Metals

44 pages, 20657 KB

Open AccessReview

Laser Shock Peening of Metallic Materials: Fatigue Mechanisms, Process-Parameter Effects, and Emerging Thermal-Assisted Variants

by Xiaohui Li, Hao Tan, Mingjia Wu, Lijie Chen, Lianhao Liu, Youxiao Chen and Zhexu Zhang

Metals 2026, 16(7), 821; https://doi.org/10.3390/met16070821 - 22 Jul 2026

Viewed by 441

Abstract

Laser shock peening (LSP) is an advanced surface modification technique that significantly enhances the fatigue resistance of metallic components through the synergistic implantation of deep compressive residual stresses (CRSs) and gradient microstructural refinement. Existing investigations have shown that LSP can generate strengthening layers [...] Read more.

Laser shock peening (LSP) is an advanced surface modification technique that significantly enhances the fatigue resistance of metallic components through the synergistic implantation of deep compressive residual stresses (CRSs) and gradient microstructural refinement. Existing investigations have shown that LSP can generate strengthening layers extending from several hundred micrometers to approximately 1 mm in depth, with affected zones reaching 5–6 times the depth typically achieved by conventional shot peening in representative titanium alloys. In specific cases, LSP has increased the fatigue limit from 483.2 MPa to 593.6 MPa, corresponding to an improvement of approximately 22.8%, while optimized treatment of Ti-17 compressor blades has extended fatigue life by more than two orders of magnitude. This review systematically elucidates the anti-fatigue strengthening mechanisms of LSP across a range of metallic systems, with emphasis on three key aspects: (i) the mechanistic retardation of fatigue crack initiation and propagation, mediated by CRS-induced reductions in the stress intensity factor and enhanced crack closure effects; (ii) the parametric sensitivity of surface integrity and stress field homogeneity to laser energy density, spot overlap ratio, and multiple-impact sequencing; and (iii) the process-specific characteristics of emerging LSP variants, including laser peening without coating, warm laser shock peening, and cryogenic laser shock peening. Furthermore, we critically evaluate the role of multiscale numerical simulations—encompassing macroscopic finite element analysis, mesoscopic crystal plasticity modeling, and molecular dynamics—in optimizing process parameters and predicting fatigue life. By integrating experimental, computational, and theoretical perspectives, this review establishes a coherent process–structure–property framework to guide the rational design of LSP protocols for targeted fatigue performance enhancement. Full article

(This article belongs to the Special Issue Advanced Metallic Materials and Forming Technologies)

► Show Figures

Figure 1

25 pages, 27496 KB

Open AccessArticle

Development of a Gaseous Hydrogen Permeation Method: Effects of Palladium-Coated Charging Surfaces and Partial Permeation Transients

by Matthew Scott, Rashiga Walallawita, Matthew C. Hinchliff and Dimitry Sediako

Metals 2026, 16(7), 820; https://doi.org/10.3390/met16070820 - 21 Jul 2026

Viewed by 322

Abstract

Hydrogen diffusion plays a central role in the susceptibility of steels to hydrogen embrittlement, yet reported diffusivity values often exhibit significant variability due to differences in experimental methodology. Gaseous hydrogen permeation experiments, while more representative of service conditions, are highly sensitive to surface [...] Read more.

Hydrogen diffusion plays a central role in the susceptibility of steels to hydrogen embrittlement, yet reported diffusivity values often exhibit significant variability due to differences in experimental methodology. Gaseous hydrogen permeation experiments, while more representative of service conditions, are highly sensitive to surface boundary conditions and trapping effects, which can bias the diffusivity obtained from analysis. In this work, a gaseous hydrogen permeation methodology was developed at the High-Performance Powertrain Materials Laboratory (HPPM) at the University of British Columbia, Okanagan. A dedicated gas management system (GMS) was implemented to enable controlled pressure step transients, allowing partial permeation transients to be collected under gaseous charging conditions. This approach was applied to commercially pure iron and API 5L X60 pipeline steel to evaluate diffusion and trapping behaviour across materials with differing microstructural complexity. The results demonstrate that diffusivity obtained from transients spanning the full charging–discharging range (0–2 MPa) reflects an effective parameter influenced by reversible hydrogen trapping, whereas transients measured over incremental pressure steps (1–2 MPa) provide a more consistent estimate of lattice-controlled diffusion. The application of palladium coatings to the charging surface was found to promote hydrogen entry, reducing surface impedance effects and further improving agreement with Fickian diffusion behaviour. Full article

(This article belongs to the Special Issue Hydrogen Embrittlement of Metals: Behaviors and Mechanisms (2nd Edition))

► Show Figures

Figure 1

17 pages, 9615 KB

Open AccessArticle

Effect of Precursor Alloy Overheating on Controlled Diffusion Solidification of Mg-Al-Zn Alloys

by Xinyi Zhao, Shanguang Liu, Tao Gu, Yang Sun, Hong Qin, Dan Wang and Peizhong Feng

Metals 2026, 16(7), 819; https://doi.org/10.3390/met16070819 - 21 Jul 2026

Viewed by 271

Abstract

Diffusion solidification is an effective method to produce non-dendritic microstructures and reduce casting defects in magnesium alloys. However, the influence of precursor alloy superheat on the solidification behavior and the resulting microstructure remains insufficiently understood. In this study, pure magnesium was used as [...] Read more.

Diffusion solidification is an effective method to produce non-dendritic microstructures and reduce casting defects in magnesium alloys. However, the influence of precursor alloy superheat on the solidification behavior and the resulting microstructure remains insufficiently understood. In this study, pure magnesium was used as the high thermal mass (HTM) alloy and three Mg-Al-Zn alloys with different aluminum and zinc contents were used as the low thermal mass (LTM) alloys. The effects of superheat on grain morphology, solute diffusion, and constitutional supercooling were investigated through a combination of experimental casting and numerical simulation using Ansys Fluent and Matlab. The results show that the solidified interface consists of five distinct regions, including two base metals, two transition zones, and a central controlled diffusion solidification zone. A higher superheat of the HTM alloy relative to the LTM alloy promotes a wider transition zone and finer globular grains, whereas equal or lower superheat leads to columnar or rosette structures. The Mg-30 wt.%Al-3.5 wt.%Zn alloy with moderate aluminum content produces fine globular grains due to a thinner constitutional supercooling layer and a higher degree of supercooling, which suppresses grain growth and increases nucleation rate. In contrast, the Mg-55 wt.%Al-6.5 wt.%Zn alloy with high aluminum content forms coarse rosette and columnar grains. Among the conditions investigated, the combination of 10 °C HTM and 5 °C LTM superheats tends to promote the formation of fine equiaxed grains. Increasing superheat above this range reduces supercooling and coarsens grains, while decreasing superheat inhibits interface diffusion and promotes solute segregation. The findings provide a theoretical basis for designing precursor alloy compositions and superheat parameters in controlled diffusion solidification of magnesium alloys. Full article

(This article belongs to the Special Issue Research Progress of Crystal in Metallic Materials, 2nd Edition)

► Show Figures

Figure 1

49 pages, 7905 KB

Open AccessReview

Research Progress and Challenges of Hydrogen Embrittlement in Hydrogen Pipeline Steels: A Comprehensive Review

by Zhenxiang Li, Shipin Wu, Junlin Dai, Yan Wang and Zhiwei Gao

Metals 2026, 16(7), 818; https://doi.org/10.3390/met16070818 - 21 Jul 2026

Viewed by 523

Abstract

Hydrogen serves as a fundamental energy carrier essential for achieving global carbon neutrality, with long-distance pipeline transportation recognized as the most efficient approach for large-scale hydrogen delivery. Nevertheless, hydrogen embrittlement (HE) in pipeline steels constitutes a significant safety challenge for this infrastructure. This [...] Read more.

