Metals, Volume 14, Issue 5 (May 2024) – 107 articles

Metallic materials are commonly characterized through tensile tests. For ductile metals, a consistent part of the test occurs after the necking onset. A first estimate of the post-necking behavior could be obtained by extrapolating the mathematical model that fits the pre-necking law. However, as well known, the accuracy of the predictions would not be guaranteed. Therefore, over the past decades many efforts have been devoted to dealing with the necking phenomenon. The most popular correction formula proposed by Bridgman is an analytical method based on the neck geometry. Despite being widely used, it may not be accurate at large strains due to the assumption of uniform distribution of the equivalent stress and equivalent strain in the specimen minimum cross-section. Starting from Bridgman’s idea and in order to overcome its limitations, the present paper develops an efficient method to calibrate the hardening law of isotropic metallic materials at large strains. The proposed method requires to record the outer contour of the necking zone during the test and to build a dataset of necking deformed shapes. Experimental quasi-static tensile tests were analyzed with the proposed approach, which appears promising when critically compared with other methods. Full article

The high demand for carbon-based products within pyrometallurgy is placing the industry in an increasingly challenging position to meet stringent requirements. To transition away from fossil carbon carriers, biochar emerges as a sustainable and CO₂-neutral alternative, presenting a viable solution without necessitating fundamental adjustments to plant technology, unlike hydrogen as an alternative reducing agent. Prior investigations have underscored the potential of woody biomass pyrolysis products for CO₂-neutral metallurgy. Nonetheless, it is imperative to recognize that biochar must meet distinct requirements across various metallurgical processes. This paper conducts a comparative analysis between biochar and petroleum coke using thermogravimetric analyses, surface measurements, reactivity assessments, and scanning electron microscopy. Furthermore, the performance in a furnace for simulating the Waelz process, specifically regarding ZnO reduction, is scrutinized. The results illustrate the optical differences between petroleum coke and biochar and the significantly higher reactivity and specific surface area of biochar. When used in solid–gas reactors, it is observed that due to its high reactivity, biochar reacts more vigorously and carbon is completely consumed. However, during the reduction of ZnO, only minor differences were monitored, making biochar comparable to petroleum coke. Therefore, under certain constraints, biochar can be considered a potential substitute for metallurgical solid–gas reactions. Full article

This study proposed a new method for homogenizing continuous casting blooms based on solidification simulation calculations and industrial tests. The text describes a theoretical analysis of the solidification route of a cast billet of high-carbon alloy steel (B300A) under different process conditions. It summarizes the changing law of different under-pressure process parameters and under-pressure efficiency. The text also presents a solution to the seriousness of center shrinkage defects in the continuous casting of a large square billet of high-carbon alloy steel with the synergistic control technology of mixed light and heavy mixing under pressure. The study indicates that the center carbon segregation index of a high carbon steel continuous casting billet is 1.05, with a carbon extreme difference of not more than 0.08% and a proportion of 98.4%. Additionally, the center shrinkage is not more than a 0.5 level with a proportion of 99.5%. Meanwhile, the internal quality of cast billets has been improved, allowing for the rolling of large-size bars with a low consolidation ratio. The pass rate for internal ultrasonic flaw detection using the GB/T4162A grade is now higher than 99.95%, significantly reducing process costs and improving production efficiency for continuous casting and rolling. Full article

The development of strong and ductile alloys for application in cryogenic temperatures has long been sought after. In this work, we have developed a face-centered cubic Ni₁₀Co_56.5V_33.5 multi-principal element alloy (MPEA) that exhibits a balanced combination of high strength and good ductility at 77 K, based on the considerations of large local lattice distortion (LLD) and low stacking fault energy. The small-grained Ni₁₀Co_56.5V_33.5 MPEA exhibits a yield strength of 1400 MPa and an ultimate tensile strength of 1890 MPa, while preserving a good ductility of 23%. Moreover, precession electron diffraction and transmission electron microscopy revealed multiple deformation mechanisms, including wavy dislocations, atypically severely twisted dislocation bands, hierarchical stacking faults, and deformation twins, which are implicated in the alloy’s outstanding mechanical performance. These insights offer a strategic guide for the design of strong and ductile alloys, particularly for utilization in extreme environments. Full article

