Metals

25 pages, 4525 KiB

Open AccessReview

Advancement in Research on Silicon/Carbon Composite Anode Materials for Lithium-Ion Batteries

by Binbin Jin, Liwei Liao, Xinyi Shen, Zhe Mei, Qingcheng Du, Liying Liang, Bingxin Lei and Jun Du

Metals 2025, 15(4), 386; https://doi.org/10.3390/met15040386 (registering DOI) - 29 Mar 2025

Abstract

Silicon stands out as an exceptionally viable anode material, distinguished by its substantial capacity, plentiful natural reserves, eco-friendliness, and favorable low working potential. Nonetheless, the material’s pronounced volume fluctuations readily induce particle fragmentation, detachment of active components, and repeated disruption of the solid [...] Read more.

Silicon stands out as an exceptionally viable anode material, distinguished by its substantial capacity, plentiful natural reserves, eco-friendliness, and favorable low working potential. Nonetheless, the material’s pronounced volume fluctuations readily induce particle fragmentation, detachment of active components, and repeated disruption of the solid electrolyte interphase (SEI) layer. These factors contribute to a shortened cycle life and rapid capacity fading, thus hindering its practical application. The carbon composite approach can efficiently counteract these issues by capitalizing on silicon’s high capacity and employing carbon as a cushioning agent to diminish volume swelling, thus enhancing the deployment of silicon-based anode materials. This paper offers an exhaustive examination of the lithiation processes involved in Si/C anodes and delves into the strategic utilization of diverse carbon materials, including graphite, graphene, graphdiyne, carbon nanotubes, carbon fibers, MXenes, pitch, heteroatom-doped polymers, biomass-derived carbon, carbon-containing gas-derived carbon, MOFs, and g-C₃N₄ to advance the application of silicon in lithium-ion battery (LIB) anodes. Overall, this paper concentrates on summarizing the current research status and technological advancement and juxtaposes the merits and demerits of various carbon sources in Si/C anodes, thus providing a comprehensive assessment and forward-looking perspective on their future development. Full article

► Show Figures

Figure 1

17 pages, 7796 KiB

Open AccessArticle

Influence of Nd:YAG Laser Melting on an Investment-Casting Co-Cr-Mo Alloy

by Francisco Cepeda Rodríguez, Carlos Rodrigo Muñiz Valdez, Juan Carlos Ortiz Cuellar, Jesús Fernando Martínez Villafañe, Jesús Salvador Galindo Valdés and Gladys Yerania Pérez Medina

Metals 2025, 15(4), 385; https://doi.org/10.3390/met15040385 (registering DOI) - 29 Mar 2025

Abstract

The investment casting process, also known as lost-wax casting, is widely used for producing ferrous and non-ferrous metal parts due to its excellent surface finish and dimensional accuracy. In recent years, the use of Co-Cr-Mo alloy has increased due to its high corrosion [...] Read more.

The investment casting process, also known as lost-wax casting, is widely used for producing ferrous and non-ferrous metal parts due to its excellent surface finish and dimensional accuracy. In recent years, the use of Co-Cr-Mo alloy has increased due to its high corrosion resistance, good biocompatibility, and relatively high wear resistance. Laser melting of materials has been demonstrated to refine the surface grain structure, reduce surface roughness, and improve both wear and corrosion resistance. The ability to fine-tune parameters such as laser power density and scanning speed facilitates the optimization of the treated layers’ thickness and homogeneity, thereby addressing many of the shortcomings inherent in conventional methods. This study investigates the microstructural, mechanical wear and bioactive behavior of investment-cast Co-Cr-Mo parts subjected to a Nd:YAG laser surface treatment. The effects of different processing parameters were analyzed quantitatively and comprehensively. The specimens were characterized using metallographic techniques, bioactivity evaluation, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), wear testing (Pin-on-Disk), and hardness testing. Our results demonstrate that Nd:YAG laser melting significantly enhances the surface properties and maintains the dimensional accuracy of complex Co-Cr-Mo biomedical components, through microstructural refinement, increased hardness, improved wear resistance, and preserved biocompatibility. The specific combination of investment casting with precisely controlled laser surface modification represents a significant advancement for improving the longevity and performance of biomedical implants. Full article

(This article belongs to the Special Issue Manufacture, Mechanical Properties and Metallurgy of Metallic Biomaterials)

