Metals

22 pages, 9034 KB

Open AccessArticle

Laser Beam Welding of IN625 Alloy with Equiaxed Grains: Influence of Process Parameters

by Giuliano Angella, Fabio Bergamini, Francesco Cognini, Alessandra Fava, Paolo Ferro, Alessandra Palombi, Maria Richetta and Alessandra Varone

Metals 2025, 15(12), 1296; https://doi.org/10.3390/met15121296 - 25 Nov 2025

Abstract

Ni-based superalloys, known for their excellent mechanical strength and corrosion resistance at high temperature, are widely used in aeronautic, aerospace, and energy industries. Since both the materials and manufacturing processes required to produce high-performance components made of these alloys are expensive, the welding [...] Read more.

Ni-based superalloys, known for their excellent mechanical strength and corrosion resistance at high temperature, are widely used in aeronautic, aerospace, and energy industries. Since both the materials and manufacturing processes required to produce high-performance components made of these alloys are expensive, the welding repair of damaged components plays a crucial role in industrial applications. High energy density welding techniques, such as laser beam welding (LBW) and electron beam welding (EBW), are the most promising to achieve high-quality welds. Nevertheless, welding processes significantly affect the microstructure and mechanical properties of both the melted zone (MZ) and the heat-affected zone (HAZ). This may result in alloying element segregation, precipitation of undesired secondary phases, and the presence of residual stresses that can lead to crack formation. Therefore, a comprehensive investigation of the effects of process parameters on weld seam properties is essential to maintain high performance standards. In this work, LBW was employed to join 2.5 mm thick plates of equiaxed IN625 superalloy. The seams were produced by varying three parameters: the two characteristic parameters of LBW, i.e., laser power (P = 1700, 2000, 2300 W) and welding speed (v = 15, 20, 25 mm/s), alongside power modulation (Γ = P_min/P_max = 0.6, 0.8, 1). The scope of this work is to evaluate the effect of the combined variation of all these welding parameters on the final characteristics of welded seams. The resulting microstructures were characterized by using digital radiography, Light Microscopy (LM), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). Vickers microhardness measurements were performed across the weld seams to evaluate the mechanical properties in the MZ and HAZ. The optimal set of welding parameters, producing defect-free seams without cracks and pores, was identified as P = 2000 W, v = 25 mm/s, and Γ = 0.6. Full article

(This article belongs to the Special Issue Weldability and Reparability of Nickel-Base Alloys)

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14 pages, 5287 KB

Open AccessArticle

Determining Residual Stress in Copper by Nanoindentation in Compressive and Tensile Stress States

by Guanna Li, Jianyuan Mei, Haidong Qi and Xiping Song

Metals 2025, 15(12), 1295; https://doi.org/10.3390/met15121295 - 25 Nov 2025

Abstract

In this study, nanoindentation was employed to determine residual stresses in copper after compression and tension deformations with different deformation levels. Rectangular and cylindrical compression specimens were prepared in order to produce residual stresses parallel or perpendicular to the stress direction. For the [...] Read more.

In this study, nanoindentation was employed to determine residual stresses in copper after compression and tension deformations with different deformation levels. Rectangular and cylindrical compression specimens were prepared in order to produce residual stresses parallel or perpendicular to the stress direction. For the compression deformation, with the increase in compressive strain, the residual compression stress parallel to the compression direction increased and exhibited a linear relationship with the compressive strain,

σ_{c o m p r e s s i o n r e s}^{p a r a l l e l} = - 1.56 ε_{rectangle compression}

, while the residual compression stress perpendicular to the compression direction were as follows:

σ_{c o m p r e s s i o n r e s}^{p e r p e n d i c u l a r} = - 0.20 ε_{cylinder compression}

. For the tension deformation, with the increase in tensile strains, the residual tension stress parallel to the tension direction increased and exhibited a linear relationship with the tensile strain,

σ_{t e n s i o n r e s}^{p a r a l l e l} = 1.03 ε_{p l a t e t e n s i o n}

, while the residual tension stress perpendicular to the tension direction were as follows:

σ_{t a n s i o n r e s}^{p e r p e n d i c u l a r} = 0.65 ε_{c y l i n d e r t e n s i o n}

. The residual stresses parallel to the stress direction exhibited significant anisotropic characteristics, while the residual stresses perpendicular to the stress direction exhibited significant isotropic characteristics. Based on the above results, the relationship between strains and residual stress were successfully determined, providing valuable data reference for engineering applications. Full article

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19 pages, 6268 KB

Open AccessArticle

Research on Arc Characteristics and Microstructure of 6061 Aluminum Alloy Multi-Pulse Composite Arc Welding

by Guangshun Zhang, Xin Ye, Fang Li, Yonggang Du, Guangcai Chang and Peng Xia

Metals 2025, 15(12), 1294; https://doi.org/10.3390/met15121294 - 25 Nov 2025

Abstract

To mitigate welding defects and optimize the microstructure of aluminum alloys, this study introduces a multi-pulse hybrid arc welding process. A comparative investigation was carried out between this novel process (AC/DC composite 1 kHz pulsed welding) and conventional methods (AC pulsed, AC/DC pulsed) [...] Read more.