This paper focuses on the study of current knowledge regarding the use of hydrogen as a reducing agent in the metallurgical processes of iron and steel production. This focus is driven by the need to introduce environmentally suitable energy sources and reducing agents in this sector. This theoretical study primarily examines laboratory research on the reduction of Fe-based, metal-bearing materials. The article presents a critical analysis of the reduction in iron oxides using hydrogen, highlighting the advantages and disadvantages of this method. Most experimental facilities worldwide employ their unique original methodologies, with techniques based on Thermogravimetric analysis (TGA) devices, fluidized beds, and reduction retorts being the most common. The analysis indicates that the mineralogical composition of the Fe ores used plays a crucial role in hydrogen reduction. Temperatures during hydrogen reduction typically range from 500 to 900 °C. The reaction rate and degree of reduction increase with higher temperatures, with the transformation of wüstite to iron being the slowest step. Furthermore, the analysis demonstrates that reduction of iron ore with hydrogen occurs more intensively and quickly than with carbon monoxide (CO) or a hydrogen/carbon monoxide (H₂/CO) mixture in the temperature range of 500 °C to 900 °C. The study establishes that hydrogen is a superior reducing agent for iron oxides, offering rapid reduction kinetics and a higher degree of reduction compared to traditional carbon-based methods across a broad temperature range. These findings underscore hydrogen’s potential to significantly reduce greenhouse gas emissions in the steel production industry, supporting a shift towards more sustainable manufacturing practices. However, the implementation of hydrogen as a primary reducing agent in industrial settings is constrained by current technological limitations and the need for substantial infrastructural developments to support large-scale hydrogen production and utilization. Full article

Hydrogen embrittlement (HE) poses the risk of premature failure for many metals, especially high-strength steels. Due to the utilization of hydrogen as an environmentally friendly energy source, efforts are made to improve the resistance to HE at elevated pressures and temperatures. In addition, applications in hydrogen environments might require specific material properties in terms of thermal and electrical conductivity, magnetic properties as well as corrosion resistance. In the present study, three high-strength Cu-base alloys (Alloy 25, PerforMet^® and ToughMet^® 3) as well as austenitic stainless AISI 321, Ni-base alloy IN 625 and ferritic steel 1.4511 are charged in pressurized hydrogen and subsequently tested by means of Slow Strain Rate Testing (SSRT). The results show that high-strength Cu-base alloys exhibit a great resistance to HE and could prove to be suitable for materials for a variety of hydrogen applications with rough conditions such as high pressure, elevated temperature and corrosive environments. Full article

The effect of pre-weld heat treatment on the microstructure and low-temperature impact toughness of the coarse-grained heat-affected zone (CGHAZ) after simulated welding was systematically investigated through the utilization of scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). The Charpy impact test validated the presence of an optimal pre-weld heat treatment condition, resulting in the highest impact toughness observed in the CGHAZ. Three temperatures for pre-weld heat treatment (690, 720 and 750 °C) were used to obtain three different matrices (Steel 1, Steel 2, Steel 3) for simulated welding. The optimal pre-weld heat treatment is 720 °C for 15 min followed by water quench. Microstructure characterization showed that there is an evident microstructure comprising bainite (B) in Steel 1 and Steel 2 after pre-weld heat treatment, while the addition of martensite (M) with the pre-weld heat treatment temperature exceeds Ac₁ by almost 60 °C (Steel 3). These differences in microstructures obtained from pre-weld heat treatment influence the refinement of high-temperature austenite during subsequent simulated welding reheating processes, resulting in distinct microstructural characteristics in the CGHAZ. After the optimal pre-weld heat treatment, Steel 2 subjected to single-pass welding thermal simulation demonstrates a refined microstructure characterized by a high density of high-angle grain boundaries (HAGBs) within the CGHAZ, particularly evident in block boundaries. These boundaries effectively prevent the propagation of brittle cracks, thereby enhancing the impact toughness. Full article