Hydrogen serves as a fundamental energy carrier essential for achieving global carbon neutrality, with long-distance pipeline transportation recognized as the most efficient approach for large-scale hydrogen delivery. Nevertheless, hydrogen embrittlement (HE) in pipeline steels constitutes a significant safety challenge for this infrastructure. This review presents a comprehensive and systematic analysis of HE in hydrogen pipeline steels, emphasizing the microstructural fracture mechanisms under hydrogen exposure, the microstructural regulation of hydrogen diffusion and trapping, the interplay of multiple influencing factors, strategies for HE mitigation, and numerical prediction methodologies. Critical factors including microstructural features, hydrogen transport dynamics, and the coupling effects between stress and hydrogen are examined in detail. The review systematically summarizes advanced HE mitigation techniques and strategies, encompassing microstructural engineering, surface modification, alloy composition optimization, finite element modeling, and machine learning applications. Additionally, several principal challenges confronting the field are identified: the ambiguous mechanisms underlying multi-field coupling effects, the limited translation of laboratory-scale findings to practical engineering contexts, especially with regard to multi-scale mitigation of hydrogen-induced fracture, and the incomplete advancement of artificial intelligence-based pipeline integrity assessment tools. To address these issues, the review proposes key research directions and recommendations for future investigations into HE in hydrogen pipeline steels. Full article

► Show Figures

Figure 1

19 pages, 3721 KB

Open AccessReview

Slightly Irregular Spheroidal Graphite (Type-V, ISO): Typical Graphite Morphology for High-Si/SiMo Ductile Cast Irons

by Iuliana Stan, Constantin Stelian Stan, Denisa Elena Anca, Eduard Stefan, Mihai Chisamera and Iulian Riposan

Metals 2026, 16(7), 817; https://doi.org/10.3390/met16070817 - 21 Jul 2026

Viewed by 290

Abstract

The present paper reviews original data obtained by the authors from recent separate publications with additional unpublished data, specifically concerning the specific graphite morphology in Si/SiMo alloyed ductile irons (2.5–5.5% Si, 0.01–2.3% Mo) with alloying grade, cooling rate, and inoculation as influencing factors. [...] Read more.

The present paper reviews original data obtained by the authors from recent separate publications with additional unpublished data, specifically concerning the specific graphite morphology in Si/SiMo alloyed ductile irons (2.5–5.5% Si, 0.01–2.3% Mo) with alloying grade, cooling rate, and inoculation as influencing factors. Different formulas used for nodularity evaluation, including different forms of graphite participating in different proportion and two graphite shape factors: Roundness (RSF, involving maximum Ferret) and Sphericity (SSF, involving real perimeter). Slightly irregular spheroidal graphite morphology (Form V, ISO 945) characterized by RSF = 0.59–0.75 was found to be typical for Si and SiMo ductile irons in all of the test conditions, such as Si level (4.2–5.25% Si), Si–Mo system (4.1–4.8% Si + 1.6–2.3% Mo), mould type (green sand, resin sand, metal mould, external metallic chill), un-inoculation and inoculation, and inoculating element type. Increasing Si content negatively affects the compactness degree of spheroidal graphite particles (transition from VI to V form) and nodularity. Metal mould versus sand mould solidification of 4.5% Si ductile iron increases nodule count, graphite shape factors (RSF = 0.68–0.7 versus 0.59–0.64) and nodularity (67% to 76%). An external metallic chill in a resin sand mould promoted directional solidification and showed a nodularity decrease for increasing Si, for all the nodularity formulas and for the cooling rate range. Inoculating elements influenced the shape factors in thin wall castings, where Ca–Ba was better than simple Ca and Ca–RE could promote graphite at higher real perimeter and with lower shape factors. The correlation of the aspect of structure, graphite parameters and nodularity led to the conclusion that the nodularity formula according to ISO/WD 945-4-2015 (100% total area of Form VI and 90% of Form V), with SSF instead of RSF, appears to be better in High-Si/SiMo DI (especially for more than 4% Si), because it takes into account the presence of slightly irregular spheroidal graphite (with high real perimeter) at a high rate. Full article

(This article belongs to the Special Issue Solidification, Microstructure and Mechanical Properties of Cast Alloys)

► Show Figures

Figure 1

14 pages, 11224 KB

Open AccessArticle

Research on Optimal Design of Multi-DoF Forming Process for High-Ribbed Ring-Groove Components

by Boyu Zheng, Yufeng Wang, Xiaorui Wan and Wuhao Zhuang

Metals 2026, 16(7), 816; https://doi.org/10.3390/met16070816 - 21 Jul 2026

Viewed by 298

Abstract

Aiming at the technical challenges in the Multi-DoF forming of 20CrMnTi high-ribbed ring-groove components, including complex metal flow behavior that easily causes under-filling defects and complicated die stress states prone to die failure, this paper proposes an optimal design method for the Multi-DoF [...] Read more.

Aiming at the technical challenges in the Multi-DoF forming of 20CrMnTi high-ribbed ring-groove components, including complex metal flow behavior that easily causes under-filling defects and complicated die stress states prone to die failure, this paper proposes an optimal design method for the Multi-DoF forming process of high-ribbed ring-groove components. The influence mechanism of different blank sizes on metal flow and component filling effect is systematically investigated, and three typical metal flow modes are identified. Furthermore, a die stress optimization method for Multi-DoF forming is proposed. Research results show that, compared with the outward-to-inward and inward-to-outward metal flow modes, the metal flow under the symmetric inward–outward flow metal flow mode is more balanced, ensuring that the two high ribs can be fully formed. Additionally, changing the blank size can balance the forces on both sides of the die boss, thus significantly reducing the risk of die cracking caused by stress concentration. On the basis of the above research results, experimental tests are conducted, and the high-ribbed ring-groove components achieve full forming quality without die failure, which verifies the feasibility and effectiveness of the process optimization design method proposed in this paper. Full article

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

► Show Figures

Figure 1

18 pages, 25079 KB

Open AccessArticle

Low-Temperature Direct Hot Stamping of a Zn-Coated Press-Hardening Steel with Enhanced Mechanical Properties

by Fatemeh Khalatbari and Joseph R. McDermid

Metals 2026, 16(7), 815; https://doi.org/10.3390/met16070815 - 21 Jul 2026

Viewed by 325

Abstract

Direct hot press forming (DHPF) of Zn-coated press-hardening steel (PHS) has not been widely adopted by industry due to liquid metal embrittlement (LME), which occurs when coated steel is hot stamped above the Fe-Zn peritectic temperature (~782 °C). In the present study, low-temperature [...] Read more.

Direct hot press forming (DHPF) of Zn-coated press-hardening steel (PHS) has not been widely adopted by industry due to liquid metal embrittlement (LME), which occurs when coated steel is hot stamped above the Fe-Zn peritectic temperature (~782 °C). In the present study, low-temperature hot stamping was performed on a 2.0 wt% Mn PHS to avoid LME by preventing liquid zinc formation during plastic deformation while achieving target mechanical properties (yield strength (YS) ≥ 1100 MPa and ultimate tensile strength (UTS) ≥ 1500 MPa) and preserving corrosion performance. The enhanced hardenability, indicated by a critical cooling rate (CCR) of 10 °C/s, enabled a predominantly martensitic microstructure following DHPF at 550–700 °C. Tensile testing of samples extracted from U-shaped panels yielded similar results for uncoated and Zn-coated samples, with a YS of ~1170 MPa, a UTS of ~1600 MPa, a uniform elongation (UE) of 0.05, and a total elongation (TE) of 0.09, demonstrating the preservation of baseline mechanical properties in the coated samples. Microstructural analysis confirmed the absence of LME-induced substrate cracking. Additionally, XRD, SEM-BSE, and EDS analyses confirmed Γ-Fe₃Zn₁₀ formation in DHPF galvanized coatings, with volume fractions averaging ~0.6, well above the critical value of 0.15, irrespective of the DHPF temperature, demonstrating the formation of a cathodically protective coating microstructure. Full article

(This article belongs to the Special Issue Hot Forming/Processing of Metals and Alloys)

► Show Figures

Figure 1

18 pages, 5358 KB

Open AccessArticle

Substrate Orientation Dependence of Local Ordering and Crystal Nucleation in Al Melts

by Qi Zhang, Yamei Jin, Sai Tang and Jiankai Ma

Metals 2026, 16(7), 814; https://doi.org/10.3390/met16070814 - 21 Jul 2026

Viewed by 301

Abstract

Heterogeneous nucleation is almost invariably responsible for the solidification of metals in practice, and this process governs the fabrication techniques for numerous advanced materials. Hence, a profound understanding of the physical essence of heterogeneous nucleation at the atomic scale is urgently required. In [...] Read more.

