Metals

27 pages, 698 KB

Open AccessReview

An Overview of the Benefits, Drawbacks and Strategies Used for the Fabrication of 316L Stainless Steel and Inconel 625 Functionally Graded Materials Using Wire Arc Additive Manufacturing

by G. Lima Antunes and J. P. Oliveira

Metals 2026, 16(5), 467; https://doi.org/10.3390/met16050467 (registering DOI) - 25 Apr 2026

Abstract

Wire arc additive manufacturing (WAAM) is an efficient, low-cost technique for fabricating large-scale metallic components and, in particular, functionally graded materials (FGMs). This review focuses on the fabrication of 316L stainless steel–Inconel 625 FGMs by arc-based WAAM processes, examining Gas Metal Arc Welding [...] Read more.

Wire arc additive manufacturing (WAAM) is an efficient, low-cost technique for fabricating large-scale metallic components and, in particular, functionally graded materials (FGMs). This review focuses on the fabrication of 316L stainless steel–Inconel 625 FGMs by arc-based WAAM processes, examining Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW) and Plasma Arc Welding (PAW) in terms of their microstructural outcomes, compositional control strategies, residual stress development and mechanical performance. A critical finding emerging from the reviewed literature is that direct compositional interfaces between 316L and Inconel 625 can yield superior tensile strength and ductility and lower residual stresses compared to smooth gradient strategies, owing to the formation of detrimental secondary phases such as δ-phase, Laves phase and MC carbides at intermediate iron–nickel compositions encountered only during graded builds. The potential of Submerged Arc Additive Manufacturing (SAAM) as a future high-deposition-rate alternative for large-scale FGM fabrication is also discussed. Key challenges, including dilution control, Laves phase formation, residual stress management and the corrosion characterization of the graded region, are identified, together with priority research directions for advancing the industrial adoption of arc-based FGM components. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: “Laser Welding and Additive Manufacturing”)

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20 pages, 2820 KB

Open AccessArticle

Corrosion Resistance of Arc Ion-Plated CrN/CrAlN Multilayer Coatings Before and After Wear Testing: Interface Effects in Marine Environments

by Songjie Zhou, Weilin Chen, Rongjun Yang, Hongwu Liu, Lingxin Zhou, Weizhou Li, Minming Jiang and Xiayun Shu

Metals 2026, 16(5), 466; https://doi.org/10.3390/met16050466 (registering DOI) - 24 Apr 2026

Abstract

In marine service environments, material surfaces inevitably suffer from wear damage, which can compromise the integrity of protective coatings and further affect their corrosion resistance. Therefore, investigating the post-wear corrosion resistance of coatings is of great significance. In this work, single-layer CrN coatings, [...] Read more.

In marine service environments, material surfaces inevitably suffer from wear damage, which can compromise the integrity of protective coatings and further affect their corrosion resistance. Therefore, investigating the post-wear corrosion resistance of coatings is of great significance. In this work, single-layer CrN coatings, CrAlN coatings, and CrN/CrAlN multilayer coatings were deposited on stainless-steel substrates by arc ion plating, and the microstructure, tribological properties, and corrosion behavior before and after wear were systematically investigated. Wear tests were performed under applied loads of 2.5 N and 5 N. The corrosion behavior in the unworn condition and the post-wear corrosion resistance condition was evaluated in a 3.5 wt.% NaCl solution. The results showed that all coatings exhibited a face-centered cubic (FCC) structure, while the CrN/CrAlN multilayer coating possessed the smallest average grain size (13.47 nm). Under applied loads of 2.5 N and 5 N, the CrN/CrAlN multilayer coating exhibited the lowest wear rate, indicating the best wear resistance. In the unworn condition, the CrN/CrAlN multilayer coating showed the lowest corrosion current density (2.74 × 10⁻¹⁰ A/cm²) and the most positive corrosion potential (0.025 V), demonstrating the best corrosion resistance. After wear under a load of 5 N, the CrN/CrAlN multilayer coating retained a low corrosion current density (3.35 × 10⁻¹⁰ A/cm²), in contrast to the marked increases observed for the single-layer coatings. The enhanced performance is considered to be mainly associated with the periodic heterogeneous interfaces in the multilayer structure, which help suppress crack propagation and prolong the penetration path of corrosive media. Full article

(This article belongs to the Section Corrosion and Protection)

17 pages, 1463 KB

Open AccessArticle

Physics-Informed Neural Networks for Process Optimization in Laser Powder Bed Fusion of Inconel 718 Superalloy: A Data-Efficient, Physics-Constrained Machine Learning Framework

by Saurabh Tiwari, Seong Jun Heo and Nokeun Park

Metals 2026, 16(5), 465; https://doi.org/10.3390/met16050465 (registering DOI) - 24 Apr 2026

Abstract

This study aimed to develop and validate a physics-informed neural network (PINN) framework for data-efficient and physically consistent process optimization in the laser powder bed fusion (LPBF) of Inconel 718 (IN718) superalloy. Laser powder bed fusion (LPBF) is widely adopted for fabricating Inconel [...] Read more.

