines contemporary research on hydrogen embrittlement in natural gas pipelines conveying hydrogen blends and elucidates the hydrogen sources, permeation pathways, and embrittlement mechanisms. By scrutinizing the intrinsic material attributes and operational environments, this study provides an in-depth analysis of the pivotal factors influencing the susceptibility of pipeline steel to hydrogen embrittlement, thereby furnishing a theoretical foundation for the enduring safety of hydrogen pipelines. Full article

► Show Figures

Figure 1

14 pages, 10237 KB

Open AccessArticle

A Correlation with the Deformation Stored Energy and Self-Annealing Behavior of ETP-Cu

by Aman Gupta and Saurabh Tiwari

Metals 2026, 16(4), 432; https://doi.org/10.3390/met16040432 - 17 Apr 2026

Abstract

In the present study, room temperature (RTR) and cryogenic (CR) rolling of electrolytic tough pitch copper (ETP-Cu) was performed to elucidate how deformation temperature and reduction ratio (40% and 80% thickness reductions) control dislocation storage, local stored energy (SE), and self-annealing. Correlated SEM/EDS [...] Read more.

In the present study, room temperature (RTR) and cryogenic (CR) rolling of electrolytic tough pitch copper (ETP-Cu) was performed to elucidate how deformation temperature and reduction ratio (40% and 80% thickness reductions) control dislocation storage, local stored energy (SE), and self-annealing. Correlated SEM/EDS and EBSD analyses were used to (i) locate Cu₂O particles, (ii) quantify local misorientation, and (iii) map the SE for self-annealing. Point EDS confirms that the intermetallic particles are copper oxides (Cu₂O), with apparent O content varying with particle size and EDS interaction volume. RTR80 (80% rolled) exhibits systematically higher KAM values and a larger area fraction of high SE than RTR40 (40% rolled), explaining the greater frequency and spatial density of self-annealed grains at higher reduction. Cryogenic rolling produces more severe fragmentation and a higher fraction of subgrains than RTR at equivalent reductions. CR80 shows the high KAM structures and locally highest SE regions among all conditions, and a higher fraction of self-annealed grains. Nevertheless, the mapped average SE for CR80 (2.93 × 10⁶ J/m³) was lower than for RTR80 (3.34 × 10⁶ J/m³) due to rapid post-deformation dislocation annihilation/self-annealing upon warming at RT. In all conditions, Cu₂O particles and bulged/irregular grain boundaries concentrate dislocations and SE and act as dominant particle-stimulated nucleation (PSN) sites and RT recrystallization, respectively. These results demonstrate that deformation temperature and reduction jointly determine the spatial distribution of SE and hence the propensity for self-annealing in ETP Cu. Full article

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

► Show Figures

Figure 1

16 pages, 1720 KB

Open AccessReview

Effect of Post-Weld Grinding on the Fatigue Strength of Thin-Walled RHS High-Strength Steel T-Joints Under Different Load Stress Ratios

by Benjamin Laher, Christian Buzzi, Peter Brunnhofer, Martin Leitner and Majid Farajian

Metals 2026, 16(4), 431; https://doi.org/10.3390/met16040431 - 16 Apr 2026

Abstract

In this work, the focus is laid on the mean stress effect on the fatigue strength of thin-walled rectangular hollow section T-joints made of high-strength steel S960 M x-treme. The specimens are cyclically tested at a stress ratio of R = −1 and [...] Read more.

In this work, the focus is laid on the mean stress effect on the fatigue strength of thin-walled rectangular hollow section T-joints made of high-strength steel S960 M x-treme. The specimens are cyclically tested at a stress ratio of R = −1 and R = 0.1 in both as-welded and ground (weld-profiled) conditions. In the context of nominal stress evaluations, the ground specimens demonstrate a distinct advantage in contrast to the as-welded condition, exhibiting an increase of +33% at R = 0.1 and +16% at R = −1. Based on the experimental results, a corresponding Haigh diagram is evaluated, revealing a notable difference in the mean stress sensitivity, with M₁ = 0.58 for the as-welded condition and M₁ = 0.39 for the ground condition. Finally, mean stress factors are presented, enabling feasible application in the fatigue design of welded and post-treated structures. The resulting factors are compared with values from the literature for steel applications, showing an increased mean stress influence using high-strength steel as the base material. Full article

(This article belongs to the Special Issue Fracture and Fatigue of Advanced Metallic Materials)

► Show Figures

Figure 1

21 pages, 2210 KB

Open AccessArticle

Material Utilization in Additively Manufactured Layered Systems with a Porous Substrate: A Numerical Case Study of a Thrust Ball Bearing

by Olaf Grutza, Simon Graf, Stefan Paulus, Stefan Thielen and Oliver Koch

Metals 2026, 16(4), 430; https://doi.org/10.3390/met16040430 - 16 Apr 2026

Abstract

In layered systems with porous substrates and a dense solid surface, stiffness and strength are inherently coupled through porosity-dependent relations, influencing their load-bearing behaviour. This work presents a systematic methodology for the assessment and design of such layer-substrate systems based on a criterion [...] Read more.