Heterogeneous nucleation is almost invariably responsible for the solidification of metals in practice, and this process governs the fabrication techniques for numerous advanced materials. Hence, a profound understanding of the physical essence of heterogeneous nucleation at the atomic scale is urgently required. In this study, we systematically investigate the substrate orientation dependence of liquid ordering and crystal nucleation in Al melts using molecular dynamics simulations (MD). Results show that the ability of nanoparticles to promote crystal nucleation originates from their capacity to facilitate the formation of crystal-like structures at the melt–substrate interface. Regarding the influence of substrate orientations on the ordered layers at the Al liquid–solid interface, the following trends are observed: the (111) plane has the strongest induction ability, followed by the (110) and then the (100) planes. For in-plane ordering, the (100) plane exhibits the highest order, followed by the (111) plane, with the (110) plane being the weakest. Notably, despite its highest atomic density in the first-ordered layer, the (111) substrate suffers from lower atomic mobility than the (100) and (110) substrates, hindering rapid rearrangement into the FCC structure. The synergy of the layer-by-layer growth mode, strong templating efficiency, and high atomic mobility leads to the fastest crystal growth for the (100) orientation. Full article

(This article belongs to the Special Issue Modeling and Simulation of Microstructural Evolution in Metallic Materials)

► Show Figures

Graphical abstract

23 pages, 23244 KB

Open AccessArticle

Multi-Objective Optimization of Casting Parameters for Mn70Ni25Cr5 Alloy Using ProCAST Simulation and Response Surface Methodology

by Shuicong Lu, Dehong Lu, Yongkun Li and Yongtai Chen

Metals 2026, 16(7), 813; https://doi.org/10.3390/met16070813 - 21 Jul 2026

Viewed by 281

Abstract

To simultaneously suppress shrinkage-related defects and refine the solidification microstructure of Mn70Ni25Cr5 alloy ingots, ProCAST simulation was combined with Box–Behnken response surface methodology to optimize pouring temperature, filling time, and mold temperature. Porosity in the ingot body and secondary dendrite arm spacing (SDAS) [...] Read more.

To simultaneously suppress shrinkage-related defects and refine the solidification microstructure of Mn70Ni25Cr5 alloy ingots, ProCAST simulation was combined with Box–Behnken response surface methodology to optimize pouring temperature, filling time, and mold temperature. Porosity in the ingot body and secondary dendrite arm spacing (SDAS) were selected as the response variables, and quadratic regression models were established for both responses. The optimized casting parameters were determined using analysis of variance, response surface analysis, and the desirability function approach. The porosity and SDAS models were both statistically significant, with non-significant lack-of-fit terms and R² values of 0.9906 and 0.9901, respectively. The optimal parameters were a pouring temperature of 1220.74 °C, a filling time of 6.34 s, and a mold temperature of 294.47 °C, corresponding to a predicted porosity of 0.426% and a predicted SDAS of 47.51 μm. A supplementary simulation and a validation casting experiment were then performed using practical process settings derived from the optimized solution. The supplementary simulation indicated that shrinkage-related defects were concentrated mainly in the riser, while metallographic examination revealed no large continuous shrinkage-porosity region in the examined ingot-body sections. The overall measured SDAS across the center, half-radius, and edge positions was 48.54 μm, differing from the response-surface prediction by approximately 2.2%. These results support the applicability of the combined ProCAST–RSM approach for simulation-assisted optimization of Mn70Ni25Cr5 alloy casting parameters within the investigated process range. Full article

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

► Show Figures

Figure 1

15 pages, 4590 KB

Open AccessFeature PaperArticle

Research on the Integration of Steel Structure Design and Fabrication Based on MBSE

by Xiang Guo, Yongyi Yang, Wei Liu, Dexing Huang, Tianhao Lin and Huang Feng

Metals 2026, 16(7), 812; https://doi.org/10.3390/met16070812 - 21 Jul 2026

Viewed by 315

Abstract

Existing BIM-based workflows for complex spatial steel bridges often support 3D visualization and documentation, but they still lack a formal requirement-to-function traceability mechanism and a reliable automated link from special-shaped surface modeling to fabrication-oriented data. To address this gap, this study develops and [...] Read more.

Existing BIM-based workflows for complex spatial steel bridges often support 3D visualization and documentation, but they still lack a formal requirement-to-function traceability mechanism and a reliable automated link from special-shaped surface modeling to fabrication-oriented data. To address this gap, this study develops and validates a Model-Based Systems Engineering (MBSE)-oriented design–fabrication integration workflow for special-shaped steel bridges. The workflow combines requirement decomposition, functional architecture modeling, ENOVIA-based collaborative data management, skeleton-driven parametric modeling, User-Defined Feature (UDF) templates, Engineering Knowledge Language (EKL) batch instantiation, an IFC-based manufacturing information extension, ProNest nesting, and model-driven NC-code generation. The method was implemented for the Q7 North Pedestrian Bridge, a spatially twisted special-shaped steel landscape bridge. In the case study, the proposed workflow reduced typical repetitive component modeling time by 70.8%, shortened drawing generation time by 80.0%, increased nesting material utilization from 84.6% to 91.8%, and controlled the maximum coordinate-transformation deviation of formwork points within 1.42 mm. Field validation showed a mean fabrication deviation of 1.6 mm and a maximum site assembly closure deviation of 4.5 mm. The results indicate that the proposed MBSE-oriented digital thread improves design consistency, reduces manual data re-entry, and strengthens traceability from requirements to manufacturing and assembly. The study provides a reproducible case-study framework for model-driven steel bridge design–fabrication integration and identifies the limitations of UDF-library construction cost, software-specific learning requirements, and single-project validation. Full article

► Show Figures

Figure 1

20 pages, 4809 KB

Open AccessArticle

DEM-FEM Coupling Simulation of Residual Stress Improvement for Q235B Welded Joint via Shot Peening

by Kaisheng Chen, Yan Chen and Kuoli Zhai

Metals 2026, 16(7), 811; https://doi.org/10.3390/met16070811 - 21 Jul 2026

Viewed by 273

Abstract

To overcome the welding-induced residual tensile stress of Q235B welded joints, a sequential thermal-mechanical welding and DEM-FEM dynamic shot peening coupled model is established. The Goldak double-ellipsoidal heat source model is adopted to simulate welding temperature evolution, and the discrete element method fully [...] Read more.

To overcome the welding-induced residual tensile stress of Q235B welded joints, a sequential thermal-mechanical welding and DEM-FEM dynamic shot peening coupled model is established. The Goldak double-ellipsoidal heat source model is adopted to simulate welding temperature evolution, and the discrete element method fully considers random shot ejection and shot–shot collision energy attenuation, which addresses the simplification defect of traditional single-shot finite element models. The effects of shot diameter d, incident angle θ, initial shot velocity v and mass flow rate r_m on the residual compressive stress layer are systematically analyzed. Results reveal that larger shot diameter and initial shot velocity deepen the residual compressive stress layer. Meanwhile, the maximum residual compressive stress first increases and then decreases with the increase in r_m and θ. The optimal parameter combination is determined as d = 1 mm, θ = 60°, v = 60 m/s, r_m = 9 kg/min. Under these parameters, the maximum residual compressive stresses reach −306 MPa (σ_x) and −310 MPa (σ_z), with the depths of the residual compressive stress layer being up to 0.78 mm for σ_x and up to 0.66 mm for σ_z, respectively. Different from previous simplified simulations, this study quantifies the collision energy attenuation caused by shot trajectory overlap. This proposed model can provide guidance for post-weld surface strengthening of low-carbon steel engineering structures. Full article

(This article belongs to the Special Issue Novel Insights into Welding and Joining Technologies of Metallic Materials)

► Show Figures

Figure 1

14 pages, 875 KB

Open AccessArticle

Melt–Vapor Phase Transition and Distillation Separation of Magnesium–Silver Alloys

by Valeriy Volodin, Sergey Trebukhov, Alina Nitsenko, Arailym Mukangaliyeva, Xeniya Linnik and Nurila Burabayeva

Metals 2026, 16(7), 810; https://doi.org/10.3390/met16070810 - 20 Jul 2026

Viewed by 289

Abstract

In this study, the partial pressure values of magnesium over Mg–Ag system alloys were determined by the boiling point method and are presented as a temperature–concentration dependence. A similar dependence for the partial vapor pressure of silver was obtained with the numerical integration [...] Read more.