Based on previous work, where Al-Si-Cu-Ni alloy was successfully manufactured by laser powder bed fusion (PBF-LB/M) technology, in this study, we further observe the microstructure of the alloy, analyze the formation mechanism of the microstructure during solidification, and discuss their implications for the mechanical properties. The results indicate that the microstructure comprises multi-level cellular heterogeneous structures, with an α-Al matrix in the interior of the cellular structure and Cu- and Ni-rich phases clustered at the boundaries, intertwined with the silicon network. During solidification, α-Al solidifies first and occupies the core of the cells, while Si phases and Cu- and Ni-rich phases deposit along the cellular boundaries under the influence of surface tension. During the solidification process of cellular boundaries, influenced by spinodal decomposition and lattice spacing, Si phases and Cu- and Ni-rich phases interconnect and distribute crosswise, collectively forming multi-level cellular structures. The refined cellular microstructure of the PBF-LB/M Al-Si-Cu-Ni alloy enhances the mechanical properties of the alloy. The alloy exhibits a bending strength of 766 ± 30 MPa, a tensile strength and yield strength of 437 ± 6 MPa and 344 ± 4 MPa, respectively, with a relatively low fracture elongation of approximately 1.51 ± 0.07%. Subsequent improvement can be achieved through appropriate heat treatment processes. Full article

In the present work, predictive modelling and optimization with the adaptive network based fuzzy inference system (ANFIS) modelling of the mechanical properties of laser-coated NB/SiC/Ni welds was studied based on the Taguchi design by laser cladding. An ANFIS model based on a Sugeno type fuzzy inference system was developed for predicting the hardness properties of SiC/BN/Ni welds by laser cladding with experimental data required for network training and prediction. Based on analysis of variance, three important factors were taken as inputs for the fuzzy logic inferences, while the hardness properties were taken as the output of the ANFIS. The microstructure of welds was analysed using scanning electron microscopy with an energy-dispersive X-Ray spectrometer. Highly developed leaf-like dendrites and eutectic crystals were found in some areas of the melting zone for the BN/SiC/Ni weld, which was significantly hardened. The ANFIS model based on Taguchi’s design provides a better pattern of response because the predicted and experimental values were highly similar. As a result, a satisfactory result was achieved between the predicted and experimental values of hardness in laser-coated NB/SiC/Ni welds, whereby the success and validity of the method was verified. Full article

The characteristics of subgrains in a deformed state after the high-temperature deformation of aluminum alloys control the subsequent recrystallization process and corresponding mechanical properties. In this study, systematic 2D phase-field simulations have been conducted to determine the role of deformed state parameters such as subgrain size and disorientation distributions on subgrain growth in an individual grain representing a single crystallographic orientation. The initial subgrain size and disorientation distributions have been varied by ±50%. To have a statistically relevant number of subgrains, large-scale simulations have been conducted using an in-house-developed phase-field code that takes advantage of distributed computing. The results of these simulations indicate that the growth of subgrains reaches a self-similar regime regardless of the initial subgrain structure. A narrower initial subgrain size distribution leads to faster growth rates, but it is the initial disorientation distribution that has a larger impact on the growth of subgrains. The results are discussed in terms of the evolution of the average diameter of subgrains and the average disorientation in the microstructure. Full article

This paper investigates the influence of the concentration and particle size of h-BN nanoparticles in a nanofluid on the surface integrity of 304 austenitic stainless steel during turning, focusing on the cutting force, friction coefficient, cutting temperature, surface roughness, surface residual stress, work hardening capacity, and 3D surface topography. The results show that, compared to dry cutting, the addition of 3 wt.% h-BN nanofluid can reduce the friction coefficient on the rake face by 38.9%, lower the cutting temperature by 43.5%, decrease the surface roughness by 53.8%, decrease the surface residual stress by 61.6%, and reduce the work hardening degree by 27.5%. Two-dimensional profiles and the 3D surface topography display a more balanced peak–valley distribution. Furthermore, by studying the effect of different h-BN particle sizes in nanofluids on the surface integrity of the machined workpiece, it was found that nanoscale particles have a greater tendency to penetrate the tool–chip interface than submicron particles. Moreover, the h-BN particles in the nanofluid play a “rolling effect” and “microsphere” effect, and the sesame oil will also form a lubricating oil film in the knife-chip contact area, thereby reducing the friction coefficient, reducing the cutting force, and improving the machining surface quality. Full article