In layered systems with porous substrates and a dense solid surface, stiffness and strength are inherently coupled through porosity-dependent relations, influencing their load-bearing behaviour. This work presents a systematic methodology for the assessment and design of such layer-substrate systems based on a criterion of balanced material utilization. A dimensionless parameter is defined to characterize the stress state in both components relative to their admissible limits, from which the optimal layer thickness is determined at equal stress levels in both constituents. Stress distributions are calculated using a numerical half-space model for layered contacts and evaluated through material-dependent equivalent stress criteria. The relationship between material utilization and load-carrying capacity is reduced to a scaling factor that combines the influence of porosity-dependent parameters. The approach establishes a direct link between the governing material parameters and structural design variables. Across the investigated parameter range, the utilization rate scales linearly with optimal layer thickness, whereas the load-carrying capacity follows a cubic relation. For a representative Ashby strength scaling coefficient of 𝐶𝜎 = 0.3, for example, a substrate porosity of 90% leads to a scaling factor of 1.6, corresponding to a possible load amplification of 60% relative to the homogeneous reference. Full article

(This article belongs to the Special Issue Surface Engineering for Additively Manufactured Metal Parts)

17 pages, 4956 KB

Open AccessArticle

Online Detection of Surface Defects in Continuous Cast Billets Based on Multi-Information Fusion Method

by Qiang Shi, Xiangyu Cao, Guan Qin, Hongjie Li, Ke Xu and Dongdong Zhou

Metals 2026, 16(4), 429; https://doi.org/10.3390/met16040429 - 15 Apr 2026

Abstract

Surface defects in high-temperature continuous cast billets are critical factors affecting the quality of steel products. Owing to high-temperature radiation, heavy dust contamination, varying billet specifications, and background interference from oxide scales and water stains, existing online surface defect detection technologies for high-temperature [...] Read more.

Surface defects in high-temperature continuous cast billets are critical factors affecting the quality of steel products. Owing to high-temperature radiation, heavy dust contamination, varying billet specifications, and background interference from oxide scales and water stains, existing online surface defect detection technologies for high-temperature continuous cast billets still suffer from limitations including high false-positive rates, inefficient identification of pseudo-defects, and the inability to simultaneously detect three-dimensional (3D) depth information alongside two-dimensional (2D) features. To solve these problems, this paper proposes a multi-dimensional online detection technology for surface defects in high-temperature continuous cast billets based on multi-information fusion. A four-channel multispectral image sensor and a corresponding three-light-source imaging system were developed. Furthermore, a defect sample augmentation method, a deep learning-based 2D recognition method, and a photometric stereo-based 3D reconstruction method were designed to mitigate problems of low detection accuracy and poor robustness caused by sample imbalance among different defect types. Finally, industrial applications were conducted on large-section continuous cast billets, beam blanks, and billets during the grinding process. According to the surface defect detection requirements of different continuous cast billets, multispectral multi-information fusion and traditional 2D defect imaging methods were adopted respectively. The results demonstrate high-precision online detection of surface defects in continuous cast billets, with favorable practical application effects. Full article

(This article belongs to the Special Issue Advanced Metal Smelting Technology and Prospects, 2nd Edition)

► Show Figures

Figure 1

22 pages, 2510 KB

Open AccessArticle

Corrosion Behavior of AISI 52100 Bearing Steel in Novel Water-Based Lubricants

by Juan Bosch, Elizabeth Kotzalas, K Zin Htut, Rowan King and Christopher DellaCorte

Metals 2026, 16(4), 428; https://doi.org/10.3390/met16040428 - 15 Apr 2026

Abstract

Water-based lubricants (WBLs) are increasingly being considered for electrified drivetrain applications; however, their electrochemical stability toward bearing steels remains insufficiently understood. This study evaluated the corrosion behavior of through-hardened AISI 52100 bearing steel in novel WBLs to elucidate the corrosion kinetics and surface [...] Read more.