In this study, the partial pressure values of magnesium over Mg–Ag system alloys were determined by the boiling point method and are presented as a temperature–concentration dependence. A similar dependence for the partial vapor pressure of silver was obtained with the numerical integration of the Gibbs–Duhem equation. The boundaries of the vapor–liquid equilibrium fields were calculated at atmospheric pressure (101.3 kPa) and under vacuum (1.33 kPa). A complete phase diagram was constructed, including the boundaries of the liquid–vapor phase transition at the specified pressures. It was shown that the composition of the equilibrium vapor phase is represented almost entirely by magnesium over nearly the entire range of component concentrations. Thus, when the melt contains 1 wt. % in the melt and exhibits a boiling temperature of 1187 °C (1460 K), the vapor phase contains 94.67 wt. % magnesium, with silver accounting for the remainder. Therefore, the separation of liquid magnesium–silver alloys presents no significant technological difficulties. Based on the thermodynamic activities of the components, the partial and integral mixing functions, namely, entropy and enthalpy, were determined. The thermodynamic functions of formation and evaporation of Mg–Ag system alloys may be used for energy calculations of distillation processes and will supplement the physicochemical database. Full article

► Show Figures

Figure 1

22 pages, 32901 KB

Open AccessArticle

Investigation of Metallic Ca on Enhancing the Cleanliness of Ni-Based Superalloy

by Shaowen Deng, Guangyao Chen, Hang Guo, Kunjie Peng, Hui Xu, Enhui Wang, Xinmei Hou and Chonghe Li

Metals 2026, 16(7), 809; https://doi.org/10.3390/met16070809 - 20 Jul 2026

Viewed by 349

Abstract

Induction melting with a crucible was a commonly employed method for the preparation of Ni-based superalloys. However, it inevitably introduced contamination to the superalloy during the melting process. In this study, the effect of Ca addition was investigated on the interaction between the [...] Read more.

Induction melting with a crucible was a commonly employed method for the preparation of Ni-based superalloys. However, it inevitably introduced contamination to the superalloy during the melting process. In this study, the effect of Ca addition was investigated on the interaction between the Al₂O₃ crucible and the superalloy melts. The variations in impurity elements and inclusion contamination for the alloys were studied. The results revealed that the interaction between the melt and the Al₂O₃ crucible led to the dissolution of Al₂O₃, introducing oxygen contamination and promoting the formation of inclusions. After adding Ca, the dissolved oxygen readily reacted with Ca to form CaO, which further reacted with the Al₂O₃ matrix and inclusions to form CaO-Al₂O₃ oxides. The total O content in the alloy was reduced from 0.0141 ± 0.0005 wt.% to 0.0030 ± 0.0003 wt.%, and the S content decreased from 1.60 ± 0.17 × 10⁻⁴ wt.% to 0.82 ± 0.05 × 10⁻⁴ wt.%. Meanwhile, the detected area-to-mass ratio of floated inclusion contamination in the alloys decreased from 0.36 cm²/kg to 0.05 cm²/kg. This process reduced both oxygen-related impurities and inclusion-derived contaminants, thereby providing an effective approach for preparing high-purity alloys. Full article

(This article belongs to the Special Issue Metal-Based Ceramics and Refractories for Metallurgical Applications)

► Show Figures

Figure 1

27 pages, 14946 KB

Open AccessArticle

Machine Learning-Based Ultimate Strength Prediction of Spherical Shells Considering Multi-Source Uncertain Imperfections

by Rongsheng Shi, Ming Zhan, Hao Wang and Yuntao Wang

Metals 2026, 16(7), 808; https://doi.org/10.3390/met16070808 - 20 Jul 2026

Viewed by 341

Abstract

Spherical shells are a commonly used structural form in submarine pressure-resistant structures. This study employed machine learning to predict the ultimate strength statistical properties of spherical shells considering inevitable multi-source uncertain imperfections. Thirty nominally identical spherical shells were fabricated, the thickness distribution and [...] Read more.

Spherical shells are a commonly used structural form in submarine pressure-resistant structures. This study employed machine learning to predict the ultimate strength statistical properties of spherical shells considering inevitable multi-source uncertain imperfections. Thirty nominally identical spherical shells were fabricated, the thickness distribution and geometric imperfections were measured, and the ultimate strength of these shells were obtained by hydrostatic experiments. Then, the measured imperfections were reconstructed and mapped into the finite element model, and the buckling performance of the spherical shells were numerically investigated. Subsequently, two XGBoost models with considerable accuracy were trained to predict the ultimate strength statistical properties. The pole-smoothing double Fourier series expansion was adopted to reconstruct the geometric imperfections with accuracies exceeding 0.985 on all tested shells. The experimental ultimate strength of the spherical shells was consistent with the numerical predictions with an error of 0.81%. The evaluation metrics R² of the XGBoost models for the mean and standard deviation of spherical shell ultimate strength were 0.9977 and 0.9246, respectively. At a confidence level of 99.74%, the margin of the upper bound prediction was 0.018 MPa, and the margin of the lower bound prediction was 0.624 MPa. The findings of this study propose an innovative method to predict the ultimate strength bounds of spherical shells, offering a generalizable workflow that can potentially inform the design of submarine pressure hulls when extended to application-specific geometric dimensions and materials. Full article

(This article belongs to the Special Issue Mechanical Structure Damage of Metallic Materials)

► Show Figures

Figure 1

22 pages, 18814 KB

Open AccessArticle

Effect of High-Pressure Torsion on the Hydrogen Storage Properties of Ti-V-Cr-Mn Medium-Entropy Alloy

by Paula C. Cintrón-Núñez, Karina Suárez-Alcántara, Ignacio A. Figueroa-Vargas, Juan R. Tena-García, Joaquín E. González-Hernández, Jorge M. Cubero-Sesin, Yoshikazu Todaka, Daniel Bahena-Uribe, Armando Salinas-Rodríguez and José G. Cabañas-Moreno

Metals 2026, 16(7), 807; https://doi.org/10.3390/met16070807 - 20 Jul 2026

Viewed by 339

Abstract

Hydrogen storage represents a key technological challenge to the widespread use of hydrogen as a fuel and energy carrier. For this purpose, the hydrogen storage properties of medium-entropy and high-entropy alloys are under extensive investigation, including the study of the effects of compositional [...] Read more.