This study aimed to develop and validate a physics-informed neural network (PINN) framework for data-efficient and physically consistent process optimization in the laser powder bed fusion (LPBF) of Inconel 718 (IN718) superalloy. Laser powder bed fusion (LPBF) is widely adopted for fabricating Inconel 718 (IN718) components in aerospace and energy applications; however, navigating its high-dimensional, nonlinear process parameter space remains a central challenge. High-fidelity finite element simulations are computationally prohibitive for extensive parameter sweeps, whereas purely data-driven machine learning (ML) models are limited by data scarcity and unphysical extrapolation behavior. This study presents a physics-informed neural network (PINN) framework that embeds the transient heat conduction equation and Goldak double-ellipsoidal heat source model directly into the neural network training loss, enforcing thermophysical consistency simultaneously with data fidelity. The model was trained on a curated, multi-source dataset of LPBF IN718 parameter combinations drawn from peer-reviewed experimental studies and validated finite element simulation outputs, spanning the laser power (70–400 W), scan speed (200–2000 mm/s), hatch spacing (50–140 µm), and layer thickness (20–50 µm). The PINN predicted the melt pool width, depth, peak temperature, and relative density with mean absolute percentage errors (MAPE) of 3.8%, 4.7%, 3.1%, and 1.9%, respectively, outperforming a baseline artificial neural network (ANN) with an identical architecture. The framework correctly identified the optimal volumetric energy density (VED) window of 55–105 J/mm³, yielding relative densities ≥99.5%, consistent with the published experimental thresholds for IN718. A data efficiency analysis demonstrated that the PINN with 25% training data achieves a performance equivalent to that of the fully trained ANN with 100% data, confirming an approximately four-fold data efficiency improvement attributable to physics-informed regularization, consistent with theoretical predictions. Sensitivity analysis via automatic differentiation confirmed that laser power and scan speed were the dominant parameters (~85% combined variance), which is in agreement with previous studies. This study provides a computationally efficient, interpretable, and physically consistent ML pathway for the accelerated process qualification of IN718 components for aerospace and energy applications. Full article

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

17 pages, 8023 KB

Open AccessArticle

Effect of H1150M Heat Treatment on Functional Properties of 15-5 PH Stainless Steel Produced by Additive Manufacturing

by Maxim Bassis, Amnon Shirizly and Eli Aghion

Metals 2026, 16(5), 464; https://doi.org/10.3390/met16050464 (registering DOI) - 24 Apr 2026

Abstract

Additive manufacturing (AM) using powder bed fusion (PBF) has been the predominant printing method used over the last decade. The capability of this approach to produce complex parts with high precision has attracted the attention of major industries as a potential tool for [...] Read more.

Additive manufacturing (AM) using powder bed fusion (PBF) has been the predominant printing method used over the last decade. The capability of this approach to produce complex parts with high precision has attracted the attention of major industries as a potential tool for replacing traditional manufacturing technologies. 15-5 PH stainless steel is one of the alloys being studied as a candidate for PBF processes. Its superior strength and corrosion resistance have made it a highly attractive option in numerous industries, including the automotive, nuclear, and petrochemical industries. To enhance the properties of 15-5 PH stainless-steel AM parts following printing, one can use a thermal treatment such as age hardening. However, very little research exists regarding the functional properties of AM parts made from this alloy after heat treatment. This study aims to evaluate the effect of H1150M age hardening heat treatment following printing on the properties of 15-5 PH steel, particularly regarding its mechanical properties and environmental behavior. The microstructure was studied using both optical and electron microscopy, along with X-ray diffraction (XRD) analysis. The mechanical properties were examined by tensile testing and fracture toughness assessment. Corrosion behavior was analyzed in terms of potentiodynamic polarization and using impedance spectroscopy. The results obtained have shown that over-aging caused by H1150M heat treatment has a detrimental effect on the mechanical and environmental behavior of the tested alloy. This was primarily attributed to the formation of an austenitic phase within the inherent martensitic matrix, the generation of brittle phases (mainly carbonitrides of Cr and Nb) and a reduction in grain size. Full article

(This article belongs to the Section Additive Manufacturing)

11 pages, 2865 KB

Open AccessArticle

Effect of Silicon Content on the Performance of Nanostructured Al-Si Alloy Fuels Prepared by Electrical Explosion Method

by Hao Liu, Jie Yao and Shi Yan

Metals 2026, 16(5), 463; https://doi.org/10.3390/met16050463 (registering DOI) - 24 Apr 2026

Abstract

Nano Al-Si alloy fuels with Si contents of 4% and 16% (designated as nAl-4Si, nAl-12Si and nAl-16Si) were prepared by using the electrical explosion method and tested by relevant tests. Subsequently, nAl, nAl-4Si, nAl-12Si, and nAl-16Si were ultrasonically mixed with CuO at stoichiometric [...] Read more.