► Show Figures

Figure 1

12 pages, 11545 KiB

Open AccessArticle

Effect of Notches on Fatigue Crack Initiation and Early Propagation Behaviors of a Ni-Based Superalloy at Elevated Temperatures

by Zuopeng Zhao, Xuteng Hu and Zhiwei Guo

Metals 2025, 15(4), 384; https://doi.org/10.3390/met15040384 (registering DOI) - 29 Mar 2025

Abstract

The role of notch stress and surface defects on fatigue crack initiation and small-crack propagation behavior has been investigated using groove simulation specimens. The naturally initiated small-crack growth tests have been performed on a FGH4099 superalloy at 500 °C and 700 °C. The [...] Read more.

The role of notch stress and surface defects on fatigue crack initiation and small-crack propagation behavior has been investigated using groove simulation specimens. The naturally initiated small-crack growth tests have been performed on a FGH4099 superalloy at 500 °C and 700 °C. The findings indicate that elevated testing temperature significantly reduced the proportion of fatigue crack initiation life, with a less pronounced effect on the proportion of life for cracks to grow to First Engineering Crack size. Competing crack initiation modes were observed in the fatigue test of groove simulation specimens. The location of maximum principal stress was dominant fatigue crack initiation sites, and for specimens with surface inclusions, the defect location can also serve as a crack initiation site. Furthermore, crack initiation modes were found to have a more pronounced effect on the small-crack growth rate. A turning point observed in the crack growth rate curves for specimens with multi-site crack initiation was attributed to crack shielding and subsequent coalescence. Full article

(This article belongs to the Special Issue Fatigue Assessment of Metals)

► Show Figures

Figure 1

24 pages, 10368 KiB

Open AccessArticle

The Effects of Alloying Elements on the Corrosion of Rebar Steel in a Chloride Environment

by Jing Yuan, Pei Li, Huanhuan Zhang, Shubiao Yin, Mingli Xu and Akun Zhou

Metals 2025, 15(4), 383; https://doi.org/10.3390/met15040383 (registering DOI) - 28 Mar 2025

Abstract

The corrosion behaviors in chloride environment of two commercial low-alloy steel bars were studied. Through cyclic wetting tests, accelerated corrosion experiments ranging from 1 to 576 h were conducted on low-alloy bars and original bars. Techniques such as OM, SEM, EDS, AFM, and [...] Read more.

The corrosion behaviors in chloride environment of two commercial low-alloy steel bars were studied. Through cyclic wetting tests, accelerated corrosion experiments ranging from 1 to 576 h were conducted on low-alloy bars and original bars. Techniques such as OM, SEM, EDS, AFM, and XRD were employed to characterize the corrosion emergence and expansion behaviors of these bars in a simulated marine wetting and sun exposure environment. The designed low-alloy corrosion-resistant rebar achieved a 500 MPa yield strength. In each corrosion cycle, its corrosion loss and rate were lower than those of same-strength ordinary rebars. Analysis of the rust layer’s macro and micro morphology and alloy element distribution revealed alloy elements had little effect at corrosion initiation. In later corrosion, their enrichment led to a denser rust layer, effectively blocking corrosion expansion and chloride salt infiltration. After 72 h of accelerated corrosion, the corrosion rate growth of both bars slowed. The inner rust layer’s electrochemical potential increased, and local corrosion pits turned into uniform corrosion. The inner rust layer of the rebar formed more stable chromic acid with ionic compounds, reducing corrosion sensitivity. This study offers insights into steel bar corrosion and alloy element roles, guiding the preparation of low-alloy corrosion-resistant steel bars. Full article

(This article belongs to the Special Issue Mechanical Properties and Corrosion Behavior of Metals after Surface Modification)

► Show Figures

Figure 1

15 pages, 1105 KiB

Open AccessArticle

The Effect of He on the Evolution of Radiation-Induced Dislocation Loops Near W/Cu Interface

by Huaqing Sang, Yifan Zhang and Jing Wang

Metals 2025, 15(4), 382; https://doi.org/10.3390/met15040382 (registering DOI) - 28 Mar 2025

Abstract

In the current work, the distribution behaviors of irradiation-induced dislocation loops near the W-Cu interface (contains a thin W₂C transition layer) under self-interstitial atom diffusion-dominated conditions were investigated based on the comparative experiment of 3 MeV Fe ion and 100 keV [...] Read more.