Hydrogen storage represents a key technological challenge to the widespread use of hydrogen as a fuel and energy carrier. For this purpose, the hydrogen storage properties of medium-entropy and high-entropy alloys are under extensive investigation, including the study of the effects of compositional variations, nanostructuring, and catalyst additions. The present work characterizes the hydrogen storage behavior of a medium-entropy, near equiatomic Ti-V-Cr-Mn alloy, both in the as-cast condition and after nanostructuring by severe plastic deformation. The alloy consists of a matrix of BCC solid solution and a dispersed C14 Laves phase. Processing by high-pressure torsion results in the refinement of the crystallite size of the BCC phase down to about 30 nm. The absorption capacity of the alloy at 45 °C and 2.5 MPa is 1.6 wt%. Regardless of its initial condition, the first hydrogenation of the Ti-V-Cr-Mn alloy at room temperature and 2.5 MPa occurs without any pre-activation treatment. On the other hand, hydrogen is partially released at room temperature, while full dehydrogenation requires a temperature of 300 °C. Severe plastic deformation considerably reduces the susceptibility of the alloy to become deactivated for hydrogen absorption. These results highlight the potential of plastic straining to tailor the hydrogen storage properties of metallic BCC alloys. Full article

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

► Show Figures

Figure 1

14 pages, 1564 KB

Open AccessArticle

Three-Dimensional Graphite Volume Partitioning in Compacted Graphite Iron Thermal Analysis Specimens with 0–0.30 wt.% 75FeSi Addition

by Zeyu Liu, Kaijiao Kang and Dequan Shi

Metals 2026, 16(7), 806; https://doi.org/10.3390/met16070806 - 18 Jul 2026

Viewed by 275

Abstract

Two-dimensional metallography cannot be used to determine how graphite volume is partitioned among three-dimensional connected structures in compacted graphite iron (CGI), even when the conventional graphite fractions are similar. This study therefore uses archived micro-CT data to determine whether 75FeSi additions in thermal [...] Read more.

Two-dimensional metallography cannot be used to determine how graphite volume is partitioned among three-dimensional connected structures in compacted graphite iron (CGI), even when the conventional graphite fractions are similar. This study therefore uses archived micro-CT data to determine whether 75FeSi additions in thermal analysis specimens alter the three-dimensional distribution of graphite volume. Three spherical specimens were cast from an industrial CGI melt with 0, 0.15, and 0.30 wt.% 75FeSi placed at the bottom of the specimen cavity. Center coupons were examined using a ZEISS Xradia 620 Versa X-ray microscope, and the retained reconstructed volumes had 3.0 µm isotropic voxels. We decoded the archived Dragonfly volumetric datasets, removed inactive historical labels, and calculated number-weighted and volume-weighted size, concentration, and shape descriptors. Graphite volume fraction remained within 8.56–8.83%, whereas connected object number density changed from 9764 mm⁻³ without additional 75FeSi to 5739 and 6854 mm⁻³ at 0.15 and 0.30 wt.%, respectively. Number-weighted median diameter remained near 13 µm, but volume-weighted D90 increased from 185.0 to 454.7 and 501.9 µm. The largest connected object contained 3.42%, 20.30%, and 31.39% of graphite volume, respectively. The main contribution is a specimen-level three-dimensional graphite volume-partitioning signature that separates graphite amount from graphite connectivity and upper-tail concentration. The results show that similar total graphite fractions can correspond to different internal graphite architectures, which conventional planar measurements cannot resolve. Full article

► Show Figures

Figure 1

15 pages, 1113 KB

Open AccessReview

Anisotropic Permeability in Solidifying Mushy Zones: Coupling Dendritic Kinetics to Interdendritic Transport for Predicting Solidification Defects in Metallic Alloys

by Bao Yang, Xiaoyong Tang, Wenming Xiong, Zhuang Li, Minglin Wang and Hui Zhang

Metals 2026, 16(7), 805; https://doi.org/10.3390/met16070805 - 17 Jul 2026

Viewed by 325

Abstract

The anisotropic permeability tensor governs interdendritic fluid flow and solute transport during the directional solidification of metallic alloys, fundamentally influencing crystal growth kinetics and microstructural evolution. Traditional scalar models, notably the Kozeny–Carman equation, are fundamentally limited by isotropic assumptions that contradict the inherent [...] Read more.

The anisotropic permeability tensor governs interdendritic fluid flow and solute transport during the directional solidification of metallic alloys, fundamentally influencing crystal growth kinetics and microstructural evolution. Traditional scalar models, notably the Kozeny–Carman equation, are fundamentally limited by isotropic assumptions that contradict the inherent anisotropy of dendritic microstructures and preclude description of microstructure–transport coupling. Recent advances in multiscale computational crystal growth modeling, integrating phase-field simulations of dendritic morphology, lattice Boltzmann calculations of interdendritic flow, and synchrotron X-ray tomography for in situ microstructural characterization, have enabled tensor-resolved quantification of permeability evolution, yet the dynamic feedback between solid skeleton deformation and permeability remains poorly understood. This work establishes a critically assessed mechanistic framework coupling dendritic microstructure evolution, anisotropic permeability tensor dynamics, and solidification transport phenomena. By explicitly addressing the hitherto unresolved dynamic feedback between solid skeleton deformation and permeability, this review provides a theoretical foundation and a conceptual framework for future predictive modeling for solidification microstructure control, offering fundamental insights into the physics of crystal growth and interdendritic transport in metallic systems. Full article

(This article belongs to the Special Issue Advanced Metallic Materials and Manufacturing Processes)

► Show Figures

Figure 1

37 pages, 41496 KB

Open AccessReview

Recent Advances in Joining Technologies for Aluminum/Magnesium Dissimilar Metals: A Review

by Tianwei Qiu and Muhammed Nafis Bin Osman Zahid

Metals 2026, 16(7), 804; https://doi.org/10.3390/met16070804 - 17 Jul 2026

Viewed by 297

Abstract

Aluminum/magnesium (Al/Mg) hybrid structures are promising candidates for lightweight engineering, but reliable joining is still limited by brittle intermetallic compounds (IMCs), oxide films, pores, cracks, and corrosion-related degradation. This review summarizes recent advances in Al/Mg dissimilar-metal joining, including solid-state welding, fusion welding, brazing, [...] Read more.

Aluminum/magnesium (Al/Mg) hybrid structures are promising candidates for lightweight engineering, but reliable joining is still limited by brittle intermetallic compounds (IMCs), oxide films, pores, cracks, and corrosion-related degradation. This review summarizes recent advances in Al/Mg dissimilar-metal joining, including solid-state welding, fusion welding, brazing, resistance-based joining, and mechanical joining. Emphasis is placed on process characteristics, interfacial reactions, defect formation, mechanical properties, service reliability, and simulation-assisted process understanding. The reviewed studies indicate that joint reliability cannot be interpreted solely from IMC thickness; phase type, continuity, spatial distribution, interfacial morphology, and involvement in the fracture path are also critical. Solid-state and high-speed impact processes can restrict continuous Al–Mg reaction layers by reducing thermal exposure and promoting plastic contact, whereas fusion-based processes provide greater manufacturing flexibility but require stricter control of molten-pool behavior, Mg evaporation, porosity, and interlayer stability. Recent numerical simulations and data-driven studies are further discussed as tools for mechanism-guided parameter design. This review provides an integrated comparison of joining routes and highlights future needs for standardized testing, fatigue and corrosion evaluation, thermal-cycling assessment, coupled service-performance analysis, and process selection for engineering applications. Full article

► Show Figures

Figure 1

26 pages, 16089 KB

Open AccessArticle

Research on Parameter Formulation Strategy of Asymmetric Four-Point Bending Progressive Process for LSAW Pipes

by Zhiyuan Zhang, Junchao An, Junfang Shen, Yi Liu and Yan Gao

Metals 2026, 16(7), 803; https://doi.org/10.3390/met16070803 - 17 Jul 2026

Viewed by 210

Abstract

The current progressive forming process for large-scale longitudinally submerged arc-welded (LSAW) pipes is continuously losing competitiveness in terms of manufacturing quality and production efficiency. Based on the asymmetric four-point bending (AFB) mechanical model and classical elastic–plastic bending theory, in this paper, we investigate [...] Read more.