To mitigate welding defects and optimize the microstructure of aluminum alloys, this study introduces a multi-pulse hybrid arc welding process. A comparative investigation was carried out between this novel process (AC/DC composite 1 kHz pulsed welding) and conventional methods (AC pulsed, AC/DC pulsed) during wire-fed overlay welding of 6061 aluminum alloy. Analyses were conducted on electrical signals, arc morphology, joint microstructure, and hardness. The results indicate that the AC/DC hybrid 1 kHz pulsed process combines the characteristics of both AC and DC pulsed signals with full-cross-section frequency pulse superposition, thereby optimizing arc welding process control. The frequency pulses induce a magnetoelectric effect, leading to significant arc constriction, which enhances arc energy density and arc pressure. This intensifies the fluid flow in the molten pool and accelerates cooling, thereby suppressing the growth of columnar grains and promoting the formation of fine equiaxed grains and an increased proportion of high-angle grain boundaries. Meanwhile, this process effectively reduces the number, area fraction, and overall porosity, and facilitates the distribution of a large amount of Al–Si eutectic structure along grain boundaries, enhancing the impediment to dislocation motion. The microstructural optimization significantly improves the hardness at the weld center to 73.1 HV, leading to enhanced mechanical properties. Full article

(This article belongs to the Special Issue Processing, Microstructure and Properties of Aluminium Alloys)

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20 pages, 3077 KB

Open AccessArticle

Recovering Battery-Grade LiOH·H₂O from Spent Lithium-Containing Sagger Crucible by Thermal Dehydration and BaSO₄-Driven Double Decomposition

by Seongbong Heo and Jei-Pil Wang

Metals 2025, 15(12), 1293; https://doi.org/10.3390/met15121293 - 25 Nov 2025

Abstract

This study develops and validates an integrated hydrometallurgical process to recover battery-grade lithium hydroxide monohydrate from spent aluminosilicate sagger crucibles. Lithium was first leached as Li₂SO₄ from the crucibles using sulfuric acid; the Li₂SO₄·H₂O [...] Read more.

This study develops and validates an integrated hydrometallurgical process to recover battery-grade lithium hydroxide monohydrate from spent aluminosilicate sagger crucibles. Lithium was first leached as Li₂SO₄ from the crucibles using sulfuric acid; the Li₂SO₄·H₂O present in the leachate was then thermally decomposed at 300 °C to Li₂SO₄ + H₂O, as confirmed by TGA-guided selection and XRD. Subsequent conversion to LiOH proceeded via double decomposition with Ba(OH)₂. Guided by HSC-based equilibrium simulations and an Eh–pH analysis of the Li–Ba–S–H₂O system, reaction conditions were optimized over 60–80 °C and [OH⁻]/[Li⁺] = 1–3. The optimum was identified at 70 °C and [OH⁻]/[Li⁺] = 1, delivering a conversion efficiency of 98.78% and a Li recovery of 98.86%. Two-end-point acid titration indicated a LiOH content of 90.29 wt.% in solution with minimal Li₂CO₃ formation, consistent with processing under vacuum–Ar to suppress CO₂ uptake. The crystallized product obtained by evaporation at ≥90 °C for 24 h was confirmed as LiOH·H₂O (with LiOH) by XRD, while the solid by-product was single-phase BaSO₄. ICP-OES measured a final LiOH·H₂O purity of 99.8%. Full article

(This article belongs to the Special Issue Metal Leaching and Recovery)

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21 pages, 8622 KB

Open AccessArticle

Direct Energy Deposition of Inconel 718 onto Cu Substrate for Bimetallic Structures with Excellent Comprehensive Properties

by Stefano Felicioni, Josip Vincic, Annalisa Zacco, Alberta Aversa, Paolo Fino and Federica Bondioli

Metals 2025, 15(12), 1292; https://doi.org/10.3390/met15121292 - 25 Nov 2025

Abstract

In the aerospace sector, integrating advanced materials with high mechanical capabilities represents the forefront of material science, especially in the field of rocketry. Bimetallic structures are increasingly used in aerospace applications due to their combination of high strength-to-weight ratio, thermal conductivity, and corrosion [...] Read more.