Nano Al-Si alloy fuels with Si contents of 4% and 16% (designated as nAl-4Si, nAl-12Si and nAl-16Si) were prepared by using the electrical explosion method and tested by relevant tests. Subsequently, nAl, nAl-4Si, nAl-12Si, and nAl-16Si were ultrasonically mixed with CuO at stoichiometric ratios to obtain the corresponding nano-thermite systems. The results indicated that the prepared nano Al-Si alloy fuel consisted of spherical particles with a core–shell structure, wherein the core was composed of aluminum and the shell was composed of silicon. Furthermore, the particle size of the alloy fuel wasn’t significantly affected by the silicon content. However, as the silicon content exceeded the eutectic point, accumulation of silicon and oxygen elements occurs on the surface of nAl-16Si. The actual combustion heat of the nAl-Si alloy fuel rose with the silicon content. The tested combustion heat of nAl-16Si reached 27.24 kJ/g, exceeding that of nAl by 8.43%. The combustion heat of the nAl-Si alloy fuels increased monotonically with the silicon content. TG-DSC tests showed that the ignition temperatures of nAl-4Si and nAl-12Si were lower than those of nAl-16Si and nAl. The onset and peak temperatures of thermal oxidation for the nAl-Si alloy experienced minimal variation with silicon content. However, the oxidation rate progressively decreased with higher silicon content and remained lower than that of pure nAl. Laser ignition tests showed that the peak pressure and pressure rise rate of nAl-4Si/CuO were increased by 8.11 kPa and 24% respectively, compared to nAl/CuO. Therefore, increasing the silicon content could enhance the combustion efficiency of nAl-Si alloy fuels. However, when the silicon content exceeded the eutectic point of Al-Si at 12.6%, the primary silicon formed on the particle surface led to the increase in the solid combustion by-products, thereby weakening the combustion performance. Full article

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18 pages, 11431 KB

Open AccessArticle

Phase Transformation of δ→σ in 24Cr-14Ni Stainless Steels Under Nitrogen Atmospheric Aging Treatment

by Chih-Chun Hsieh and Huei-Sen Wang

Metals 2026, 16(5), 462; https://doi.org/10.3390/met16050462 - 23 Apr 2026

Abstract

This work investigates the δ→σ phase transformation in 24Cr-14Ni stainless steel, specifically focusing on how heat treatment temperature, time, and nitrogen atmospheric ratios (NARs) dictate microstructural stability. Understanding the formation mechanism of the σ phase is critical for alloy design, as it remains [...] Read more.

This work investigates the δ→σ phase transformation in 24Cr-14Ni stainless steel, specifically focusing on how heat treatment temperature, time, and nitrogen atmospheric ratios (NARs) dictate microstructural stability. Understanding the formation mechanism of the σ phase is critical for alloy design, as it remains the most detrimental intermetallic phase in austenitic steels. The results show that δ-ferrite decomposes into σ and secondary γ₂ phases through a cellular eutectoid reaction driven by elemental diffusion. Higher Cr and Si levels stabilize δ-ferrite and promote σ phase precipitation, accelerating the δ→σ transformation. Furthermore, the σ phase exhibits the highest Cr_eq/Ni_eq ratio among all constituent phases. The σ phase fraction is highest with 0 vol.% NAR during 1–8 h of aging and decreases progressively with increasing NARs (20–40 vol.%), reaching a minimum at 80 vol.% under all conditions. JMAK model analysis (n ≈ 0.531, k ≈ 0.905) indicates that σ phase precipitation at 800 °C with 40 vol.% NAR is governed by diffusion-controlled growth with early nucleation site saturation in δ-ferrite. Consequently, rapid σ phase formation occurs, reaching ~21.3% within 1 h. This behavior is attributed to the instability of δ-ferrite and the faster diffusion of Cr and Si compared to austenite. Full article

(This article belongs to the Special Issue Phase Transformations in Metals and Alloys)

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14 pages, 10801 KB

Open AccessArticle

Tailoring Strength and Corrosion Resistance of Al-Zn-Mg-Cu Alloy by Double Aging Processes

by Jianping Huang, Youxuan Ouyang, Yuanyuan Zeng, Huayu Xiao, Juangang Zhao and Qiang Zhang

Metals 2026, 16(5), 461; https://doi.org/10.3390/met16050461 - 23 Apr 2026

Abstract

This study investigated the effects of double aging processes on the tensile properties and salt spray corrosion resistance of an Al-Zn-Mg-Cu alloy. The mechanisms by which microstructural evolution influences these properties were elucidated using tensile testing, salt spray corrosion testing, electrochemical measurements, scanning [...] Read more.

