Metals

46 pages, 6690 KiB

Open AccessReview

Optimising Additive Manufacturing of NiTi and NiMnGa Shape Memory Alloys: A Review

by Ali Ramezannejad, Daniel East, Anthony Bruce Murphy, Guoxing Lu and Kun Vanna Yang

Metals 2025, 15(5), 488; https://doi.org/10.3390/met15050488 - 25 Apr 2025

NiTi and NiMnGa stand out as prime thermal and magnetic shape memory alloys (SMAs), possessing a superior shape memory effect (SME) and superelasticity (SE). These alloys have crucial current and potential future applications across industries. Additive manufacturing (AM) offers a transformative approach to [...] Read more.

NiTi and NiMnGa stand out as prime thermal and magnetic shape memory alloys (SMAs), possessing a superior shape memory effect (SME) and superelasticity (SE). These alloys have crucial current and potential future applications across industries. Additive manufacturing (AM) offers a transformative approach to fabricating these materials into complex geometries; however, the quest to create integral additively manufactured structures with reliable thermal or magnetic shape memory properties remains a recent and fast-emerging research frontier. This article provides a comprehensive review on (i) the intricate principles giving rise to the thermal SME and SE in NiTi, and the magnetic SME in NiMnGa alloys, emphasising their specific relevance in the realm of AM, and (ii) the latest developments, recent findings, and ongoing challenges in the AM of NiTi- and NiMnGa-based SMAs, including their functional lattice structures. Based on this review, for the first time, novel, empirically derived AM process design maps tailored to maximise SME and SE in laser powder bed fusion- and directed-energy deposition-processed NiTi structures are proposed. Similarly, promising avenues to resolve the key challenges regarding the AM of NiMnGa magnetic SMAs are suggested. This article concludes by outlining the most promising future research directions shaping the trajectory of AM of these SMAs. Full article

(This article belongs to the Special Issue Recent Developments in Laser Additive Manufacturing of Metallic Materials)

20 pages, 2762 KiB

Open AccessArticle

Machine Learning-Enabled Prediction and Mechanistic Analysis of Compressive Yield Strength–Hardness Correlation in High-Entropy Alloys

by Haiyu Wan, Baobin Xie, Hui Feng and Jia Li

Metals 2025, 15(5), 487; https://doi.org/10.3390/met15050487 - 25 Apr 2025

Abstract

High-entropy alloys (HEAs) represent a paradigm-shifting material system offering vast compositional space for tailoring mechanical properties. The yield strength and hardness are critical performance metrics, yet their interrelationships in diverse HEAs remain incompletely understood, partly due to data limitations. This work employs an [...] Read more.

High-entropy alloys (HEAs) represent a paradigm-shifting material system offering vast compositional space for tailoring mechanical properties. The yield strength and hardness are critical performance metrics, yet their interrelationships in diverse HEAs remain incompletely understood, partly due to data limitations. This work employs an integrated machine learning framework to investigate the compressive yield strength (σ_y) and hardness (HV) correlation across a dataset of cast HEAs. Random forest models are successfully developed for phase structure classification (accuracy = 92%), hardness prediction (test R² = 0.90), and yield strength prediction (test R² = 0.91), enabling data imputation to expand the analysis dataset. Correlation analysis on the expanded dataset reveals a general positive trend between σ_y and HV (overall Pearson r = 0.75) but highlights a strong dependence on the predicted phase structure. The single-phase BCC alloys exhibit the strongest linear correlation between σ_y and HV (r = 0.88), whereas the single-phase FCC alloys show a weaker linear dependence (r = 0.59), and multiphase alloy systems display varied behavior. The specific ranges of compositional parameters (highly negative mixing enthalpy ΔH, low atomic size difference δ, high mixing entropy ΔS, and intermediate-to-high valence electron concentration VEC) are associated with a stronger σ_y-HV correlation, potentially linked to the formation of stable solid solutions. Furthermore, artificial neural network modeling confirms the varying complexity of the σ_y-HV relationship across different phases, outperforming simple models for some multiphase systems. This work provides robust predictive models for HEA properties and advances the fundamental understanding of the composition- and phase-dependent coupling between yield strength and hardness, aiding rational HEA design. Full article

21 pages, 19235 KiB

Open AccessArticle

Insight to the Microstructure Analysis of a HP Austenitic Heat-Resistant Steel Under Short-Term High-Temperature Exposure

by Milica Timotijević, Olivera Erić Cekić, Petar Janjatović, Aleksandar Kremenović, Milena Rosić, Srecko Stopic and Dragan Rajnović

Metals 2025, 15(5), 486; https://doi.org/10.3390/met15050486 - 25 Apr 2025

Abstract

The HP40Nb alloy, commonly used in the petrochemical industry as a heat-resistant material, undergoes significant microstructural changes at high temperatures. This study examined samples from the HP40Nb radiant tube used in a reformer furnace, exposed to 950, 1050, and 1150 °C for 2 [...] Read more.