The current progressive forming process for large-scale longitudinally submerged arc-welded (LSAW) pipes is continuously losing competitiveness in terms of manufacturing quality and production efficiency. Based on the asymmetric four-point bending (AFB) mechanical model and classical elastic–plastic bending theory, in this paper, we investigate sheet bending behavior during the four-point bending stage. Analytical expressions are derived for the main influencing factors during the forming and springback process. Finite element simulation and experimental research into the mechanical model are conducted to analyze the effects of various process parameters on the forming results. On this basis, an AFB progressive forming process parameter formulation strategy is established and programmed. Experiments and simulations were conducted using the process parameters formulated by this strategy. The results showed that pipes could complete the progressive forming process in fewer passes, thereby improving production efficiency. The ovality of most experimental pipes was less than 1.5% and consistently below 0.7% in simulations—significantly lower than the engineering requirement of 2%. These results demonstrate the feasibility and reliability of the strategy, highlight the significant improvement in pipe quality achieved through the AFB process, and lay a solid foundation for the development and intelligentization of future progressive forming processes for LSAW pipes. Full article

► Show Figures

Figure 1

20 pages, 3490 KB

Open AccessArticle

Optimized Cycloid Caster-Curve Design for Slab Continuous Casting Based on High-Temperature Creep Mechanism

by Xiangqian Bai, Zize Zhang and Xingzhong Zhang

Metals 2026, 16(7), 802; https://doi.org/10.3390/met16070802 - 17 Jul 2026

Viewed by 231

Abstract

Internal cracks during slab bending and straightening are continuous-casting defects. Existing caster curves rely on plastic deformation, while curvature variation is concentrated within short sections, causing excessive strain rates and increasing the risk of internal straightening cracks. This study proposes a novel method [...] Read more.

Internal cracks during slab bending and straightening are continuous-casting defects. Existing caster curves rely on plastic deformation, while curvature variation is concentrated within short sections, causing excessive strain rates and increasing the risk of internal straightening cracks. This study proposes a novel method for slab straightening through creep deformation and develops a curve for an R9300 caster by connecting cubic transition curves with cycloidal main segments. High-temperature tensile and constant-stress creep tests of Q345C steel were combined with transient thermal simulation and geometric strain-rate calculations. Under constraints on caster height, minimum curvature radius, and steady-state creep rate, the optimized parameters were a = 2600 mm and t = 3.6 rad. The curve eliminates the circular-arc section and ensures continuous position, tangent, and curvature. Its bending and straightening sections are each 9379 mm long, increases of 8349 and 7859 mm, respectively, while caster height increases by only 0.47 m. At the internal 1200 °C isotherm, the maximum strain rates are

6.75 \times 10^{- 5} s^{- 1}

and

5.19 \times 10^{- 5} s^{- 1}

, reductions of 82.2% and 81.1% relative to the conventional caster. Both remain below the steady-state creep rate of

7.45 \times 10^{- 5} s^{- 1}

under ±10% secondary-cooling and ±10 °C casting-temperature fluctuations. The curve alleviates deformation concentration and enables the slab region at 1200 °C and above to bend and straighten through creep deformation. Full article

(This article belongs to the Special Issue Continuous Casting and Solidification of Steels)

► Show Figures

Figure 1

25 pages, 22789 KB

Open AccessArticle

The Evolution of Intergranular Second-Phase Precipitation and Matrix Microstructure of SLM-Formed Fe-Mn-Al-C Lightweight Steel Under Different Solution Treatments

by Jiaxiang Zheng, Chengwei Fei, Tian Xie, Chuangliang Wu, Xi Gao and Wei Jiang

Metals 2026, 16(7), 801; https://doi.org/10.3390/met16070801 - 17 Jul 2026

Viewed by 293

Abstract

Fe-Mn-Al-C lightweight high-strength steels are promising for aerospace and defense applications, but selective laser melting (SLM) introduces steep thermal gradients and rapid solidification, causing directional grain growth, crystallographic texture, and the non-uniform precipitation of κ-carbides and B2 phase at grain boundaries. This results [...] Read more.

Fe-Mn-Al-C lightweight high-strength steels are promising for aerospace and defense applications, but selective laser melting (SLM) introduces steep thermal gradients and rapid solidification, causing directional grain growth, crystallographic texture, and the non-uniform precipitation of κ-carbides and B2 phase at grain boundaries. This results in pronounced mechanical anisotropy between XY and YZ planes, limiting engineering use. To eliminate this anisotropy, we investigate the post-SLM solution treatment of an SLM-fabricated Fe-Mn-Al-C steel at 1050–1150 °C for 0.5–1.5 h followed by oil quenching, and characterize microstructures and tensile properties on both planes. At 1050 °C, the XY plane remained equiaxed γ-austenite, while the YZ plane transformed to α and became equiaxed over time, causing strength–ductility anisotropy. At 1100 °C for 1 h, anisotropy was effectively removed: XY and YZ planes exhibited tensile strengths of ~1159 and 1154 MPa and elongations of ~40% and 41%. TEM revealed that uniform fine κ-carbides and coarsened B2 at grain boundaries suppressed direction-dependent strain. At 1150 °C, dissolved boundary phases and diffuse intragranular κ-carbides severely reduced ductility. The optimal treatment is 1100 °C for 1 h, yielding a homogeneous microstructure and excellent isotropic properties. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing of Metallic Alloys)

► Show Figures

Figure 1

14 pages, 6495 KB

Open AccessArticle

Spatiotemporal Evolution of Electron Density During Femtosecond Laser Ablation of Grain-Oriented Silicon Steel

by Hanzheng Zhang, Guobao Li, Yongjie Yang, Fang Zhang and Yuhui Sha

Metals 2026, 16(7), 799; https://doi.org/10.3390/met16070799 - 17 Jul 2026

Viewed by 266

Abstract

Grain-oriented silicon steel is a key soft magnetic material for transformer cores, and femtosecond laser scribing provides a potential approach for achieving high-precision magnetic-domain refinement while reducing thermal damage. However, the near-surface electronic response and charge-imbalance behavior of grain-oriented silicon steel during femtosecond [...] Read more.

Grain-oriented silicon steel is a key soft magnetic material for transformer cores, and femtosecond laser scribing provides a potential approach for achieving high-precision magnetic-domain refinement while reducing thermal damage. However, the near-surface electronic response and charge-imbalance behavior of grain-oriented silicon steel during femtosecond laser irradiation are still not well understood. In this study, a two-temperature model coupled with an electron transport model was employed to investigate the evolution of electron temperature and net charge density under different laser fluences and pulse durations. The results showed that laser fluence and pulse duration jointly affected the near-surface electron-temperature response, electron-emission process, and net charge-density evolution in grain-oriented silicon steel. Increasing laser fluence enhanced electron excitation and the degree of charge-distribution imbalance. Meanwhile, increasing pulse duration promoted the extension of the net charge distribution along the depth direction, which indicated that there was a pulse-duration range that can simultaneously promote charge accumulation at the surface and in the near-surface region. These results provided comprehensive insight into the near-surface charge-imbalance behavior during femtosecond laser etching of grain-oriented silicon steel. Full article

► Show Figures

Figure 1

17 pages, 3107 KB

Open AccessArticle

Comparative Study on the Weldability and Low-Temperature Toughness of Thick TMCP Steel for Offshore Wind Power Substructures According to Grade and Welding Position

by Eulyong Ha, Myungsu Yi, Younghyun Kim and Jaewoong Kim

Metals 2026, 16(7), 800; https://doi.org/10.3390/met16070800 - 16 Jul 2026

Viewed by 340

Abstract

As the demand for eco-friendly energy increases, offshore wind power structures are gradually becoming larger to increase power generation capacity, which in turn requires the use of thick TMCP steels and the securing of structural integrity. In this study, multi-pass FCAW was applied [...] Read more.

