Metals

21 pages, 3919 KB

Open AccessArticle

Particle-Level Engineering of Cu–Al–Ni Shape Memory Alloy Powders via Cryogenic Milling and Electroless Ni Coating

by Onur Güler, Mücahit Kocaman, Yaren Adabaş, Serdar Özkaya, Temel Varol, Serhatcan Berk Akçay and Hamdullah Çuvalcı

Metals 2026, 16(5), 529; https://doi.org/10.3390/met16050529 (registering DOI) - 13 May 2026

Abstract

At particle-level engineering, this study mainly focused on the issues of microstructural heterogeneity and the high oxidation susceptibility of Cu-Al-Ni shape memory alloys (SMAs) suitable for high-temperature actuation. Initial powders of Cu (82–83 wt.%) and Al (14–15 wt.%) were first milled mechanically and [...] Read more.

At particle-level engineering, this study mainly focused on the issues of microstructural heterogeneity and the high oxidation susceptibility of Cu-Al-Ni shape memory alloys (SMAs) suitable for high-temperature actuation. Initial powders of Cu (82–83 wt.%) and Al (14–15 wt.%) were first milled mechanically and the Cu-Al particles were modified using an electroless Nickel (Ni) coating process to achieve a controlled Ni enrichment of 4–5 wt.%. The SEM-EDS, XRD, and TGA findings reveal that the cryogenic milling effectively reforms dendritic Cu and spherical Al particles into a refined composite structure. This process resulted in particle size reduction from 40–70 µm to 5–20 µm, and apparent density values increased from 3.45 g·cm⁻³ to 4.10 g·cm⁻³. Microstructural investigations showed that the continuous Ni layer, without generating unwanted intermetallic phases, was obtained with the help of an electroless coating process. In addition, it was confirmed that the crystallite size decreased from 52.10 nm to 41.71 nm. Additionally, the oxidation of nickel-coated and cryogenically milled powders occurred at temperatures above 350 °C owing to the formation of a protective surface layer. In other words, these powders exhibited higher thermal stability. Consequently, this dual processing procedure represents a very useful method for changing particle shape and interfacial composition. These combined methods can help to create a powder structure with a composition optimum for the making of high-performance Cu-Al-Ni SMAs. Full article

(This article belongs to the Section Powder Metallurgy)

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16 pages, 20407 KB

Open AccessArticle

Cu-Interlayer-Enhanced Flexible Porous Ni-B on Waste Polyester Fabric Electrode: Robust Electrocatalytic Performance Under Repeated Bending and Twisting

by Guangya Hou, Siqi Chen, Jianli Zhang, Qiang Chen and Yiping Tang

Metals 2026, 16(5), 528; https://doi.org/10.3390/met16050528 (registering DOI) - 13 May 2026

Abstract

The functional valorization of waste fabrics, particularly their conversion into flexible low-cost, high-performance electrodes, holds significant promise for resource sustainability and the development of advanced energy technologies. Here, a NiB/Cu/polyester fabric (PF) composite electrode was fabricated via two-step electroless plating on waste PF [...] Read more.

The functional valorization of waste fabrics, particularly their conversion into flexible low-cost, high-performance electrodes, holds significant promise for resource sustainability and the development of advanced energy technologies. Here, a NiB/Cu/polyester fabric (PF) composite electrode was fabricated via two-step electroless plating on waste PF and was demonstrated as a bifunctional electrocatalyst for methanol oxidation (MOR) and urea oxidation (UOR). The morphology, crystal structure, surface chemical state, and wettability of the electrodes were characterized using SEM, TEM, XRD, XPS, and contact angle measurements. The Cu interlayer critically enhanced interfacial wettability, intrinsic catalytic activity and stability. At 0.8 V, the NiB/Cu/PF electrode delivered average current densities of 312 mA·cm⁻² for MOR and 288 mA·cm⁻² for UOR, outperforming NiB/PF by 27.9% and 9.1%, respectively. After 2000 accelerated degradation cycles with electrolyte renewal, MOR and UOR activities were retained at 91.6% and 105.0%, respectively. Remarkably, the Cu interlayer conferred exceptional mechanical–electrochemical robustness: following 100 sequential bending and twisting deformations, current density retention ranged from 84.6% to 96.7% across multiple test configurations. The Cu interlayer acted as a flexible stress buffer during mechanical deformation, effectively improving the adhesion between the coating and the substrate. Full article

(This article belongs to the Special Issue Advances in Metallic Battery Materials)

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28 pages, 8851 KB

Open AccessArticle

Energy Absorption Behavior of Thickness-Dependent Functionally Graded Inconel 718 Auxetic Structures Produced by Laser Powder Bed Fusion

by Orhan Gülcan, Burak Özcan, Umut Çalışkan and Güher Pelin Toker

Metals 2026, 16(5), 527; https://doi.org/10.3390/met16050527 (registering DOI) - 13 May 2026

Abstract

Auxetic metamaterials have outstanding negative Poisson’s ratio characteristics which can be beneficial in different industrial applications. The main aim of the present study is to investigate the effect of thickness-dependent functional grading (FG) on the mechanical response of two widely known auxetic geometries, [...] Read more.