Geometrically necessary dislocations (GNDs) play a pivotal role in polycrystalline plastic deformation, with their characteristics notably affected by strain rate and other factors, but the underlying mechanisms are not well understood yet. We investigate GND characteristics in pure copper polycrystals subjected to tensile deformation at varying strain rates (0.001 s⁻¹, 800 s⁻¹, 1500 s⁻¹, 2500 s⁻¹). EBSD analysis reveals a non-linear increase in global GND density with the strain rate rising, and a similar trend is also observed for local GND densities near the grain boundaries and that in the grain interiors. Furthermore, GND density decreases from the grain boundaries towards the grain interiors and this decline slows down at high strain rates. The origin of these trends is revealed by the connections between the GND characteristics and the behaviors of relevant microstructural components. The increase in grain boundary misorientations at higher strain rates promotes the increase of GND density near the grain boundaries. The denser distribution of dislocation cells, observed previously at high strain rates, is presumed to increase the GND density in the grain interiors and may also contribute to the slower decline in GND density near the grain boundaries. Additionally, grain refinement by higher strain rates also promotes the increase in total GND density. Further, the non-linear variation with respect to the strain rate, as well as the saturation at high strain rates, for grain boundary misorientations and grain sizes align well with the non-linear trend of GND density, consolidating the intimate connections between the characteristics of GNDs and the behaviors of these microstructure components. Full article

Al-Si-Cu-Mg alloys are among the most significant types of aluminum alloys, accounting for 85–90% of all castings used in the automotive sector. These alloys are used, for example, in the manufacturing of engine blocks and cylinder heads due to their excellent specific strength (ratio of strength to specific weight) and superior castability and thermal conductivity. This study investigated the effect of using Zr as an alternative grain refiner in the novel AlSi5Cu2Mg cylinder head alloy. The microstructure of this alloy could not be refined via common Al-Ti-B grain refiners due to its specifically designed chemical composition, which limits the maximum Ti content to 0.03 wt.%. The results showed that the addition of Zr via the AlZr20 master alloy led to a gradual increase in the solidus temperature and to the grain refinement of the microstructure with the addition of as little as 0.05 wt.% Zr. The addition of more Zr (0.10, 0.15, and 0.20 wt.%) led to a gradual grain refinement effect for the alloy. The presence of Zr in the AlSi5Cu2Mg alloy was reflected in the formation of Zr-rich intermetallic phases with acicular morphology. Such phases acted as potent nucleants for the α-Al grain. Full article

Reactor pressure vessel (RPV) steels are highly susceptible to irradiation embrittlement due to prolonged exposure to high temperature, high pressure, and intense neutron irradiation. This leads to the shift in nil-ductility transition reference temperature—∆RT_NDT. The change in ∆RT_NDT follows a certain distribution pattern and is impacted by factors including chemical composition, neutron fluence, and irradiation temperature. Existing empirical procedures can estimate ∆RT_NDT based on fitting extensive irradiation embrittlement data, but their reliability has not been thoroughly investigated. Probability statistical distributions and the Gamma stochastic process were performed to model material property degradation in RPV steels from a pressurized water reactor due to irradiation embrittlement, with the probability models considered being normal, Weibull, and lognormal distributions. Comparisons with existing empirical procedures showed that the Weibull distribution model and the Gamma stochastic model demonstrate good reliability in predicting ∆RT_NDT for RPV steels. This provides a valuable reference for studying irradiation embrittlement in RPV materials. Full article