In the current work, the distribution behaviors of irradiation-induced dislocation loops near the W-Cu interface (contains a thin W₂C transition layer) under self-interstitial atom diffusion-dominated conditions were investigated based on the comparative experiment of 3 MeV Fe ion and 100 keV He ion irradiation. The size distribution and number density of radiation-induced dislocation loops in both sides of the interface were characterized using Transmission Electron Microscopy with different two-beam conditions. The impact of the phase boundary on the dislocation loop distribution and the influence of He on this mechanism was discussed. The results showed that the phase boundary (PB) has a significant effect on the distribution of radiation-induced dislocation loops. In the Fe-irradiated sample, the proportion of b = 1/2<111> type dislocation loops near the phase boundary on the W side increases significantly, and b = 1/2<110> type dislocation loops dominate on the Cu side. He will significantly affect the loop distribution near the W/Cu phase boundary due to the strong binding of He with vacancies in W, which suppresses the recombination of SIA and vacancies and promotes the formation and growth of interstitial-type dislocations. Full article

10 pages, 5951 KiB

Open AccessCommunication

Investigation of High-Temperature Tensile Properties and Fracture Mechanisms of GH3536 Alloy Fabricated by Selective Laser Melting

by Biao Zhou, Shuai Huang, Tianyuan Wang, Cheng Wang and Bingqing Chen

Metals 2025, 15(4), 381; https://doi.org/10.3390/met15040381 (registering DOI) - 28 Mar 2025

Abstract

This work revealed the mechanism of microstructure evolution on tensile properties in selective laser melted (SLM) GH3536 superalloys in the range of room temperature to 1000 °C. The results showed that SLM-GH3536 alloy exhibited isotropic tensile properties along X, Z, and 45° directions. [...] Read more.

This work revealed the mechanism of microstructure evolution on tensile properties in selective laser melted (SLM) GH3536 superalloys in the range of room temperature to 1000 °C. The results showed that SLM-GH3536 alloy exhibited isotropic tensile properties along X, Z, and 45° directions. The carbide at the grain boundary changed from banded to granular, resulting in a significant decrease in tensile strength at elevated temperatures, and the fracture mode transitioned from a mixed fracture to transgranular fracture. Full article

16 pages, 3415 KiB

Open AccessArticle

Catalytic Properties of ZnZrO_x Obtained via Metal–Organic Framework Precursors for CO₂ Hydrogenation to Prepare Light Olefins

by Rundong Cai, Heping Zheng, Hong Liang, Xiankun Chen and Jianhua Tang

Metals 2025, 15(4), 380; https://doi.org/10.3390/met15040380 (registering DOI) - 28 Mar 2025

Abstract

The conversion of CO₂ into light olefins over bifunctional catalysts is a promising route for producing high-value-added products. This approach not only mitigates excessive CO₂ emissions but also reduces the chemical industry’s reliance on fossil fuels. Among bifunctional catalysts, ZnZrO_x [...] Read more.

The conversion of CO₂ into light olefins over bifunctional catalysts is a promising route for producing high-value-added products. This approach not only mitigates excessive CO₂ emissions but also reduces the chemical industry’s reliance on fossil fuels. Among bifunctional catalysts, ZnZrO_x is widely used due to its favorable oxide composition. In this work, ZnZrO_x solid solution was synthesized by calcining an MOF precursor, resulting in a large specific surface area and a small particle size. Characterization studies revealed that ZnZrO_x prepared via MOF calcination exhibited an enhanced CO₂ activation and H₂ dissociation capacity compared to that synthesized using the co-precipitation method. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that CO₂ adsorption on ZnZrO_x led to the formation of carbonate species, while HCOO* and CH₃O* intermediates were generated upon exposure to the reaction gas. When ZnZrO_x was combined with SAPO-34 molecular sieves under reaction conditions of 380 °C, 3 MPa, and 6000 mL·g_cat⁻¹·h⁻¹, the CO₂ conversion reached 34.37%, with a light olefin yield of 15.13%, demonstrating a superior catalytic performance compared to that of the co-precipitation method. Full article

► Show Figures

Figure 1

12 pages, 6050 KiB

Open AccessArticle

Effects of Fine Cu Particle Size on Sinter-Bondability in Die Bonding Using Cu Paste Possessing Effective Reducing Formulation

by Horyun Kim and Jong-Hyun Lee

Metals 2025, 15(4), 379; https://doi.org/10.3390/met15040379 - 28 Mar 2025

Abstract

The application of wide-bandgap semiconductors in next-generation power modules requires cost-effective Cu particles and a reduced bonding time in the die attachment process to enable efficient industrial-scale manufacturing. Therefore, this study aimed to analyze the effect of Cu particle size variation on pressure-assisted [...] Read more.