Water-based lubricants (WBLs) are increasingly being considered for electrified drivetrain applications; however, their electrochemical stability toward bearing steels remains insufficiently understood. This study evaluated the corrosion behavior of through-hardened AISI 52100 bearing steel in novel WBLs to elucidate the corrosion kinetics and surface degradation mechanisms. Round steel disks were cleaned and tested in 50 wt% aqueous dilutions of glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), and polyalkylene glycol (PAG). Electrochemical measurements were conducted using a three-electrode cell in accordance with ASTM G3-14, employing open circuit potential (OCP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. Among the uninhibited fluids, DI water exhibited the highest corrosion current density (19.85 µA/cm²), while glycerol- and PEG-based systems showed the lowest values (0.79 and 0.85 µA/cm², respectively), attributed to organic adsorption at the steel/electrolyte interface. EIS analysis revealed a single charge-transfer-controlled process across all fluids, consistent with a weak, non-passive interfacial oxide whose protective character is modulated by organic adsorption. The addition of NaNO₃ produced divergent effects depending on the base fluid chemistry: the corrosion activity was reduced in DI water and glycerol systems through enhanced passivation, while PEG- and PAG-based formulations showed increased corrosion current densities and reduced charge transfer resistance, attributed to competitive disruption of the polymer boundary layer by nitrate ions. Surface characterization by SEM/EDAX and white-light interferometry corroborated the electrochemical findings, revealing fluid-dependent corrosion morphologies ranging from uniform attack in DI water to localized pitting in polymer-based systems, with NaNO₃ shifting the corrosion mode in PEG/PAG systems from localized to combined localized and uniform attack. These findings highlight the critical role of fluid chemistry in controlling corrosion processes in water-based lubricants and provide mechanistic insight for the development of corrosion-stable formulations for high-performance electrified drivetrain applications. Full article

(This article belongs to the Special Issue Corrosion and Fracture of Metallic Materials)

► Show Figures

Figure 1

13 pages, 4804 KB

Open AccessArticle

Effect of Thickness on Connection Strength and Pull-Out Behavior of TiNiFe Shape Memory Alloy Pipe Couplings

by Yunbo Li, Haofeng Xie, Zhihao Zhang, Songxiao Hui, Yanfeng Li, Xiaoyun Song, Wenjun Ye, Yang Yu and Yumeng Luo

Metals 2026, 16(4), 427; https://doi.org/10.3390/met16040427 - 15 Apr 2026

Abstract

TiNiFe shape memory alloy pipe couplings exhibit excellent radial recovery capability and therefore show great potential for pipeline fastening applications. In this study, the radial recovery stresses at different locations within a TiNiFe SMA pipe coupling were determined using a finite element inverse [...] Read more.

TiNiFe shape memory alloy pipe couplings exhibit excellent radial recovery capability and therefore show great potential for pipeline fastening applications. In this study, the radial recovery stresses at different locations within a TiNiFe SMA pipe coupling were determined using a finite element inverse method. These stresses were subsequently applied as boundary conditions to establish a numerical model describing the fastening connection and pull-out process between the TiNiFe coupling and a TA18 tube. The effects of coupling wall thickness on the connection state and pull-out failure behavior were systematically investigated. The results indicate that the radial recovery stress increases monotonically with increasing wall thickness, although the growth rate gradually decreases. When the wall thickness ranges from 1.25 to 1.75 mm, the interfacial contact stress increases with thickness, thereby enhancing the fastening effect. However, when the thickness exceeds 1.75 mm, the intensified radial deformation of the inner convexes leads to a significant reduction in contact stress. The pull-out process of the assembly can be divided into three stages, namely the initial, intermediate, and final stages, during which the pull-out force first increases and then decreases with the evolution of the contact state. These findings provide a theoretical basis for the structural optimization and engineering application of TiNiFe SMA pipe couplings. Full article

► Show Figures

Figure 1

29 pages, 3661 KB

Open AccessArticle

A Numerical Study on Crashworthiness in 3D Lattice Structures: Employing Shape Transformers

by Autumn R. Bernard, Muhammet Muaz Yalçın and Mostafa S. A. ElSayed

Metals 2026, 16(4), 426; https://doi.org/10.3390/met16040426 - 14 Apr 2026

Abstract

Periodic lattice materials exhibit tunable mechanical properties, yet the impact of non-cylindrical, non-circular strut cross-sections on crashworthiness remains largely unexplored. This study extends the concept of shape transformers—dimensionless ratios representing the area and second moment of area of a strut cross-section relative to [...] Read more.