The forming process of multi-alloy gears by metal powder injection molding is tedious, and the current design process mainly depends on the experience of designers, which seriously affects the product development cycle and forming quality. In order to solve the problem of the gear feature expression being missing, which hinders the automatic retrieval of similar parts in the analogical design process, a feature recognition and intelligent retrieval method for a multi-alloy powder injection molding gear based on partition templates is proposed in this paper. The partition templates of the gear are defined, and gear digitization is completed by using the automatic recognition algorithm. Searching for similar gear parts in the knowledge base, designers can analogically design the forming process for new parts according to the mature process of the parts in the knowledge base. The automatic identification and intelligent retrieval system developed according to this method has been implemented in two MIM (metal injection molding) product manufacturing enterprises. Case studies and industrial applications have proved the effectiveness of the system, the efficiency of identification and retrieval has been improved by more than 97%, and the number of mold tests has been reduced by 60%. Full article

Characterizing the behavior of ductile metals at high strains is essential in various fields. In the case of thin sheets, rectangular cross-section specimens are used to characterize these materials, typically by tensile tests. Unlike cylindrical specimens, flat ones pose additional challenges for the hardening characterization at high strains, especially in the post-necking phase, which, for many high-strength steels, may cover most of the plastic strain range. After the onset of global necking, the rectangular cross-sections tend to distort with respect to their original shape, as their edges progressively curve and bulge inward. The localized necking occurring after the global one in thinner specimens, further distorts the necked zone. Additionally, sheet metals usually exhibit anisotropic characteristics that affect the derivation of the stress–strain curve and need to be dealt with. No exact method exists for the stress–strain characterization of ductile thin sheets at high strains from tensile tests. Although several approximate methods are available in the literature, they either discard the post-necking range or require highly advanced and complex experimental setups not suitable for industrial applications (e.g., 3D DIC). Then, this work proposes a relatively simple methodology for the experimental characterization of anisotropic thin sheet metals through tensile tests on rectangular cross-section specimens that delivers the true stress–strain curve of the material, extended over the necking range and up to fracture, accurately assessing the anisotropy and the distortion of the neck section. The proposed methodology, employing a standard single-camera experimental setup, is illustrated here, referring to four different steels for automotive applications with reference to a single material orientation; it is intended as representative of the repeated procedure involving tensile tests along 3 or more material directions in order to describe the whole anisotropic plastic response. A detailed comparison between the novel methodology and four other common approaches is carried out, highlighting the differences and the enhanced capabilities of the novel one proposed. Full article

This study delved into exploring microstructural states in a Ti–7Ag alloy to achieve targeted functional and structural properties. Specifically, the focus was on attaining a homogeneously precipitated state and a solid solution, known for their potential to combine functional traits like corrosion resistance and antibacterial activity with structural properties such as mechanical strength. However, obtaining these optimized microstructures presents challenges due to kinetic considerations. A key finding of this study was the crucial role of a pre-deformation stage, prior to heat treatment, to create an even distribution of fine Ti₂Ag precipitates. Moreover, we demonstrated that starting from this precipitated state, a controlled dissolution step could yield a single-phase solid solution with similar grain size. Therefore, a tailored set of thermomechanical treatments was developed to achieve both microstructures, and these metallurgical states were fully characterized combining SEM (BSE imaging and EDS analysis), TEM, and XRD. Associated mechanical properties were also assessed by tensile testing. In addition, the process was proven to be robust enough to overcome potential industrial problems, such as slow cooling rates when water-quenching large ingots. Considering the limited existing documentation on microstructural features in Ti–Ag alloys, this work on this model alloy significantly advanced our current understanding of the broader Ti–Ag alloy system by providing new data and showcasing a tailored approach involving thermomechanical treatments. Full article

This study proposes a method for determining aluminum alloys’ yield stress and hardening index based on indentation experiments and finite element simulations. Firstly, the dimensionless analysis of indentation variables was performed on three different aluminum alloys using the same maximum indentation depth to obtain load-displacement curves. Then, laser confocal microscopy was used to observe the residual indentation morphology. And four dimensionless parameters were derived from the load-displacement curves while another dimensionless parameter was obtained from the projection area of the contact zone. Subsequently, a genetic algorithm was employed to solve these five dimensionless parameters and estimate the yield stress and hardening index. Finally, the predicted results are compared with uniaxial tensile experiments and the results obtained are essentially the same. The yield stress and hardening index can be predicted using this method. And an example is used to verify that this method enables predictions for unidentified “mysterious material” and the expected results agree with the experiments. Full article