The HP40Nb alloy, commonly used in the petrochemical industry as a heat-resistant material, undergoes significant microstructural changes at high temperatures. This study examined samples from the HP40Nb radiant tube used in a reformer furnace, exposed to 950, 1050, and 1150 °C for 2 and 8 h. Metallographic analysis, including optical microscopy, SEM, EDS, and XRPD, revealed that the as-cast alloy has an austenitic dendritic matrix with primary eutectic-like carbides (M₂₃C₆ and MC types). Prolonged exposure to high temperatures transformed the primary carbides into coarse M₂₃C₆ forms, losing their lamellar shape. The number of secondary carbides decreased with increasing temperature, and at 1150 °C for 480 min, secondary Cr₂₃C₆ carbides nearly decomposed, and Nb carbides dissolved into the austenitic matrix. Full article

(This article belongs to the Special Issue Novel Insights and Advances in Steels and Cast Irons)

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16 pages, 7457 KiB

Open AccessArticle

Stress Determination by IHD in Additively Manufactured Austenitic Steel Samples: A Validation Study

by João Paulo Nobre, Maria José Marques and António Castanhola Batista

Metals 2025, 15(5), 485; https://doi.org/10.3390/met15050485 - 25 Apr 2025

Abstract

The present work aims to verify whether the incremental hole-drilling technique (IHD), a widely accepted technique, is suitable for determining residual stresses in AISI 316L samples obtained by selective laser melting (SLM). The thermo-mechanical effects of cutting during the application of this technique [...] Read more.

The present work aims to verify whether the incremental hole-drilling technique (IHD), a widely accepted technique, is suitable for determining residual stresses in AISI 316L samples obtained by selective laser melting (SLM). The thermo-mechanical effects of cutting during the application of this technique can induce unwanted residual stresses due to the relatively low thermal conductivity of this material, leading to erroneous results. To accomplish this aim, a hybrid experimental-numerical method was implemented to analyze the ability of IHD to determine an imposed stress state. Experimentally, samples were subjected to a tensile calibration stress using a horizontal tensile test machine. To eliminate pre-existing residual stress, the samples were subjected to differential loads, instead of absolute ones. In this way, experimental strain-depth relaxation curves related to the imposed calibration stress were obtained. Based on the experimental data, IHD was numerically simulated using the finite element method. Numerical strain-depth relaxation curves, related to the same calibration stress used in the experimental study, were obtained. The comparison between the experimental and numerical strain-depth relaxation curves, as well as the stresses calculated using the so-called integral method for determining stresses via IHD, shows that IHD is a suitable technique for measuring residual stresses in additively manufactured AISI 316L samples. Full article

(This article belongs to the Special Issue Surface Integrity and Functional Performance Induced by Hybrid Processing of Metallic Alloys)

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17 pages, 15675 KiB

Open AccessArticle

The Role of Si Element on the Precipitation Behavior of GH2907 Superalloys

by Mengxuan Li, Jianping Wan, Zuojun Ding and Rengeng Li

Metals 2025, 15(5), 484; https://doi.org/10.3390/met15050484 - 25 Apr 2025

Abstract

GH2097, a Fe-Ni-Co-based superalloy extensively employed in high-temperature critical components such as aircraft engines, was investigated to elucidate the influence of Si content on its precipitation behavior and mechanical properties. By systematically adjusting Si concentrations, it was demonstrated that Si significantly modulates the [...] Read more.

GH2097, a Fe-Ni-Co-based superalloy extensively employed in high-temperature critical components such as aircraft engines, was investigated to elucidate the influence of Si content on its precipitation behavior and mechanical properties. By systematically adjusting Si concentrations, it was demonstrated that Si significantly modulates the size, distribution, and stability of γ′ phase (Ni₃TiNb). As Si content increases, γ′ phase coarsening (mean size: 30.1→40.3 nm) results in a marginal increase in volume fraction of 2%. Mechanical testing revealed a direct correlation between Si content and yield strength enhancement, achieving a maximum increment of 97.1 MPa. Post solution-aging treatment, γ′ strengthening dominated the strengthening mechanisms in GH2097, contributing over 50% to the overall strength. Microstructural characterization (SEM/TEM) further confirmed that optimal Si addition balances precipitation kinetics and grain boundary stabilization without inducing detrimental phases. Therefore, it is important to consider the role of the Si element in the microstructure control of GH2907 alloy. Full article

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12 pages, 2287 KiB

Open AccessArticle

Fracturing in 14MoV6-3 Steel Weld Joints—Including Base Metals—After a Short Time in Service

by Esmail Ali Salem Ahmed, Nenad Radović, Dragomir Glišić, Stefan Dikić, Nikola Milovanović, Mirjana Opačić and Jasmina Lozanović

Metals 2025, 15(5), 483; https://doi.org/10.3390/met15050483 - 25 Apr 2025

Abstract

In order to establish the influence of prolonged exposure to high temperatures on 14MoV6-3 steel, three different weld joints were designed. New-to-new material, new-to-used material, and used-to-used material joints were welded using two welding technologies—GTAW and a combination of GTAW + MMA. The [...] Read more.