This study investigated the effects of double aging processes on the tensile properties and salt spray corrosion resistance of an Al-Zn-Mg-Cu alloy. The mechanisms by which microstructural evolution influences these properties were elucidated using tensile testing, salt spray corrosion testing, electrochemical measurements, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that, under double aging processes, increasing the duration or temperature of either the first- or second-stage aging leads to a slight decrease in tensile strength but a significant improvement in salt spray and electrochemical corrosion resistance. This is attributed to the gradual coarsening of intergranular and grain boundary precipitates, a decrease in their number density, and a widening of the precipitate-free zone (PFZ). Furthermore, the second-stage aging exerts a more pronounced influence on the alloy’s properties and microstructure than the first-stage aging, and their quantitative contributions are systematically distinguished. The alloy treated with the 110 °C/3 h + 155 °C/20 h double aging processes exhibits the optimal overall performance, achieving a better balance between strength and corrosion resistance compared to conventional T6 treatment. Full article

(This article belongs to the Special Issue Recent Advances in High-Performance Alloys and Cermets: Fabrication, Microstructure, and Properties)

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21 pages, 14123 KB

Open AccessArticle

Accelerated Hardening and Corrosion Behavior of Low Cu/Mg Al–Cu–Mg Alloys Modified by Si and Ag

by Guanfeng Huang, Shuai Pan, Chao Dong, Qiliang Chen, Khadija Fnu and Zian Li

Metals 2026, 16(5), 460; https://doi.org/10.3390/met16050460 - 23 Apr 2026

Abstract

The precipitation characteristics and grain-boundary structure of Al–Cu–Mg alloys strongly affect their corrosion behavior, whereas the roles of Si and Ag microalloying in low Cu/Mg ratio systems are not yet fully understood. In this work, the effects of Si and Ag additions on [...] Read more.

The precipitation characteristics and grain-boundary structure of Al–Cu–Mg alloys strongly affect their corrosion behavior, whereas the roles of Si and Ag microalloying in low Cu/Mg ratio systems are not yet fully understood. In this work, the effects of Si and Ag additions on age-hardening response, precipitation characteristics, and corrosion performance were systematically investigated by combining transmission electron microscopy with electrochemical and corrosion measurements. Si addition significantly accelerated the age-hardening kinetics, enabling the alloy to reach a hardness of 147 HV after only 6 h of aging, whereas the base alloy required 24 h to reach a similar level. This accelerated response was accompanied by refined S-phase precipitation and a markedly narrowed precipitation-free zone along grain boundaries. Further Ag addition introduced coherent Ω precipitates and a more complex multi-phase precipitation structure, which increased microstructural heterogeneity. As a result, the Al–Cu–Mg–Si alloy exhibited the lowest corrosion current density and the shallowest corrosion depth, whereas the Al–Cu–Mg–Si–Ag alloy showed deteriorated corrosion resistance. These results indicate that Si microalloying alone can simultaneously accelerate aging and improve corrosion resistance, while further Ag addition enhances precipitation complexity and strengthening potential but increases susceptibility to localized corrosion. Full article

(This article belongs to the Special Issue Advances in Corrosion and Failure Analysis of Metallic Materials)

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25 pages, 10948 KB

Open AccessArticle

Experimental Investigation of Material Characteristics That Can Affect Fatigue Behavior of Ti6Al4V Alloys Produced by Additive Manufacturing SLM and EBM Processes

by Francesco Sordetti, Niki Picco, Marco Pelegatti, Riccardo Toninato, Marco Petruzzi, Federico Milan, Emanuele Avoledo, Alessandro Tognan, Elia Marin, Lorenzo Fedrizzi, Michele Magnan, Enrico Salvati, Michele Pressacco and Alex Lanzutti

Metals 2026, 16(5), 459; https://doi.org/10.3390/met16050459 - 22 Apr 2026

Abstract

Ti alloys are widely used in aerospace and biomedical fields due to their high mechanical properties under severe loading. Interest in additively manufactured Ti6Al4V has increased, but further research is needed to fully characterize their properties. This work compares the effects of surface [...] Read more.

Ti alloys are widely used in aerospace and biomedical fields due to their high mechanical properties under severe loading. Interest in additively manufactured Ti6Al4V has increased, but further research is needed to fully characterize their properties. This work compares the effects of surface properties, internal defects, microstructure, hardness, and Hot Isostatic Pressing (HIP) or Vacuum Heat Treatment (VHT) on the fatigue behavior of Ti6Al4V produced by Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Printing parameters and post-processing were optimized to achieve high density and minimal porosity, providing a solid basis for realistic fatigue comparisons. Samples were characterized in terms of microstructure (optical microscopy and SEM), mechanical properties (hardness mapping), surface texture (confocal microscopy), and internal defects (image-based analysis). Uniaxial fatigue limits were determined by a Dixon-Mood staircase method, and failed specimens were analyzed for fracture surfaces and defect areas. Applied load on flaws was evaluated to identify root causes of fatigue failure. Results showed that fatigue of as-printed samples is governed by surface roughness, while machined specimens are controlled by internal defect size. Machining increased the fatigue limit roughly threefold, and HIP further improved it by 10–20% by reducing internal porosity. In conclusion, with properly optimized melting parameters, both EBM and SLM produce similar mechanical performance at comparable roughness, supporting their use for structural components. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metallic Materials Under Heat Treatment)

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15 pages, 5165 KB

Open AccessArticle

Intelligent Defect Identification in Girth Welds of Phased Array Ultrasonic Testing Images Using Median Filtering, Spatial Enrichment, and YOLOv8

by Mingzhe Bu, Shengyuan Niu, Xueda Li and Bin Han

Metals 2026, 16(5), 458; https://doi.org/10.3390/met16050458 - 22 Apr 2026

Abstract

Girth welds are susceptible to defects under high internal pressure and stress. While phased array ultrasonic testing (PAUT) is widely used for non-destructive evaluation, manual inspection remains inefficient and highly dependent on expertise. Furthermore, existing deep learning models often struggle with low accuracy [...] Read more.