This review offers a comprehensive analysis of thermal barrier coatings (TBCs) applied to metallic materials. By reviewing the recent literature, this paper reports on a collection of technical information, involving the structure and role of TBCs, various materials and coating processes, as well as the mechanisms involved in the durability and failure of TBCs. Although TBCs have been successfully utilized in advanced applications for nearly five decades, they continue to be a subject of keen interest and ongoing study in the world of materials science, with overviews of the field’s evolution remaining ever relevant. Thus, this paper outlines the current requirements of the main application areas of TBCs (aerospace, power generation and the automotive and naval industries) and the properties and resistance to thermal, mechanical and chemical stress of the different types of materials used, such as zirconates, niobates, tantalates or mullite. Additionally, recent approaches in the literature, such as high-entropy coatings and multilayer coatings, are presented and discussed. By analyzing the failure processes of TBCs, issues related to delamination, spallation, erosion and oxidation are revealed. Integrating TBCs with the latest generations of superalloys, as well as examining heat transfer mechanisms, could represent key areas for in-depth study. Full article

This study investigated the influence of high silicon (4.2 wt%) and varying aluminum (3.5–4.8 wt%) content on the high temperature oxidation behavior and thermophysical properties of SiMoAl vermicular graphite cast iron for hot-end exhaust components. Isothermal oxidation tests at 800 °C and nonisothermal oxidation tests in a dry-air atmosphere were conducted on SiMo nodular iron, along with two SiMoAl vermicular graphite cast iron variants alloyed with 3.5 wt% Al and 4.8 wt% Al. The investigations revealed the formation of a thin duplex layer of oxide scale, consisting of an iron-rich external oxide layer and continuous aluminum oxide at the metal/oxide interface. Although aluminum oxide acted as a protective barrier by impeding the solid-state diffusion of oxygen, severe subsurface oxidation was observed due to the interconnected vermicular graphite covered by aluminum oxides after decarburization. Furthermore, based on nonisothermal oxidation experiments, the effective activation energy of oxidation was found to be significantly increased by the addition of aluminum, even though the oxidation activation energies of SiMoAl samples exhibited small changes in comparison to each other. Additionally, thermophysical analysis demonstrated a substantial decrease in the thermal conductivity and a slight increase in the thermal expansion with the addition of aluminum. Full article

To investigate the dissolution mechanism of Ti metal, ab initio calculations were conducted to observe the impact of Ti vacancy defects on the O-adsorbed Ti(0001) surface, focusing on the formation energies of Ti vacancy, geometric structures, and electronic structures. The surface structures subsequent to Ti dissolution were simulated by introducing a Ti cavity on both clean and O-adsorbed Ti(0001) surfaces. Our findings indicated that Ti vacancy formation energies and electrochemical dissolution potential on the O-adsorbed Ti(0001) surface surpassed those on the clean surface, and they increased with increasing O coverage. This suggested that O adsorption inhibited Ti dissolution and enhanced O atom interaction with the Ti surface as O coverage increased. Furthermore, at higher O coverage, Ti vacancies contributed to the strengthening of Ti-O bonds on the O-adsorbed Ti(0001) surface, indicating that Ti dissolution aided in stabilizing the Ti surface. The formation of Ti vacancies brought the atomic ratio of Ti to O on the Ti surface closer to that of TiO₂, potentially explaining the increased stability of the structure with Ti vacancies. Full article