Auxetic metamaterials have outstanding negative Poisson’s ratio characteristics which can be beneficial in different industrial applications. The main aim of the present study is to investigate the effect of thickness-dependent functional grading (FG) on the mechanical response of two widely known auxetic geometries, namely re-entrant and anti-tetrachiral. Three different thickness-dependent FG versions of these geometries were compared against their counterparts without FG by using numerical simulations. The effect of thickness-dependent FG was also compared against non-auxetic geometry (honeycomb) to understand the effect of auxeticity. The validation experiments were performed by the production of sample geometries by laser powder bed fusion technology from Inconel 718 material and quasi-static compression testing. The results revealed that the grading direction is a key variable in design that significantly influences the deformation stability and stress distribution, and it was shown that thickness-dependent FG is a promising way to decrease the weight of auxetic structures without sacrificing SEA considerably. Full article

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19 pages, 14061 KB

Open AccessArticle

A Study on the TiC Precipitation Behavior of High-Strength Weathering Steel for Photovoltaic Supports and Its Impact on Performance

by Zhiwei Liu, Xiuhua Gao, Changyou Zhu, Shuo Gao, Zhiyong Chang, Linxiu Du and Hongyan Wu

Metals 2026, 16(5), 526; https://doi.org/10.3390/met16050526 (registering DOI) - 12 May 2026

Abstract

To address the strength fluctuation observed in Ti microalloyed steel, the effects of final rolling temperature, coiling temperature, and Ti content on the microstructure, secondary phase precipitation behavior, and grain size were investigated through simulation experiments. Various characterization techniques were employed to elucidate [...] Read more.

To address the strength fluctuation observed in Ti microalloyed steel, the effects of final rolling temperature, coiling temperature, and Ti content on the microstructure, secondary phase precipitation behavior, and grain size were investigated through simulation experiments. Various characterization techniques were employed to elucidate the underlying causes of the strength variation, and key control strategies were proposed. The results indicate that the strength fluctuation is primarily influenced by the presence of nano-sized TiC precipitates. The precipitation behavior of TiC can be effectively controlled by adjusting the content of non-metallic elements as well as the final rolling and coiling temperatures. Higher final rolling temperatures combined with appropriate coiling temperatures promote increased TiC precipitation; however, excessively high temperatures may result in grain coarsening and inhomogeneous precipitate distribution. The optimal processing parameters were determined to be a final rolling temperature of 860 °C and a coiling temperature of 600 °C. Full article

16 pages, 3803 KB

Open AccessArticle

Effect of Heat Treatment on Mechanical Properties and Fatigue Behaviors of a Selective Laser Melting Nickel-Based Superalloy

by Zongxian Song, Zhiwei Gao, Lina Zhu, Hao Jin, Jian Zhao and Caiyan Deng

Metals 2026, 16(5), 525; https://doi.org/10.3390/met16050525 (registering DOI) - 12 May 2026

Abstract

This investigation elucidates the elevated-temperature (650 °C) monotonic mechanical response and very-high-cycle fatigue (VHCF) characteristics of Inconel 718 superalloys additively manufactured via selective laser melting (SLM), with a comparative assessment between the as-built and post-process heat-treated states. The results indicate that mechanical performance [...] Read more.

This investigation elucidates the elevated-temperature (650 °C) monotonic mechanical response and very-high-cycle fatigue (VHCF) characteristics of Inconel 718 superalloys additively manufactured via selective laser melting (SLM), with a comparative assessment between the as-built and post-process heat-treated states. The results indicate that mechanical performance improves after heat treatment, primarily due to the formation of γ′ and γ″ precipitates, which interact with dislocations to strengthen the alloy. Relative to the as-built specimens, the fatigue strength of the specimen after heat treatment has increased by more than twice. For the as-built specimen, fatigue cracks nucleate at the specimen surface. However, in the high stress range, crack initiation in the heat-treated specimens consistently occurs at the free surface, whereas under low stress conditions, the crack initiation site transitions to the subsurface region encompassing internal defects. Post heat treatment, the fatigue crack trajectory adopts a markedly ductile and tortuous morphology, engendered by the concerted influence of grain-boundary (Laves/δ) precipitates that enforce repeated crack deflection, matrix-strengthening phases that homogenize plastic strain and the attendant reduction in local strain accumulation under the effect of cyclic load. Full article

(This article belongs to the Special Issue Laser-Assisted Processing of Metals)

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29 pages, 21563 KB

Open AccessArticle

Effect of Lower Sheet Hole on Joint Strength in Pre-Holed Hot Clinching of Al-Si-Coated 22MnB5 Steel Sheets

by Jarupong Charoensuk, Takuma Iwai, Taiga Hongo, Tomoyoshi Maeno and Surasak Suranuntchai

Metals 2026, 16(5), 524; https://doi.org/10.3390/met16050524 (registering DOI) - 12 May 2026

Abstract

This study introduced a pre-holed hot clinching process for hot stamping patchwork blanks, using the lower sheet pre-hole as a forming cavity to facilitate material flow and minimize deformation resistance. Evaluated through mechanical testing and finite element analysis (FEA), the process induced ausforming [...] Read more.