The application of wide-bandgap semiconductors in next-generation power modules requires cost-effective Cu particles and a reduced bonding time in the die attachment process to enable efficient industrial-scale manufacturing. Therefore, this study aimed to analyze the effect of Cu particle size variation on pressure-assisted sinter-bondability and bond line shear strength. Cu particles were synthesized through a simple wet-chemical process, in which pH variation was employed to obtain submicrometer-sized Cu particles with average diameters of 500, 300, and 150 nm. The synthesized particles exhibited pure Cu composition, forming only a native oxide layer on their surfaces. In pastes containing these Cu particles, smaller particle sizes led to the delayed evaporation of the reducing solvent, which in turn delayed the exothermic reactions associated with particle sintering and oxidation. However, the sintering-induced exothermic peak became more pronounced as the particle size decreased, confirming that smaller particles improved sinterability. Pressure-assisted sinter bonding performed in air at 300 °C indicated that a decreased particle size contributed to the densification of the bond line structure and an increase in shear strength. Specifically, the paste containing 150 nm Cu particles achieved a highly dense microstructure and an exceptional shear strength of 36.7 MPa within just 30 s of sinter bonding. These findings demonstrate that reducing the particle size is essential for enhancing the sinter-bondability of cost-effective Cu particle-based sinter-bonding pastes. Full article

► Show Figures

Graphical abstract

49 pages, 2136 KiB

Open AccessReview

History of Metallic Orthopedic Materials

by Elia Marin and Alex Lanzutti

Metals 2025, 15(4), 378; https://doi.org/10.3390/met15040378 - 28 Mar 2025

Abstract

The history of metallic orthopedic materials spans a few centuries, from the use of carbon steel to the widespread adoption of titanium and its alloys. This paper explores the evolution of these materials, emphasizing their mechanical properties, biocompatibility, and the roles that they [...] Read more.

The history of metallic orthopedic materials spans a few centuries, from the use of carbon steel to the widespread adoption of titanium and its alloys. This paper explores the evolution of these materials, emphasizing their mechanical properties, biocompatibility, and the roles that they have played in improving orthopedic care. Key developments include the discovery of titanium’s osseointegration capability, the advent of porous coatings for osseointegration, surface modifications, and the rise of additive manufacturing for patient-specific implants. Beyond titanium, emerging materials such as biodegradable alloys, tantalum, zirconium, and amorphous metals are creating a completely new field of application for orthopedic metals. These innovations address longstanding challenges, including stress shielding, corrosion, and implant longevity, while leading the way for bioresorbable and 3D-printed patient-specific solutions. This paper concludes by examining future trends and their potential for industrial application. By understanding the historical developments in metallic orthopedic materials, this review highlights how past advancements have laid the foundation for both current and future innovations, guiding research towards solutions that better mimic the properties of biological tissues, offer higher reliability in vivo, and enable patient-specific treatments. Full article

► Show Figures

Graphical abstract

13 pages, 8991 KiB

Open AccessArticle

Effect of In Situ Al Roll Coating on Strip Surface Quality in Traditional Twin-Roll Casting of Aluminum Alloys

by Han-Gyoung Cho, Young Do Kim and Min-Seok Kim

Metals 2025, 15(4), 377; https://doi.org/10.3390/met15040377 - 28 Mar 2025

Abstract

The twin-roll casting (TRC) process is widely used in the aluminum industry due to its cost efficiency and continuous production capability. However, maintaining consistently high surface quality remains challenging due to complex heat transfer behavior at the roll/strip interface. This study examines the [...] Read more.