As the demand for eco-friendly energy increases, offshore wind power structures are gradually becoming larger to increase power generation capacity, which in turn requires the use of thick TMCP steels and the securing of structural integrity. In this study, multi-pass FCAW was applied to 40 mm thick S355ML and S420ML steels in 2G and 3G welding positions, and the welding conditions for each experiment were designed to simulate actual industrial site construction conditions. After the experiments, tensile, low-temperature impact, and hardness tests were performed on the welded joints, and a comparative analysis was conducted on whether the relevant standards were satisfied and their major characteristics. As a result of the tensile test, tensile strengths exceeding the standard requirements were measured under all conditions, and base metal fracture occurred. In addition, the low-temperature impact test conducted at −50 °C exceeded the standard requirement of 27 J, ensuring sufficient low-temperature toughness, and the Vickers hardness test results were measured to be less than the reference value of 380 HV10. Through this study, the structural integrity and mechanical reliability of multi-pass FCAW welded joints for thick TMCP steel plates were secured. Full article

(This article belongs to the Special Issue Nonlinear Structural Behavior and Failure of Marine and Offshore Steel Structures)

► Show Figures

Figure 1

13 pages, 9054 KB

Open AccessArticle

Microstructure Evolution and Mechanical Properties of New High-Performance Mg Alloy with Low RE Content

by Liqiang Ma and Dongdong Zhang

Metals 2026, 16(7), 798; https://doi.org/10.3390/met16070798 - 16 Jul 2026

Viewed by 361

Abstract

High-strength Mg alloys always contain heavy RE solutes, which leads to the high cost of Mg alloys preventing commercial use. In this work, we developed a new high-performance Mg–3Nd–1Yb–0.6Zn–0.4Zr alloy with low RE content and investigated the effects of heat treatment on the [...] Read more.

High-strength Mg alloys always contain heavy RE solutes, which leads to the high cost of Mg alloys preventing commercial use. In this work, we developed a new high-performance Mg–3Nd–1Yb–0.6Zn–0.4Zr alloy with low RE content and investigated the effects of heat treatment on the microstructure and mechanical properties. The results show that the main secondary phase in the as-cast alloy is the eutectic Mg₁₂RE phase at grain boundaries. The average grain size is measured to be 24.6 μm. After solution treatment, the grain-boundary eutectic Mg₁₂RE phase is completely dissolved into the matrix, without obvious grain growth. The alloy exhibits an obvious age-hardening effect during aging at 200 °C, and its hardness reaches a peak at 15 h, with a hardness increment of ~31 HV. A high-density prismatic β′ phase is formed in the matrix after peak aging. The peak-aged alloy presents optimal mechanical properties, with ultimate tensile strength, yield strength and elongation of 282 MPa, 202 MPa and 6.8%, respectively, which are remarkably superior to those of typical alloys such as EV31A and WE43. Quantitative calculation of strengthening mechanisms indicates that age hardening is the dominant strengthening mechanism of the peak-aged alloy, and the precipitation strengthening contribution of prismatic β′ phase is 158 MPa, accounting for approximately 78% of the yield strength. Full article

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

► Show Figures

Figure 1

19 pages, 5163 KB

Open AccessArticle

Electrochemical Corrosion Performance of W-MoS₂ Coatings Fabricated by Electrospark Deposition

by Xinying Zhang, Chunmao Jiang, Fengsheng Lu, Lei Zhang, Minghuang Bi, Hao Jin, Xudong Lu, Guanglin Zhu, Cean Guo and Jian Zhang

Metals 2026, 16(7), 797; https://doi.org/10.3390/met16070797 - 16 Jul 2026

Viewed by 281

Abstract

The self-lubricating MoS₂ coating is highly susceptible to degradation in marine environments due to oxidative corrosion. To expand its application in high-humidity and high-salt-fog conditions, this study mixed W with MoS₂ and prepared W-MoS₂ self-lubricating coatings on the surface of [...] Read more.

The self-lubricating MoS₂ coating is highly susceptible to degradation in marine environments due to oxidative corrosion. To expand its application in high-humidity and high-salt-fog conditions, this study mixed W with MoS₂ and prepared W-MoS₂ self-lubricating coatings on the surface of CrNi3MoVA steel by electrospark deposition technology. The electrochemical corrosion behaviors of these coatings, with varying W/MoS₂ mass ratios, were examined using an electrochemical workstation in a 3.5 wt.% NaCl solution. The findings indicated that as the MoS₂ content increased, the low-frequency impedance modulus (LIMs) of the W-MoS₂ coating initially rose and then declined. At a MoS₂ content of 20 wt.%, the coating exhibited the highest LIM and the greatest corrosion resistance. In comparison to the CrNi3MoVA steel substrate, the corrosion current density was reduced by 67.4%, a result attributed to the coating’s dense microstructure and improved charge transfer resistance, thereby demonstrating its optimal protective performance. These results provide a laboratory electrochemical basis for designing corrosion-resistant self-lubricating ESD coatings for steel components exposed to chloride-containing environments; however, long-term immersion, cyclic salt-spray, field-exposure, and quantitative adhesion tests are still required before direct long-term marine-service durability can be confirmed. Full article

► Show Figures

Figure 1

16 pages, 8466 KB

Open AccessFeature PaperArticle

Phase-Field Simulation of the Solidification Process of Particle-Reinforced Cu Matrix Composites

by Zhenliang Zhang, Can Guo, Shengkai Cao, Zhangle Xie, Jiankai Ma, Yiming Hao, Junhao Zhu, Wanli Cao, Daniel Safranchik and Chunjie Xu

Metals 2026, 16(7), 796; https://doi.org/10.3390/met16070796 - 16 Jul 2026

Viewed by 379

Abstract

As a typical class of high-strength and high-conductivity materials, particle-reinforced copper matrix composites show great promise for application in critical conductive components. However, when such composites are prepared via melting methods, challenges such as the agglomeration of reinforcing particles and difficulty controlling their [...] Read more.

As a typical class of high-strength and high-conductivity materials, particle-reinforced copper matrix composites show great promise for application in critical conductive components. However, when such composites are prepared via melting methods, challenges such as the agglomeration of reinforcing particles and difficulty controlling their spatial distribution often arise, limiting the application of these composites in conductive parts. In this study, a phase-field method is employed with order parameters introduced to characterize the interaction between solid–liquid interfaces and reinforcing phases. By reconstructing the free-energy functional of the multi-phase-field model, the effects of undercooling and solid–liquid interface properties on particle–interface interactions are investigated. Simulations are conducted for solidification for different particle sizes and in different particle aggregation states, dynamically illustrating the evolution behavior of nanoparticles at the solid–liquid interface. The results indicate that particle migration velocity and distance rise with increased particle mobility due to reduced melt flow resistance. Higher undercooling accelerates solidification front propagation but curtails particle pushing distance, while the interface gradient coefficient (ε²) only inhibits particle migration distance with negligible influence on peak migration velocity. In single-crystal matrices, agglomerate morphology, orientation angle, and aggregation degree jointly affect migration behavior: irregular agglomerates undergo obvious morphological deformation, and migration distance increases when the orientation angle ranges from 0° to 90° and decreases with higher aggregation degrees. Fine particles are repelled to grain boundaries for agglomeration, whereas large particles are engulfed inside grains. Powders were fabricated via gas atomization, and the results of scanning electron microscopy characterization experiments confirm the simulation reliability. The results provide valuable insights for the controlled distribution of nanoparticles within composite materials. Full article

(This article belongs to the Special Issue Modeling and Simulation of Microstructural Evolution in Metallic Materials)

► Show Figures

Figure 1

34 pages, 8240 KB

Open AccessArticle

Comparison of Performances of Machine Learning and Deep Learning Models for Prediction of Creep Rupture Life

by Muhammad Bilal Jan, Zengchao Wu and Mengyu Chai

Metals 2026, 16(7), 795; https://doi.org/10.3390/met16070795 - 14 Jul 2026

Viewed by 513

Abstract

Accurate prediction of creep rupture life is essential for ensuring the long-term reliability of high-temperature components in power generation and petrochemical industries. Selecting appropriate data-driven models for limited and heterogeneous creep datasets remains a critical challenge, as conventional accuracy-based comparisons do not fully [...] Read more.