This study introduced a pre-holed hot clinching process for hot stamping patchwork blanks, using the lower sheet pre-hole as a forming cavity to facilitate material flow and minimize deformation resistance. Evaluated through mechanical testing and finite element analysis (FEA), the process induced ausforming and maintained material homogeneity (~500 HV), and an optimal interfacial gap up to 10 mm effectively prevented localized soft-zone fractures. Results identified interfacial slip, driven by a critical differential surface expansion rate, as the primary mechanism for geometric anchoring and solid-state bonding. Experimental validation established optimal joining at a 60% penetration ratio and a 0.9 hole-to-punch diameter ratio. While prior studies on forge joining reported average maximum strengths limited to 1.2 kN due to the absence of a mechanical hook, the optimized pre-holed joints in this work achieved a superior tensile shear capacity of 11.5 kN. Furthermore, the cross-tension load reached 0.77 kN, representing a nearly tenfold increase compared to the 0.08 kN observed in the no-hole with offset condition. These results demonstrate that the pre-holed hot clinching method significantly enhances joint integrity while reducing the forming load from 70 kN without a pre-hole to 12 kN with a 10 mm pre-hole. Full article

(This article belongs to the Special Issue Advances in Welding Processes of Metallic Materials—2nd Edition)

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22 pages, 12269 KB

Open AccessArticle

Effect of Rare Earth Ce on the Evolution Behavior and Modification Mechanism of Inclusions in GCr15 Bearing Steel

by Haolong Cheng, Jun Peng, Yingtie Xu, Jing Li, Fei Huang and Lixia Liu

Metals 2026, 16(5), 523; https://doi.org/10.3390/met16050523 (registering DOI) - 12 May 2026

Abstract

The precise control of non-metallic inclusions is crucial for high-end GCr15 bearing steel. This study investigates cerium (Ce)-induced inclusion modification mechanisms. Smelting experiments with 0 to 0.017 wt% Ce additions, high-temperature in situ observations, thermodynamics, and first-principles calculations were used to evaluate inclusion [...] Read more.

The precise control of non-metallic inclusions is crucial for high-end GCr15 bearing steel. This study investigates cerium (Ce)-induced inclusion modification mechanisms. Smelting experiments with 0 to 0.017 wt% Ce additions, high-temperature in situ observations, thermodynamics, and first-principles calculations were used to evaluate inclusion evolution and aggregation behaviors. Without Ce, coarse Al₂O₃ and MnS phases dominate. As Ce increases to 0.017 wt%, inclusions evolve sequentially into CeAlO₃, Ce₂O₃, and ultimately, finely dispersed Ce₂O₂S and CeS. Thermodynamics indicate CeAlO₃ nucleates preferentially, acting as heterogeneous nucleation sites for MnS. In situ observations and interparticle force calculations reveal an aggregation tendency order of Al₂O₃ > CeAlO₃ > Ce₂O₃ > Ce₂O₂S. Furthermore, first-principles simulations confirm that Ce₂O₂S possesses the lowest formation energy and optimal stability, wherein Ce effectively modifies coarse inclusions into fine, well-dispersed spherical particles. Coupled with its intrinsic deoxidizing and desulfurizing effects, Ce addition synergistically modifies coarse inclusions into fine, well-dispersed spherical particles. These findings elucidate the rare-earth modification micro-mechanisms, providing a theoretical foundation for manufacturing high-quality bearing steel. Full article

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17 pages, 7136 KB

Open AccessArticle

Effect of Mechanical Activation on Spinel Transformation and Chromium Reduction from Ferroalloy Waste Under SHS Conditions

by Sanat Tolendiuly, Nursultan Rakhym, Kaster Kamunur, Sharafkhan Assylkhan, Lyazzat Mussapyrova and Sandugash Tanirbergenova

Metals 2026, 16(5), 522; https://doi.org/10.3390/met16050522 (registering DOI) - 12 May 2026

Abstract

Chromium-containing ferroalloy wastes represent an important secondary resource; however, chromium is mainly bound in thermodynamically stable spinel phases, which complicates its reduction. Unlike previous studies focusing on pure oxide systems, this work demonstrates the enhanced destabilization and subsequent reduction of MgCr₂O [...] Read more.