In order to establish the influence of prolonged exposure to high temperatures on 14MoV6-3 steel, three different weld joints were designed. New-to-new material, new-to-used material, and used-to-used material joints were welded using two welding technologies—GTAW and a combination of GTAW + MMA. The weldments were tested by means of microstructure and tensile testing. The results showed that in all weldments, a fracture occurred in the base metal. Also, in the case of the new-to-used welded sample, the fracture always occurred in the used base metal. Since both materials have the same chemical composition, the difference in microstructure was related to long exposure to high temperatures. New steel has a considerably smaller grain size, while the used material underwent grain growth coupled with carbide coarsening, which decreased its strength. The yield strength (YS) of the new material was higher than the YS of the used material, which exhibited similar values in the used base metal and both weldments. It can be assumed that, since deformation starts in the area with the lowest yield point, the used material is the critical place in a given weldment. Therefore, the accurate extent of strength decrease cannot be evaluated based on the testing of new material, i.e., there is a need to reconsider the traditional qualifications of welding technology. Full article

(This article belongs to the Special Issue Fracture Mechanics and Failure Analysis of Metallic Materials)

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17 pages, 8805 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Brass-Clad Copper Stranded Wires in High-Speed Solid/Liquid Continuous Composite Casting and Drawing

by Yu Lei, Xiao Liu, Yanbin Jiang, Fan Zhao, Xinhua Liu and Jianxin Xie

Metals 2025, 15(5), 482; https://doi.org/10.3390/met15050482 - 24 Apr 2025

Abstract

A solid/liquid continuous composite casting technology was developed to produce brass-clad copper stranded wire billets efficiently with continuous casting speeds ranging from 200 mm/min to 1000 mm/min. As the casting speed increased, the microstructure of the brass cladding transformed at an angle to [...] Read more.

A solid/liquid continuous composite casting technology was developed to produce brass-clad copper stranded wire billets efficiently with continuous casting speeds ranging from 200 mm/min to 1000 mm/min. As the casting speed increased, the microstructure of the brass cladding transformed at an angle to the radial direction. The wire billet prepared at a casting speed of 600 mm/min was then subjected to drawing. As the percentage reduction in area of the billet increased from 11.9 to 81.5% during the drawing process, the tensile strength improved from 336 MPa to 534 MPa, while the elongation after fracture decreased from 30.1 to 4.7%. Meanwhile, dislocation, dislocation cells, and microbands successively formed in the pure copper strand wires, while twins, shear bands, dislocation pile-ups, and secondary twins gradually formed in the brass cladding. During the drawing process, the interface between copper and brass remained metallurgically bonded, exhibiting coordinated deformation behavior. This paper clarified the evolution of microstructure and mechanical properties of brass-clad copper stranded wires in high-speed solid/liquid continuous composite casting and drawing, which could provide important reference for industrial production. Full article

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19 pages, 1200 KiB

Open AccessArticle

Numerical Simulation of the Effect of Pre-Strain on Fatigue Crack Growth in AA2024-T351

by Diogo M. Neto, Edmundo Sérgio, André Agra and Fernando V. Antunes

Metals 2025, 15(5), 481; https://doi.org/10.3390/met15050481 - 24 Apr 2025

Abstract

The objective here is to study the effect of pre-strain on fatigue crack growth (FCG) in 2024-T351 aluminum alloy. Three pre-strain conditions were considered: without pre-strain, compressive and tensile permanent pre-strains of 4%. A numerical approach based on cumulative plastic strain at the [...] Read more.

The objective here is to study the effect of pre-strain on fatigue crack growth (FCG) in 2024-T351 aluminum alloy. Three pre-strain conditions were considered: without pre-strain, compressive and tensile permanent pre-strains of 4%. A numerical approach based on cumulative plastic strain at the crack tip was followed to predict FCG rate. The compressive pre-strain increased FCG rate, while the tensile pre-strain reduced the da/dN relative to the situation without pre-strain. The influence of pre-strain was linked with plasticity-induced crack closure. In fact, a linear trend was obtained between da/dN and ΔK_eff for three crack lengths (a = 16.184; a = 15.048 mm and a = 15.152 mm) and three pre-strain conditions. The increase in the stress ratio from R = 0.1 to R = 0.5 and the elimination of the contact of crack flanks significantly reduced the effect of pre-strain, also pointing to the huge relevance of crack closure in this context. Finally, the effect of pre-strain on da/dN after an overload was also explained by crack closure variations. Full article

(This article belongs to the Section Metal Failure Analysis)

15 pages, 3860 KiB

Open AccessArticle

Prediction of Enthalpy of Mixing of Binary Alloys Based on Machine Learning and CALPHAD Assessments

by Shuangying Huang, Guangyu Wang and Zhanmin Cao

Metals 2025, 15(5), 480; https://doi.org/10.3390/met15050480 - 24 Apr 2025

Abstract

The enthalpy of mixing, a critical thermodynamic property in the liquid phase reflecting element interaction strength and pivotal for studying phase equilibria, can now be predicted efficiently using machine learning. This study proposes a model combining machine learning with the Calculation of Phase [...] Read more.