Girth welds are susceptible to defects under high internal pressure and stress. While phased array ultrasonic testing (PAUT) is widely used for non-destructive evaluation, manual inspection remains inefficient and highly dependent on expertise. Furthermore, existing deep learning models often struggle with low accuracy and high complexity. This paper proposes a PAUT defect classification method based on YOLOv8. First, median filtering is employed for denoising, and the results show that noise is effectively reduced while preserving key features, achieving PSNR values of 35.132, 35.938, and 36.138 for slag inclusion, pores, and lack of fusion (LOF), respectively. Subsequently, the spatial enrichment algorithm (SEA) is applied to enhance image details without amplifying noise, yielding a PSNR of 33.71 and an SSIM of 0.96. Finally, the YOLOv8 model is implemented for defect recognition. Experimental results demonstrate that the proposed approach achieves a superior balance between precision and recall with high reliability. This method offers a robust and efficient solution for automated PAUT evaluation in practical engineering applications. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: “Welding and Joining” (2nd Edition))

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15 pages, 13862 KB

Open AccessArticle

Tribological Performance of Graphene-Based Sacrificial Coatings

by Luís Vilhena, Tsering Wangmo, Barnabas Erhabor, Bruno Figueiredo and Amílcar Ramalho

Metals 2026, 16(5), 457; https://doi.org/10.3390/met16050457 - 22 Apr 2026

Abstract

Graphene solution was spin coated onto an aluminum substrate to investigate its tribological behavior compared to bare 6082–T6 aluminum alloy. The coefficient of friction (COF) was measured for varying loads (1–5 N) and sliding speeds (0.05–0.25 m/s) using a pin-on-disk tribometer in a [...] Read more.

Graphene solution was spin coated onto an aluminum substrate to investigate its tribological behavior compared to bare 6082–T6 aluminum alloy. The coefficient of friction (COF) was measured for varying loads (1–5 N) and sliding speeds (0.05–0.25 m/s) using a pin-on-disk tribometer in a ball-on-flat configuration. Results indicated that, under all tested conditions, the graphene coating reduced the COF by more than 70–80% compared to uncoated aluminum. Specifically, at 0.25 m/s and 1 N, the COF decreased from approximately 0.63 for uncoated aluminum to about 0.13 for the coated sample. The samples were analyzed using optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), providing insights into morphology and composition. Furthermore, the coated samples exhibited a stable friction regime, with COF values consistently in the range of 0.10–0.15, while uncoated samples showed higher and more fluctuating values between 0.40 and 0.60. The graphene coating reached steady-state conditions within the first 50 m of sliding, in contrast to the pronounced running-in behavior of uncoated aluminum. SEM and EDS analyses confirmed the formation of a graphene transfer layer on the counterface, which maintained low friction even after partial coating removal. Additionally, the average coating thickness was approximately 15 μm, and the coating significantly reduced adhesive wear and material transfer, demonstrating its effectiveness as a sacrificial, self-lubricating tribological layer. Full article

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12 pages, 2924 KB

Open AccessArticle

Influence of Ferric Chloride–Oxalic Acid Polishing Slurry on the Chemical Mechanical Polishing of 304 Stainless Steel

by Nannan Zhu, Kerong Wang, Bing Liu, Jiejing Li, Jianxiu Su, Yongwei Zhu and Jiapeng Chen

Metals 2026, 16(5), 456; https://doi.org/10.3390/met16050456 - 22 Apr 2026

Abstract

The effects of mass fractions of ferric chloride (FeCl₃) and oxalic acid (H₂C₂O₄) in polishing slurry on the polishing of 304 stainless steel were studied. The stainless steel polishing experiments with different compositions of polishing [...] Read more.

The effects of mass fractions of ferric chloride (FeCl₃) and oxalic acid (H₂C₂O₄) in polishing slurry on the polishing of 304 stainless steel were studied. The stainless steel polishing experiments with different compositions of polishing liquids were designed, the material removal rate was calculated, the surface roughness value was measured, and the Fe²⁺ content in the polishing waste liquid was determined by spectrophotometry. The mechanism of FeCl₃ on stainless steel polishing was investigated. The results indicated the existence of the reaction 2Fe³⁺ + Fe → 3Fe²⁺ during the polishing process; Fe³⁺ in the polishing slurry promoted the reaction and significantly increased the material removal rate; and the composition ratio of the FeCl₃-H₂C₂O₄ slurry for polishing 304 stainless steel was optimized. After optimization, the material removal rate achieved more than 200 nm/min, and the surface roughness after polishing was reduced to less than 10 nm. Qualitative analysis of the surface material of the polished 304 stainless steel with FeCl₃ polishing slurry by XRD proved that the phase of the matter was basically unchanged. This experiment provides reference value for the preparation of polishing slurry for 304 stainless steel. Full article

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15 pages, 7085 KB

Open AccessArticle

Hydrothermal Synthesis of Hierarchical Boehmite from Co-Processed Stainless Steel Dust and Aluminum Dross Residue

by Hongda Yao, Nan Wang, Min Chen and Xiaoqing Chen

Metals 2026, 16(5), 455; https://doi.org/10.3390/met16050455 - 22 Apr 2026

Abstract

Stainless steel dust and aluminum dross are large-volume solid wastes in the metallurgical industry. Synergistic treatment of these wastes recovers some metals but yields an Al-rich residue (Al₂O₃ > 50%) that represents both a resource loss and an environmental threat [...] Read more.

Stainless steel dust and aluminum dross are large-volume solid wastes in the metallurgical industry. Synergistic treatment of these wastes recovers some metals but yields an Al-rich residue (Al₂O₃ > 50%) that represents both a resource loss and an environmental threat if untreated. In this work, boehmite (γ-AlOOH) was synthesized via a hydrothermal route using the Al-rich residue as the aluminum source. The aim was to valorize this waste stream while comprehensively evaluating the product’s phase, morphology, pore characteristics, efficacy and underlying mechanism for Cr(VI) removal from aqueous solutions. The hydrothermal process was optimized as pH = 11.0, under which high-purity and well-crystallized γ-AlOOH was successfully prepared without harmful by-products. The product had uniform particle size distribution without obvious agglomeration, with a specific surface area of 156.7 m²/g, pore volume of 0.60 cm³/g and average pore diameter of 14.6 nm. The boehmite synthesized at pH 11.0 achieved a Cr(VI) removal efficiency of 31.28% and a maximum adsorption capacity of 15.64 mg/g. This study provides a new path for the resource utilization of high-aluminum residue, with both environmental and economic benefits and potential application value. Full article

(This article belongs to the Special Issue Advances in Hydrometallurgy of Metals: Sources, Pretreatment, Leaching, Extraction, Recovery, Raffination)

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16 pages, 7104 KB

Open AccessArticle

Phase Field Simulation Study of Competitive Growth of Polycrystalline in Directional Solidification Under Natural Convection Conditions

by Qiao Yin, Huaxiang Zha, Chunwen Guo, Junjie Li, Hongliang Zhao, Shuya Zhang, Xianglei Dong and Yuheng Fan

Metals 2026, 16(5), 454; https://doi.org/10.3390/met16050454 - 22 Apr 2026

Abstract

Directional solidification technology is the core process for manufacturing single-crystal blades in aero-engines, but transverse grain boundaries caused by the competitive growth of polycrystals severely degrade blade performance. To gain a deeper understanding of polycrystalline competitive growth behavior, this study investigates the competitive [...] Read more.

Directional solidification technology is the core process for manufacturing single-crystal blades in aero-engines, but transverse grain boundaries caused by the competitive growth of polycrystals severely degrade blade performance. To gain a deeper understanding of polycrystalline competitive growth behavior, this study investigates the competitive growth of polycrystals during directional solidification under natural convection based on the phase field and lattice Boltzmann coupling model. By adjusting the solutal expansion coefficient, grain configuration, and pulling velocity, the influence of the flow field on polycrystalline competitive growth is analyzed. The results indicate that changes in the solutal expansion coefficient affect the dendritic competition process and outcome, particularly for dendrites with larger favorably oriented (FO) angles, which are more likely to be eliminated at higher solutal expansion coefficients. Additionally, grain configurations with greater orientation differences between adjacent dendrites are more sensitive to changes in the solutal expansion coefficient, whereas configurations with smaller orientation differences are less affected. It was also found that as the pulling velocity increases, the primary dendrite arm spacing decreases and the growth direction of the dendrites deflects towards the temperature gradient direction. This leads to a reduction in vortices at the dendrite tips and grain boundaries, thereby decreasing the overall flow field intensity. During dendrite growth, solute is rejected from the solid phase, creating a concentration gradient between the dendrite tips and the liquid region. This induces convection in the liquid phase. The interaction between the flow field and the solute concentration in the liquid phase causes the flow field strength and solute concentration to exhibit periodic fluctuations. Full article

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

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32 pages, 12681 KB

Open AccessArticle

Effect of Dynamic Recrystallization Response on Ductility Dip Cracking Susceptibility in Welds of High-Chromium Nickel-Based Alloys

by Anil Singh, Andreas Bezold, Michael J. Mills and Boian T. Alexandrov

Metals 2026, 16(4), 453; https://doi.org/10.3390/met16040453 - 21 Apr 2026

Abstract

Ductility dip cracking (DDC) remains a persistent challenge in multipass welds of high-chromium nickel-based alloys used in the nuclear power generation industry. While dynamic recrystallization (DRX) has been observed to arrest DDC crack growth and has been associated with weld regions that experience [...] Read more.