Chromium-containing ferroalloy wastes represent an important secondary resource; however, chromium is mainly bound in thermodynamically stable spinel phases, which complicates its reduction. Unlike previous studies focusing on pure oxide systems, this work demonstrates the enhanced destabilization and subsequent reduction of MgCr₂O₄ spinel in real ferroalloy wastes under SHS conditions, revealing a non-monotonic relationship between activation time and reduction efficiency. A critical activation threshold (~30 min) was identified, beyond which particle agglomeration suppresses reaction kinetics. Powder mixtures based on HShP and KEK wastes with Al–C–Si reducing agents were mechanically activated for 10–120 min and subsequently subjected to SHS at 950 °C. The combustion parameters, phase composition (XRD), microstructure (SEM), and elemental composition (EDS) were analyzed. The results show a pronounced non-monotonic dependence of combustion temperature and front velocity on activation time, with maximum values at ~30 min (1920 °C and 1.10 mm/s for HShP; 1765 °C and 0.98 mm/s for KEK). XRD analysis indicates that MgCr₂O₄ was not detected within the XRD detection limits and that the highest relative amount of metallic chromium phase (~8% for HShP and ~6.8% for KEK) was observed at the same activation time. SEM observations reveal the formation of a more dispersed and porous structure, while EDS indicates an increase in chromium content up to ~15 wt.% in local regions. At longer activation times, overgrinding and agglomeration reduce process efficiency. Mechanical activation enhances chromium reduction through improved mass transfer, with an optimal activation time of ~30 min. The chromium reduction efficiency was evaluated using a semi-quantitative approach based on XRD phase analysis and supported by EDS data, allowing comparative assessment of reduction efficiency rather than absolute extraction values. These results highlight the existence of a critical mechanochemical activation threshold governing the balance between enhanced reactivity and agglomeration effects. Full article

(This article belongs to the Section Powder Metallurgy)

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15 pages, 12802 KB

Open AccessArticle

Impact Toughness Anisotropy of Hot-Rolled Ti-6Al-4V-0.5Ni-0.5Nb Alloy Sheet: Roles of Texture and Microstructure

by Bo Fu, Jialiang Sun, Boya Wang, Yang Yu, Wenjun Ye, Yumeng Luo, Yanfeng Li and Songxiao Hui

Metals 2026, 16(5), 521; https://doi.org/10.3390/met16050521 (registering DOI) - 11 May 2026

Abstract

The α-phase microstructure and texture of a Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy hot-rolled plate can easily lead to anisotropy in impact toughness. This study observed the microstructure and texture of the alloy plate on different planes, conducted impact toughness tests using four combinations of loading [...] Read more.

The α-phase microstructure and texture of a Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy hot-rolled plate can easily lead to anisotropy in impact toughness. This study observed the microstructure and texture of the alloy plate on different planes, conducted impact toughness tests using four combinations of loading direction and crack propagation plane, analyzed the fracture morphology, and investigated the effects of texture and microstructure on the anisotropy of impact toughness. The differences in crack initiation and propagation behavior are discussed. The results show that the impact toughness of the four types of specimens exhibits strong anisotropy. Among them, the L-S specimen (fracture on TD-ND plane, loading along ND) shows the highest impact toughness (97.75 J/cm²), while the T-L specimen (fracture on RD-ND plane, loading along RD) shows the lowest (46.7 J/cm²). Analysis suggests that the strong T-type texture in the plate makes activating slip systems significantly easier for fracture on the TD-ND plane compared to the RD-ND plane. Consequently, the former demonstrates better plastic deformation ability during both crack initiation and propagation. Additionally, the elongated characteristic of α laths along the RD/TD direction and the grain boundary features cause a more tortuous crack path and greater energy consumption when the crack propagates along the ND direction. The combined effect of texture and microstructure determines the anisotropy of impact toughness in this alloy. Full article

(This article belongs to the Special Issue Advanced Ti-Based Alloys and Ti-Based Materials)

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25 pages, 2846 KB

Open AccessArticle

Effects of Cutting Insert Flank Wear in Previous Turning and Subsequent Diamond Burnishing on the Surface Integrity, Microstructure and Fatigue Limit of Heat-Treated C45 Steel

by Jordan Maximov, Galya Duncheva, Angel Anchev, Vladimir Dunchev, Kalin Anastasov and Mariana Ichkova

Metals 2026, 16(5), 520; https://doi.org/10.3390/met16050520 (registering DOI) - 11 May 2026

Abstract

Burnishing technologies are a cheap and effective means of improving the surface integrity (SI) and performance of metal components. However, there is practically no information about the integral influence of the preceding turning process on the initial (pre-burnishing) SI. This study answers the [...] Read more.

Burnishing technologies are a cheap and effective means of improving the surface integrity (SI) and performance of metal components. However, there is practically no information about the integral influence of the preceding turning process on the initial (pre-burnishing) SI. This study answers the question of how the white layer resulting from flank wear on the cutting insert in pre-turning affects the SI and fatigue limit, and determines the extent to which subsequent diamond burnishing (DB) is able to improve the SI and rotating bending fatigue limit of normalised, quenched and high-temperature-tempered C45 steel. The (DB)–SI–fatigue limit correlation was investigated using a holistic approach that took into account the effects of the dynamic pattern of flank wear on the initial SI. An explicit relationship was established between the flank wear, the affected surface layer structure and the fatigue limit. Increasing flank wear to the 60th minute intensified the formation of a gradient layer with finer and thinner grains that formed a texture. As a result, a synergistic effect was observed from turning with an insert operating for 60 min and subsequent DB, which maximised the fatigue limit (741 MPa). After 60 min, the structure of the affected layer changed qualitatively towards the formation of a nanostructured (white) layer, which reversed the trend, worsening the fatigue behaviour. As the thickness of the white layer increased, the fatigue limit was sharply reduced to below 560 MPa after the 90th minute. Regardless of the degree of flank wear, DB significantly improved the SI characteristics and increased the fatigue limit after turning with a worn insert, although the absolute dimensions of the positive DB effect depend on the initial SI and fatigue limit due to pre-turning. To achieve a synergistic effect, the cutting insert should be replaced with a new one after every 60 min of operation. Full article

(This article belongs to the Special Issue Recent Advances in High-Performance Steel (2nd Edition))

45 pages, 3245 KB

Open AccessArticle

Acoustic and Inertial Sensor Techniques for Top Submerged Lance Technology: A Practical Framework for Characterizing Bubble Dynamics Under High-Temperature Conditions

by Avinash Kandalam, Markus Andreas Reuter, Michael Stelter, Andreas Richter, Christian Kupsch and Alexandros Charitos

Metals 2026, 16(5), 519; https://doi.org/10.3390/met16050519 (registering DOI) - 11 May 2026

Abstract

Top Submerged Lance (TSL) technology is widely used in non-ferrous smelting, yet in-situ bath dynamics remain challenging to quantify because the process operates in a closed, high-temperature, highly turbulent and optically inaccessible environment. The absence of direct diagnostics limits the ability to relate [...] Read more.

Top Submerged Lance (TSL) technology is widely used in non-ferrous smelting, yet in-situ bath dynamics remain challenging to quantify because the process operates in a closed, high-temperature, highly turbulent and optically inaccessible environment. The absence of direct diagnostics limits the ability to relate operating conditions to bubble dynamics, gas penetration and bath agitation and constrains validation of multiphase CFD models under realistic conditions. This study introduces a multimodal sensing framework that combines spectral acoustic analysis with lance-mounted inertial motion sensing to characterize dynamic bath behavior across cold-model, laboratory-scale and pilot-scale systems. Water-glycerin experiments establish repeatable acoustic signatures of individual bubble-collapse events, with dominant emission bands in the 300–900 Hz range and higher-frequency components extending into the kilohertz domain. High-temperature laboratory trials using fayalitic slag reproduce these frequency regions while exhibiting depth-dependent attenuation and clear spectral separation between submerged and non-submerged lance operation. Power Spectral Density (PSD) and cumulative spectral power analyses resolve the influence of gas flow rate and lance submersion depth on acoustic spectral power distribution, while inertial measurements capture corresponding increases in vertical lance acceleration associated with back-pressure fluctuations. Pilot-scale trials at 120 Nm³/h air and 13 L/h diesel confirm that shallow lance submersion substantially increases measured acoustic spectral power below 3 kHz, whereas deeper penetration enhances periodic vertical acceleration response measured by the inertial sensor. The combined acoustic-inertial methodology provides a physically interpretable and cross-scale framework for assessing bubble collapse activity, plume interaction and bath agitation under high-temperature TSL conditions. The approach enables frequency-based diagnostics that can be systematically compared with CFD predictions of plume oscillation and collapse-related dynamics. Once baseline frequency ranges are established for a given slag system, the method can support process monitoring and may provide indirect indicators related to changes in surface agitation or foaming tendency, enabling structured data-driven analysis. The framework thus provides a practical bridge between cold-model experiments, high-temperature measurements, multiphase modeling and industrial TSL operation. Full article

(This article belongs to the Section Extractive Metallurgy)

20 pages, 4183 KB

Open AccessArticle

Fused Deposition Modeling and Mechanical Properties of Porous Titanium Scaffolds

by Suli Li, Zhijie Guo, Yang Gao and Jing Guo

Metals 2026, 16(5), 518; https://doi.org/10.3390/met16050518 (registering DOI) - 11 May 2026

Abstract

To address issues such as thermal stress concentration in metal bone implants produced via high-energy beam direct additive manufacturing, a method was proposed to fabricate porous titanium scaffolds. This approach combined Fused Deposition Modeling (FDM) with a debinding–sintering process. Ti/ABS composite filaments with [...] Read more.

To address issues such as thermal stress concentration in metal bone implants produced via high-energy beam direct additive manufacturing, a method was proposed to fabricate porous titanium scaffolds. This approach combined Fused Deposition Modeling (FDM) with a debinding–sintering process. Ti/ABS composite filaments with titanium volume fractions of 35%, 40%, and 45% were successfully developed via a single-screw extrusion process. Their feasibility in the FDM process was subsequently verified. The effects of different processing parameters on the forming quality and dimensional accuracy of the green bodies were investigated. After debinding and sintering the composite scaffolds prepared with optimized parameters, structurally intact porous titanium scaffolds were obtained. Microscopic characterization shows that the scaffold surface consists primarily of titanium, and the pore structure remains intact. Furthermore, compression tests were performed on three types of porous titanium scaffolds with different porosities. The results indicate that the combination of ABS/titanium alloy composite filaments, FDM technology, and debinding–sintering post-processing enables the high-quality and efficient production of porous titanium scaffolds. The elastic modulus of the resulting scaffolds ranges from 1.2 to 1.6 GPa, and the compressive strength is between 25.7 and 68.3 MPa. The elastic modulus matches that of human cancellous bone. Meanwhile, the compressive strength is significantly higher than that of cancellous bone and falls between the values for cancellous and cortical bone. These mechanical properties meet the requirements for human bone, providing a new approach for the manufacture of orthopedic implants. Full article

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

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19 pages, 3133 KB

Open AccessArticle

Microstructure Evolution and Thermal Performance Enhancement of Ultrasonically Brazed Cu/Al Composite Heat Sinks via Gradient Heat Treatment

by Ming-Jun Xie, Peng-Fei Wang, Lin Gao, Yan-Fei Bian and Zhi Cheng

Metals 2026, 16(5), 517; https://doi.org/10.3390/met16050517 (registering DOI) - 11 May 2026

Abstract

Aiming at the urgent heat dissipation demands of high-power, high-integration electronic devices, Cu/Al composite heat sinks combine the high thermal conductivity of copper and the lightweight advantage of aluminum, becoming a mainstream solution for advanced thermal management systems. The significant physicochemical differences between [...] Read more.

Aiming at the urgent heat dissipation demands of high-power, high-integration electronic devices, Cu/Al composite heat sinks combine the high thermal conductivity of copper and the lightweight advantage of aluminum, becoming a mainstream solution for advanced thermal management systems. The significant physicochemical differences between Cu and Al, however, make high-quality joining a technical bottleneck. In this study, flux-free ultrasonic brazing with a Zn-based filler metal was used to join 6061 aluminum alloy and industrial pure copper. Gradient heat treatment (55–300 °C) was subsequently applied to systematically investigate its effect on the microstructure, microhardness, and thermal properties of the joints. The results show that the as-brazed joint exhibited excellent bonding (97.3% bonding rate) and shear strength (95.24 MPa). The weld seam consisted of Zn solid solution, Cu solid solution, and Al-Cu-Zn ternary compounds. Heat treatment did not induce new phases but led to the coarsening of Zn-Al-Cu compounds and aggregation of the eutectic structure, reducing grain boundaries. Consequently, the microhardness at the weld center varied non-monotonically, and the thermal conductivity of the joint showed an overall increasing trend with rising heat treatment temperature. This enhancement is attributed to reduced phonon scattering at diminished grain boundaries. This study clarifies the heat treatment–microstructure–thermal properties relationship, providing important guidance for the thermal performance optimization of Cu/Al composite heat sinks. Full article

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15 pages, 16972 KB

Open AccessArticle

Structural Design of Aluminum Hollow Extrusions for High-Speed Trains via Friction Stir Welding

by Xiangqian Liu, Wei Wang, Yanmo Li, Peiyue Li, Yaozong Li, Xiaoyi Guo, Linlin Zhang, Zhihua Sun and Gaosong Wang

Metals 2026, 16(5), 516; https://doi.org/10.3390/met16050516 (registering DOI) - 10 May 2026

Abstract

We designed a specialized structure for friction stir-welded hollow extrusions for high-speed trains in order to fulfill security and economic requirements. A sequentially coupled thermo-mechanical model was used to investigate the thermal stress distribution in the designed structure. The results show that stress [...] Read more.

We designed a specialized structure for friction stir-welded hollow extrusions for high-speed trains in order to fulfill security and economic requirements. A sequentially coupled thermo-mechanical model was used to investigate the thermal stress distribution in the designed structure. The results show that stress concentration was the most important factor in high calculated stress and that increasing the supporting rib width and the arc radius on the advancing side of the supporting rib can effectively improve structural security. Finally, an optimized structure was obtained, and friction stir welding experiments were carried out to verify the simulation’s precision. Full article

(This article belongs to the Topic Advances in Processing, Microstructure and Mechanical Properties of Lightweight Alloys)

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16 pages, 3676 KB

Open AccessArticle

Study on the Mechanical Properties of Composite Special-Shaped Columns with RAC-Filled Square Steel Tubes

by Tengfei Ma, Xuanran Gao, Zhifeng Ma and Ziqi Hao

Metals 2026, 16(5), 515; https://doi.org/10.3390/met16050515 (registering DOI) - 9 May 2026

Abstract

The L-shaped columns of recycled aggregate concrete-filled steel tubes (L-RACFSTs) with a 40% coarse aggregate replacement ratio were selected as the research subject, and axial compression and eccentric compression tests were conducted. Based on validated finite element numerical simulation methods, a parametric analysis [...] Read more.

The L-shaped columns of recycled aggregate concrete-filled steel tubes (L-RACFSTs) with a 40% coarse aggregate replacement ratio were selected as the research subject, and axial compression and eccentric compression tests were conducted. Based on validated finite element numerical simulation methods, a parametric analysis was carried out, incorporating key parameters such as steel strength, width-to-thickness ratios of the square steel tube and connecting plate, and load eccentricity. The mechanical properties of L-RACFSTs under axial compression and eccentric compression loads were studied. The results show the following: (1) At a 40% replacement rate, axial compression specimens exhibited obvious in-plane deformation of the column limbs, whereas eccentric compression specimens showed overall bending toward the inner side of the column. (2) As the strength of the steel increases, the axial and eccentric compressive bearing capacities of the specimens gradually increase. It is recommended that structural steel with a strength grade of Q355 is adopted. (3) When the width of a square steel tube is fixed, the axial and eccentric compressive bearing capacities of the test specimen gradually increase as the width-to-thickness ratio decreases. (4) In contrast, for a connecting plate of a fixed width, an increase in the width-to-thickness ratio results in a decrease in bearing capacity. Additionally, due to the increased width of the connecting plate, bearing capacity will decrease in some cases. (5) The bearing capacity under eccentric loading decreases gradually as the eccentricity increases; it is recommended that the eccentricity be kept below 120 mm. Full article

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19 pages, 9391 KB

Open AccessArticle

Influence of Deposition Voltage on Microstructural Development, Frictional Behavior, and Thermal Stress-Induced Cracking Mechanisms in Ta-10W Wear-Resistant Coatings Fabricated via Electricspark Deposition

by Guanglin Zhu, Jianmin Song, Jinpeng Yang, Liang Hu, Cean Guo and Wenhuan Shen

Metals 2026, 16(5), 514; https://doi.org/10.3390/met16050514 (registering DOI) - 9 May 2026

Abstract

High-load sliding components, including gun barrels, are susceptible to accelerated wear and damage due to coupled thermal-mechanical stresses and reciprocating frictional conditions. Therefore, enhancing their operational lifespan requires the application of wear-resistant coatings with high melting points for effective surface protection. In this [...] Read more.

High-load sliding components, including gun barrels, are susceptible to accelerated wear and damage due to coupled thermal-mechanical stresses and reciprocating frictional conditions. Therefore, enhancing their operational lifespan requires the application of wear-resistant coatings with high melting points for effective surface protection. In this study, Ta-10W alloy coatings were deposited on CrNi3MoVA steel substrates through electricspark deposition, focusing on deposition voltage as a critical parameter. Experimental results indicate that the Ta-10W coatings are primarily composed of α-Fe, α-Ta₂O₅, δ-Ta₂O₅, α-Ta(W), and Fe-W intermetallic phases. An increase in deposition voltage facilitates enhanced melting and mass transfer, thereby promoting solid solution and oxidation strengthening, which results in improved hardness. However, higher voltages also induce defects such as porosity and microcracks. Hardness measurements and friction-wear tests demonstrate that coatings deposited at 80 V exhibit optimal performance, attaining the highest hardness (~753 HV) and a friction coefficient similar to that at 60 V. Conversely, the friction coefficient increases at 100 V due to defects and coating spalling. The wear mechanism transitions from adhesive wear at 60 V to adhesive wear with minor plastic deformation at 80 V and ultimately to spalling wear at 100 V. Finite element thermomechanical simulations reveal that increasing voltage significantly elevates the equivalent interfacial stress (600–1150 MPa), thus correlating with the propensity for microcracks to propagate into longitudinal semi-penetrating cracks at elevated voltages. This study establishes a theoretical foundation for optimizing electricspark deposition process parameters and contributes to the reliability design of Ta-W alloy coatings. Full article

13 pages, 12782 KB

Open AccessArticle

Influence of Hot Deformation Strain on Austenite Stability in High Nitrogen Martensitic Stainless Steel 30Cr15Mo1N0.37

by Shuilin Tan, Qian Wang and Chaobin Lai

Metals 2026, 16(5), 513; https://doi.org/10.3390/met16050513 (registering DOI) - 9 May 2026

Abstract

Hot deformation effectively refines the microstructure and homogenizes the composition of high-nitrogen martensitic stainless steel (HNMSS), but its influence on austenite stability during subsequent cooling remains unclear. In this study, the effect of the hot deformation strain on austenite stability in HNMSS 30Cr15Mo1N0.37 [...] Read more.

Hot deformation effectively refines the microstructure and homogenizes the composition of high-nitrogen martensitic stainless steel (HNMSS), but its influence on austenite stability during subsequent cooling remains unclear. In this study, the effect of the hot deformation strain on austenite stability in HNMSS 30Cr15Mo1N0.37 was investigated by means of a Gleeble thermomechanical simulator, X-ray diffraction (XRD), electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM). The austenite stability is evaluated by the austenite fraction measured via XRD at room temperature. The results show that the austenite content in HNMSS 30Cr15Mo1N0.37 gradually increases with the strain range from 0 to 0.8. The austenite fractions are 69.5%, 73.1%, and 80.7% when the strains are 0, 0.4, and 0.8, respectively. At a strain of 0.14, dislocation accumulation leads to the formation of dislocation cells and sub-grains within austenite, which enhances its stability. When the strain exceeds 0.36, the austenite grains are significantly refined, the austenite stability is attributed to the synergistic effects of dislocation accumulation and grain refinement, which collectively increase the resistance to martensitic transformation. Furthermore, both recrystallized grains and dislocation cells influence the morphology and size of martensite laths. The martensite laths are significantly refined from 100 nm at a strain of 0 to 35 nm as the strain reaches 0.8, and their morphology changes from straight to curved. Full article

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11 pages, 984 KB

Open AccessArticle

Hydrometallurgical Processing of Polymetallic Sublimates Containing Arsenic: Features of Leaching and Thermodynamic Analysis

by Aitbala Narembekova, Kalkaman Zhumashev, Pheruza Berdikulova, Yelena Zhinova and Anna Bogdanova

Metals 2026, 16(5), 512; https://doi.org/10.3390/met16050512 (registering DOI) - 9 May 2026

Abstract

This article presents the results of developing a hydrometallurgical method for processing polymetallic sublimates containing arsenic, zinc, copper, and lead. Using sublimates from “BalkhashPolymetal” LLP (Kazakhstan) as an example, the optimal conditions for sulfuric acid leaching were determined as follows: t = 80–85 [...] Read more.

This article presents the results of developing a hydrometallurgical method for processing polymetallic sublimates containing arsenic, zinc, copper, and lead. Using sublimates from “BalkhashPolymetal” LLP (Kazakhstan) as an example, the optimal conditions for sulfuric acid leaching were determined as follows: t = 80–85 °C, H₂SO₄ = 25 g/dm³, τ = 60 min. Under these conditions, extraction of arsenic was 93%, zinc 80%, and copper 42% was achieved. Iron(II) hydroxide was used to remove arsenic from the solution, which made it possible to reduce the residual As content in the solution to 0.02 g/L and return approximately 97% of copper to the process cycle. Eh–pH analysis of the Fe–As–Cu–H₂O system confirmed the thermodynamic stability of Fe(II/III) arsenates in the selected pH range 3–5. The obtained results can be used to develop safe and resource-saving technologies for processing technogenic raw materials. Full article

(This article belongs to the Section Computation and Simulation on Metals)

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14 pages, 1639 KB

Open AccessArticle

Dissociation Behavior of the Congruently Melting FeSi Compound in the Fe-Si System: A Bjerrum–Guggenheim Thermodynamic Analysis

by Gauhar Yerekeyeva, Bauyrzhan Kelamanov, Vera Tolokonnikova and Bakyt Suleimen

Metals 2026, 16(5), 511; https://doi.org/10.3390/met16050511 (registering DOI) - 9 May 2026

Abstract

This study presents a thermodynamic analysis of the dissociation and association behavior of the Fe–Si system using the Bjerrum–Guggenheim osmotic coefficient. An equilibrium thermodynamic approach was applied to evaluate the Gibbs free energy, equilibrium constant, and degree of association of the congruently melting [...] Read more.

This study presents a thermodynamic analysis of the dissociation and association behavior of the Fe–Si system using the Bjerrum–Guggenheim osmotic coefficient. An equilibrium thermodynamic approach was applied to evaluate the Gibbs free energy, equilibrium constant, and degree of association of the congruently melting compound FeSi over a wide temperature range. The Fe–Si system was analyzed across three characteristic crystallization regions: Fe-rich, FeSi, and Si-rich. It was established that the Fe-rich region exhibits behavior approaching ideality with a nearly linear dependence of the osmotic coefficient, whereas the Si-rich region is characterized by strong deviations from ideality due to intensive association processes. The FeSi crystallization region represents a transitional regime in which association and dissociation processes occur simultaneously. The formation and partial dissociation of [Fe_xSi_y] clusters significantly affect the thermodynamic behavior of the melt. It was shown that accounting for FeSi dissociation leads to a linearization of the osmotic coefficient dependence and improves the accuracy of thermodynamic description. The proposed analytical approximations demonstrate high correlation coefficients (R² ≈ 0.99), confirming the reliability of the developed approach. The results provide a consistent thermodynamic framework for describing phase transformations and structural evolution in Fe–Si melts and can be applied to the optimization of metallurgical processes involving silicon-containing alloys. Full article

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