The twin-roll casting (TRC) process is widely used in the aluminum industry due to its cost efficiency and continuous production capability. However, maintaining consistently high surface quality remains challenging due to complex heat transfer behavior at the roll/strip interface. This study examines the critical influence of roll surface conditions, especially the formation of an Al coating layer, on solidification behavior and resulting strip quality in the TRC of an Al-5Mg alloy. Experimental results demonstrated that casting without an Al coating layer led to surface defects such as hot tears and porosity due to insufficient cooling. In contrast, strips produced with a stable Al coating layer exhibited excellent surface quality with no surface defects. Numerical simulations further indicated that a stable Al coating enhanced the interfacial heat transfer coefficient (up to 30,000 W/m²K), ensuring effective cooling and complete solidification before the strip exited the roll nip. Moreover, simulations validated the feasibility of using steel rolls in industrial applications, provided the coating layer was consistently maintained. This research highlights the significance of roll surface control in improving TRC product quality. Full article

(This article belongs to the Special Issue Special and Short Processes of Aluminum Alloys)

► Show Figures

Figure 1

16 pages, 7646 KiB

Open AccessArticle

Optimized and Additively Manufactured Face Mills for Enhanced Cutting Performance

by Ozgur Poyraz, Daniel Tomlinson, Anthony Molyneux, Marie E. Baxter, Evren Yasa and James Hughes

Metals 2025, 15(4), 376; https://doi.org/10.3390/met15040376 - 28 Mar 2025

Abstract

With the growing acceptance of additive manufacturing (AM) across various sectors, laser-based powder bed fusion (PBF-LB) has widely been utilized to create intricately shaped parts from a range of metals alloys. The factors contributing to this reception are limited not only to the [...] Read more.

With the growing acceptance of additive manufacturing (AM) across various sectors, laser-based powder bed fusion (PBF-LB) has widely been utilized to create intricately shaped parts from a range of metals alloys. The factors contributing to this reception are limited not only to the achievable geometrical complexity but also enhanced product functionality. Prominent sectors such as aerospace, defense, and biomedical have begun to leverage PBF-LB for a wide range of applications; its use in other industries, such as cutting tool manufacturing, remains more limited. Therefore, to address the potential of LPBF for higher performance in cutting tool applications, this study examines topology optimization and the laser powder bed fusion of face mills with experimental modal characteristics and cutting performance. The objectives in topology optimizations were to decrease the vibration magnitudes of face mills while keeping them stiff against deformation due to cutting forces. Three distinct designs were benchmarked, each with different weight reduction targets, and were fabricated using PBF-LB with M300 maraging steel. The optimized face mills demonstrated better performance with diminished vibration magnitudes and less tool wear patterns. Full article

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

► Show Figures

Graphical abstract

3 pages, 129 KiB

Open AccessEditorial

Advances in Copper, Copper Alloys and Their Processing

by Ulrich Prahl, Andreas Zilly and Julia Dölling

Metals 2025, 15(4), 375; https://doi.org/10.3390/met15040375 - 28 Mar 2025

Abstract

Copper, renowned for its exceptional electrical and thermal conductivity, preferable technological properties, and recyclability, plays a pivotal role in various industries, from electronics and energy to transportation and construction [...] Full article

(This article belongs to the Special Issue Advances in Copper, Copper Alloys and Their Processing)

13 pages, 4390 KiB

Open AccessArticle

Froth Flotation for Boehmite Recovery from a Water-Treatment Process Using Electrocoagulation

by Elvin J. Guzmán-Jarquín, Roberto Pérez-Garibay, Francisco A. Acosta-González and Ramón Arellano-Piña

Metals 2025, 15(4), 374; https://doi.org/10.3390/met15040374 - 28 Mar 2025

Abstract

Boehmite is an aluminum oxyhydroxide (AlO(OH)) and one of bauxite’s main mineral phases. This mineral is highly valued as an important source of aluminum for the metallurgical industry. However, the formation of synthetic boehmite has been observed in water treatment when aluminum anodes [...] Read more.

Boehmite is an aluminum oxyhydroxide (AlO(OH)) and one of bauxite’s main mineral phases. This mineral is highly valued as an important source of aluminum for the metallurgical industry. However, the formation of synthetic boehmite has been observed in water treatment when aluminum anodes are used for electrocoagulation. This boehmite occurs in flocs that capture impurities from the water, but removing these flocs is a slow process. Therefore, the froth-flotation method was employed in the present study to float synthetic boehmite. This was achieved by evaluating the particle size of synthetic boehmite, generating microbubbles, and using an anionic collector system in a novel experimental setup. The results show that the surfactants sodium dodecyl sulfate (SDS) and potassium oleate (PO) favor the recovery of synthetic boehmite in different particle sizes, with the particle size favored related to the bubble size generated. It was noted that increasing the SDS concentration enabled the microbubbles to recover up to 95% of boehmite particles with diameters of less than 30 microns. Full article

(This article belongs to the Special Issue Advances in Flotation Separation and Mineral Processing)

► Show Figures

Figure 1

18 pages, 5161 KiB

Open AccessArticle

Hot Deformation Behavior and Optimization of Processing Parameters for 4Cr16MoCu Martensitic Stainless Steel

by Jiayuan Li, Ling Li, Zhongchao Wu, Tianhao Zeng and Xiaochun Wu

Metals 2025, 15(4), 373; https://doi.org/10.3390/met15040373 - 28 Mar 2025

Abstract

The hot deformation behavior of 4Cr16MoCu martensitic stainless steel alloyed with 1% Cu was investigated through hot compression tests at temperatures ranging from 900 to 1150 °C and strain rates of 0.001 to 1 s⁻¹. The addition of Cu is strategically [...] Read more.

The hot deformation behavior of 4Cr16MoCu martensitic stainless steel alloyed with 1% Cu was investigated through hot compression tests at temperatures ranging from 900 to 1150 °C and strain rates of 0.001 to 1 s⁻¹. The addition of Cu is strategically employed to synergistically enhance precipitation hardening and corrosion resistance, yet its complex interplay with hot deformation mechanisms remains poorly understood, demanding systematic investigation. The results revealed a narrow forging temperature range and significant strain rate sensitivity, with deformation resistance increasing markedly at higher strain rates. An Arrhenius constitutive model incorporating a seventh-degree polynomial for strain compensation was developed to describe the flow stress dependence on deformation temperature and strain rate. The model demonstrated high accuracy, with a correlation coefficient (R²) of 0.9917 and an average absolute relative error (AARE) of 3.8%, providing a reliable theoretical foundation for practical production applications. Furthermore, a hot processing map was constructed based on the dynamic material model (DMM), and the optimal hot working parameters were determined through microstructural analysis: an initial forging temperature of 1125 °C, a final forging temperature of 980 °C, and a strain rate of 0.1 s⁻¹. These conditions resulted in a fine and uniform grain structure, while strain rates above 0.18 s⁻¹ were identified as unfavorable due to the risk of uneven deformation. Full article

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

► Show Figures

Figure 1

41 pages, 15178 KiB

Open AccessArticle

Combined Effect of the Sc/Zr Ratio and Mg Concentration on the Intergranular Corrosion Resistance of Al–Mg–Sc–Zr Alloys: A Case of Cast Alloys and Ultrafine-Grained Alloys

by Vladimir Chuvil’deev, Aleksey Nokhrin, Nataliya Kozlova, Iana Shadrina, Aleksandr Bobrov, Vladimir Kopylov, Andrey Komel’kov and Ekaterina Morozkina

Metals 2025, 15(4), 372; https://doi.org/10.3390/met15040372 - 27 Mar 2025

Abstract

The aim of this study was to investigate the effect of the Sc/Zr ratio (Sc/Zr = 0.45–2.2) on the intergranular corrosion (IGC) resistance of Al–Mg alloys with different Mg content (2.5, 4, and 6%) and with a Sc + Zr = 0.32%. A [...] Read more.

The aim of this study was to investigate the effect of the Sc/Zr ratio (Sc/Zr = 0.45–2.2) on the intergranular corrosion (IGC) resistance of Al–Mg alloys with different Mg content (2.5, 4, and 6%) and with a Sc + Zr = 0.32%. A change in the Mg concentration led to a change in the number of β-phase particles. A change in the Sc/Zr ratio led to a change in the composition of Al₃(Sc,Zr) particles. The IGC resistance of Al–Mg–Sc–Zr alloys was investigated by Tafel electrochemical tests and stationary tests. It has been demonstrated for the first time that two types of IGC defects appear during electrochemical tests. Large Type I defects were associated with the destruction of primary β-phase particles located along the dendrite boundaries. Fine Type II defects were associated with the grain boundaries (GBs). It has been demonstrated that during the stationary tests, Type I defects are formed. ECAP and subsequent annealing affect the ratio of the number of Type I and II defects. Increasing the Sc/Zr ratio reduced the depth of Type I defects, increased the fraction of Type II defects, and reduced the corrosion current density i_corr. It has been shown for the first time that the dependence of i_corr(T) had a three-stage character with a maximum at 450 °C in alloys with 2.5% and 4% Mg. A two-stage dependence of i_corr(T) is observed in alloys with 6% Mg. Increasing i_corr at T < 450 °C is due to the precipitation of the secondary β-phase particles on Al₃(Sc,Zr) particles and due to the effect of solid-phase wetting of the GBs by β-phase, which leads to an increase in the proportion of GBs containing thin layers of β-phase. Decreasing i_corr at T > 450 °C is associated with the dissolution of β-phase particles. Full article

(This article belongs to the Section Corrosion and Protection)

► Show Figures

Figure 1

14 pages, 3146 KiB

Open AccessArticle

Research on Performance Prediction Method of Refractory High-Entropy Alloy Based on Ensemble Learning

by Guangxiang Tian, Pingluo Zhao, Yangwei Wang, Hongmei Zhang, Liying Xing and Xingwang Cheng

Metals 2025, 15(4), 371; https://doi.org/10.3390/met15040371 - 27 Mar 2025

Abstract

Due to the huge component space of refractory high-entropy alloy, the traditional, experimental “trial and error method” can not meet the design requirements. In order to improve the “trial and error method”, guidance is provided for the prediction and design of refractory high-entropy [...] Read more.

Due to the huge component space of refractory high-entropy alloy, the traditional, experimental “trial and error method” can not meet the design requirements. In order to improve the “trial and error method”, guidance is provided for the prediction and design of refractory high-entropy alloys. Based on the literature data, a comprehensive dataset was constructed, including the composition, phase composition, and strength data of various high-entropy alloys. On this basis, nine regression models were established for strength prediction. By comparison, the XGBoost (XGB) model achieves better prediction performance in the test set; the root mean square error (RMSE) is 195.53 MPa, and the coefficient of determination (R²) is 0.87. By using Shapley additive interpretation (SHAP) to analyze the explainability of the model, it was found that the key characteristics affecting the mechanical properties of the high-entropy alloy were mixed entropy and electronegativity. In order to further evaluate the precision of the model, through the vacuum arc melting preparation, Ti27.5Zr26.5Nb25.5Ta8.5Al12 high-entropy alloys were experimentally verified. The alloy experiments’ yield strength was 1356 MPa, predicting strength was 1304.71 MPa, external validation error was 3.81%, and the average accuracy of the model was 87.38%. Full article

(This article belongs to the Special Issue Progress in Advanced High-Entropy Alloy Design and Applications: Microstructures, Mechanical, Electrochemical and Tribological Properties)

► Show Figures

Graphical abstract

26 pages, 10949 KiB

Open AccessArticle

Tribological Investigation of Plasma-Based Coatings for Use in Quasi-Monolithic Engine Cylinder Bores

by Siddharth Banerjee, Joshua Stroh, Dimitry Sediako and Jimi Tjong

Metals 2025, 15(4), 370; https://doi.org/10.3390/met15040370 - 27 Mar 2025

Abstract

This study evaluates the tribological characteristics of quasi-monolithic engine cylinder coatings and piston rings using a custom-built linear reciprocating tribometer. The coatings were deposited on an Al-Si alloy cylinder bore using the Plasma Transfer Wire Arc (PTWA) and Electrolytic Jet Plasma Oxidation (EJPO) [...] Read more.

This study evaluates the tribological characteristics of quasi-monolithic engine cylinder coatings and piston rings using a custom-built linear reciprocating tribometer. The coatings were deposited on an Al-Si alloy cylinder bore using the Plasma Transfer Wire Arc (PTWA) and Electrolytic Jet Plasma Oxidation (EJPO) processes. The coatings’ tribological performances were investigated in the boundary lubrication regime. The performance of conventional chrome-coated cast iron piston rings was tested and compared to that of EJPO- and PTWA-coated engine cylinder samples that were extracted from a cast Al-Si engine block. Scanning electron microscopy and profilometry were used to compare the evolution of wear and the prevalent wear mechanism. This paper also presents the verification and repeatability analysis of a custom-built tribometer against a standard industry-calibrated tribometer. The wear test results showed that the EJPO coating had 0.05% to 10.35% lower wear rates than its PTWA counterpart throughout a wide range of loading conditions and sliding distances. The variation in the counter-face behavior is likely due to the different surface topographic parameters such as skewness, kurtosis, and porosity. Full article