In the aerospace sector, integrating advanced materials with high mechanical capabilities represents the forefront of material science, especially in the field of rocketry. Bimetallic structures are increasingly used in aerospace applications due to their combination of high strength-to-weight ratio, thermal conductivity, and corrosion resistance. Among these, Inconel-copper (In718-Cu) systems are particularly promising, although large differences in thermophysical and mechanical properties between the two materials can induce residual stresses, cracks, and other interfacial defects, requiring careful process control. This study evaluates the fabrication of In718-Cu structures through Direct Energy Deposition (DED), in which In718 was deposited onto a copper substrate using an innovative deposition strategy. Interface quality and microstructure were characterized by SEM/EDS and X-ray diffraction, whereas the mechanical properties were evaluated by nanoindentation, indentation creep, and tensile testing. The results showed that crack-free samples can be achieved, with strong diffusion bonding at the interface and efficient precipitation strengthening on the copper side already in the as-built condition. A uniform distribution of precipitates and consistent penetration depth were also observed, confirming the effectiveness of the deposition strategy for producing reliable In718-Cu components. Full article

(This article belongs to the Section Additive Manufacturing)

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15 pages, 28718 KB

Open AccessArticle

The Impact of Structural Units on Copper Grain Boundary–Dislocation Interactions

by Ke Wang, Yongsheng Xu, Lingchao Xu, Weigang Zhang and Jinquan Xu

Metals 2025, 15(12), 1291; https://doi.org/10.3390/met15121291 - 25 Nov 2025

Abstract

A molecular dynamics approach was employed to investigate the interaction behavior between tilt-[110] copper grain boundaries (GBs) and dislocations, with particular emphasis on elucidating the role of GB structural unit (SU) types in the mechanisms of dislocation absorption and transmission. The results reveal [...] Read more.

A molecular dynamics approach was employed to investigate the interaction behavior between tilt-[110] copper grain boundaries (GBs) and dislocations, with particular emphasis on elucidating the role of GB structural unit (SU) types in the mechanisms of dislocation absorption and transmission. The results reveal that singular GBs composed of continuous and uniform B-type or C-type SUs exhibit a pronounced ability to absorb dislocations, whereby incident dislocations are fully absorbed by the GB and prevented from transmitting across it. In contrast, for discrete GBs containing both C SUs and intrinsic stacking fault facets, the dislocation accommodation capacity of the GB is closely related to the number of C SUs within the discrete region. Multiple continuous C SUs can effectively facilitate dislocation absorption and energy dissipation through a synergistic linkage mechanism. This study underscores the critical role of GB SUs in governing GB–dislocation interactions and provides atomic-scale insights into the microstructural regulation mechanisms of GBs during plastic deformation. Full article

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20 pages, 22468 KB

Open AccessArticle

Effect of CMT Welding Heat Input on Microstructure and Mechanical Properties of Different Groove Angles for Al-6061-T6 Alloy Joint

by Guo Xian, Zhen Gao, Yunfeng Fu, Zhao Ding, Xianshu Que and Jingbang Pan

Metals 2025, 15(12), 1290; https://doi.org/10.3390/met15121290 - 25 Nov 2025

Abstract

Air suspension components are critical elements of automotive chassis and are commonly fabricated by welding 6061-T6 aluminum using 4043 filler wire with the cold metal transfer (CMT) process. Variations in vehicle architecture necessitate different groove angles and matching parameter windows. This study aims [...] Read more.

Air suspension components are critical elements of automotive chassis and are commonly fabricated by welding 6061-T6 aluminum using 4043 filler wire with the cold metal transfer (CMT) process. Variations in vehicle architecture necessitate different groove angles and matching parameter windows. This study aims to elucidate how groove angle and heat input govern weld quality to inform process optimization. Two groove angles (120° and 90°) were investigated under distinct heat-input conditions (denoted 120-H and 90-L). Characterization covered chemical composition, macroscopic morphology, porosity, microstructure, hardness, and mechanical properties. The key novelty lies in elucidating the relationship between liquation cracking and metal flow lines, which jointly govern crack propagation. Integrating evidence from porosity measurements, crack characterization, and numerical simulations indicates that the 120-H parameter set requires further optimization. Overall, the results underscore the pivotal roles of groove angle and heat input in CMT welding of 6061-T6 aluminum and provide a basis for process parameter optimization in air suspension manufacturing. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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21 pages, 8710 KB

Open AccessArticle

The Impact of Ce on the Microstructure and Properties of Weld Metal in Corrosion-Resistant Steel

by Yuwei Wang, Jun Qiu, Qiuming Wang and Qingfeng Wang

Metals 2025, 15(12), 1289; https://doi.org/10.3390/met15121289 - 25 Nov 2025

Abstract

In this study, two types of submerged arc welding (SAW) wires were prepared—one without cerium (Ce) and another containing 0.14 wt.% Ce. Deposition experiments were carried out on corrosion-resistant crude oil storage tank steel plates using a multi-layer, multi-pass welding process. Through a [...] Read more.