Accurate prediction of creep rupture life is essential for ensuring the long-term reliability of high-temperature components in power generation and petrochemical industries. Selecting appropriate data-driven models for limited and heterogeneous creep datasets remains a critical challenge, as conventional accuracy-based comparisons do not fully capture model behavior under varying service conditions. This study presents a unified evaluation framework for systematically comparing multiple machine learning and deep learning models for creep rupture life prediction of 2.25Cr–1Mo steel. The framework integrates predictive accuracy, prediction reliability, regime-specific error analysis, and computational efficiency, enabling a comprehensive assessment beyond global error metrics. The input feature space is reduced from seventeen to eight physically meaningful variables without loss of predictive performance. To further assess model robustness, prediction errors are analyzed across four distinct rupture life regimes, revealing significant variations in model behavior that are not reflected in aggregate metrics. Results indicate that support vector regression (SVR) provides the most consistent overall performance across all regimes and offers a strong balance between accuracy and computational efficiency. Among deep learning models, a Bayesian neural network (BNN) achieves competitive predictive performance while additionally enabling uncertainty estimation. These findings demonstrate that, for small tabular creep datasets, appropriately regularized models outperform complex neural network architectures, highlighting the importance of matching model complexity to dataset characteristics. This study is limited to a single steel grade, moderate dataset size, and extrapolation beyond trained stress and temperature ranges, which are key directions for future work. Full article

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

► Show Figures

Figure 1

43 pages, 33571 KB

Open AccessArticle

Smelting–Aluminothermic Reduction of Hydrogen Pre-Reduced Manganese Ores in a 200 kW DC Arc Furnace

by Dursman Mchabe, Sello Tsebe, Madinoge Mampuru, Jafar Safarian and Elias Matinde

Metals 2026, 16(7), 794; https://doi.org/10.3390/met16070794 - 14 Jul 2026

Viewed by 261

Abstract

The escalating demand for sustainable metallurgical practices necessitates innovative approaches to manganese production. The smelting–aluminothermic reduction of hydrogen pre-reduced manganese ores in a direct current (DC) arc furnace offers a resilient and sustainable trajectory for optimizing manganese recovery efficiencies while minimizing waste generation [...] Read more.

The escalating demand for sustainable metallurgical practices necessitates innovative approaches to manganese production. The smelting–aluminothermic reduction of hydrogen pre-reduced manganese ores in a direct current (DC) arc furnace offers a resilient and sustainable trajectory for optimizing manganese recovery efficiencies while minimizing waste generation under low-carbon operating conditions. This study presents a comparison of smelting–aluminothermic reduction of two Mn ores pre-reduced with hydrogen using two distinct approaches, namely, a packed-bed vertical retort and a plasma rotary furnace. A 200 kW DC arc furnace was used for smelting. The scope of this assessment integrates technical, environmental, and operational metrics of smelting–aluminothermic reduction. For partial process energy estimation, the considered metrics are power stability metrics, specific energy requirement, and load factor/power-on time. The metrics considered for material are reductant efficiency, elemental accountability, elemental recovery, elemental deportment, and slag-to-metal ratio. For process sustainability, refractory and electrode consumption were considered. The environmental indicators considered include CO₂-equivalent emissions per ton of product, dust and particulate emissions, NO_x/SO_x emissions. This research provides critical insights into the viability and environmental advantages of hydrogen pre-reduction coupled with smelting–aluminothermic reduction for cleaner manganese production. Full article

► Show Figures

Figure 1

37 pages, 25585 KB

Open AccessArticle

Effect of Si₃N₄ Reinforcement on Compressive Properties and Cell Morphology of AA7075 Composite Metal Foams

by Krishna Kanth Varadarajula, Veeresh Kumar Gonal Basavaraja and Mohammed Aman

Metals 2026, 16(7), 793; https://doi.org/10.3390/met16070793 - 14 Jul 2026

Viewed by 371

Abstract

Lightweight materials with improved strength characteristics are increasingly required in aerospace, automotive, impact protection, and vibration damping applications to enhance structural efficiency and service life. Although aluminum metal foams have been found to be promising lightweight cellular materials, their load-bearing performance is rather [...] Read more.

Lightweight materials with improved strength characteristics are increasingly required in aerospace, automotive, impact protection, and vibration damping applications to enhance structural efficiency and service life. Although aluminum metal foams have been found to be promising lightweight cellular materials, their load-bearing performance is rather limited, thus limiting their use for high-performance structural applications. The composite metal foams in the present study were produced by CaCO₃ as foaming agent and AA7075 as the base material by gas-releasing particle decomposition method, in which the foaming agent is transformed into CO₂ gas to generate pores during foaming. Cell size distribution analysis, density, and energy-dispersive spectroscopy were used to investigate the composite foams containing 0, 1, 2 and 3 wt.% Si₃N₄, while quasi-static uniaxial compression testing was employed to measure the compressive strength of these foams. Si₃N₄ of 2 wt.% and 3 wt.% resulted in better pore refinement and uniformity of cells, as revealed in the microstructural analysis. The density was raised from 0.21 to 0.61 g/cm³ by reinforcement addition. The compression strength increased from 7.85 to 23.64 MPa, while energy absorption increased from 5.10 to 20.52 MJ/m³ for foams containing 0 and 3 wt.% Si₃N₄, respectively. The yield strength also improved from 4.92 to 15.98 MPa, and the plateau stress from 7.37 to 22.57 MPa. Improved mechanical behavior is due to the following: refinement of pores, thickness of the ligaments, more compact structure, and load transfer in the cellular structure. Full article

(This article belongs to the Section Metal Matrix Composites)

► Show Figures

Figure 1

20 pages, 61935 KB

Open AccessArticle

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Ti–6Al–4V Alloy Produced by L-PBF and PA-DED

by Svetlana Gatina, Andrey Stotskiy, Alfiz Gareev, Alexander Ryzhkin, Irina Semenova, Alexey Mamalat, Olga Klimova-Korsmik, Sergey Zherebtsov and Nariman Enikeev

Metals 2026, 16(7), 792; https://doi.org/10.3390/met16070792 - 14 Jul 2026

Viewed by 327

Abstract

The manufacturing of personalized implants from Ti–6Al–4V alloy using additive manufacturing technologies is a promising direction in modern medicine. However, components produced by these methods are characterized by a non-equilibrium microstructure, high residual stresses, and anisotropy of mechanical properties, which necessitates subsequent heat [...] Read more.

The manufacturing of personalized implants from Ti–6Al–4V alloy using additive manufacturing technologies is a promising direction in modern medicine. However, components produced by these methods are characterized by a non-equilibrium microstructure, high residual stresses, and anisotropy of mechanical properties, which necessitates subsequent heat treatment. The aim of the present work was a systematic comparative study of the effect of three heat treatment regimes—stress relief annealing (600 °C, 3 h), subtransus annealing in the (α + β) region (950 °C, 1 h, furnace cooling), and solution treatment followed by aging (STA: 950 °C, 0.5 h, water quenching + aging at 675 °C, 3 h)—on the microstructure and mechanical properties of Ti–6Al–4V alloy manufactured by laser powder bed fusion (L-PBF) and plasma arc directed energy deposition (PA-DED). The microstructure was examined using scanning electron microscopy, transmission electron microscopy, and electron backscatter diffraction (EBSD). Tensile mechanical properties were determined in two directions: parallel and perpendicular to the build direction. Stress-relief annealing led to an increase in the ductility of the alloy without a noticeable decrease in strength and without significant changes in the microstructure. Subtransus annealing resulted in the formation of an equilibrium lamellar (α + β) structure, which provided a substantial increase in ductility with a moderate decrease in strength. Solution treatment and aging resulted in formation of a bimodal microstructure. Subtransus annealing (both alloys), STA (L-PBF) and stress relief annealing (PA-DED) provided properties comparable to those of wrought material. The obtained results form the basis for a scientifically informed selection of both the manufacturing route and the heat treatment regime for biomedical implants made of Ti–6Al–4V alloy. Full article

(This article belongs to the Special Issue Structure and Properties of Biomedical Alloys)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Metals, Volume 16, Issue 7 (July 2026) – 137 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI