Metals doi: 10.3390/met16050526

Authors: Zhiwei Liu Xiuhua Gao Changyou Zhu Shuo Gao Zhiyong Chang Linxiu Du Hongyan Wu

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.

Metals doi: 10.3390/met16050525

Authors: Zongxian Song Zhiwei Gao Lina Zhu Hao Jin Jian Zhao Caiyan Deng

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.

Metals doi: 10.3390/met16050524

Authors: Jarupong Charoensuk Takuma Iwai Taiga Hongo Tomoyoshi Maeno Surasak Suranuntchai

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.

Metals doi: 10.3390/met16050523

Authors: Haolong Cheng Jun Peng Yingtie Xu Jing Li Fei Huang Lixia Liu

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.

Metals doi: 10.3390/met16050522

Authors: Sanat Tolendiuly Nursultan Rakhym Kaster Kamunur Sharafkhan Assylkhan Lyazzat Mussapyrova Sandugash Tanirbergenova

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.

Metals doi: 10.3390/met16050521

Authors: Bo Fu Jialiang Sun Boya Wang Yang Yu Wenjun Ye Yumeng Luo Yanfeng Li Songxiao Hui

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.

Metals doi: 10.3390/met16050520

Authors: Jordan Maximov Galya Duncheva Angel Anchev Vladimir Dunchev Kalin Anastasov Mariana Ichkova

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.

Metals doi: 10.3390/met16050519

Authors: Avinash Kandalam Markus Andreas Reuter Michael Stelter Andreas Richter Christian Kupsch Alexandros Charitos

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.

Metals doi: 10.3390/met16050518

Authors: Suli Li Zhijie Guo Yang Gao Jing Guo

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.

Metals doi: 10.3390/met16050517

Authors: Ming-Jun Xie Peng-Fei Wang Lin Gao Yan-Fei Bian Zhi Cheng

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.

Metals doi: 10.3390/met16050516

Authors: Xiangqian Liu Wei Wang Yanmo Li Peiyue Li Yaozong Li Xiaoyi Guo Linlin Zhang Zhihua Sun Gaosong Wang

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.

Metals doi: 10.3390/met16050514

Authors: Guanglin Zhu Jianmin Song Jinpeng Yang Liang Hu Cean Guo Wenhuan Shen

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.

Metals doi: 10.3390/met16050515

Authors: Tengfei Ma Xuanran Gao Zhifeng Ma Ziqi Hao

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.

Metals doi: 10.3390/met16050513

Authors: Shuilin Tan Qian Wang Chaobin Lai

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.

Metals doi: 10.3390/met16050512

Authors: Aitbala Narembekova Kalkaman Zhumashev Pheruza Berdikulova Yelena Zhinova Anna Bogdanova

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.

Metals doi: 10.3390/met16050511

Authors: Gauhar Yerekeyeva Bauyrzhan Kelamanov Vera Tolokonnikova Bakyt Suleimen

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 [FexSiy] 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.

Metals doi: 10.3390/met16050510

Authors: Lu Cheng Chenxi Shao Peng Cheng

Accurate constitutive modeling of TC4 titanium alloy at elevated temperatures is critical for process design and numerical simulation in aerospace manufacturing. However, purely data-driven deep neural networks (DNNs) often suffer from severe overfitting and may yield physically unreasonable predictions in data-sparse or strictly out-of-distribution (OOD) regions. To address this issue, this study proposes a physics-guided two-stage neural network framework, termed NN-PhysicsInit, for the constitutive modeling of TC4 alloy. In Stage I, a large synthetic dataset generated from a strain-compensated Arrhenius-type constitutive equation is used to pre-train the network, thereby introducing analytical prior knowledge into the initial topological space. In Stage II, the pre-trained model is fine-tuned using rigorously corrected experimental data obtained from isothermal compression tests conducted over 800–980 °C and 0.001–1 s−1 to improve material-specific predictive accuracy. To evaluate generalization capability, a rigorous dual-perspective extrapolation validation scheme is designed separately in the temperature (1010 °C) and strain-rate (10 s−1) dimensions. The results demonstrate that, compared with direct black-box training, the proposed framework successfully prevents non-physical divergence and better preserves macroscopic thermodynamic smoothness in unseen domains. Specifically, the extrapolation average absolute relative error (AARE) is significantly reduced from 34.21% to 14.34% in the temperature extrapolation task, and from 27.91% to 8.92% in the strain-rate extrapolation task. These findings confirm that physics-based initialization acts as a powerful implicit regularizer, effectively mitigating the extrapolation catastrophe while maintaining high fitting accuracy. The proposed framework provides a robust and practical strategy for the constitutive modeling of complex alloys under limited-data conditions.

Metals doi: 10.3390/met16050509

Authors: Taoran Shao Bingbing Wu Yanxin Wu Zhenli Mi

High-manganese steel has emerged as a potential alternative material to austenitic stainless steel for liquid hydrogen storage and transportation environments, owing to its superior mechanical characteristics and limited hydrogen diffusivity. However, its hydrogen embrittlement (HE) susceptibility limits its engineering applications. This study investigates the effect of microstructural regulation through trace titanium (Ti, 0.021 wt%) addition on HE resistance in high-manganese steel. By means of Electron Backscatter Diffraction (EBSD), TEM, SEM, and Slow Strain Rate Tensile (SSRT) tests, the effects of Ti on the microstructure, mechanical properties, and HE susceptibility of high-manganese steel are systematically investigated. The results show that the addition of Ti did not significantly alter the average austenite grain size or phase composition, but it generated a large number of Ti(C,N) nanoscale precipitates with sizes ranging from 20 to 70 nm within the matrix. The elongation loss of the 25Mn-Ti specimen was significantly lower than that of the 25Mn specimen when hydrogen-charged for 72 h, decreasing from 18.4% to 9.3%. The fracture surfaces consistently exhibited ductile dimple morphology, whereas 25Mn steel demonstrated significant cleavage-induced brittle fracture. EBSD analysis revealed that hydrogen-charged 25Mn-Ti steel exhibited higher Kernel Average Misorientation (KAM) value retention rate and more uniform grain strain distribution, indicating enhanced microstructural deformation compatibility. The main mechanism was that Ti pre-formed nanoscale Ti(C,N) precipitates during the preparation of 25Mn high-manganese steel, which played a key role in inhibiting HE. These precipitates altered hydrogen diffusion behavior and distribution patterns, reduced stress concentration levels, and inhibited hydrogen-induced crack initiation. This work is of great significance for improving the HE resistance of high-manganese steels.

Metals doi: 10.3390/met16050508

Authors: Askhat Akuov Alibek Baisanov Bauyrzhan Kelamanov Aidana Baisanova Nina Vorobkalo Yerulan Samuratov

This study investigates the thermodynamic and kinetic features of chromium reduction from chromium ore using complex Fe–Si–Cr and Al–Si–Cr alloys as reducing agents for the refined ferrochrome production. The thermodynamic probability of Cr2O3 reduction by silicon and aluminum was evaluated using thermodynamic equilibrium calculations based on reference thermodynamic data, including determination of the standard Gibbs free energy change over the studied temperature range. The results showed that both reduction routes are thermodynamically feasible, while aluminum exhibits a higher affinity for oxygen and a greater reducing capacity. The thermal behavior of chromium ore and its mixtures with Fe–Si–Cr and Al–Si–Cr alloys was studied by differential thermal and thermogravimetric analysis. The use of Al–Si–Cr, especially in briquetted form, was found to shift several thermal transformation stages to lower temperatures and to reduce the apparent activation energy of the high-temperature interaction stages compared with Fe–Si–Cr-containing mixtures. The obtained results indicate that Al–Si–Cr alloy is a promising complex reductant for intensifying chromium recovery and improving process conditions in refined ferrochrome production.

Metals doi: 10.3390/met16050507

Authors: Tomasz Chmielewski Piotr Siwek Marcin Chmielewski Anna Piątkowska Agnieszka Grabias Dariusz Golański

The journal retracts the article “Structure and Selected Properties of Arc Sprayed Coatings Containing In-Situ Fabricated Fe-Al Intermetallic Phases” [...]

Metals doi: 10.3390/met16050506

Authors: Vinamra Bhushan Sharma Saurabh Tewari Susham Biswas Bharat Lohani Umakant Dhar Dwivedi Deepak Dwivedi Ashutosh Sharma Jae Pil Jung

There were some errors in the original publication [...]

Metals doi: 10.3390/met16050505

Authors: Rongxin Lan Zhengbing Meng Meiqiao Wu Jiangbo Deng Dinghua Feng

S136 mold steel is widely used in the injection molding industry due to its excellent properties. However, during actual production, the mold is inevitably exposed to harsh service conditions involving high temperature, high pressure, chemical corrosion, and mechanical wear, leading to risks of failure caused by pitting corrosion, intergranular corrosion, electrochemical corrosion, selective dissolution, and surface fatigue wear. To enhance the surface protection performance of the mold, a TiC-reinforced 440C stainless steel composite coating was fabricated on the S136 substrate using plasma spray welding technology. Composite powders with different TiC contents (wt.%) were prepared via mechanical mixing. The phase composition, microstructure, microhardness, corrosion resistance, and wear resistance of the coatings were characterized by XRD, SEM, Vickers microhardness tester, electrochemical workstation, and vertical universal friction and wear tester. Furthermore, the corresponding strengthening mechanisms were elucidated. The results show that the incorporation of TiC refines the microstructure and synergistically enhances both corrosion and wear resistance. Among the tested coatings, the one with 1.0 wt.% TiC exhibits the best overall performance, with a significantly increased microhardness of 858.85 HV (approximately 1.5 times that of the substrate), an Ecorr of –0.286 ± 0.002 V, an Icorr of 4.51 × 10−7 A·cm−2, and a friction coefficient of 0.591. This study provides important theoretical and technological insights for the surface strengthening of S136 mold steel using plasma spray welding of TiC/440C composite coatings to improve corrosion and wear resistance and extend service life.

Metals doi: 10.3390/met16050504

Authors: Fakhri Ali Salem Mohammed Yahui Zhang

As critical rare earth elements (REEs), the industrial demand for neodymium (Nd) and dysprosium (Dy) increases rapidly due to their specific physical and chemical properties. Recycling these REEs from secondary resources such as spent NdFeB magnetic materials is an efficient approach for sustainable production. However, the separation of neodymium and dysprosium in aqueous solutions is an arduous task because of their close chemical properties. Recovering and purifying neodymium and dysprosium from a simulated leaching solution of spent NdFeB magnets were conducted by employing selective ion exchange resins. It was found that Purolite S950 PLUS resin functionalized with aminophosphonic groups demonstrated selective adsorption toward Nd3+ and Dy3+ while maintaining low affinity for Fe(II) at low pH (i.e., 0.65), which could realize efficient iron removal from the solution. Purolite MTX7010 resin impregnated with di-(2-ethylhexyl) phosphoric acid (D2EHPA) had a strong adsorption preference for Dy3+ over Nd3+, which is highly suitable for Dy separation from their mixed solutions under optimized conditions. By employing a multistage adsorption–elution process analogous to distillation, a prospective purity of 98.51% for Dy and a purity over 99.90% for Nd were realized with high metal recoveries from the synthetic leaching solution of spent NdFeB magnets. This research demonstrates that recovery and purification of single REEs from leaching solutions containing mixed REEs and other metals can be achieved with selective resin adsorption processes analogous to distillation despite large concentration differences in the metals in the solutions, which presents a new approach.

Metals doi: 10.3390/met16050503

Authors: Pengyu Gao Yali Huang Hong Xiao Xindu Chen Yanxi Zhang Xiangdong Gao

Accurate and interpretable weld-quality assessment is essential for ensuring the reliability of resistance spot welding in industrial production. This study develops a data-efficient classification framework that integrates dual-interval mean discretization (DIMD) of dynamic-resistance signals with gradient-boosting models. The proposed DIMD method applies fine discretization during the rapid heating–melting and coarse discretization during the subsequent slow-evolving period, effectively preserving the peak–valley morphology of resistance curves while reducing feature dimensionality. Using these compact features, XGBoost and CatBoost classifiers were trained on a dataset of DC01 low-carbon steel, covering five weld conditions. CatBoost achieved the highest accuracy of 98.9%, attributed to its ordered-boosting mechanism and symmetric-tree structure. Validation on an independent 198-sample dataset confirmed the generalization capability of the proposed approach. SHapley Additive exPlanations (SHAP)-based interpretability analysis further revealed that resistance-peak characteristics and energy-related descriptors dominate model decisions, aligning with the physical process of nugget formation and expulsion. Experimental results demonstrate that the DIMD–CatBoost framework provides a physically consistent, interpretable, and high-accuracy solution for intelligent weld-quality inspection.

Metals doi: 10.3390/met16050502

Authors: Iurii Dovgaliuk Yaroslav Tokaychuk Roman Gladyshevskii Viktor Hlukhyy

Lithium-containing intermetallic compounds, in particular tin-based systems, are attracting significant attention as potential anode materials for battery applications. In this work, we present the crystal structure of a new ternary compound, Li11Co1.8Sn20, which was solved and refined from single-crystal X-ray diffraction data: new structure type, space group C2/m, Pearson symbol mS66; a = 15.2320(5), b = 6.3334(2), c = 14.8033(4) Å, β = 99.758(4)°. The structure consists of a framework of pentagonal, square and trigonal prisms formed by Sn atoms and partially centered by Li or Co atoms.

Metals doi: 10.3390/met16050501

Authors: Yuli Zhou Huilin Zhang Yuxin Chen Fan Li Cai Chen Mohammed El Ganaoui Hélène Elias-Birembaux Mourad Khelifa Shuai Zhang Peijian Wang Dunming Liao

The influence of Cu content on the thermal conductivity and mechanical properties of Al-9Si-0.7Fe casting alloy were investigated in this paper. The results show that as the Cu content increases from 0.1 wt.% to 2.0 wt.%, the thermal conductivity of the alloy decreases from 173.6 W/(m·K) to 154.8 W/(m·K), while the yield strength increases from 72.2 MPa to 90.9 MPa. Metallographic, XRD, and EPMA analyses revealed that Cu has a relatively small impact on the secondary dendrite arm spacing of α-Al and the morphology of eutectic silicon. Its influence on the thermal conductivity and mechanical properties primarily stems from Cu atoms dissolving in the α-Al matrix, leading to a decreased lattice constant, increased lattice distortion, enhanced electron scattering, and improved solid solution strengthening effect. Based on the measured solubility of Cu, the Maxwell and Hashin–Shtrikman thermal conductivity models were modified. The correlation coefficients between the predicted values of the modified models and the experimental data were 92.77% and 93.11%, respectively, indicating a significant improvement in prediction accuracy.

Metals doi: 10.3390/met16050500

Authors: Matúš Gavalec Mária Dománková Marek Kudláč Katarína Bártová Gabriela Stachová

Extending the service life of nuclear power plant components beyond their originally designed operational period requires a detailed understanding of the microstructural stability of the materials used. This study focuses on low-temperature precipitation in the austenitic stainless steel 08CH18N10T, which is employed in the main circulation piping of pressurized water reactors. During long-term operation in the temperature range of 100–320 °C, secondary phases such as M23C6 carbides and intermetallic phase sigma (σ) can precipitate, which can lead to local chromium depletion at grain boundaries, subsequent sensitization of the steel, and susceptibility to intergranular corrosion. The research includes the analysis of samples taken from the decommissioned V1 unit of the Jaslovské Bohunice Nuclear Power Plant, which has been in operation for 28 years. The samples were subjected to thermal aging under laboratory conditions, with an emphasis on evaluating microstructural changes and their impact on corrosion resistance. Based on the experimental results, it can be concluded that the thermal stability of all tested materials is suitable for the operation of the main circulation piping, as the service temperatures to which the main circulation piping is exposed during operation remain below the activation of precipitation that would lead to sensitization and, consequently, susceptibility to intergranular corrosion. Activation of low-temperature precipitation was observed only at 450 °C, while at temperatures up to 400 °C, the structural stability of the material was confirmed, demonstrating its suitability for operation within the specified temperature range of the nuclear power plants’ main circulation piping.

Metals doi: 10.3390/met16050499

Authors: Airat M. Fairushin Elena Yu. Tumanova Andrey S. Tokarev Natalya B. Mulyashova Azamat S. Ilalov Alsu R. Kanaeva Arseny M. Kazakov Galiia F. Korznikova

Martensitic chromium-molybdenum steels such as 15Kh5M are widely used in high-temperature oil and gas equipment, but their weldability is limited by high hardenability and susceptibility to cold cracking, which usually necessitate energy-intensive preheating. This study evaluates an alternative route based on the combination of root-pass mechanical vibration (50 Hz, ~1 mm amplitude) and post-pass water-air jet cooling during mechanized GMAW. Three welding variants were compared: conventional preheated welding, vibration-assisted welding without preheating, and hybrid thermo-vibrational welding with active cooling. Among the tested conditions, the hybrid route produced the narrowest heat-affected zone, reducing its width from about 7 mm to about 3 mm, which is consistent with a compressed thermal cycle. Microhardness in the heat-affected zone decreased from 380 to 440 HV in the preheated condition to 330–370 HV in the hybrid condition. Optical microscopy further indicated a finer and more homogeneous transformed microstructure in the hybrid case. Results indicate that simultaneous vibro-treatment and controlled cooling effectively mitigate harmful metallurgical effects typically induced by rapid cooling, enabling preheat-free fabrication of thick-walled components. The proposed hybrid approach may offer energy savings, shorter production cycles, and improved automation compatibility in field welding applications.

Metals doi: 10.3390/met16050498

Authors: Xiaoyan Wang Weiguo Li Erlin Zhang

CoCrMo alloys are widely used as orthopedic and dental implants, owing to their superior mechanical properties, wear resistance, and biocompatibility. Copper (Cu) ion exhibits strong antibacterial activity, making it a promising alloying element. A systematic study was conducted on the corrosion resistance and ion release behavior of CoCrMo-xCu (Co-xCu) alloys in both as-cast and heat-treated states in different simulated solutions. The results indicated that the corrosion resistance of Co-xCu alloys decreased with the increasing Cu content, which was mainly attributed to the formation of micro-galvanic couples between the alloy matrix and Cu-rich phases. The synergistic effect of heat treatment and an appropriate Cu content can effectively improve the corrosion resistance of the alloys, and the corrosion current density (icorr) of Cu-containing cobalt alloys was comparable to that of Cu-free cobalt alloys. Maximum concentrations of Co, Cr, and Cu ions released from Co-xCu alloys were lower than the corresponding recommended safety limits. Through the combined optimization of Cu content and heat treatment, the metal ion release levels of Cu-containing cobalt alloys can be reduced to values even lower than those of Cu-free cobalt alloys.

Metals doi: 10.3390/met16050497

Authors: Sude Akin Esra Gul Unluer Yaël Maurinier Akram Younes Riad Mecabih Jean-Louis Bobet

This review provides an overview of magnesium-rich compounds and Long-Period Stacking Ordered (LPSO) phases for their hydrogen storage properties. Thanks to their high volumetric density, safety, and exceptional purity, metal hydrides are promising for hydrogen storage. Magnesium is a great candidate as it can form MgH2, which has a weight capacity of 7.6 wt.%. However, due to its high stability (at 283 °C, equilibrium pressure is 1 bar (i.e., atmospheric pressure)) and slow hydrogen sorption kinetics, Mg is alloyed with TMs (transition metals) and/or REs (rare earths) to overcome these problems. Some alloys that are synthesized with both TMs and REs (ternary system) form LPSO phases, which irreversibly decompose under hydrogenation. The LPSO phases discussed in this review are mostly the 14H- and 18R-type phases, although, rarely, other types of LPSO phases can still be observed as well. These discussed phases may lead to good hydrogen sorption properties depending on the REs and TMs used. This review focuses on the recent literature addressing Mg-rich binary Mg-TM and Mg-RE alloys and ternary (TMx-REy-Mgz) systems and their hydrogen storage properties with an emphasis on LPSO phases.

Metals doi: 10.3390/met16050496

Authors: Vladimir G. Pushin

The attractive physical, mechanical, and operational characteristics of the structural metal materials most widely used in the world economy can be achieved through diffusion-free phase martensitic transformations (MT) in combination with their atomic ordering and decomposition of the supersaturated solid solutions [...]

Metals doi: 10.3390/met16050495

Authors: Xinyu Gao Guanjun Gao Kai Wen Zhihui Li Lizhen Yan Xiwu Li Hongwei Yan Tianlong Hu Lei Chen Yongan Zhang Baiqing Xiong

High-quality, large-weight alloy wires (>200 kg per coil) for aerospace fasteners require intermediate annealing prior to final cold drawing, as well as subsequent solution and aging heat treatments, which are critical processes during their manufacturing. However, the evolution of microstructure and mechanical properties during these procedures has not been systematically investigated. In this study, different cooling methods after intermediate annealing were comparatively investigated to clarify their influence on the microstructure evolution, precipitation behavior, and mechanical properties of Al–Zn–Mg–Cu alloy wires. The results revealed that the cold heading performance of alloy wires is determined by the strength–ductility balance, crystallographic texture, and precipitation behavior. Furnace cooling promoted η′ phase coarsening, resulting in lower strength and higher ductility, which enhanced deformation homogeneity and cold heading formability. The near-zero Δr reduced strain localization and cracking susceptibility, whereas higher Δr in water- and air-cooling samples increased anisotropy and cracking tendency. After heat treatment, strength differences became negligible, whereas elongation remained texture dependent, with the weaker texture in the furnace-cooling sample yielding superior ductility.

Metals doi: 10.3390/met16050494

Authors: Xuelin Wang

Welding and joining technologies, as well as metal forming processes, are the foundation of modern manufacturing industries and are widely used in fields such as automotive, aerospace, pipeline engineering, and electronic packaging [...]

Metals doi: 10.3390/met16050493

Authors: Guojun Ma

The metallurgical industry constitutes a fundamental pillar of the global industrial system and national economies [...]

Metals doi: 10.3390/met16050492

Authors: Lenka Girmanová Marek Šolc Dominik Dubec Peter Blaško Jozef Petrík Kristína Kovalčíková Tomasz Małysa

Life cycle assessment (LCA) is an important analytical method used to evaluate the environmental impacts of products, services, or processes throughout their entire life cycles—from the extraction of raw materials and production to use and end-of-life treatment. LCA enables the identification of stages with the highest environmental impact burden (hotspots) and supports strategic environmental initiatives, the circular economy, standards, and policies aimed at improving sustainability. This paper analyses the application of LCA in metallurgy, with a focus on primary aluminium production. It outlines the principles of life cycle thinking and explores decarbonisation opportunities within the aluminium industry. This study includes a life cycle impact assessment case study comparing the most significant environmental impacts of primary aluminium production in different regions of the world, including Europe and Asia. The analysis was performed using openLCA software 2.5 with the OzLCI2019 database. Environmental impacts were calculated using the ReCiPe 2016 Midpoint (H) method. The results indicate that primary aluminium production mainly affects impact categories related to high energy consumption, the use of carbon anodes, and associated emissions. The highest impacts were identified in ecotoxicity, followed by global warming, land use, ozone formation, and fossil resource scarcity. No significant regional differences were observed.

Metals doi: 10.3390/met16050491

Authors: Liang Hu Hui Zhao Guanglin Zhu Wenqi Han Fengling Zhang Xiaohao Yi Qinru Tang Wenhuan Shen

A detailed analysis of the effects of magnesium on the microstructure of hypereutectic Al–20Si alloys is provided in this study. Experimental results show that the addition of Mg significantly refines the primary silicon phase relative to the unmodified Al–20Si alloy, transforming its morphology from a complex form to a singular plate-like structure. Notably, for the first time, equiaxed aluminum grains appear in the aluminum matrix under conventional solidification conditions. The generation of these grains is closely related to the quenching effect caused by rapid cooling during metal mold casting, which promotes the generation of equiaxed aluminum grains within tightly constrained temporal and spatial parameters. The Al–Si eutectic structure exhibits a regular lamellar morphology, with an average eutectic silicon spacing of 930.97 nm. The phase analysis shows that the alloy mainly consists of Al, Si, and Mg2Si phases after the addition of Mg. With the increase in Mg concentration, the diffraction peaks for Al(200) and Si(220) first shift to lower angles and then move to higher angles, along with significant peak broadening. Ambient temperature mechanical testing indicates that tensile strength first increases with increasing Mg concentration, then declines, with the highest tensile strength of 235.1 MPa at 3 wt.% Mg in the Al–20Si alloy. The fracture mechanism of the testing specimens changes from cleavage fracture to ductile fracture. Microhardness testing indicates a continuous increase in the hardness of the aluminum matrix with rising Mg concentration; the hardness of primary silicon declines first and then increases, whereas the hardness of the eutectic structure exhibits a first increase followed by a decline.

Metals doi: 10.3390/met16050490

Authors: Vesna M. Marjanović Dragana Božić Bernd Friedrich

Water pollution, caused by selenium contamination, is a significant global issue due to its toxic effects on humans and animals. Selenium occurs in several oxidation states, among which selenite and selenate are the most mobile and bioavailable forms. Traditional water treatment methods are often limited in efficiency, whereas adsorption offers a simple, cost-effective, and efficient solution. Various adsorbents, including metal and mineral oxides, carbon-based materials (activated carbon, graphene oxide), biosorbents, and nanocomposites, have shown high potential for Se removal. Adsorbent modifications—physical, chemical, or composite—significantly enhance adsorption capacity, selectivity, and material stability. Studies have demonstrated that nanomaterials and nanocomposites, such as MnFe2O4, PAA-MGO, magnetic MOFs, and magnetite-based biochars, enable rapid removal of Se(IV) and Se(VI) with high adsorption capacities. Se(IV) is primarily adsorbed through innersphere complexation, while Se(VI) forms weaker outer-sphere interactions, explaining differences in removal efficiency. Factors such as pH, the presence of surface hydroxyl and amino groups, surface charge, and competing ions strongly influence the adsorption process. Multivalent ions reduce Se adsorption efficiency, whereas monovalent ions (NO3− and Cl−) have minimal impact. Modified adsorbents, nanomaterials, and nanocomposites provide sustainable and practical solutions for selenium removal from water, combining high efficiency, selectivity, and reusability, making them suitable for real-world water treatment applications.

Metals doi: 10.3390/met16050489

Authors: Ehsan Jebellat Brian G. Thomas

Accurate thermal analysis of steel solidification and heat transfer in the continuous casting mold is essential for understanding and controlling solidification, shell thickness uniformity, interfacial gap phenomena, and defects such as cracks and breakouts. This study investigates heat transfer in a funnel mold slab caster using the in-house thermal model, Con1D. A new methodology is introduced to predict the slag layer roughness, and its effect on interface resistance. To account for the multidimensional thermal behavior near water channels and thermocouples, finite-element models are developed in Abaqus to calibrate Con1D to match three-dimensional calculations of mold heat transfer. After calibration to match plant measurements for one set of casting conditions, Con1D predictions are validated with plant measurements at different casting speeds and mold plate thicknesses. Key outputs analyzed include the heat flux profile, mold and shell temperatures, shell thickness, shell shrinkage, and interfacial parameters such as slag layer thickness. Increasing casting speed causes higher heat flux, higher shell surface and mold temperatures, and decreased shell and slag layer thicknesses. Decreasing mold plate thickness increases heat flux slightly due to reduced thermal resistance of both the mold and interfacial gap. The modeling approach presented here is a powerful methodology to gain quantitative fundamental understanding of mold heat transfer in continuous casting, especially including phenomena in the interfacial gap.

Metals doi: 10.3390/met16050488

Authors: Harold Joyson Dsouza Sathish Rao Dilifa Jossley Noronha Girish Hariharan Gowri Shankar Nitesh Kumar Manjunath Shettar Siddhanth D. Pai

Aluminum alloys, particularly those in the Al-Cu and Al-Mg-Si series, are extensively employed in aerospace, automotive, and structural applications owing to their favorable strength-to-weight ratio. However, optimizing their mechanical and surface properties to meet advanced performance requirements remains a critical challenge. Over the past three decades, extensive research has explored thermochemical treatments, precipitation hardening, and thermomechanical processing, yet most studies have examined these methods in isolation. This review systematically analyzes the influence of each treatment route on microstructural evolution, precipitation behavior, and mechanical performance, with emphasis on grain refinement, precipitation kinetics, surface hardening, and fatigue resistance. Particular attention is given to severe plastic deformation, advanced surface modification techniques, and aging behavior under different conditions. The review also highlights gaps in the current literature, including limited integration of hybrid treatment cycles, insufficient understanding of coupled diffusion-precipitation mechanisms, a lack of high-temperature performance data, and minimal industrial-scale validation. Future research directions are proposed to develop optimized hybrid processing strategies, predictive computational models, and scalable treatment cycles. This consolidated review provides a comprehensive foundation for advancing aluminum alloy design, aiming to achieve tailored surface-to-core property gradients suitable for next-generation aerospace and automotive applications.

Metals doi: 10.3390/met16050487

Authors: Zenghao Song Chengcong Ma Yuelu Chen Ke Li Feixiang Wang Tiqiao Xiao

The dynamic behavior within the melt pool governs the final quality of components fabricated by laser powder bed fusion (LPBF). To address key technical challenges—rapid keyhole evolution, low absorption contrast from metal vapor, and difficulties in quantifying internal flow fields—this study introduces move contrast X-ray imaging (MCXI), a technique leveraging time-series frequency characteristics. Combined with a multi-scale Horn–Schunck global optical flow method, MCXI enables full-field quantitative extraction of the melt-pool velocity field. Experimental validation across feature points shows a relative deviation of less than 2% compared to independent manual feature-point tracking, confirming consistency with the best available experimental ground truth. Analysis reveals the keyhole tail evolution cycle comprises three distinct dynamic stages: expansion, stratification, and contraction, with its area increasing from 1329 μm2 to 6508 μm2 before stabilizing. For the first time, pore pinch-off events were quantitatively measured, revealing front and rear wall collision velocities of 7.98 m/s and 8.04 m/s, respectively, consistent with available high-fidelity simulations. Furthermore, analysis of the overall melt-pool momentum field demonstrates a near-equal distribution of positive and negative momentum, providing an internal self-consistency check confirming the absence of systematic directional bias in the extracted velocity field. This study enables quantitative analysis of LPBF melt-pool dynamics, providing a novel tool for process optimization and defect control.

Metals doi: 10.3390/met16050485

Authors: Cristiano Fragassa Jacopo Vetricini Mattia Latini Mattia Merlin Carlo Santulli

During the machining processes, surfaces are often contaminated by cutting fluids, metallic debris, and residual films, which may compromise subsequent operations (e.g., coating, bonding, or precision assembly). In the present study, the effectiveness of several cleaning methods applied to machined metallic surfaces was experimentally evaluated. A set of commonly used industrial metals, including stainless steels, alloy steels, aluminum alloys, and brass, was machined under controlled conditions and subjected to various cleaning treatments, including solvent-based cleaning, ultrasonic washing, and aqueous detergent processes. Surface conditions were first assessed through optical microscopy, focusing on machining grooves as preferential sites for contaminant accumulation. Then, scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) was employed to better identify residual contaminants. Optical observations highlighted the progressive removal of debris and lubricant residues, while SEM–EDS analyses revealed the presence of thin organic films and localized carbon-rich contaminants, even on apparently clean surfaces. Results show a consistent trend across all materials, with increasing cleaning effectiveness from solvent-based treatments to ultrasonic cleaning and specific aqueous detergent processes. Ultrasonic cleaning proved particularly effective in removing thin films and contaminants in complex geometries, whereas aqueous detergent treatment demonstrated superior performance in eliminating larger debris and achieving overall surface cleanliness. The findings, combining a broad experimental campaign across multiple materials, cleaning treatments, and characterization techniques, underline the importance of multi-scale characterization for a reliable assessment of cleaning efficiency and suggest that combined cleaning approaches may further enhance surface quality in demanding industrial applications.

Metals doi: 10.3390/met16050486

Authors: Kangning Shi Wanting Sun Zhenggang Niu Kebin Sun Yachao Wang Jinghui Xie Xiangqing Kong Ying Fu

Selective laser melting (SLM) offers a promising route for fabricating high-performance Cu–Sn alloys; however, the extremely transient thermal behavior of the molten pool and its influence on microstructural evolution and mechanical properties remain insufficiently understood. In this study, a finite element model based on ABAQUS was developed to simulate the transient temperature field and molten pool dynamics of Cu–10Sn alloy during the SLM process. By systematically varying the volumetric energy density (VED), the interplay among molten pool geometry, thermal characteristics, microstructure, and mechanical performance was investigated through a combination of numerical simulation and experimental investigation. The results reveal that increasing VED significantly enlarges the molten pool dimensions, elevates the peak temperature, and intensifies the maximum heating and cooling rates, thereby altering solidification conditions. At a VED of 208.33 J/mm3, the molten pool reached its maximum dimensions, with a length of 230 μm, a width of 161 μm, and a depth of 85 μm, resulting in the highest relative density within the investigated range (98.33%). Under this processing condition, the Cu–10 wt.% Sn (Cu–10Sn) alloy exhibited microhardness values of 190 HV near the solidified areas of melt pool interior and 208.4 HV near the solidified areas of melt pool boundary, accompanied by an ultimate tensile strength of 494 MPa. These findings elucidate the critical role of molten pool thermal behavior in governing microstructural refinement and mechanical properties of SLM-fabricated Cu–10Sn alloys and provide a mechanistic basis for understanding the effect of process parameters.

Metals doi: 10.3390/met16050484

Authors: Kaixuan Xue Jiayun Li Zhiqiang Yu Lin Ma Wenhui Ma Zekun Li Yukun Zhao Jijun Wu

Metallurgical batching—governing raw material proportioning across sintering, blast furnace ironmaking, converter steelmaking, and non-ferrous smelting—critically determines product quality, energy consumption, and production cost throughout the full process chain. Its inherent complexity, characterized by strong nonlinear physicochemical coupling, measurement delays of up to 1.5 h, and multi-source raw material disturbances, renders conventional linear programming and empirical methods inadequate for dynamic, multi-objective industrial environments. This review systematically examines 98 representative studies (2020–2026) on intelligent algorithms applied to metallurgical batching optimization. A two-dimensional analysis framework of the fusion algorithm function and metallurgical scene is established. All kinds of methods are divided into three categories: prediction-oriented, optimization-oriented and decision-oriented, covering four typical scenes of sintering burdening, blast furnace ironmaking, converter steelmaking and non-ferrous metal smelting. Traditional machine learning models achieve sintering burn-through point prediction with R2 ≈ 0.85 and offer superior interpretability via SHAP analysis. Deep learning architectures deliver blast furnace silicon content prediction with RMSE ≈ 0.04%, while multi-objective evolutionary algorithms provide mature Pareto optimization for batching cost and carbon objectives. Reinforcement learning holds long-term potential for closed-loop adaptive control but remains constrained by Sim-to-Real safety barriers. Converter steelmaking and non-ferrous smelting are identified as underexplored domains. Three priority directions are proposed: domain-adaptive predictive modeling for cross-plant generalization, real-time re-optimization embedding mechanism constraints, and safe reinforcement learning transfer via high-fidelity digital twins.

Metals doi: 10.3390/met16050483

Authors: Sergio Elizalde Mohammad Jahazi Henri Champliaud

Heat-assisted metal spinning comprises incremental forming routes, conventional spinning, shear spinning and flow forming, performed at elevated temperature to increase formability. This review consolidates the main advances of the last fifteen years. It outlines spinning mechanics and the rationale for heating (higher ductility, lower forming forces and microstructure control), then compares global and local heating strategies (furnace, flame, induction, laser and hot-gas convection) in terms of temperature uniformity, industrial practicality, energy efficiency and cost. Key process parameters (spindle speed, feed rate and thickness reduction) are discussed with respect to defect formation, and representative windows for defect mitigation are reported. Progress in modeling is reviewed, including coupled thermo-mechanical finite element simulations, damage/formability prediction and emerging data-driven optimization. The review also summarizes microstructural evolution under heat-assisted conditions, phase transformation, dynamic recrystallisation and grain growth, and its impact on final properties. Across more than 100 studies, evidence shows that robust thermal management can roughly double achievable deformation before failure and enables property tailoring in difficult-to-form alloys (Ni-based alloys, high-strength steels, Al, Mg and Ti). Remaining challenges include reliable in situ temperature measurement/control and improved predictive fidelity of simulations. Future opportunities include digital twins, real-time sensing and adaptive, machine-learning-assisted control.

Metals doi: 10.3390/met16050482

Authors: Hongwei Zhang Jiuju Zhang Yuming Chen Jiaqi Zhang Yantao Dou

Residual stress induced by shot peening (SP) is inherently unstable. Stress relaxation has attracted widespread attention, and related research has been carried out. This study aims to study the residual stress relaxation phenomenon in a shot-peened TC4 titanium alloy due to cyclic load. Numerical simulations and experiments were performed to investigate the effects of the applied load amplitude, the number of cycles, the depth and the load ratios. The study may make contributions to the literature on understanding the residual stress relaxation induced by shot peening. The numerical and experimental results showed that the relaxation rate of the residual stress is correlated to the applied stress amplitude. Most of the relaxation of the residual stress was observed in the first cycle, which is up to 47.2% and 62.3% after 1000 cycles for the two different shot peening intensities. After the high relaxation at the first cycle, the residual stresses gradually decreased at a lower rate, remaining almost stable for up to 1000 cycles. The experimental residual stress in the specimens at a load of 550 MPa decreased more than that for a load of 450 Mpa; the decrease was more than 29.6% for the 550 MPa load with 1000 cycles, and the relaxation was stable after 10,000 cycles. Also, the relaxations in the surface and depth were studied. The maximum residual stress was more prone to relaxation. The presented model of residual stress relaxation, validated with experimental data, showed good agreement for the residual stress relaxation.

Metals doi: 10.3390/met16050481

Authors: Saniya Arinova Aristotel Issagulov Gaukhar Koshebaeva Konstantin Okishev Assem Tuganbayeva Gulnara Ulyeva

This study investigates the effect of complex nanomodification combined with the simultaneous application of magnetic fields and mechanical vibration on the structure formation and performance properties of medium-alloy steel 40CrNi3MoV. Improving the structural homogeneity and operational characteristics of such steels remains an important task due to their widespread use in components operating under severe loading and wear conditions. The introduction of the nanostructured modifier InSteel-7 at a concentration of 0.03%, together with simultaneous magnetic and vibrational treatment of the melt, resulted in pronounced structural homogenization and grain refinement. Quantitative metallographic analysis using Thixomet Pro image analyzer revealed a significant refinement of the dendritic structure, with the secondary dendrite arm spacing decreasing from 73.9 μm to 27.9 μm. X-ray phase analysis confirmed the preservation of phase composition while indicating increased structural uniformity of the BCC matrix. Energy-dispersive spectroscopy and elemental micro-mapping demonstrated high chemical purity of the alloy and a uniform distribution of the modifier components. The combined treatment significantly improved the mechanical and tribological characteristics of the material. The average hardness increased from 390 HV to 510 HV, while tribological tests showed a reduction in wear track depth from 5.16 μm to 0.87 μm and a decrease in surface roughness from Ra 2.13 μm to 0.20 μm, indicating enhanced wear resistance.

Metals doi: 10.3390/met16050480

Authors: Bin Wu Zhaobo Wu Bibo Li Fengshuang Lu Ran Li Xiaojun Zhang Xinqing Zhao Feiyu Zhao Dongliang Zhao

This study investigated the relationship between Mn segregation, damping capacity, and mechanical properties of a Mn–Cu damping alloy after aging at different temperatures. The results showed that after aging, the alloy underwent spinodal decomposition, forming Mn-segregated regions, while α-Mn precipitates appeared at the grain boundaries. The microstructure resulting from spinodal decomposition promoted martensitic transformation, created twin boundaries, and enhanced damping capacity. As the aging temperature increased, the Mn content in the Mn-rich regions gradually rose, thereby raising the martensitic transformation temperature. The twin density first increased and then decreased, which may be attributed to the precipitation and broadening of the α-Mn phase along the grain boundaries of the Mn-rich regions when the aging temperature was too high. At an aging temperature of 425 °C, the tanδ reaches a maximum of 0.05, and the martensitic transformation temperature reaches 100 °C, at which point the tanδ remains 0.04. After aging at 425 °C, a preferred orientation along <001> develops. The [001] orientation has the largest Schmid factor, which is most favorable for the reversible motion of twin boundaries under external stress, thus achieving the highest energy dissipation. To summarize, by promoting the creation of fine {011} twins by means of spinodal decomposition and by increasing the [001] oriented grain fraction through texture development, aging enhances the damping properties of the Mn–Cu alloy. In particular, the aging at 425 °C can provide the best combination of the microstructure and texture conditions, providing the highest damping performance in a wide temperature range.

Metals doi: 10.3390/met16050479

Authors: Romanus C. Uwaoma Xolisa C. Goso Kgaogelo E. Lekgau Mopeli I. Khama Elias Matinde

Driven by global decarbonisation efforts and the pursuit of carbon neutrality in metallurgical processes, this study aimed to comparatively evaluate the performance of conventional fossil-fuel-based reductants (anthracite and coke) and an unconventional biochar alternative (charcoal) for the solid-state reduction of titanomagnetite concentrate. Reduction experiments were conducted at 1100–1400 °C under an inert argon atmosphere. The results showed that coke was a more effective reductant for titanomagnetite ore at 1400 °C, yielding degrees of reduction (DOR) and metallisation (DOM) of 97.3% and 96.9%, respectively. Overall, the results indicate that all three reductants exhibited varying degrees of metallisation and reactivity. The order of reactivity observed was charcoal > anthracite > coke; charcoal showed superiority in DOR at lower temperatures and also, the reaction rate of charcoal was higher compared to other reductants used in this study. The apparent average activation energies of charcoal, anthracite and coke, at 1100–1400 °C were calculated based on the Arrhenius equation, and they are 40.2, 60.0, and 74.4 kJ/mol, respectively. The activation energy of the charcoal is less than that using other reduction agents. Overall, the interfacial chemical reaction was found to be rate-controlling for the three reductants. This suggests that using a carbon-neutral reductant, such as charcoal, can be effectively utilised to reduce titanomagnetite ore at lower temperatures and at a fast reaction rate.

Metals doi: 10.3390/met16050478

Authors: Jiyao Wang Yifan Shi Shencheng He Zihao Zhao Heng Xiong Zhaowang Dong Yuhong He

The increasing demand for high-purity lead sulfide (PbS) for optoelectronic applications necessitates efficient methods to remove residual antimony sulfide (Sb2S3) from complex ores—a challenge due to their chemical similarity and fine intergrowth. This study presents a hybrid purification strategy combining vacuum distillation pretreatment with oxygen-free alkaline selective leaching. Thermodynamic analysis using Eh-pH diagrams revealed significant differences in the behavior of trace Sb2S3 and bulk PbS under alkaline conditions (pH 9–11), identifying a suitable window for selective dissolution. The process begins with mechanical ball milling to break Sb2S3 inclusions and improve reaction kinetics, followed by anaerobic leaching in a sealed reactor under inert atmosphere using a NaOH solution at a controlled potential (Eh 0.1–0.35 V vs. SHE). Multiple characterization techniques confirmed that Sb2S3 undergoes dissolution and conversion while the PbS phase remains intact. Notably, zeta potential measurements (−12.3 mV) and high conductivity (204 mS/cm) indicated the formation of a stable colloidal dispersion system favorable for interfacial reactions. Under optimal conditions, antimony removal exceeded 99% with lead loss below 1%. Overall, the proposed strategy offers a technically viable route to produce ≥99.9% pure PbS from polymetallic sources, addressing a longstanding separation challenge.

Metals doi: 10.3390/met16050477

Authors: Tomohiro Nishimura Daisuke Matsuwaka Hitoshi Ishida Masami Nohara Tetsuya Nakamura Yusuke Yamada Aoi Shoji

In this study, a Ti–48 at.% Al–2 at.% Nb–2 at.% Cr alloy was cast by bottom-pouring cold crucible induction melting (CCIM), and the shrinkage depressions formed in ingots during solidification were investigated. Ingots with different heights were produced, and shrinkage depression height and yield were evaluated based on longitudinal cross-sectional observations. The normalized ingot height ranged from 4 to 25, and the shrinkage depression height increased from 20 mm to 105 mm with increasing ingot height. The yield ranged from 77% to 97% and did not increase monotonically, exhibiting noticeable scatter even among ingots with similar heights. The casting rate ranged from 0.025 kg/s to 0.18 kg/s, and the shrinkage depression height increased with increasing casting rate, whereas no clear correlation was observed between the yield and the casting rate. When the nozzle inner diameter ranged from 2 mm to 5 mm, both the shrinkage depression height and the yield increased, accompanied by scatter. The Reynolds number was evaluated as a parameter representing the average flow condition of the pouring stream; however, shrinkage depression formation could not be uniquely explained by the Reynolds number alone, indicating that melt feeding behavior and heat extraction conditions must also be considered.

Metals doi: 10.3390/met16050476

Authors: Yuzhou Shi Arko Suryadip Dey Yazhou Qin

The prediction of metal fatigue life has evolved from classical empirical approaches to advanced, data-driven computational models. However, traditional methods struggle with large data scatter, complex variable-amplitude loading, and the cost of experimental testing. These limitations are particularly pronounced in additively manufactured (AM) components, which exhibit random porosity and are highly sensitive to process parameters. This review integrates classical fatigue mechanics with modern data-driven methodologies. It evaluates fatigue-life prediction for metallic alloys, welded assemblies, and AM materials. We review classical prediction tools, machine learning (ML) algorithms, deep learning architectures, and physics-informed neural networks (PINNs). ML models capture nonlinear degradation patterns but suffer from limited interpretability (“black-box” behavior) and are unable to extrapolate from small datasets. Embedding governing physical laws into PINNs helps mitigate these limitations. This approach enhances physical consistency, reduces training-data requirements, and strengthens extrapolation capability. In additively manufactured metals, defect location is often a more critical predictor of fatigue failure than defect size or morphology. To address data scarcity, we highlight the use of generative adversarial networks and transfer learning. Integrated models, combined with real-time structural health monitoring data, enable accurate, dynamic digital twins and preemptive fatigue prognosis.

Metals doi: 10.3390/met16050475

Authors: Pedro F. Mayuet Ares Lucía Rodríguez-Parada Sergio de la Rosa Moises Batista

Abrasive waterjet machining (AWJM) is widely used for cutting aerospace aluminum alloys, but exit-side defects associated with jet lag can degrade surface integrity and dimensional accuracy. This work investigates the influence of water pressure, abrasive mass flow rate, and traverse feed rate on the formation of jet-lag defects at the exit side of cuts in UNS A92024 aluminum alloy plates of 10 mm thickness. A full factorial 33 experimental design was implemented to manufacture 27 square samples (20 × 20 mm), which were subsequently characterized by optical microscopy at 20× magnification. The semicircular jet-lag defects were quantified using Imaging processing techniques to determine their projected area, and the resulting data were analyzed with multifactor ANOVA and multiple linear regression. The results show that traverse feed rate and water pressure have a statistically significant effect on defect area, with traverse feed rate being the most influential factor, whereas the abrasive mass flow rate plays a secondary role within the investigated range. Combinations of high water pressure and low traverse feed rate led to cleaner cuts with reduced exit-side damage, and contour plots allowed the identification of operational windows that minimize defect formation. The proposed methodology provides a systematic framework for characterizing jet-lag defects in AWJM and can be extended to other alloys, thicknesses, and advanced characterization techniques to support process optimization in industrial applications.

Metals doi: 10.3390/met16050474

Authors: Xin Xin Meixia Fu Wei Li Hongbing Wang Qu Wang Yifan Lu Zhenqian Wang Yuntian Brian Bai Tao Gu Changyuan Yu Jianquan Wang

The stability of mold level fluctuations (MLFs) is crucial for product quality and process efficiency in continuous casting. Abnormal mold level fluctuations, which are typically associated with multiple factors including stopper rod opening, casting speed, and mold width, are known to lead to slab quality defects. In this paper, an Informer-based prediction framework is proposed for the early detection of abnormal MLF. A threshold-based labeling method is developed to quantify the future likelihood and severity of anomalies across different time horizons. Considering the importance of frequency-domain features in mold level prediction, power spectral density (PSD) features are incorporated and smoothed using the exponential moving average (EMA) to enhance predictive performance. Through the integration of temporal and processed spectral features, early indicators of abnormality can be captured, and proactive warnings can be issued. The proposed architecture is validated using approximately 32.5 million data points from a real-world continuous casting process. This approach provides a robust and data-driven solution for predicting and diagnosing abnormal MLF events in continuous casting. Experimental results show that the mean ROC-AUC and PR-AUC reach 0.821 and 0.418, respectively.

Metals doi: 10.3390/met16050473

Authors: Kunjie Luo Pu Zhao Kewei Fang Wanxiang Zhao Jiachang Lu Hongqun Liu Shuiyong Wang Mengmeng Zhu Yanxin Qiao

In nuclear power, marine engineering, and other fields, a matching system composed of duplex steel and copper alloy is a common combination for rotating components in a seawater environment. However, this system is susceptible to galvanic corrosion that seriously threatens its service safety and service life, with ZCuAl10Fe5Ni5 being the main component corroded. Additionally, current corrosion research on this system has evident gaps. Specifically, the influence of area ratio on galvanic corrosion remains insufficiently understood, and the action mechanism of Cl− on the ZCuAl10Fe5Ni5-based corrosion product film in seawater, as well as the product evolution path, has not been fully revealed, which restricts the development of targeted protection technologies. This study explores the degradation mechanism of ZCuAl10Fe5Ni5 in a specific high-salinity environment (20,000 mg/L Cl−), characteristic of nuclear power plant service conditions. The results show that due to the significant electrode potential difference between the SAF2507 duplex steel and ZCuAl10Fe5Ni5 copper alloy, a stable galvanic couple is formed, with ZCuAl10Fe5Ni5 acting as the anode and undergoing dissolution corrosion. When the area ratio of ZCuAl10Fe5Ni5 (anode) to SAF2507 duplex steel (cathode) is 1:50, a significantly stronger galvanic effect is observed. The high concentration of Cl− in seawater can damage the surface of the ZCuAl10Fe5Ni5-based corrosion product film, leading to intensified local corrosion. The ZCuAl10Fe5Ni5-derived corrosion products have a layered structure mainly comprising a mixed system of Cu-Al-Mg oxides/hydroxides, and the corrosion process is accompanied by selective aluminum depletion corrosion. This study provides insight into the corrosion mechanism and key influencing factors of ZCuAl10Fe5Ni5 in the matching system, as well as a theoretical basis and technical support for the design of compatibility metal materials in a seawater environment and the control of corrosion in ZCuAl10Fe5Ni5.

Metals doi: 10.3390/met16050470

Authors: Shuo Yang Hongxiang Hu Wentao An Zitong Wen Jihang Liu Zhanwei Zhang Yanjie Yuan Zhengbin Wang

This study investigates the influence of the depth of lattice-array micro-pillar surface microstructures on the cavitation erosion (CE) of nickel-aluminum bronze (NAB) in a saline solution using both experimental and simulation methods. Mass-loss measurements, electrochemical tests, and morphological characterizations (SEM, white-light interferometry, EBSD) were conducted to clarify the erosion, corrosion, and synergistic components. Pressure distribution, vapor volume fraction, and bubble dynamics were revealed by numerical simulation in the cavitation region. Results show that shallow microstructures (0.02 and 0.07 mm depths) significantly reduce the CE by up to 74% compared to the smooth surface. This structure can form a shielding field and suppress the mechanical erosion component. In contrast, deep microstructures (0.18 and 0.22 mm depths) aggravate CE, which is attributed to increased bubble nucleation and localized vapor content, and intensified pressure difference. The pure erosion component dominates the damage, followed by synergistic action, and the pure corrosion component is the least. This trend is independent of the change in the microstructure. These findings extend the knowledge on how to design the microstructure depth to alleviate CE.

Metals doi: 10.3390/met16050472

Authors: Zhang Liu Li Chen Ma Dang Ying Wu Xu

As a strategically important metal, vanadium (V) plays a crucial role in resource security, and its efficient extraction is therefore of great significance. Traditional sodium roasting processes suffer from gaseous pollutant emissions and high costs, while calcification roasting–acid leaching has emerged as an alternative due to its environmental friendliness and economic viability. This study focuses on VTS (mainly composed of FeV2O4 and Fe2SiO4), systematically optimizing the calcification roasting–hydrochloric acid leaching process and investigating its reaction mechanism. By comparing the Gibbs free energy changes of reaction products and the acid leaching process with different additives using DFT calculations, calcium oxide was selected as the optimal calcifying agent. Experimental results show that CaO significantly promotes the transformation of FeV2O4 into soluble calcium vanadate and preferentially reacts with SiO2 to inhibit vanadate encapsulation, creating a structural basis for the selective dissolution of V. Under optimal process conditions, the leaching efficiency of V can reach 94.23%. Furthermore, density functional theory (DFT) calculations substantiate that the inherently weak bonding in Ca2V2O7 facilitates its effortless dissociation during the acid leaching phase. The Douglas hierarchical decision-making method is further adopted for secondary economic potential, and this proposed method has the lowest investment risk. This study provides an experimental and theoretical basis for the efficient and clean extraction of vanadium.

Metals doi: 10.3390/met16050471

Authors: Jie Wang Libin Yang Jiaqing Zeng Shengtao Qiu Yong Yang

Given the increasing demand for low-phosphorus molten iron in high-value-added steel production and the rising phosphorus content in raw materials caused by the use of high-phosphorus ores in blast furnaces, the traditional converter single-slag process faces challenges such as high dephosphorization pressure, high slag consumption, and unstable endpoint control. This study systematically investigates the process principles and key influencing factors of the converter double-slag method (MURC process) as an efficient pretreatment technology for molten iron. Through thermodynamic analysis combined with industrial tests, the core process parameters affecting dephosphorization efficiency were identified, including temperature, slag basicity (R), iron oxide (T.Fe) content, and bottom-blowing stirring intensity. The results show that the optimal temperature during the dephosphorization stage is 1350–1400 °C, with slag alkalinity controlled at 1.6–2.0 and T.Fe content maintained at 19–23%. During the decarburization stage, the optimal temperature is 1620–1640 °C, and the final slag alkalinity should be increased to above 3.5. After applying the optimized “low-high-low” oxygen supply pattern and enhanced bottom-blowing stirring (0.04–0.20 Nm3/(t·min)), significant improvements were achieved in industrial practice on 180-t and 60-t converters. Lime consumption was reduced by more than 30%, the average endpoint phosphorus content decreased by approximately 0.005%, the phosphorus removal rate remained stable at above 90%, and the oxygen content in molten steel at the endpoint decreased by 50–100 ppm. This study provides a systematic theoretical basis and practical guidance for efficient and stable dephosphorization using the converter double-slag process.

Metals doi: 10.3390/met16050469

Authors: Shucheng Yang Jiahao Liu Shuwen Guo Jing Zhang Huaikun Zhu Zhenjie Ren Yanting Pan Lida Che Zhanfang Wu Xiangyang Li Dianchun Ju

The corrosion behavior of high-entropy alloys under cyclic wet–dry conditions simulating the salt-lake atmosphere was investigated. The composition, morphology, and electrochemical properties of the corrosion products formed on the alloy surface after corrosion were systematically analyzed. The results show that in a chloride-containing environment with alternating temperature and humidity, the Cr-containing oxide passive film formed on the alloy surface effectively inhibits the corrosion process in the early stages. In addition, electrochemical results show that the charge transfer resistance in the MgCl2 system reaches 4.96 × 105 Ω·cm2 at prolonged exposure, which is significantly higher than that in the NaCl system, indicating a lower corrosion rate. However, over time, the passive film undergoes localized rupture due to chloride ion attack and stress, leading to pitting corrosion and expansion toward the substrate. This study reveals the corrosion mechanism of high-entropy alloys in high-altitude salt-lake atmospheric environments and provides crucial insights for material design and performance optimization for their engineering applications in salt-lake scenarios.

Metals doi: 10.3390/met16050467

Authors: G. Lima Antunes J. P. Oliveira

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

Metals doi: 10.3390/met16050468

Authors: Mirza Manjgo Gorazd Lojen Jure Bernetič Mihajlo Aranđelović Tomaž Vuherer

Welded joints are widely recognized as the most critical point in structures made of armour steels due to pronounced thermal effects, microstructural heterogeneity, and the degradation of mechanical and fatigue properties. This study investigates the mechanical properties and fatigue crack growth resistance of a welded joint produced on SA 500 armour steel, with the aim of preserving the properties of the base material as much as possible. To achieve this, a welding procedure incorporating a high-strength filler wire and optimized welding parameters was applied. Hardness and tensile testing was conducted to evaluate the extent of property degradation caused by welding. The results demonstrate that the applied welding process effectively limited the reduction in hardness and tensile strength, achieving values reasonably close to those of the base material. In addition, fatigue crack growth behaviour was investigated in accordance with ASTM E647, using both the Paris law and the McEvily law. The obtained fatigue crack growth curves and threshold stress intensity factor (ΔKth) values indicate the nearly identical fatigue behaviour of the base material and the heat-affected zone, confirming the successful preservation of base material fatigue behaviour in the thermally affected zone. Moreover, the weld metal exhibited superior resistance to fatigue crack initiation and growth. Overall, the results confirm that the proposed welding approach provides favourable mechanical and fatigue performance for welded joints in armour steel applications.

Metals doi: 10.3390/met16050466

Authors: Songjie Zhou Weilin Chen Rongjun Yang Hongwu Liu Lingxin Zhou Weizhou Li Minming Jiang Xiayun Shu

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

Metals doi: 10.3390/met16050465

Authors: Saurabh Tiwari Seong Jun Heo Nokeun Park

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

Metals doi: 10.3390/met16050464

Authors: Maxim Bassis Amnon Shirizly Eli Aghion

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

Metals doi: 10.3390/met16050463

Authors: Hao Liu Jie Yao Shi Yan

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

Metals doi: 10.3390/met16050462

Authors: Chih-Chun Hsieh Huei-Sen Wang

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

Metals doi: 10.3390/met16050461

Authors: Jianping Huang Youxuan Ouyang Yuanyuan Zeng Huayu Xiao Juangang Zhao Qiang Zhang

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

Metals doi: 10.3390/met16050460

Authors: Guanfeng Huang Shuai Pan Chao Dong Qiliang Chen Khadija Fnu Zian Li

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

Metals doi: 10.3390/met16050459

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

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

Metals doi: 10.3390/met16050458

Authors: Mingzhe Bu Shengyuan Niu Xueda Li Bin Han

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

Metals doi: 10.3390/met16050457

Authors: Luís Vilhena Tsering Wangmo Barnabas Erhabor Bruno Figueiredo Amílcar Ramalho

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

Metals doi: 10.3390/met16050456

Authors: Nannan Zhu Kerong Wang Bing Liu Jiejing Li Jianxiu Su Yongwei Zhu Jiapeng Chen

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

Metals doi: 10.3390/met16050455

Authors: Hongda Yao Nan Wang Min Chen Xiaoqing Chen

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

Metals doi: 10.3390/met16050454

Authors: Qiao Yin Huaxiang Zha Chunwen Guo Junjie Li Hongliang Zhao Shuya Zhang Xianglei Dong Yuheng Fan

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

Metals doi: 10.3390/met16040453

Authors: Anil Singh Andreas Bezold Michael J. Mills Boian T. Alexandrov

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

Metals doi: 10.3390/met16040452

Authors: Yanqi Ye Tianliang Fu Yueman He Chenyang Gu Guanghao Liu

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

Metals doi: 10.3390/met16040451

Authors: Yuyu Guo Yanlin Gu Zhen Yan Juan Hou

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

Metals doi: 10.3390/met16040450

Authors: Majid Ramezanpour Aghdami Ashkan Mohammad Beygian Eskandar Keshavarz Alamdari

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

Metals doi: 10.3390/met16040449

Authors: Jose Luis Lanzagorta Julen Mendikute Irati Sanchez Paula Ruiz Iratxe Aizpurua-Maestre Jokin Munoa

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

Metals doi: 10.3390/met16040448

Authors: Meirong Jiang Yulun Wu Qing Wang Jie Fu Jinjin Shang Tao He Longchao Huang Kaixuan Wang Zhongqiu Liu Xianghong Liu

Vacuum arc remelting (VAR) is essential for producing premium titanium alloys, where an externally applied alternating magnetic field enables circumferential stirring to control ingot homogeneity. However, current magnetic field parameter design relies on empirical trial-and-error approaches, lacking systematic theoretical guidance. To address this issue, this study establishes a comprehensive multi-physics framework through a two-dimensional axisymmetric swirl model integrating electromagnetic, fluid dynamics, thermal, and solute transport phenomena. Our findings demonstrate that both the magnetic field strength and period exhibit optimal operating ranges, which directly influence ingot homogeneity. As magnetic field strength increases progressively, ingot uniformity shows a distinctive non-monotonic response—initially improving before subsequently deteriorating. Correspondingly, with increasing stirring period, macrosegregation undergoes a distinct three-stage evolution: initial mitigation, subsequent aggravation, and final alleviation. These phenomena originate from the small-scale circulatory flow generated by the external magnetic field on the surface of the VAR molten pool. The interactions among the flow, the solute diffusion layer, and the mushy zone collectively alter elemental diffusion behavior, ultimately determining the homogeneity of the ingot. This study provides a theoretical foundation for precise control of ingot homogeneity in titanium alloy VAR processes and demonstrates significant potential for engineering applications.

Metals doi: 10.3390/met16040447

Authors: Mengze He Zhiyao Ouyang Qiang Zhong Jianxiong Zhang Ziyu Li Jinwen Ye

The demanding operational requirements of ultra-deep oil and gas exploration present formidable challenges for material performance, necessitating the development of novel cemented carbides that combine high strength-toughness with exceptional corrosion resistance. In this study, Cr2(C,N) was employed as a grain inhibitor to introduce N into the dual-scale structured WC-Co cemented carbide system for the fabrication of novel cemented carbides. The effects of Cr2(C,N) addition on the microstructural organization, mechanical properties and corrosion resistance behavior were systematically investigated. The experimental results show that the addition of Cr2(C,N) effectively prevents the direct contact of these coarse WC grains and allows more fine WC grains to be retained to fill the regions between these coarse WC grains and the Co binder phase, thereby suppressing Co pool formation and resulting in a continuous and uniform Co binder network. When the addition amount of Cr2(C,N) reaches 0.6 wt.%, the dual-scale structured cemented carbide achieves the optimal comprehensive mechanical properties, with a transverse rupture strength of 3182.3 MPa, a fracture toughness of 18.68 MPa·m1/2, and a hardness of 1140.4 HV30. Meanwhile, the optimization of microstructure, the formation of a passive film, and the stabilization of the fcc-Co phase jointly contribute to the superior corrosion resistance of this composition.

Metals doi: 10.3390/met16040446

Authors: Yong-Woo Kim Min-Kyu Paek Sun-Joong Kim

The present work investigated the thermodynamic behaviors of oxygen in a liquid Fe–Ti alloy over a wide Ti concentration range of 11.6–71.2 wt% at 1873 K by integrating equilibrium experiments with thermodynamic modeling. To prevent excessive oxidation during the equilibrium experiments, the liquid alloys were equilibrated in a purified Ar atmosphere with an oxygen partial pressure below ~10−20 atm. Two quenching methods—furnace quenching with He gas injection and water quenching via quartz tube suction—were employed to evaluate the effect of cooling rate on total oxygen measurements. While He gas quenching led to higher measured oxygen contents owing to the formation of secondary Ti oxides, the quartz tube suction quenching method consistently yielded significantly lower oxygen values. The dissolved oxygen content increased with increasing Ti content. Electron probe microanalysis identified TiO as a stable equilibrium oxide phase above 11.6 wt% Ti, which was characterized as a face-centered cubic (FCC) rock-salt structure via electron backscatter diffraction analysis. Based on these results, a thermodynamic assessment of oxygen behavior in a liquid Fe–Ti alloy in equilibrium with TiO was performed for the first time using a modified quasichemical model. Consequently, the present model successfully reproduced the Ti–O relationship in the liquid Fe–Ti alloy across both the high-Ti concentration region saturated with TiO and the low-Ti concentration region saturated with Ti2O3 and Ti3O5.

Metals doi: 10.3390/met16040445

Authors: Valentin Kamburov Rayna Dimitrova

The article discusses the methods for classifying processes for testing and processing metals by plastic deformation, based on the characteristics of their stress–strain state. The basic methods for determining the stress and strain states using fundamental scalar quantities representing the stress and strain tensors are discussed. Equations have been derived for the quantitative determination of the type of stress–strain state through a combination of principal stresses, represented as the strain rigidity of the deformation mode. A deformable work-hardening alloy, AA7075, from the database Quantor Form 8.2.4 software product, is used, which is deformed at room temperature with an analysis of elastic–plastic deformations. A classification of deformation processes for testing and processing metals by plastic deformation is proposed, using the stress triaxiality parameter and the strain rigidity coefficient. Some 2D and 3D diagrams have been created based on simulation modeling of plastic deformation processes using virtual tools, allowing the grouping of processes according to the measured principal stresses and their combinations, which represent the stress triaxiality and strain rigidity of the deformation mode. By determining the type of grouping in these diagrams and the change in the stress–strain state with increasing strain levels, the characteristic features of the deformation processes used in materials testing and in the processing metals by plastic deformation of metals/alloys have been confirmed.

Metals doi: 10.3390/met16040444

Authors: Yaning Cui Chenggang Hao Bofan Dai Hui Peng Wenchao Yang

X ray photoelectron spectroscopy (XPS) is a key technique routinely employed for the chemical analysis of alloy surfaces, enabling precise nanoscale characterization of near surface elemental composition and chemical states. This review outlines the fundamental principles of XPS, typical data analysis workflows, and critical analytical considerations specific to alloy systems. Given the propensity for oxidation, multicomponent nature, and heterogeneous phase characteristics of alloys, standardized protocols are reviewed for sample preparation, binding energy calibration, peak fitting, quantitative analysis, and depth profiling. For conductive alloys, calibration using the Fermi edge or gold reference standards is specified, and the use of Auger parameters is highlighted to improve the reliability of chemical state identification. This article also systematically summarizes applications of XPS in corrosion protection, high temperature oxidation, surface modification, phase transformation, and failure analysis. It is emphasized that near surface chemical information must be validated in combination with bulk phase, microstructural, and electrochemical characterization to rationally establish relationships between surface chemistry and macroscopic performance. Finally, recent advances in near ambient pressure, in situ, high resolution, and intelligent XPS techniques are reviewed, providing a standardized reference and technical support for alloy research.

Metals doi: 10.3390/met16040443

Authors: Jidapa Leelaseat Aekkapon Sunanta Surasak Suranuntchai

This study presents a comparison between the results of process parameter optimization for the deep drawing of an AA5754-O automotive fuel tank, which utilizes two different objective functions. The first objective function is the maximum thinning percentage (max. %Thinning) of the formed part, which is a conventional formability index. The second is Q-value, a metric derived from the Thinning Limit Diagram that accounts for both necking-prone (excessive thinning) and wrinkling-prone (thickening) regions. The experiments were conducted using finite element simulation to model the forming behavior under an inscribed central composite design within the response surface methodology. Three process parameters, which are well known to be important for controlling material flow and achieving a balance between wrinkling and excessive thinning in deep drawing, were varied: blank holder pressure, the height of the male drawbead, and the radius of the female drawbead. Refined second-order response surface models were developed for both objective functions. Optimization based on the response surface models showed that, for the max. %Thinning objective function, the final part exhibited 19.46% maximum thinning but suffered from substantially higher wrinkling, as indicated by a maximum thickening of 36.39%. In contrast, the Q-value-based optimization resulted in a more balanced formability condition, with maximum thinning of 21.74% and maximum thickening of 13.17%. Moreover, the normalized density of elements in the safe zone of the Thinning Limit Diagram was higher, indicating an improvement in formability robustness. Therefore, this study highlights the limitations of conventional thinning-based optimization and demonstrates the potential of the Q-value as an extended practical quantitative formability tool that can simultaneously address necking and wrinkling in sheet metal forming, as presented through the studied automotive fuel tank on behalf of complex components.

Metals doi: 10.3390/met16040442

Authors: Bo Su Siqi Zhang Xingyang Xu Tong Zhao Huifen Yang Junyao Liu

To achieve the large-scale, high-value utilization of vanadium–titanium slag (VTS) in the metallurgical industry, this study replaces blast furnace slag (BFS) with VTS to construct a quaternary all-solid-waste cementitious system composed of VTS, BFS, steel slag (SS), and desulfurization gypsum (DG). It systematically investigates the effects of VTS content (0–60%) on the mechanical properties, leaching toxicity, and hydration heat behavior of the system. XRD, TG–DSC, and SEM–EDS techniques are employed to explore the influence of VTS on hydration behavior and microstructural evolution. The results show that when VTS replaces 30% of the BFS (A3, VTS:BFS:SS:DG = 3:3:3:1), the 28-day compressive strength reaches 31.33 MPa. The leaching concentrations of heavy metals in all specimens are far below the standards for drinking water quality. Hydration heat analysis reveals that the incorporation of VTS advances the acceleration period of hydration. The A3 specimen maintains a relatively high heat release rate in the middle and later stages (after 72 h), and its cumulative heat release is significantly higher than that of the system without VTS, revealing the “slow hydration” mechanism of VTS at later stages. The [SiO4]–[AlO4] bonds in VTS undergo a depolymerization–repolymerization process. In addition, an appropriate amount of VTS promotes the deposition of hydration products such as ettringite (AFt), C–S–H, and C–A–S–H gels through micro-filling effects and heterogeneous nucleation, thereby improving the microstructure of the system. However, excessive VTS (≥45%) significantly inhibits the hydration reaction and reduces gel formation due to the decrease in highly reactive BFS components and the increased TiO2 content. This study provides new insights into the resource utilization of VTS in multi-solid-waste cementitious materials. In addition, VTS-based cementitious materials are suitable for practical scenarios with low early strength requirements, such as goaf backfilling. Therefore, future studies should further investigate the long-term sulfate resistance and carbonation resistance of these materials under real application conditions.

Metals doi: 10.3390/met16040441

Authors: Mutian Niu Jiahao Chen Zhenbao Liu Jiarui Hu Zhiyong Yang Yonghua Duan Xiaohui Wang

High-strength stainless steels are essential materials for critical load-bearing aerospace components, and solution treatment serves as a core process governing their strength–toughness balance. However, in novel multi-element alloy systems, the complex dissolution behavior of precipitates and its underlying mechanisms affecting matrix phase transformations require further investigation. This study systematically explores the thermodynamic evolution and microstructural response of a novel Fe-Ni-Cr-Mo-Al-Ti ultra-high-strength stainless steel during solution treatment. The research highlights how solution temperature drives Laves phase dissolution, controls prior austenite grain growth, redistributes local chemical elements, and dictates retained austenite stability. By establishing the relationship between microstructural features and macroscopic properties, this study aims to provide crucial theoretical guidance for optimizing heat treatment protocols to achieve superior comprehensive mechanical properties in advanced high-strength stainless steels.

Metals doi: 10.3390/met16040440

Authors: Nicole Atmadja Mamidala Ramulu

This article comprehensively reviews the fatigue crack growth (FCG) models applied to Ti6Al4V alloy manufactured by electron beam melting (EBM) powder bed fusion (PBF). The current progress in FCG analytical and numerical models and their application to EBM Ti6Al4V are reviewed. Much experimental data for the creation of historical FCG models was based on conventionally manufactured (CM) aluminum alloys and various steels. With the growth of additive manufacturing (AM), recent studies have applied traditional models and modified new models to EBM Ti6Al4V and validated their use as accurate predictive models for the da/dN-ΔK curve and ΔKth. Due to pores and surface roughness inherent in AM and the unique anisotropic microstructure developed from the EBM process, classical models may require modifications to accurately predict FCG of EBM Ti6Al4V.

Metals doi: 10.3390/met16040439

Authors: Olga Samoilova Svetlana Pratskova Polina Plotnikova Nataliya Shaburova Mariappan Anandkumar Evgeny Trofimov

The microstructure, phase composition, and high-temperature oxidation behavior of Al0.5CoCr0.5NiPt0.1 and AlCoCr0.5NiPt0.1 multi-principal element alloys (MPEAs) at 1100 °C in air were investigated. Depending on the content of aluminum, the microstructure of as-cast samples contains FCC and BCC solid solutions. Similarly, the ratio of two solid solutions varies depending on the aluminum content in the alloy. When the content of aluminum is x = 0.5, the microstructure is dominated by the FCC solid solution, while a BCC solid solution is dominated when the concentration of aluminum is increased to x = 1.0. Moreover, in both MPEAs, platinum exists as a part of solid solutions rather than a separate phase. High-temperature oxidation was carried out in a Plavka.Pro PM-1 SmartKiln muffle furnace under isothermal conditions at 1100 °C for 100 h exposure in air, and weighing was performed every 10 h. The maximum specific weight gain for the Al0.5CoCr0.5NiPt0.1 alloy was 0.965 mg/cm2, and 0.675 mg/cm2 for the AlCoCr0.5NiPt0.1 alloy. Based on the high-temperature oxidation experiment results, it was established that AlCoCr0.5NiPt0.1 MPEA exhibits greater resistance towards high-temperature dry air corrosion with the formation of an exclusive Al2O3 scale on the surface with 3–5 μm thickness; the parabolic oxidation rate constant for this alloy is kp = 20.2 × 10–13 (g2/cm4s). Introduction of platinum into the composition of the Fe-free AlCoCr0.5Ni alloy reduces the value of the parabolic oxidation rate constant by half.

Metals doi: 10.3390/met16040438

Authors: Florian Funcke Sebastian Brummer Marinus Kolbinger Peter Mayr

Laser Powder Bed Fusion (PBF-LB) is currently one of the most versatile and adopted additive manufacturing technologies for printing metals. To take new PBF-LB machines into service, a thorough characterization and calibration is often necessary to get the desired output. This is commonly achieved empirically; however, data-driven methods have become more and more available over the last few years. This research explores the use of transfer learning (TL) to transfer process knowledge from an already-established source machine (Nikon SLM 500) to a target machine (Trumpf TruPrint 5000) with different hardware specifications. To predict the tensile properties of AlSi10Mg0.5 utilizing a minimal data set of merely 25 training samples, eight TL model variants, determined by their degrees of training freedom, were investigated. The results showed that TL is effective in transferring machine learning (ML)-based process models. High prediction accuracy was achieved on the target machine, with coefficient of determination (R2) values reaching 75.5% for yield strength, 82.1% for ultimate tensile strength, and up to 92.0% for elongation at break in testing. Additionally, a weighted mean model ensemble of all eight single models was developed, including all eight TL variants, to enable higher prediction robustness. Validation trials for three different use cases confirmed the capability of the approach to optimize processing conditions, like increasing hatch scan speed by 167% to 292% while maintaining high mechanical performance. Additional microstructure analysis was given to support the findings. The results demonstrate a time- and resource-efficient approach for rapid industrialization of PBF-LB machines, combining ML-based process modeling with machine-specific data.

Metals doi: 10.3390/met16040437

Authors: Gauhar Yerekeyeva Bauyrzhan Kelamanov Vera Tolokonnikova Assylbek Abdirashit

This study investigates the phase formation and smelting process of a complex Al-Si-Mn alloy based on thermodynamic diagram analysis (TDA). The Fe-Si-Mn-Al system was analyzed considering binary and ternary subsystems, and the standard Gibbs free energy of formation of selected ternary compounds was calculated using the additive method. Based on these results, phase equilibrium diagrams were constructed, and the system was tetrahedralized, leading to the identification of 15 thermodynamically stable tetrahedra. It was established that compositions of industrial interest are predominantly localized within tetrahedra enriched in silicide and aluminosilicide phases, particularly FeSi-Fe2Al2Si-Fe3Al11Si6-Mn5Si3. Experimental verification was carried out in a 250 kVA ore-thermal furnace using manganese ore, high-ash coal, and quartzite. The smelting process was conducted under slag-free conditions with stable electrical operation. The obtained alloy had the following composition (wt.%): Fe ~ 12.1, Si ~ 44.7, Mn ~ 34.5, and Al ~ 5.1, with low impurity levels (C < 0.5%, S < 0.02%, p < 0.09%). Microstructural analysis using SEM-EDS confirmed the formation of silicide (FeSi, Mn5Si3) and aluminosilicide phases, which ensure the structural stability of the alloy. It is shown that the localization of alloy compositions within specific tetrahedra of the Fe-Si-Mn-Al system prevents self-disintegration. The results demonstrate that TDA is an effective tool for predicting phase composition and optimizing the production technology of complex ferroalloys.

Metals doi: 10.3390/met16040436

Authors: Kirill V. Pikulin Stanislav N. Tyushnyakov Roza I. Gulyaeva Sofya A. Petrova Andrey N. Dmitriev Galina Yu. Vitkina

Phase formation characteristics during the thermochemical reduction of metals from natural coltan using aluminum and calcium–aluminum alloy at 1400–1450 °C were investigated to develop methods for extracting niobium and tantalum from rare metal raw materials. The studied coltan sample consists of a columbite–tantalite solid solution with the composition (Mn,Fe)(Nb,Ta)2O6, cassiterite Sn0.9O2, tapiolite (Ta,Nb)2(Mn,Fe)O6, and calcioolivine Ca2SiO4. This study established that the choice of reducing agent determines the sequence of oxide phase transformations. During the aluminothermic process, orthorhombic columbite–tantalite is completely reduced, while tetragonal tapiolite persists even at 1400 °C. The use of a calcium–aluminum alloy containing 69.4 wt.% Ca results in a reversal of this trend: tapiolite is reduced at the early stages (800–1250 °C) through an intermediate (Ta,Nb)O2 phase, whereas the columbite–tantalite solid solution remains up to 1250 °C. Calcium, having a high affinity for oxygen, forms intermediate perovskite-type oxide phases that act as diffusion barriers, limiting the access of the reducing agent to residual mineral inclusions (mainly Nb-Ta minerals of the orthorhombic crystal system). A temperature rise to 1450 °C initiates the redistribution of oxide components: the content of CaNbO3 decreases, the Ca2(Nb,Ta)AlO6 phase disappears, and its components are involved in the formation of Ca(Nb,Ta)0.25MnO2.74 and Ca4Nb2O9. Diffusion constraints are reduced, and the residual columbite–tantalite solid solution is reduced, as confirmed by its complete absence in the products at 1450 °C. In the metallic phase, solid solutions of tantalum and niobium, Ta-Nb-Sn intermetallic compounds (Ta,Nb)3Sn, titanium aluminide, and ferroalloys with an increased (Ta,Nb)/(Fe,Mn) ratio are formed. The phase transformations elucidated during metallothermic reduction of coltan using different reducing agents, together with the formation of metallic and intermetallic phases, establish a scientific foundation for the development of advanced rare metal extraction processes.

Metals doi: 10.3390/met16040435

Authors: Karina Suárez-Alcántara Nidia Libia Torres-García Paula del Carmen Cintron-Núñez Joaquín Eduardo González-Hernández Jorge Mauricio Cubero-Sesin Espiridión Martínez-Aguilar Rigoberto López-Juárez

A mandatory prerequisite for a good hydrogen storage material is long-term stability in hydriding/dehydriding reactions, in a suitable temperature interval (250–350 °C for magnesium intermetallics). A 50-cycle hydriding/dehydriding stability test of two Mg2(Co1/3Fe1/3Ni1/3) materials is presented. Mg2(Co1/3Fe1/3Ni1/3) was processed progressively by ball milling and annealing, followed by high-pressure torsion. A comparison of the effects of the processing on the cycling test is presented. X-ray diffraction, scanning and transmission electron microscopy, and infrared characterization indicate the morphological and structural changes in the materials after production and cycling. The highest hydrogen storage was 3.55 wt.% and 3.25 wt.% for the ball-milled and annealed Mg2(Co1/3Fe1/3Ni1/3) and high-pressure torsion processed Mg2(Co1/3Fe1/3Ni1/3), respectively, at 15 bar and 300 °C. After 50 cycles of hydriding/dehydriding reactions, the hydriding onset temperature is 69 °C and 50 °C for the ball-milled and annealed Mg2(Co1/3Fe1/3Ni1/3) and high-pressure torsion processed Mg2(Co1/3Fe1/3Ni1/3), respectively. Meanwhile, the dehydriding onset temperatures are 257 °C and 223 °C, with hydrogen storage losses of 16% and 7.4% for the ball-milled and annealed Mg2(Co1/3Fe1/3Ni1/3) and the high-pressure torsion processed Mg2(Co1/3Fe1/3Ni1/3), respectively. Overall, the ball-milled and annealed Mg2(Co1/3Fe1/3Ni1/3) material presented better performance.

Metals doi: 10.3390/met16040433

Authors: Zongneng Zheng Di Liu Xinming Sun Yinghu Wang Yanhui Zhao Jianyan Xu

To mitigate fossil fuel dependency and facilitate the transition towards a green economy, utilization of hydrogen energy has emerged as a paramount objective. Nevertheless, during transportation, this goal introduces novel challenges pertaining to material integrity, notably hydrogen embrittlement. This review systematically examines contemporary research on hydrogen embrittlement in natural gas pipelines conveying hydrogen blends and elucidates the hydrogen sources, permeation pathways, and embrittlement mechanisms. By scrutinizing the intrinsic material attributes and operational environments, this study provides an in-depth analysis of the pivotal factors influencing the susceptibility of pipeline steel to hydrogen embrittlement, thereby furnishing a theoretical foundation for the enduring safety of hydrogen pipelines.

Metals doi: 10.3390/met16040434

Authors: Alok Sarkar Elias Trondsen Dahl Jafar Safarian

Hydrogen-based reduction of manganese ores has attracted increasing attention as a promising route for low-carbon manganese production. In this study, the reduction behavior, microstructural evolution, and kinetics of a high-barium-rich manganese ore were investigated in both dried and calcined states under isothermal hydrogen atmospheres at 600–800 °C. The ore was characterized using XRF, XRD, optical microscopy, SEM-EDS, and porosity measurements to evaluate mineralogical and structural changes during calcination and reduction. Calcination at 900 °C transformed MnO2 into Mn2O3/Mn3O4, removed volatile components, and generated micro-porosity that improved gas accessibility. Isothermal reduction experiments revealed a rapid initial reduction stage followed by a slower reaction regime, with increasing temperature significantly accelerating the reduction rate. Despite isothermal furnace conditions, a temporary rise in sample temperature was observed due to the exothermic nature of manganese oxide reduction by hydrogen. XRD analysis confirmed that manganese oxides were predominantly reduced to MnO, while iron oxides were converted to metallic Fe. Porosity measurements showed significant pore development during reduction at moderate temperatures due to oxygen removal and gas evolution; however, at higher temperatures, partial sintering led to pore coalescence and densification, reducing the overall porosity. Kinetic analysis showed that the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model effectively describes the reduction behavior. The apparent activation energies were 21.92 kJ.mol−1 for dried ore and 17.40 kJ.mol−1 for calcined ore, indicating diffusion-influenced kinetics. The results demonstrate that calcination enhances hydrogen reducibility by improving gas accessibility and reducing kinetic resistance, highlighting its importance for hydrogen-based manganese pre-reduction processes.

Metals doi: 10.3390/met16040432

Authors: Aman Gupta Saurabh Tiwari

In the present study, room temperature (RTR) and cryogenic (CR) rolling of electrolytic tough pitch copper (ETP-Cu) was performed to elucidate how deformation temperature and reduction ratio (40% and 80% thickness reductions) control dislocation storage, local stored energy (SE), and self-annealing. Correlated SEM/EDS and EBSD analyses were used to (i) locate Cu2O particles, (ii) quantify local misorientation, and (iii) map the SE for self-annealing. Point EDS confirms that the intermetallic particles are copper oxides (Cu2O), with apparent O content varying with particle size and EDS interaction volume. RTR80 (80% rolled) exhibits systematically higher KAM values and a larger area fraction of high SE than RTR40 (40% rolled), explaining the greater frequency and spatial density of self-annealed grains at higher reduction. Cryogenic rolling produces more severe fragmentation and a higher fraction of subgrains than RTR at equivalent reductions. CR80 shows the high KAM structures and locally highest SE regions among all conditions, and a higher fraction of self-annealed grains. Nevertheless, the mapped average SE for CR80 (2.93 × 106 J/m3) was lower than for RTR80 (3.34 × 106 J/m3) due to rapid post-deformation dislocation annihilation/self-annealing upon warming at RT. In all conditions, Cu2O particles and bulged/irregular grain boundaries concentrate dislocations and SE and act as dominant particle-stimulated nucleation (PSN) sites and RT recrystallization, respectively. These results demonstrate that deformation temperature and reduction jointly determine the spatial distribution of SE and hence the propensity for self-annealing in ETP Cu.

Metals doi: 10.3390/met16040431

Authors: Benjamin Laher Christian Buzzi Peter Brunnhofer Martin Leitner Majid Farajian

In this work, the focus is laid on the mean stress effect on the fatigue strength of thin-walled rectangular hollow section T-joints made of high-strength steel S960 M x-treme. The specimens are cyclically tested at a stress ratio of R = −1 and R = 0.1 in both as-welded and ground (weld-profiled) conditions. In the context of nominal stress evaluations, the ground specimens demonstrate a distinct advantage in contrast to the as-welded condition, exhibiting an increase of +33% at R = 0.1 and +16% at R = −1. Based on the experimental results, a corresponding Haigh diagram is evaluated, revealing a notable difference in the mean stress sensitivity, with M1 = 0.58 for the as-welded condition and M1 = 0.39 for the ground condition. Finally, mean stress factors are presented, enabling feasible application in the fatigue design of welded and post-treated structures. The resulting factors are compared with values from the literature for steel applications, showing an increased mean stress influence using high-strength steel as the base material.

Metals doi: 10.3390/met16040430

Authors: Olaf Grutza Simon Graf Stefan Paulus Stefan Thielen Oliver Koch

In layered systems with porous substrates and a dense solid surface, stiffness and strength are inherently coupled through porosity-dependent relations, influencing their load-bearing behaviour. This work presents a systematic methodology for the assessment and design of such layer-substrate systems based on a criterion of balanced material utilization. A dimensionless parameter is defined to characterize the stress state in both components relative to their admissible limits, from which the optimal layer thickness is determined at equal stress levels in both constituents. Stress distributions are calculated using a numerical half-space model for layered contacts and evaluated through material-dependent equivalent stress criteria. The relationship between material utilization and load-carrying capacity is reduced to a scaling factor that combines the influence of porosity-dependent parameters. The approach establishes a direct link between the governing material parameters and structural design variables. Across the investigated parameter range, the utilization rate scales linearly with optimal layer thickness, whereas the load-carrying capacity follows a cubic relation. For a representative Ashby strength scaling coefficient of Cσ=0.3, for example, a substrate porosity of 90% leads to a scaling factor of 1.6, corresponding to a possible load amplification of 60% relative to the homogeneous reference.

Metals doi: 10.3390/met16040429

Authors: Qiang Shi Xiangyu Cao Guan Qin Hongjie Li Ke Xu Dongdong Zhou

Surface defects in high-temperature continuous cast billets are critical factors affecting the quality of steel products. Owing to high-temperature radiation, heavy dust contamination, varying billet specifications, and background interference from oxide scales and water stains, existing online surface defect detection technologies for high-temperature continuous cast billets still suffer from limitations including high false-positive rates, inefficient identification of pseudo-defects, and the inability to simultaneously detect three-dimensional (3D) depth information alongside two-dimensional (2D) features. To solve these problems, this paper proposes a multi-dimensional online detection technology for surface defects in high-temperature continuous cast billets based on multi-information fusion. A four-channel multispectral image sensor and a corresponding three-light-source imaging system were developed. Furthermore, a defect sample augmentation method, a deep learning-based 2D recognition method, and a photometric stereo-based 3D reconstruction method were designed to mitigate problems of low detection accuracy and poor robustness caused by sample imbalance among different defect types. Finally, industrial applications were conducted on large-section continuous cast billets, beam blanks, and billets during the grinding process. According to the surface defect detection requirements of different continuous cast billets, multispectral multi-information fusion and traditional 2D defect imaging methods were adopted respectively. The results demonstrate high-precision online detection of surface defects in continuous cast billets, with favorable practical application effects.

Metals doi: 10.3390/met16040428

Authors: Juan Bosch Elizabeth Kotzalas K Zin Htut Rowan King Christopher DellaCorte

Water-based lubricants (WBLs) are increasingly being considered for electrified drivetrain applications; however, their electrochemical stability toward bearing steels remains insufficiently understood. This study evaluated the corrosion behavior of through-hardened AISI 52100 bearing steel in novel WBLs to elucidate the corrosion kinetics and surface degradation mechanisms. Round steel disks were cleaned and tested in 50 wt% aqueous dilutions of glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), and polyalkylene glycol (PAG). Electrochemical measurements were conducted using a three-electrode cell in accordance with ASTM G3-14, employing open circuit potential (OCP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization curves. Among the uninhibited fluids, DI water exhibited the highest corrosion current density (19.85 µA/cm2), while glycerol- and PEG-based systems showed the lowest values (0.79 and 0.85 µA/cm2, respectively), attributed to organic adsorption at the steel/electrolyte interface. EIS analysis revealed a single charge-transfer-controlled process across all fluids, consistent with a weak, non-passive interfacial oxide whose protective character is modulated by organic adsorption. The addition of NaNO3 produced divergent effects depending on the base fluid chemistry: the corrosion activity was reduced in DI water and glycerol systems through enhanced passivation, while PEG- and PAG-based formulations showed increased corrosion current densities and reduced charge transfer resistance, attributed to competitive disruption of the polymer boundary layer by nitrate ions. Surface characterization by SEM/EDAX and white-light interferometry corroborated the electrochemical findings, revealing fluid-dependent corrosion morphologies ranging from uniform attack in DI water to localized pitting in polymer-based systems, with NaNO3 shifting the corrosion mode in PEG/PAG systems from localized to combined localized and uniform attack. These findings highlight the critical role of fluid chemistry in controlling corrosion processes in water-based lubricants and provide mechanistic insight for the development of corrosion-stable formulations for high-performance electrified drivetrain applications.

Metals doi: 10.3390/met16040427

Authors: Yunbo Li Haofeng Xie Zhihao Zhang Songxiao Hui Yanfeng Li Xiaoyun Song Wenjun Ye Yang Yu Yumeng Luo

TiNiFe shape memory alloy pipe couplings exhibit excellent radial recovery capability and therefore show great potential for pipeline fastening applications. In this study, the radial recovery stresses at different locations within a TiNiFe SMA pipe coupling were determined using a finite element inverse method. These stresses were subsequently applied as boundary conditions to establish a numerical model describing the fastening connection and pull-out process between the TiNiFe coupling and a TA18 tube. The effects of coupling wall thickness on the connection state and pull-out failure behavior were systematically investigated. The results indicate that the radial recovery stress increases monotonically with increasing wall thickness, although the growth rate gradually decreases. When the wall thickness ranges from 1.25 to 1.75 mm, the interfacial contact stress increases with thickness, thereby enhancing the fastening effect. However, when the thickness exceeds 1.75 mm, the intensified radial deformation of the inner convexes leads to a significant reduction in contact stress. The pull-out process of the assembly can be divided into three stages, namely the initial, intermediate, and final stages, during which the pull-out force first increases and then decreases with the evolution of the contact state. These findings provide a theoretical basis for the structural optimization and engineering application of TiNiFe SMA pipe couplings.