The enthalpy of mixing, a critical thermodynamic property in the liquid phase reflecting element interaction strength and pivotal for studying phase equilibria, can now be predicted efficiently using machine learning. This study proposes a model combining machine learning with the Calculation of Phase Diagram (CALPHAD) to predict the enthalpy of mixing. We obtained data for 583 binary alloy systems from the SGTE database, ensuring experimental constraints for accuracy. Using pure element properties and Miedema’s model parameters as descriptors, we trained and evaluated four machine learning algorithms, finding LightGBM to perform best (R² = 92.2%, MAE = 3.5 kJ/mol). The model performance was further optimized through Recursive Feature Elimination (REF) and Maximal Information Coefficient (MIC) feature selection methods. Shapley Additive Explanations reveals that the primary factors affecting the mixing enthalpy, such as atomic radius and electronegativity, align with the key parameters of the Miedema model, thereby confirming the physical interpretability of our data-driven approach. This work offers an accelerated method for predicting complex multi-component system thermodynamics. Future research will focus on collecting more high-quality data to enhance model accuracy and generalization. Full article

(This article belongs to the Special Issue Machine Learning in Metallic Materials Processing and Optimizing)

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45 pages, 60152 KiB

Open AccessArticle

Realization of a Novel FeSiAlCuSn Multicomponent Alloy and Characterization of Intermetallic Phases Formed at Different Temperatures During Cooling

by Pradeep Padhamnath, Filip Kuśmierczyk, Mateusz Kopyściański, Łukasz Gondek, Piotr Migas and Mirosław Karbowniczek

Metals 2025, 15(5), 479; https://doi.org/10.3390/met15050479 - 24 Apr 2025

Abstract

Ferrosilicon (FeSi) is a commercially important material with multiple uses in metallurgical processes. Recently, in an attempt to reduce the carbon impact of the FeSi production process, researchers have proposed using recycled Si recovered from electronic waste in the production of FeSi. However, [...] Read more.

Ferrosilicon (FeSi) is a commercially important material with multiple uses in metallurgical processes. Recently, in an attempt to reduce the carbon impact of the FeSi production process, researchers have proposed using recycled Si recovered from electronic waste in the production of FeSi. However, Si recovered from electronic waste usually contains Al, Cu, and Sn as impurities. Hence, FeSi alloys produced with recycled Si from electronic waste may contain all these elements in varying proportions. Al, Cu, and Sn have been explored as alloying elements to produce alloys with Fe. FeSiAl alloys have also been studied recently for their superior properties. In this work, a multicomponent FeSiAlCuSn alloy is produced, and the phases formed at different temperatures are analyzed using different phase identification techniques. We also analyze the hardness of the multicomponent alloy to find any deviation from the standard FeSi alloy without the additional alloying elements. Understanding the phases and the composition of such alloys may help design future multi-component or high-entropy alloys involving Fe, Si, Al, Cu, and Sn for specific applications. Full article

(This article belongs to the Special Issue Processing Technology and Properties of Light Metals)

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15 pages, 5235 KiB

Open AccessArticle

Sb₂S₃/Sb₂O₃ Heterojunction for Improving Photoelectrochemical Properties of Sb₂S₃ Thin Films

by Honglei Tan, Jia Yang, Zhaofeng Cui, Renjie Tan, Teng Li, Baoqiang Xu, Shaoyuan Li and Bin Yang

Metals 2025, 15(5), 478; https://doi.org/10.3390/met15050478 - 24 Apr 2025

Abstract

We prepared antimony metal films via electrodeposition, followed by the synthesis of Sb₂S₃ films through a chemical vapor phase reaction. Finally, an Sb₂O₃ film was deposited onto the Sb₂S₃ film using a chemical bath [...] Read more.

We prepared antimony metal films via electrodeposition, followed by the synthesis of Sb₂S₃ films through a chemical vapor phase reaction. Finally, an Sb₂O₃ film was deposited onto the Sb₂S₃ film using a chemical bath method, successfully constructing a heterojunction photocathode of Sb₂S₃/Sb₂O₃; the synthesized Sb₂S₃/Sb₂O₃ heterojunction is classified as a Type I heterostructure. The resulting Sb₂S₃/Sb₂O₃ heterojunction exhibited a photocurrent density of −0.056 mA cm⁻² at −0.15 V (vs. RHE), which is 1.40 times higher than that of Sb₂S₃ alone under simulated solar illumination. Additionally, the Sb₂S₃/Sb₂O₃ heterojunction demonstrated a lower carrier recombination rate and a faster charge transfer rate compared to Sb₂S₃, as evidenced by photoluminescence and electrochemical impedance spectroscopy tests. For these reasons, the Sb₂S₃/Sb₂O₃ heterojunction obtained a hydrogen precipitation rate of 0.163mL cm⁻² h⁻¹, which is twice the hydrogen precipitation rate of Sb₂S₃, under the condition of 60 min of light exposure. The significant enhancement in photoelectrochemical performance is attributed to the formation of the Sb₂S₃/Sb₂O₃ heterojunction, which improves both carrier separation and charge transfer efficiency. This heterojunction strategy holds promising potential for visible light-driven photoelectrochemical water splitting. Full article

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18 pages, 3675 KiB

Open AccessArticle

Experimental Investigation and Optimization of Tool Life in High-Pressure Jet-Assisted Turning of Inconel 718

by Davorin Kramar and Djordje Cica

Metals 2025, 15(5), 477; https://doi.org/10.3390/met15050477 - 23 Apr 2025

Abstract

The application of high-pressure jet-assisted (HPJA) machining can increase tool life during machining, as the cutting fluid penetrates better into the interfaces between the tool and the workpiece. In this work, tool life in semi-finish turning of Inconel 718 with coated carbide tools [...] Read more.

The application of high-pressure jet-assisted (HPJA) machining can increase tool life during machining, as the cutting fluid penetrates better into the interfaces between the tool and the workpiece. In this work, tool life in semi-finish turning of Inconel 718 with coated carbide tools and a high-pressure coolant supply is investigated. In a preliminary experiment, tool life was compared between conventional flooding and HPJA machining. The results show tool life that is more than twice as long with HPJA at higher cutting speeds. In the main experiment, tool life was investigated as a function of various high-pressure-jet parameters (nozzle diameter, distance between the point of impact of the jet and the cutting edge and pressure of the jet) and basic cutting parameters (cutting speed and feed rate). The relationship between the above-mentioned process parameters and tool life was analyzed and modeled using response surface methodology (RSM). Analysis of variance (ANOVA) was performed to evaluate the statistical significance of each process parameter for the response. The results revealed that cutting speed is the most important factor for maximizing tool life, followed by pressure of the jet and feed rate. In addition, optimization using the biogeographic optimization (BBO) algorithm was performed and validated in this study. The results of the confirmation experiments show that the proposed optimization method is very effective and results in approximately 8.4% longer tool life compared to the best trial results. Full article

(This article belongs to the Special Issue Surface Integrity and Functional Performance Induced by Hybrid Processing of Metallic Alloys)

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24 pages, 7632 KiB

Open AccessArticle

Quantitative Microstructure of Multiphase Al-Zn-Si-(Mg) Coatings and Their Effects on Sacrificial Protection for Steel

by Guilherme Adinolfi Colpaert Sartori, Blandine Remy, Tiago Machado Amorim and Polina Volovitch

Metals 2025, 15(5), 476; https://doi.org/10.3390/met15050476 - 23 Apr 2025

Abstract

A new combined analysis of SEM-BSE and EDX images using Aphelion^TM software was proposed to describe the quantitative microstructure (quantity and neighborhood of sacrificial phases) of Al-Zn-Si-(Mg) coatings on steel. Three materials with different Al/Zn ratios and Mg content were analyzed. The [...] Read more.

A new combined analysis of SEM-BSE and EDX images using Aphelion^TM software was proposed to describe the quantitative microstructure (quantity and neighborhood of sacrificial phases) of Al-Zn-Si-(Mg) coatings on steel. Three materials with different Al/Zn ratios and Mg content were analyzed. The quantitative microstructure allowed us to describe their corrosion behaviors in a chloride environment and understand their ranking for sacrificial protection of steel in accelerated corrosion tests. For the analyses, interdendritic Zn-rich or Mg-rich phases were expected to be more sacrificial to steel than Al-rich dendrites. Without Mg (AZ coating), Al-rich dendrites created a percolating network, but interdendritic phases did not, suggesting their sacrificial protection to steel to be very limited. Additionally, significant Zn gradients inside dendrites led to a premature coating consumption on the surface, creating new zones of naked steel. In the coatings with Mg (AZM), sacrificial interdendritic phases created a percolating network, which is expected to improve long-time sacrificial protection and contribute to a more uniform formation of Zn corrosion products. For Al content between 30 wt.% and 45 wt.%, a lowering of the Al/Zn ratio (L-AZM) increased the connectivity of the sacrificial interdendritic phases, which is expected to improve the long-term sacrificial effect. Accelerated corrosion tests of scratches in the steel coatings validated the hypotheses. Full article

(This article belongs to the Section Corrosion and Protection)

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21 pages, 11678 KiB

Open AccessArticle

Finite Element Simulation and Process Analysis for Hot-Forming WE43 Magnesium Alloy Fasteners: Comparison of Crystal Plasticity with Traditional Method

by Anqi Jiang, Yuanming Huo, Zixin Zhou, Zhenrong Yan and Yue Sun

Metals 2025, 15(5), 475; https://doi.org/10.3390/met15050475 - 23 Apr 2025

Abstract

The WE43 magnesium alloy has gained attention in orthopedic implants due to its biodegradable properties, particularly for fabricating degradable fasteners. However, research on its hot-forming processes remains limited, primarily focusing on macroscopic finite element mechanical analyses. This study introduces a simplified high-temperature upsetting [...] Read more.