Ductility dip cracking (DDC) remains a persistent challenge in multipass welds of high-chromium nickel-based alloys used in the nuclear power generation industry. While dynamic recrystallization (DRX) has been observed to arrest DDC crack growth and has been associated with weld regions that experience less DDC, there exists no quantitative relationship between the extent of recrystallization in a microstructure and DDC susceptibility. This research examines the influence of intragranular carbides on DRX behavior and establishes an experimental relationship between DDC susceptibility and extent of recrystallization in high-chromium nickel-based weld metals, novel contributions for this alloy system. In this work, the DRX behavior of the weld metal of high-chromium nickel-based filler metals (FM-52, FM-52M, FM-52i, and FM-52xl) was investigated under controlled thermo-mechanical conditions, and its effect on DDC susceptibility was established. Weld metal specimens were subjected to uniaxial deformation at 1100 °C to a true strain of 2% at strain rates of 10⁻³/s and 10⁻⁴/s using a Gleeble 3800^TM. Recrystallization was quantified using electron backscatter diffraction (EBSD) via grain orientation spread (GOS) analysis and dislocation–precipitate interactions were examined using transmission electron microscopy (TEM). Strain-to-fracture (STF) testing at 950 °C was employed to assess DDC susceptibility as a function of the extent of recrystallization and grain surface area. All tested weld metals exhibited increased recrystallization and grain refinement, as the strain rate decreased from 10⁻³/s to 10⁻⁴ s. The FM-52i weld metal specimens exhibited the highest grain refinement under high temperature deformation, followed by the FM-52xl, FM-52, and FM-52M weld metals with a percent reduction in average grain surface area of 51.22%, 41.66%, 35.48%, and 24.40%, respectively. The FM-52i weld metal specimens also exhibited the highest recrystallization response, followed by FM-52M, FM-52xl, and FM-52 weld metals at 75%, 40%, 39% and 21% recrystallized, respectively. Weld metals containing strong carbide formers experienced higher recrystallization responses than those without due to precipitate–carbide interactions. All tested weld metals experienced drastic reductions in DDC response with increasing extent of recrystallization and decreasing average grain surface areas. DRX in STF specimens was observed to facilitate uniform plastic strain accumulation, lowering overall DDC susceptibility compared to non-recrystallized specimens. Full article

(This article belongs to the Section Welding and Joining)

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17 pages, 3195 KB

Open AccessArticle

Effects of Nozzle Configuration on Flow and Heat Transfer of Confined Jet in Semi-Enclosed Space

by Yanqi Ye, Tianliang Fu, Yueman He, Chenyang Gu and Guanghao Liu

Metals 2026, 16(4), 452; https://doi.org/10.3390/met16040452 - 21 Apr 2026

Abstract

The quenching deformation of ultra-high-strength steel sheets is a technical challenge in the steel industry. Although air-jet quenching can effectively improve shape quality, it requires substantial energy consumption. How to improve the heat transfer intensity of air jets by improving key components has [...] Read more.

The quenching deformation of ultra-high-strength steel sheets is a technical challenge in the steel industry. Although air-jet quenching can effectively improve shape quality, it requires substantial energy consumption. How to improve the heat transfer intensity of air jets by improving key components has become the keypoint of using this technology in industry. In this study, a CFD model was established to investigate the impacts of nozzle shapes and jet arrangements on the flow structure, wall heat transfer intensity and wall heat transfer uniformity under the same total flow rate. The results show that the impingement heat transfer could only be realized by adopting a symmetrical nozzle design (including the symmetric nozzle shape and jet arrangement). And the intensity and uniformity of wall heat transfer were hardly affected by the specific symmetrical nozzle shape. Moreover, under the S/B (ratio of slot spacing to slot width) condition adopted in this study, multiple jets did not significantly enhance heat transfer uniformity but instead tended to reduce the overall heat transfer intensity. In this paper, the configuration of the horizontal nozzle with the central single jet was optimal due to its high heat transfer intensity, good heat transfer uniformity and lower energy consumption. Full article

(This article belongs to the Topic Numerical Modelling on Metallic Materials, 2nd Edition)

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24 pages, 2843 KB

Open AccessReview

Research Progress on Proton Irradiation Damage and Irradiation Resistance of Austenitic Stainless Steel

by Yuyu Guo, Yanlin Gu, Zhen Yan and Juan Hou

Metals 2026, 16(4), 451; https://doi.org/10.3390/met16040451 - 21 Apr 2026

Abstract

Nuclear energy is a clean and efficient energy source crucial for the future energy supply. The harsh conditions in reactors, including high temperature, high pressure, and intense neutron irradiation, cause structural materials to accumulate irradiation damage, leading to performance degradation. Austenitic stainless steel, [...] Read more.

Nuclear energy is a clean and efficient energy source crucial for the future energy supply. The harsh conditions in reactors, including high temperature, high pressure, and intense neutron irradiation, cause structural materials to accumulate irradiation damage, leading to performance degradation. Austenitic stainless steel, due to its superior mechanical properties, irradiation resistance, and corrosion resistance, has been extensively utilized as a core structural material in light water reactors and emerged as a candidate material for Generation IV nuclear reactors. Therefore, understanding irradiation damage and macroscopic properties evolution in austenitic stainless steels is critical for enhancing the safety and long-term service life of reactor core materials. This review began by elucidating the application of charged particles in irradiation studies, emphasizing the prevailing substitution of neutron irradiation with proton irradiation experiments in current studies. Subsequently, the work systematically synthesized irradiation damages and their consequential impacts on macroscopic properties. Finally, it consolidated the progress and provided prospects for research on improving the resistance of austenitic stainless steel to irradiation-induced segregation, irradiation hardening, irradiation swelling, and irradiation-corrosion synergies. Full article

19 pages, 4341 KB

Open AccessArticle

Detoxification-Oriented Carbonate Leaching of Selenium and Tellurium from Lead-Rich Fly Ash: Experimental and Kinetic Analysis

by Majid Ramezanpour Aghdami, Ashkan Mohammad Beygian and Eskandar Keshavarz Alamdari

Metals 2026, 16(4), 450; https://doi.org/10.3390/met16040450 - 21 Apr 2026

Abstract

Copper anodic slime is often smelted with lead to improve silver and gold recovery, generating a fine lead-rich fly ash that contains notable amounts of selenium and tellurium. Due to its high lead content and sub-micron particle size, this residue poses significant environmental [...] Read more.

Copper anodic slime is often smelted with lead to improve silver and gold recovery, generating a fine lead-rich fly ash that contains notable amounts of selenium and tellurium. Due to its high lead content and sub-micron particle size, this residue poses significant environmental and occupational health risks. This study evaluates sodium carbonate (Na₂CO₃) leaching as an environmentally benign pre-treatment aimed at partially removing selenium and tellurium while stabilizing lead through carbonate formation. The goal is detoxification rather than maximum metal recovery, enabling safer disposal or subsequent recycling. A central composite design (CCD) in Design-Expert software (Version 12) was used to assess the effects of Na₂CO₃ concentration, temperature, solid-to-liquid ratio, and time on selenium and tellurium dissolution. Selenium recovery reached up to 53.9%, while tellurium recovery peaked at approximately 33.9%. Scanning electron microscopy showed the dust to consist mainly of semi-spherical and elongated particles, with lead carbonate forming preferentially on particle surfaces during leaching. Energy-dispersive spectroscopy confirmed conversion of lead sulfate phases to lead carbonate, which increasingly restricted selenium and tellurium dissolution. Kinetic evaluation suggested selenium leaching follows mixed control involving both surface reaction and diffusion through product layers, whereas tellurium dissolution lacked consistent kinetic behavior. Thermodynamic calculations supported the stabilization of lead as cerussite (PbCO₃), indicating improved environmental safety. The overall dissolution trends were successfully represented using an apparent Shrinking Core Model (SCM) based on measurements collected at 20 °C, 60 °C, and 100 °C. Full article

(This article belongs to the Special Issue Extractive Metallurgy: From Metallurgical Waste to New Products)

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11 pages, 1430 KB

Open AccessArticle

Integrated Eddy Current Inspection in Turning Machines with Deployable Algorithms for Automated Defect Detection in Railway Wheels

by Jose Luis Lanzagorta, Julen Mendikute, Irati Sanchez, Paula Ruiz, Iratxe Aizpurua-Maestre and Jokin Munoa

Metals 2026, 16(4), 449; https://doi.org/10.3390/met16040449 - 21 Apr 2026

Abstract

Ensuring the structural integrity and service reliability of railway wheels has become a key challenge in modern manufacturing and maintenance strategies within the railway sector. In this context, Eddy Current (EC)-based Non-Destructive Testing (NDT) provides an automated and efficient approach for detecting surface [...] Read more.

Ensuring the structural integrity and service reliability of railway wheels has become a key challenge in modern manufacturing and maintenance strategies within the railway sector. In this context, Eddy Current (EC)-based Non-Destructive Testing (NDT) provides an automated and efficient approach for detecting surface and near-surface defects, while reducing inspection time and operator dependency compared to conventional manual methods. This study presents the integration of an EC inspection system into a precision lathe, enabling in-machining evaluation during wheel turning. Experimental validation was conducted on wheels with artificial defects, yielding high signal-to-noise ratios and enabling reliable defect characterization. Furthermore, computationally efficient and easily deployable machine learning algorithms were developed to enable automatic defect detection, localization, and size estimation. The results confirm the feasibility of in-machine EC inspection during machining operations, enabling early defect detection and contributing to safer, more efficient, and higher-quality manufacturing processes in the railway sector. Full article

(This article belongs to the Special Issue Nondestructive Testing Methods for Metallic Material)

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