In this study, two types of submerged arc welding (SAW) wires were prepared—one without cerium (Ce) and another containing 0.14 wt.% Ce. Deposition experiments were carried out on corrosion-resistant crude oil storage tank steel plates using a multi-layer, multi-pass welding process. Through a combination of microstructural characterization techniques, including optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), along with mechanical property testing, a systematic investigation was conducted to evaluate the influence of Ce on the weld metal microstructure and its impact toughness at −20 °C. The results reveal that Ce introduced via the welding wire into the weld seam refines and disperses inclusions, leading to the formation of composite inclusions primarily composed of Ce₂O₃, Ce₂O₂S, and CeS. These Ce-enriched inclusions serve as heterogeneous nucleation sites, increasing the area fraction of acicular ferrite (AF) within the weld columnar grain region from 52% to 83%, and within the heat-affected zone from 20% to 37%. Correspondingly, the proportions of blocky and polygonal ferrite decrease, while the size of martensite/austenite (M/A) constituents is reduced. The addition of Ce thus diminishes the size of hard phase inclusions and M/A constituents in the weld metal, enhancing the critical fracture stress and increasing the energy required for crack initiation. Meanwhile, the higher proportion of AF elevates the density of high-angle grain boundaries, thereby improving crack propagation resistance. These combined effects raise the −20 °C impact energy of the weld metal from 117 J to 197 J. Full article

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23 pages, 4527 KB

Open AccessArticle

Aluminum Surface Corrosion Behavior and Microstructural Evolution in Dissimilar AA6016-T4 Aluminum to DP600 Steel via Refill Friction Stir Spot Welding

by Willian S. de Carvalho, Guilherme dos Santos Vacchi, Uceu F. H. Suhuddin, Rodrigo da Silva, Danielle C. C. Magalhães and Carlos A. D. Rovere

Metals 2025, 15(12), 1288; https://doi.org/10.3390/met15121288 - 25 Nov 2025

Abstract

Refill friction stir spot welding (refill FSSW) is a solid-state joining technique that enables dissimilar welding between aluminum and steel alloys with minimal intermetallic compound (IMC) formation. Previous studies have focused on the interfacial mechanical performance of such joints, limited attention has been [...] Read more.

Refill friction stir spot welding (refill FSSW) is a solid-state joining technique that enables dissimilar welding between aluminum and steel alloys with minimal intermetallic compound (IMC) formation. Previous studies have focused on the interfacial mechanical performance of such joints, limited attention has been given to the localized corrosion behavior of the aluminum surface after welding, particularly in relation to microstructural evolution. This study investigates the effect of refill FSSW on the localized corrosion resistance of the aluminum surface in dissimilar joints with DP600 steel, since the Al side is typically the exposed surface in automotive service conditions. Emphasis is placed on the correlation between microstructural changes induced by the welding thermal cycle, such as grain refinement and precipitate coarsening, and localized corrosion behavior. The welded samples were characterized by optical and scanning electron microscopy, Vickers hardness measurements and potentiodynamic polarization techniques. Corrosion tests revealed a slight reduction in corrosion resistance in the stir zone compared to the base metal, mainly attributed to Mg₂Si coarsening. Pit initiation sites were associated with Al(Fe, Mn)Si and Mg₂Si precipitates. These findings offer new insights into the corrosion mechanisms acting on the aluminum surface of refill FSSW joints, supporting the development of more corrosion-resistant dissimilar structures. Full article

(This article belongs to the Special Issue Corrosion and Oxidation of Metals: Mechanisms, Kinetics, and Protection)

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12 pages, 2809 KB

Open AccessArticle

Effect of Precipitation Behavior on Mechanical Properties of 6082 Aluminum Alloy

by Zhi Yang, Enjun Piao, Wenhao Li, Weikun Wang, Chengxiang Feng and Mei Zhang

Metals 2025, 15(12), 1287; https://doi.org/10.3390/met15121287 - 24 Nov 2025

Abstract

The mechanical properties of 6082 aluminum alloy under different aging conditions were investigated in this study. Precipitation behavior leading to an increase in strength was confirmed by the observation of the microstructure using TEM. The β″ precipitate, which is coherent with the [...] Read more.

The mechanical properties of 6082 aluminum alloy under different aging conditions were investigated in this study. Precipitation behavior leading to an increase in strength was confirmed by the observation of the microstructure using TEM. The β″ precipitate, which is coherent with the Al matrix, contributes to the high tensile strength and hardness of the alloy. The transformation of the β″ phase into the β′ phase observed under TEM was proven to be responsible for the decrease in strength and hardness. The hardness curves indirectly reveal that a higher aging temperature could accelerate the transformation of β″ into β′. The coherent strain field introduced by the β″ precipitate was clearly observed and is discussed. In addition, an ideal artificial aging window is proposed, with a combined performance of a TS of 360 MPa, hardness of 105 HB and elongation over 10%. Full article

(This article belongs to the Special Issue Light Alloy and Its Application (3rd Edition))

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28 pages, 5475 KB

Open AccessArticle

A Deep Learning-Based CNN-LSTM Framework for Constitutive Parameter Inversion in Alloy Gradient-Grained Materials

by Hao Jiang, Mengyi Chen, Jianxin Hou, Zhenfei Guo, Zixuan Hu, Zongzhe Man, Xiao Wei and Da Liu

Metals 2025, 15(12), 1286; https://doi.org/10.3390/met15121286 - 24 Nov 2025

Abstract

Alloy gradient-grained structures (represented by copper as a typical single-phase face-centered cubic (FCC) metal), known for their superior mechanical properties such as enhanced strength, ductility, and fatigue resistance, have become increasingly important in aerospace and automotive industries. These alloys are often fabricated using [...] Read more.

Alloy gradient-grained structures (represented by copper as a typical single-phase face-centered cubic (FCC) metal), known for their superior mechanical properties such as enhanced strength, ductility, and fatigue resistance, have become increasingly important in aerospace and automotive industries. These alloys are often fabricated using advanced processing techniques such as laser welding, electron beam melting, and controlled cooling, which induce spatial gradients in grain size and optimize material properties by overcoming the traditional strength–ductility trade-off. In this study, a deep learning-based inversion framework combining Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) networks is proposed to efficiently predict key constitutive parameters, such as the initial critical resolved shear stress and hardening modulus, in alloy gradient-grained structures. The model integrates spatial features extracted from strain-field sequences and grain morphology images with temporal features from loading sequences, providing a comprehensive solution for path-dependent mechanical behavior modeling. Trained on high-fidelity Crystal Plasticity Finite Element Method (CPFEM) simulation data, the proposed framework demonstrates high prediction accuracy for the constitutive parameters. The model achieves an error margin of less than 5%. This work highlights the potential of deep learning techniques for the efficient and physically consistent identification of constitutive parameters in alloy gradient-grained structures, offering valuable insights for alloy design and optimization. Full article

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

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9 pages, 482 KB

Open AccessEditorial

Electric Arc Furnace Steelmaking

by Ville-Valtteri Visuri and Thomas Echterhof

Metals 2025, 15(12), 1285; https://doi.org/10.3390/met15121285 - 24 Nov 2025

Abstract

Research and development regarding the electric arc furnace (EAF) started as early as the late 19th century [...] Full article

(This article belongs to the Special Issue Electric Arc Furnace Steelmaking)

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17 pages, 18661 KB

Open AccessArticle

Effect of Yttrium Treatment on Inclusions and Microstructure of High-Strength Peritectic Steel

by Min Liu, Chaobin Lai, Xiaogang Yang, Kexin Li, Zhi Zhang, Yasheng Chen and Weirong Li

Metals 2025, 15(12), 1284; https://doi.org/10.3390/met15121284 - 24 Nov 2025

Abstract

The morphology and types of inclusion, as well as the microstructure, fundamentally affect the properties of high-strength peritectic steel. Rare earth elements not only modify inclusions but also act on the transformation of the microstructure. In this paper, the evolution mechanism of yttrium [...] Read more.

The morphology and types of inclusion, as well as the microstructure, fundamentally affect the properties of high-strength peritectic steel. Rare earth elements not only modify inclusions but also act on the transformation of the microstructure. In this paper, the evolution mechanism of yttrium for the inclusions and microstructure in high-strength peritectic steel was investigated through experimental testing and thermodynamic analysis. The results show that yttrium treatment can modify the main large-sized irregular inclusions into spherical or near-spherical rare earth inclusions, accompanied by a reduction in the number density, area fraction, average diameter, and aspect ratio of inclusions. The evolution route for the inclusions follows Al₂O₃ + MnS + Al₂O₃-MnS→Y₂O₃ + Y-O-S + Y-S + Y-O-S-MnS with yttrium addition. The microstructural characteristics of yttrium-free steel show significant differences from those of yttrium-containing steel. Compared to yttrium-free steel, the yttrium-0.015 wt.% steel shows a refined austenite structure with more uniform size distribution and the absence of grain boundary ferrite films. The Y₂O₃ and Y₂O₂S inclusions mainly formed in liquid steel were found along the austenite grain boundary to prevent the grain growth and the formation of ferrite films. Additionally, after adding rare earth yttrium, the fraction of high-angle grain boundaries (HAGBs) increases, together with a decrease in the fraction of low-angle grain boundaries (LAGBs) in steel. The research results can provide a theoretical basis for the application of adding rare earth yttrium to high-strength peritectic steel. Full article

(This article belongs to the Special Issue State-of-the-Art of Inclusion/Precipitate Engineering in Steels)

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21 pages, 28528 KB

Open AccessArticle

Effect of B₄C Amount on Microstructural and Mechanical Properties of Cu/h-BN/B₄C Metal Matrix Composites Fabricated via Spark Plasma Sintering

by Müslim Çelebi, Abdullah Hasan Karabacak, Serdar Özkaya, Ertuğrul Çelik, Dursun Murat Sekban, Aykut Çanakçı and Harun Yanar

Metals 2025, 15(12), 1283; https://doi.org/10.3390/met15121283 - 24 Nov 2025

Abstract

Copper (Cu) is widely used in electrical, electronic, and tribological systems owing to its excellent electrical and thermal conductivity. However, its relatively low hardness and poor wear resistance limit its use in demanding engineering applications. In this study, Cu-based hybrid metal matrix composites [...] Read more.

Copper (Cu) is widely used in electrical, electronic, and tribological systems owing to its excellent electrical and thermal conductivity. However, its relatively low hardness and poor wear resistance limit its use in demanding engineering applications. In this study, Cu-based hybrid metal matrix composites (MMCs) reinforced with hexagonal boron nitride (h-BN) and boron carbide (B₄C) were fabricated via spark plasma sintering (SPS) to improve their mechanical and tribological performance. The h-BN content was fixed at 1 wt.% to ensure solid lubrication, while the B₄C content was varied (0.25, 0.5, 0.75, and 1 wt.%) to examine its influence on the microstructural, mechanical, electrical, and wear properties of the composites. Microstructural analyses confirmed a homogeneous distribution of h-BN and B₄C particles in the Cu matrix at low and moderate reinforcement levels, whereas excessive B₄C resulted in partial agglomeration and reduced densification. All composites achieved relative densities above 95%, demonstrating the high densification efficiency of the SPS process. Hardness increased markedly with B₄C addition due to dispersion strengthening and grain refinement, while electrical conductivity decreased slightly because of the insulating nature of the reinforcements. Tribological tests showed that the composite containing 0.75 wt.% B₄C exhibited the best performance, with the lowest wear rate and stable friction behavior. Overall, the results indicate that co-reinforcing Cu with h-BN and B₄C through SPS is a promising strategy for developing multifunctional materials suitable for electrical contact and sliding applications. Full article

(This article belongs to the Special Issue Microstructure and Characterization of Metal Matrix Composites)

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12 pages, 3534 KB

Open AccessArticle

Characterizing the Vertical Heterogeneity in Ultra-High Bed Sintering: From Mixture Properties to Stratified Phase Composition and Sinter Strength

by Yuchao Zhao, Hongzhuang Dong, Peng Li, Wenzheng Jiang, Qiang Zhong and Mingjun Rao

Metals 2025, 15(12), 1282; https://doi.org/10.3390/met15121282 - 24 Nov 2025

Abstract

With the growing demand for efficiency, low consumption, and environmental sustainability in the iron and steel industry, ultra-high bed sintering technology emerges as a research hotspot due to its advantages in significantly reducing fuel consumption and pollutant emissions. However, studies on the influence [...] Read more.

With the growing demand for efficiency, low consumption, and environmental sustainability in the iron and steel industry, ultra-high bed sintering technology emerges as a research hotspot due to its advantages in significantly reducing fuel consumption and pollutant emissions. However, studies on the influence of fuel on mineralization behavior under ultra-high bed sintering conditions remained limited. This study systematically analyzes the effects of particle size, chemical composition, alkalinity, and MgO/Al₂O₃ ratio on mineralization behavior using a 500 m² sintering machine, while evaluating the tumbler strength and phase composition of the sinter. The results reveal that particle size segregation in the mixture was primarily caused by the upper layer, with the lower layer having a lesser impact on overall segregation. Chemical composition also exhibited significant segregation, particularly in TFe and fuel distribution along the bed height. Fuel segregation was pronounced vertically but negligible horizontally. Under the current fuel distribution, uneven heat distribution was observed, with excessive heat in the lower layer leading to increased liquid phase formation, reduced porosity, and improved sinter strength downward along the bed. Additionally, the phase composition varied markedly across layers: hematite content gradually increases from top to bottom, calcium ferrite (SFCA) content peaks in the middle layers, and magnetite decreases with bed depth. Full article

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35 pages, 6084 KB

Open AccessReview

Advances in the Design and Development of Lightweight Metal Matrix Composites: Processing, Properties, and Applications

by Sónia Simões

Metals 2025, 15(12), 1281; https://doi.org/10.3390/met15121281 - 23 Nov 2025

Abstract

Lightweight metal matrix composites (MMCs) continue to attract significant interest due to their potential to deliver high mechanical performance at reduced weight, meeting the increasing demands of aerospace, automotive and advanced manufacturing sectors. Among these systems, aluminum-, magnesium- and titanium-based MMCs stand out [...] Read more.

Lightweight metal matrix composites (MMCs) continue to attract significant interest due to their potential to deliver high mechanical performance at reduced weight, meeting the increasing demands of aerospace, automotive and advanced manufacturing sectors. Among these systems, aluminum-, magnesium- and titanium-based MMCs stand out for their favorable strength-to-weight ratios, corrosion resistance and versatility in processing. Although numerous studies have explored individual MMC families, the literature still lacks comparative reviews that integrate quantitative mechanical data with a broad evaluation of processing, microstructural control and application-driven performance. This review addresses these gaps by providing a comprehensive and data-driven assessment of lightweight MMCs. Recent advances in reinforcement strategies, hybrid architectures and processing routes—including friction stir processing, powder metallurgy and semi-solid techniques—are systematically examined. Emerging developments in syntactic metal foams and functionally gradient MMCs are analyzed in detail, along with practical considerations such as machinability, corrosion resistance, and high-temperature performance, integrated with AI/machine learning for predictive optimization. Overall, this work provides an integrated and critical perspective on the capabilities, limitations, and design trade-offs of lightweight MMCs, positioning them as sustainable and high-performance alternatives for extreme environments. By combining qualitative insights with quantitative meta-analyses and new experimental contributions, it offers a valuable reference for researchers and engineers seeking to optimize material selection and tailor the performance of MMCs for next-generation lightweight structures, surpassing previous reviews through holistic and innovation-driven insights. Full article

(This article belongs to the Special Issue Design and Development of Metal Matrix Composites (2nd Edition))

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12 pages, 15632 KB

Open AccessArticle

Effects of Sn Microalloying on the Microstructure and Properties of Al-Mg-Mn-Si Alloy

by Yue Chai, Shengping Wen, Xiaolan Wu, Kunyuan Gao, Wu Wei, Li Rong, Hui Huang and Zuoren Nie

Metals 2025, 15(12), 1280; https://doi.org/10.3390/met15121280 - 23 Nov 2025

Abstract

Microalloying with Sn is a pivotal strategy for enhancing the strength and thermal stability of Al-Mg-Mn-Si alloys by enabling microstructural optimization. This study systematically investigates the influence of 0.1 wt.% Sn on an Al-4.0Mg-1.0Mn-0.2Si alloy through a comparative analysis with a Sn-free counterpart. [...] Read more.

Microalloying with Sn is a pivotal strategy for enhancing the strength and thermal stability of Al-Mg-Mn-Si alloys by enabling microstructural optimization. This study systematically investigates the influence of 0.1 wt.% Sn on an Al-4.0Mg-1.0Mn-0.2Si alloy through a comparative analysis with a Sn-free counterpart. The experimental methodology included isochronal aging and isothermal aging, room-temperature tensile testing, electrical conductivity measurements, and detailed microstructural characterization via transmission electron microscopy (TEM) and optical microscopy (OM). The results unequivocally demonstrate that Sn addition significantly enhances the alloy’s microhardness, tensile properties, and heat resistance. Specifically, the Sn-containing alloy (1#) achieved a peak hardness of 98.4 HV during a three-stage aging process, which is 14.1% higher than the 84.5 HV of the Sn-free alloy (2#). In the as-rolled state, alloy 1# exhibited ultimate tensile strength (UTS) and yield strength (YS) of 397 MPa and 344 MPa, representing increases of 20.2% and 15.7%, respectively, without compromising ductility. Microstructural analysis revealed that the enhancement is attributed to the Sn-promoted formation of finely dispersed α-AlMnSi precipitates. These precipitates effectively pin dislocations, strengthening the alloy, and simultaneously suppress recrystallization nucleation and growth, thereby elevating the recrystallization temperature and improving overall heat resistance. This work confirms that microalloying with Sn is an effective strategy for developing high-performance Al-Mg-Mn-Si alloys with superior mechanical properties and thermal stability. Full article

(This article belongs to the Special Issue Design, Processing and Characterization of Advanced Metallic Materials)

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18 pages, 8528 KB

Open AccessArticle

Effect of PVD Nitride Coating Deposition on the High-Temperature Pin–Disc Friction Properties Between WC/Co Carbide and Ti₂AlNb Alloy

by Liangliang Li, Xin Pan, Jianwei Mu, Jinfu Zhao, Wenqian Li, Zhifeng Liu and Jiru Wang

Metals 2025, 15(12), 1279; https://doi.org/10.3390/met15121279 - 22 Nov 2025

Abstract

Suitable nitride coating deposition could improve the wear resistance of WC/Co carbide tools when cutting Ti₂AlNb typical difficult-to-machine alloy. However, there is no clear conclusion on which nitride series coating is suitable for improving the friction characteristics between WC/Co carbide and [...] Read more.

Suitable nitride coating deposition could improve the wear resistance of WC/Co carbide tools when cutting Ti₂AlNb typical difficult-to-machine alloy. However, there is no clear conclusion on which nitride series coating is suitable for improving the friction characteristics between WC/Co carbide and Ti₂AlNb alloy. In this research, the CrAlN, CrAlN/(CrAlB)N/CrAlN, and TiAlN/ZrN coatings were deposited on WC/Co carbide with the only variable of coating type, which were utilized to conduct the high-temperature pin disc experiments with Ti₂AlNb alloy at 600 °C, respectively. The high-temperature friction characteristics were analyzed by the friction coefficient with time, the alloy wear rate, the surface morphology, and element distribution after wear. The results showed that the three types of coating all improved the high temperature friction and wear characteristics of WC/Co carbide. The Ti₂AlNb alloy also exhibited good surface morphology after wear with TiAlN/ZrN-coated carbide. It is speculated that TiAlN/ZrN coating was the suitable coating deposition on WC/Co carbide tools to improve cutting performance of Ti₂AlNb alloy. Full article

(This article belongs to the Special Issue Advances in Metal Cutting and Machining Processes)

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19 pages, 9799 KB

Open AccessArticle

Influence of Experimental Parameters on the Determination of Copper Dissolution in Corrosion Processes Using Gold Microelectrodes

by Javier Izquierdo, Adrián Méndez-Guerra, Raquel Rodríguez-Raposo and Ricardo M. Souto

Metals 2025, 15(12), 1278; https://doi.org/10.3390/met15121278 - 21 Nov 2025

Abstract

In situ electrochemical imaging of corrosion reactions is performed directly by scanning electrochemical microscopy (SECM) in generation-collection mode. This method involves redox conversion of soluble metal ions at the amperometric tip for quantification. Unfortunately, many metals, such as copper, do not undergo redox [...] Read more.

In situ electrochemical imaging of corrosion reactions is performed directly by scanning electrochemical microscopy (SECM) in generation-collection mode. This method involves redox conversion of soluble metal ions at the amperometric tip for quantification. Unfortunately, many metals, such as copper, do not undergo redox conversion to a soluble state and are deposited on the SECM tip. They therefore modify the electrochemical behavior of the tip and require consideration of metal stripping processes. In addition, the miniaturization of the electrode to operate as a microelectrode tip can be accompanied by variations in the potential range and distribution of the redox processes related to copper deposition and redissolution, thus complicating the adequate choice of electrochemical conditions applied to the tip for the unambiguous operation of SECM in the generation-collection mode to study the corrosion of copper-based materials. Therefore, in this work, a study of different parameters for the amperometric determination of Cu²⁺ ions was conducted using gold disk electrodes of 500 and 10 μm diameter to represent the typical sizes employed in conventional and scanning microelectrochemical measurements. The investigation was performed to analyze the effect of underpotential deposition (UPD) and overpotential deposition (ODP) on the voltammetric characteristics of copper deposition and redissolution resulting from variations in the solution composition, i.e., the nature of anions and pH. The dependence and limits of the reduction and reoxidation waves were analyzed as functions of the Cu²⁺ ion concentration, the ionic strength of the electrolyte, and the pH of the solution. The results were interpreted as UPD and OPD. Under conditions close to the marine environment, the release of Cu²⁺ ions can be unambiguously detected and quantified from potentials above −0.1 V vs. Ag/AgCl. Full article

(This article belongs to the Section Corrosion and Protection)

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