The WE43 magnesium alloy has gained attention in orthopedic implants due to its biodegradable properties, particularly for fabricating degradable fasteners. However, research on its hot-forming processes remains limited, primarily focusing on macroscopic finite element mechanical analyses. This study introduces a simplified high-temperature upsetting process and employs a mesoscale crystal plasticity finite element method to model the thermoforming behavior of WE43 fasteners for the first time. Comparative analyses with conventional finite element methods reveal that the crystal plasticity finite element method effectively captures the influence of microstructural evolution on macroscopic deformation. Additionally, temperature effects (25–650 °C) on mechanical performance were systematically evaluated. The results demonstrate that temperatures between 350 °C and 450 °C optimize formability, balancing thermal softening and strain hardening. The crystal plasticity finite element method framework provides enhanced predictive accuracy for micro–macro interactions, offering critical insights for designing biodegradable magnesium alloy implants. Full article

(This article belongs to the Special Issue Modeling, Simulation and Experimental Studies in Metal Forming)

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16 pages, 5388 KiB

Open AccessArticle

Effects of Composition on Melt Fillability and Impact Resistance of TiAl Alloys for Thin-Blade Turbine Wheels: Laboratory Predictions and Product Verification

by Toshimitsu Tetsui, Yu-Yao Lee, Thomas Vaubois and Pierre Sallot

Metals 2025, 15(5), 474; https://doi.org/10.3390/met15050474 - 22 Apr 2025

Abstract

Scaling up the production of TiAl turbine wheels for passenger car turbochargers requires the fabrication of thin blades that are similar to those of nickel-based superalloys. To achieve this, the molten metal fillability and impact resistance of thin blades must be improved. In [...] Read more.

Scaling up the production of TiAl turbine wheels for passenger car turbochargers requires the fabrication of thin blades that are similar to those of nickel-based superalloys. To achieve this, the molten metal fillability and impact resistance of thin blades must be improved. In this study, the effects of composition on these properties are predicted using simple laboratory experiments with binary, ternary, and practical alloys and are then verified with actual turbine wheels. The melt fillability of the turbine wheel blade is predicted using the amount of molten metal passing through an Al₂O₃-1%SiO₂ mesh. The binary alloy exhibits the best fillability, which is reduced by the addition of Cr and Si. Charpy impact tests on as-cast materials at 25 and 850 °C show that the addition of Cr and Mn improves the impact resistance, but the addition of Nb, W, Mo and Si reduces it. Therefore, the molten metal fillability and/or impact resistance of practical TiAl alloys containing such additives owing to other requirements are low and require improvement for use in thin-blade turbine wheel applications. Full article

(This article belongs to the Special Issue Properties, Microstructure and Forming of Intermetallics)

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13 pages, 10824 KiB

Open AccessArticle

Study of the Surface Structural Transformation and Mechanical Properties of 65Mn Steel Modified by Pulsed Detonation–Plasma Technology

by Youxing He, Mingming Zhang, Xuebing Yang, Wenfu Chen and Lei Lu

Metals 2025, 15(5), 473; https://doi.org/10.3390/met15050473 - 22 Apr 2025

Abstract

Pulsed detonation–plasma technology (PDT) is a surface-modification technology used in an atmospheric environment, where plasma, a detonation impact and thermal conditions are combined and have an effect on the material’s surface. In this study, annealed 65Mn steel was selected to further study the [...] Read more.

Pulsed detonation–plasma technology (PDT) is a surface-modification technology used in an atmospheric environment, where plasma, a detonation impact and thermal conditions are combined and have an effect on the material’s surface. In this study, annealed 65Mn steel was selected to further study the principle of PDT modification. The results show that the modified layer with fine grains was divided into an infiltration layer with a large amount of non-uniformly distributed granular CW₃ carbides and a heat-affected layer below the infiltration layer after PDT treatment. However, a higher amount of acicular martensite and a lower amount of austenite was achieved in the modified layer, containing a large number of small-angle grain boundaries, dislocations, and twin grains. After the PDT treatment, the hardness of the modified layer, heat-affected layer, and substrate was 980 HV, 856.2 HV, and 250 HV, respectively. The mass loss of the sample before and after PDT treatment was 21.1 mg and 12.4 mg, respectively. The hardness and wear resistance of the modified layer were greatly improved compared with the substrate because of the combined effect of the solid-phase transformation, element infiltration, and distortion. Full article

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13 pages, 9762 KiB

Open AccessArticle

Fatigue Damage Assessment in AL6XN Stainless Steel Based on the Strain-Hardening Exponent n-Value

by Donovan Ramírez-Acevedo, Ricardo Rafael Ambriz, Christian Jesús García, Cesar Mendoza Gómora and David Jaramillo

Metals 2025, 15(5), 472; https://doi.org/10.3390/met15050472 - 22 Apr 2025

Abstract

The fatigue life curve was determined for the AL6XN stainless steel under strain-controlled Low Cycle Fatigue (LCF) tests. Additionally, a specific number of loading cycles were applied to new specimens made from the same AL6XN alloy batch to set an Accumulated Fatigue Damage [...] Read more.