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

► Show Figures

Figure 1

28 pages, 11152 KiB

Open AccessArticle

In-Depth DFT-Based Analysis of the Structural, Mechanical, Thermodynamic, and Electronic Characteristics of CuP₂ and Cu₃P: Insights into Material Stability and Performance

by Ching-Feng Yu and Hsien-Chie Cheng

Metals 2025, 15(4), 369; https://doi.org/10.3390/met15040369 - 27 Mar 2025

Abstract

This study employed density functional theory (DFT) to investigate the structural, mechanical, thermodynamic, and electronic properties of monoclinic CuP₂ and hexagonal Cu₃P. The analysis confirmed the mechanical stability of both compounds, with distinct anisotropic behaviors arising from crystallographic symmetries. Cu [...] Read more.

This study employed density functional theory (DFT) to investigate the structural, mechanical, thermodynamic, and electronic properties of monoclinic CuP₂ and hexagonal Cu₃P. The analysis confirmed the mechanical stability of both compounds, with distinct anisotropic behaviors arising from crystallographic symmetries. Cu₃P exhibits a higher bulk modulus (130.1 GPa), indicating superior resistance to volumetric compression, while CuP₂ demonstrates greater shear (52.9 GPa) and Young’s moduli (133.3 GPa), reflecting enhanced stiffness and tensile resistance. The K/G ratio (1.749 for CuP₂ vs. 3.120 for Cu₃P) and Cauchy pressure analyses revealed the brittle nature of CuP_2, with covalent bonding, and the ductility of Cu₃P, with metallic bonding. The thermodynamic evaluations highlighted the higher Debye temperature of CuP₂ (453.1 K) and its lattice thermal conductivity (8.37 W/mK), suggesting superior heat dissipation, whereas Cu₃P shows greater thermal expansion (38.4 × 10⁻⁶/K) and a higher volumetric heat capacity (3.29 × 10⁶ J/m³K). The electronic structure calculations identified CuP₂ as a semiconductor with a 0.824 eV bandgap and Cu₃P as a conductor with metallic states at the Fermi level. These insights are critical for optimizing Cu-P compounds in microelectronic packaging, where thermal management and mechanical reliability are paramount. Full article

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

► Show Figures

Figure 1

22 pages, 9031 KiB

Open AccessArticle

Characterizing the Behavior and Microstructure of Cu-La₂O₃ Composite Processed via Equal Channel Angular Pressing

by Lenka Kunčická and Radim Kocich

Metals 2025, 15(4), 368; https://doi.org/10.3390/met15040368 - 27 Mar 2025

Abstract

Cu-based alloys and composites are popular to prepare electroconductive parts. However, their processing can be challenging, especially in case of composites strengthened with oxides. To save the necessary time and costs, numerical simulations can be of help when determining the deformation behaviour of [...] Read more.

Cu-based alloys and composites are popular to prepare electroconductive parts. However, their processing can be challenging, especially in case of composites strengthened with oxides. To save the necessary time and costs, numerical simulations can be of help when determining the deformation behaviour of (newly introduced) materials. The study presents a combined method of strengthening of Cu by adding 5 wt.% of La₂O₃ particles and performing shear-based deformation by equal channel angular pressing (ECAP). The effects of the method on the microstructure, mechanical properties, and thermal stability of the composite are examined both numerically and experimentally. The results showed that the La₂O₃ addition caused the maximum imposed strain to be higher for the composite than for commercially pure Cu, which led to the development of subgrains and shear bands within the microstructure, and a consequent increase in microhardness. The numerical predictions revealed that the observed differences could be explained by the differences in the material plastic flow (comparing the composite to commercially pure Cu). The work hardening supported by the addition of La₂O₃ led to a significant increase in stress and punch load during processing, as well as contributed to a slight increase in deformation temperature in the main deformation zone of the ECAP die. Certain inhomogeneity of the parameters of interest across the processed workpiece was observed. Nevertheless, such inhomogeneity is typical for the ECAP process and steps prospectively leading to its elimination are proposed. Full article

(This article belongs to the Special Issue Design and Development of Metal Matrix Composites)

► Show Figures

Figure 1

Journal Description

Metals

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Further Information

Guidelines

MDPI Initiatives

Follow MDPI