Periodic lattice materials exhibit tunable mechanical properties, yet the impact of non-cylindrical, non-circular strut cross-sections on crashworthiness remains largely unexplored. This study extends the concept of shape transformers—dimensionless ratios representing the area and second moment of area of a strut cross-section relative to its enclosing envelope—to two canonical lattice topologies: the octet and rhombic dodecahedron topologies (stretching-dominated and bending-dominated, respectively). Eleven distinct cross-sectional shapes (solid and hollow circular, diamond, and square) were systematically varied under constant area and constant envelope conditions to isolate microscale geometric effects on macroscopic impact response. Results demonstrate that adjusting Ψ_i alone can enhance specific energy absorption by up to 62% in bending-dominated lattices (compared to 18% in stretching-dominated lattices). Furthermore, the influence of geometric efficiency (λ = Ψ_i/Ψ_a) on plateau stress and energy absorption trends across topologies has been quantified. These findings establish shape transformers as significant design parameters for crashworthy lattice materials, and design charts are presented to facilitate the development of additive-manufactured cellular structures aimed at optimized energy absorption performance. Full article

(This article belongs to the Section Additive Manufacturing)

11 pages, 1154 KB

Open AccessArticle

CNN-Based Microstructural Carbide Detection in Stainless Steel: Effects of Dataset Size

by Fuad Khoshnaw and Weigang Yao

Metals 2026, 16(4), 425; https://doi.org/10.3390/met16040425 - 14 Apr 2026

Abstract

This study developed a machine learning approach to detect carbide precipitation in the microstructure of austenitic stainless steel, specifically grade 316, using a convolutional neural network (CNN). Microstructural images were prepared and classified into three categories: as-received, heat-treated without carbide precipitation, and heat-treated [...] Read more.

This study developed a machine learning approach to detect carbide precipitation in the microstructure of austenitic stainless steel, specifically grade 316, using a convolutional neural network (CNN). Microstructural images were prepared and classified into three categories: as-received, heat-treated without carbide precipitation, and heat-treated with carbide precipitation. A CNN was trained and validated using two separate datasets of varying sizes to assess the impact of data quantity on classification performance. This automated microstructure recognition system offers potential benefits for additive manufacturing (AM) by enabling real-time quality assessment and feedback control, particularly for avoiding undesirable carbide formation during metal 3D printing. By linking microstructural analysis to processing conditions, this approach supports the development of defect-free, corrosion-resistant components and contributes to the integration of intelligent monitoring within digital manufacturing workflows. Full article

► Show Figures

Figure 1

15 pages, 16090 KB

Open AccessArticle

Effect of the Annealing Treatment on the Microstructure and Properties of TC4 Titanium Alloy TIG and Laser-Welded Joints

by Yansong Wang, Yulang Xu, Jingyong Li, Xuzhi Lan, Dan Song and Yanxin Qiao

Metals 2026, 16(4), 424; https://doi.org/10.3390/met16040424 - 13 Apr 2026

Abstract

This study compares the microstructural evolution and mechanical properties of TC4 (Ti-6Al-4V) titanium alloy joints welded by Tungsten Inert Gas (TIG) and laser processes, following a post-weld annealing treatment at 650 °C for 2 h. Distinct microstructures were obtained: the TIG-welded joint developed [...] Read more.

This study compares the microstructural evolution and mechanical properties of TC4 (Ti-6Al-4V) titanium alloy joints welded by Tungsten Inert Gas (TIG) and laser processes, following a post-weld annealing treatment at 650 °C for 2 h. Distinct microstructures were obtained: the TIG-welded joint developed a heterogeneous mixture of short-rod α and lamellar β, while the laser-welded joint formed a more homogeneous equiaxed α structure with uniformly distributed β-phase nanoparticles. Electron backscatter diffraction (EBSD) results confirmed that the annealing treatment significantly weakened the strong welding-induced texture and disrupted the epitaxial growth mode of columnar grains. Mechanical testing demonstrated that annealing improved the strength-toughness balance, but the extent and mechanism differed between the two processes. For the TIG-welded joint, the ultimate tensile strength slightly decreased, while elongation and impact toughness increased by 18% and 10.4%, respectively. In contrast, the laser-welded joint maintained its original strength while achieving greater improvements in ductility and toughness, with elongation and impact toughness increasing by 20% and 15.2%, respectively. This divergence is attributed to insufficient recrystallization and the persistence of residual coarse grains, limiting the TIG joint’s performance. However, in the laser-welded joint, the pinning effect of β-phase nanoparticles and associated grain refinement enhanced ductility without compromising strength. Full article

(This article belongs to the Special Issue Perspectives of Joints and Joining Technology Development for Metallic and Hybrid Materials)

► 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