The fatigue life curve was determined for the AL6XN stainless steel under strain-controlled Low Cycle Fatigue (LCF) tests. Additionally, a specific number of loading cycles were applied to new specimens made from the same AL6XN alloy batch to set an Accumulated Fatigue Damage (AFD) based on the Palmgren–Miner rule. The AFD was 0.25, 0.50 and 0.75; subsequently, these specimens were subjected to tensile tests. It was observed that all AFD specimens exhibited a yield strength increment with respect to the AL6XN material property, thus, it was similar to a strain-hardening mechanism. However, the stress–strain behavior and microstructure characterization showed a microvoid nucleation and growth mechanism that competed against the strain-hardening one. The fracture in the 0.75 AFD specimens was dominated by this microvoid-based mechanism. The experimental results indicated that the strain-hardening exponent (n-value) and electrical resistivity (

ρ

-value) were consistently modified by the AFD in all the specimens, with an inverse linear relationship for the n-value and a nonlinear increasing behavior for the

ρ

-value. Full article

(This article belongs to the Special Issue Fatigue of Metals and Welded Joints)

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25 pages, 14859 KiB

Open AccessArticle

The Effect of Drag Finishing on Additively Manufactured Customized Dental Crowns

by Cosmin Cosma, Martin Melichar, Stelian Libu, Alexandru Popan, Glad Contiu, Cristina Teusan, Petru Berce and Nicolae Balc

Metals 2025, 15(5), 471; https://doi.org/10.3390/met15050471 - 22 Apr 2025

Abstract

Cobalt–chromium (CoCr) alloys are frequently used to produce customized dental applications such as crowns, bridges, or prostheses. These medical products have anatomical forms, and can be effectively manufactured using the laser-based powder bed fusion (PBF-LB/M) technique. A major disadvantage of this approach is [...] Read more.

Cobalt–chromium (CoCr) alloys are frequently used to produce customized dental applications such as crowns, bridges, or prostheses. These medical products have anatomical forms, and can be effectively manufactured using the laser-based powder bed fusion (PBF-LB/M) technique. A major disadvantage of this approach is the extended time required to refine the resultant surface. The purpose of this research is to reduce the surface roughness of PBF-LB/M/CoCr dental crowns by adopting drag finishing (DF) technology. To evaluate the impact of this automatic post-processing, surface roughness measurements and geometrical investigations were undertaken. The microstructure was characterized using scanning electron microscopy (SEM), and the chemical composition was verified by energy-dispersive X-ray spectroscopy (EDAX). On outside surfaces, the DF post-processing decreased the initial surface roughness by 70–90%. The dental crown’s surface roughness value after DF post-processing was comparable to that of the basic form (cylinder). The lowest roughness was obtained with DF3 post-processing (Ra~0.60 μm). The inner surfaces were limitedly finished. The 3D surface texture showed that the DF method reduced the height of peaks, uniformizing the surfaces. CMM work compared the deviations between the virtual model and the printed samples before and after DF post-processing. This analysis revealed that dimensional deviations were reduced on the outside crown walls, ranging from +0.01 to +0.05 mm. The laser parameters and the heat treatment applied increased the hardness of CoCr crowns to 520 HV, but the proper DF conditions identified reduced the surface roughness and improved the accuracy. Full article

(This article belongs to the Special Issue Advances in Additive Manufacturing for Metallic Materials and Their Applications (3rd Edition))

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28 pages, 25525 KiB

Open AccessReview

Ultrasonic Vibration-Assisted Machining Particle-Reinforced Al-Based Metal Matrix Composites—A Review

by Xiaofen Liu, Yifeng Xiong and Qingwei Yang

Metals 2025, 15(5), 470; https://doi.org/10.3390/met15050470 - 22 Apr 2025

Abstract

Particle-reinforced Al-based matrix composites have great potential for application in aerospace, automotive manufacturing, and defense due to their high strength, hardness, and excellent wear and corrosion resistance. However, the presence of particles increases the processing difficulty, making it a typical difficult-to-machine material. In [...] Read more.

Particle-reinforced Al-based matrix composites have great potential for application in aerospace, automotive manufacturing, and defense due to their high strength, hardness, and excellent wear and corrosion resistance. However, the presence of particles increases the processing difficulty, making it a typical difficult-to-machine material. In recent years, ultrasonic vibration-assisted machining has been quite popular in manufacturing this kind of material. This paper reviews the research advancements in ultrasonic vibration-assisted machining of particle-reinforced Al-based matrix composites, providing a comprehensive analysis of the effects of introducing an ultrasonic energy field on tool wear, chip morphology, cutting force, cutting temperature, and surface integrity. Ultrasonic vibration periodically alters the contact state between the tool and the workpiece, effectively reducing the tool wear rate and extending the tool life. Meanwhile, ultrasonic vibration facilitates the fracture and ejection of chips, enhancing chip morphology and reducing energy consumption during the cutting process. Additionally, ultrasonic vibration significantly decreases cutting force and cutting temperature, contributing to the stability of the cutting process and improving processing efficiency. Regarding surface integrity, ultrasonic vibration-assisted machining refines the machined surface’s microstructure, reducing surface defects and residual stress, thereby significantly enhancing the machining quality. In the future, we will conduct in-depth research on the effects of ultrasonic energy on material properties in terms of softening effect, thermal effect, and stress superposition, further revealing the mechanism of ultrasonic vibration-assisted processing of particle-reinforced aluminum-based composite materials. Full article

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20 pages, 15332 KiB

Open AccessArticle

Synergistic Effects of Thermal Cycles and Residual Stress on Microstructural Evolution and Mechanical Properties in Monel 400 and AISI 316L Weld Joints

by Balram Yelamasetti, Sri Phani Sushma, Zubairuddin Mohammed, Hussain Altammar, Mohammad Faseeulla Khan and Syed Quadir Moinuddin

Metals 2025, 15(5), 469; https://doi.org/10.3390/met15050469 - 22 Apr 2025

Abstract

The current study investigates the thermal, metallurgical, and mechanical results in similar and dissimilar weldments of Monel 400 and AISI 316L. Infrared thermography (IRT) was employed to record thermal cycles, while X-ray diffraction (XRD) was used to analyze the residual stresses post-welding. Mechanical [...] Read more.

The current study investigates the thermal, metallurgical, and mechanical results in similar and dissimilar weldments of Monel 400 and AISI 316L. Infrared thermography (IRT) was employed to record thermal cycles, while X-ray diffraction (XRD) was used to analyze the residual stresses post-welding. Mechanical properties were assessed through tensile and microhardness tests, and microstructural evolution was examined using energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). IRT results showed peak temperatures of 1788 °C for Monel 400 and 1750 °C for AISI 316L. Residual stress analysis revealed compressive stresses of 293 MPa in dissimilar welds, compared to 235 MPa in Monel 400 and tensile stresses of 57 MPa in AISI 316L. Ultimate tensile strength (UTS) values were 543 MPa for dissimilar welds, 533 MPa for Monel 400, and 556 MPa for AISI 316L, with corresponding microhardness values of 207 HV, 203 HV, and 168 HV, respectively. Microstructural analysis identified coarse Ni-Cu phases in the Monel 400 heat-affected zone (HAZ), austenitic structures in AISI 316L, and intermetallic compounds in dissimilar welds. The findings highlight the impact of thermal distribution, residual stress, and microstructural evolution on weld performance, providing insights into optimized welding parameters for improved joint integrity and mechanical properties. Full article

(This article belongs to the Special Issue Advanced Metal Welding and Joining Technologies—2nd Edition)

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14 pages, 3594 KiB

Open AccessArticle

Selective Extraction of Zirconium from Sulfuric Acid Solutions at High Concentration with Trioctylamine (TOA)

by Shuo Tian, Jing Song, Hongqian Sun, Congcong Zhao, Zhiyu Zhang, Mingming Han and Tao Qi

Metals 2025, 15(5), 468; https://doi.org/10.3390/met15050468 - 22 Apr 2025

Abstract

Zirconium (Zr) and hafnium (Hf) are very important in nuclear and high-temperature applications, but their similar physical and chemical properties bring great challenges to separation. The current extraction methods have defects, such as low efficiency at high metal concentration. In this article, a [...] Read more.

Zirconium (Zr) and hafnium (Hf) are very important in nuclear and high-temperature applications, but their similar physical and chemical properties bring great challenges to separation. The current extraction methods have defects, such as low efficiency at high metal concentration. In this article, a zirconium (Zr)/hafnium (Hf) solvent extractive separation from sulfuric acid solutions using trioctylamine (TOA) as the extractant was researched at room temperature. The aqueous solution is prepared using zirconium sulfate (containing Hf), and the concentration of metal ions (Zr⁴⁺ and Hf⁴⁺) was about 1.096 mol·L⁻¹. The effects of the aqueous acidity, the concentration of TOA, the contacting time, and the organic to aqueous O/A ratio on the separation of Zr and Hf were investigated. It is observed that the Zr can be extracted in the organic phase selectively, and the optimal conditions were: TOA concentration of 40 vol%, organic to aqueous O/A ratio of 3, contacting time of 5 min. Under these conditions, the single-stage extraction rate of Zr is 61.23%, while the Hf is almost not extracted. The mechanism of Zr extraction by TOA was studied through the saturation capacity and slope methods. Based on the results, it is believed that the structure of the extracted complex may be [R₃NH]₂[Zr(SO₄)₃]. This study provides a new approach for the development of industrialized Zr-Hf separation. Full article

(This article belongs to the Special Issue Comprehensive Recycling of Metallurgical Solid Waste and Mineral Resources)

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Metals, Volume 15, Issue 5 (May 2025) – 21 articles

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