In this work, Ce-doped Ti₆Cr₁₄V₈₀ BCC hydrogen-storage alloys have been synthesized as catalysts to enhance the hydrogen-storage performance of MgH₂ based on its room-temperature activation features and excellent durability. The Ti₆Cr₁₄V₈₀Ce₁ alloy was pre-ball milled under a hydrogen atmosphere into a Ti₆Cr₁₄V₈₀Ce₁H_x hydride. Different amounts of the Ti₆Cr₁₄V₈₀Ce₁H_x hydride were incorporated into MgH₂ by ball milling to obtain the MgH₂ + y wt%Ti₆Cr₁₄V₈₀Ce₁H_x (y = 0, 3, 5, 10, 15) nano-composites. With an optimization doping of 10 wt%Ti₆Cr₁₄V₈₀Ce₁H_x, the initial dehydrogenated temperature was decreased to 160 °C. Moreover, the composite can rapidly release 6.73 wt% H₂ within 8 min at 230 °C. Also, it can absorb 2.0 wt% H₂ within 1 h even at room temperature and uptake 4.86 wt% H₂ within 10 s at 125 °C. In addition, the apparent dehydrogenated activation energy of the MgH₂ + 10 wt%Ti₆Cr₁₄V₈₀Ce₁H_x composite was calculated to be 62.62 kJ mol⁻¹ fitted by the JMAK model. The capacity retention was kept as 84% after 100 cycles at 300 °C. The ball milled Ti₆Cr₁₄V₈₀Ce₁H_x transformed from the initial FCC phase structure into a BCC phase after complete dehydrogenation and back into an FCC phase when fullly hydrogenated. A catalyst mechanism analysis revealed that the ‘autocatalytic effect’ originating in Ti₆Cr₁₄V₈₀Ce₁H_x plays a crucial role in boosting the de-/hydrogenation properties of MgH₂. This work provides meaningful insights into rational designs of nano-compositing with different hydrogen-storage alloy catalyzed MgH₂. Full article

The study focuses on the four-strand tundish as the research object, aiming at the phenomenon of fewer strand casting (stable blockage) and sudden blockage of the tundish in industrial production. Numerical simulation methods are employed to compare the velocity vectors, flow fields, residence time distribution (RTD) curves, and outflow percentage curves under stable blockage and sudden blockage of the tundishes with a double-weir structure, U-shaped weir structure, and U-shaped weir structure with holes in the front. The results indicate that, after sudden blockage of the tundish strands, the flow field transitions from an unstable four-strand flow field to a stable three-strand flow field. Both the double-weir tundish and the U-shaped weir tundish reach a stable state after 200 s, while the U-shaped weir tundish with holes in the front reaches stability after 150 s. Additionally, compared to other structures, the tundish strands of the U-shaped weir with holes in the front are less affected by blockage, showing better consistency among strands and better adaptability under non-standard casting conditions. Full article

The exploration of the relationship between process parameters and grain evolution during the thermal deformation of rare-earth magnesium alloys using simulation software has significant implications for enhancing research and development efficiency and advancing the large-scale engineering application of high-performance rare-earth magnesium alloys. Through single-pass hot compression experiments, this study obtained high-temperature flow stress curves for rare-earth magnesium alloys, analyzing the variation patterns of these curves and the softening mechanism of the materials. Drawing on physical metallurgical theories, such as the evolution of dislocation density during dynamic recrystallization, recrystallization nucleation, and grain growth, the authors of this paper establish a cellular automaton model to simulate the dynamic recrystallization process by tracking the sole internal variable—the evolution of dislocation density within cells. This model was developed through the secondary development of the DEFORM-3D finite element software. The results indicate that the model established in this study accurately simulates the evolution process of grain growth during heat treatment and the dynamic recrystallization microstructure during the thermal deformation of rare-earth magnesium alloys. The simulated results align well with relevant theories and metallographic experimental results, enabling the simulation of the dynamic recrystallization microstructure and grain size prediction during the deformation process of rare-earth magnesium alloys. Full article

The presence of inherent micro-pores and micro-cracks in the micro-arc oxidation (MAO) film of Mg alloys is a key factor contributing to substrate corrosion. A composite film layer with high corrosion resistance was achieved through silanizing the micro-arc oxidation film. The corrosion performance of the MAO films treated with various silane coupling agents was assessed through morphological characterization and electrochemical tests. SEM graphs depicted that the silane film can effectively seal the defects existing in micro-arc oxidation film, and electrochemical tests indicated the significant corrosion resistance improvement of MAO film after silanization treatment. Full article

This study reports on the magnetic hardening phenomenon of heavily helium ion-irradiated iron–chromium alloys. The alloys are important structural materials in next-generation nuclear reactors. In some cases, problems may arise when the magnetic properties of the materials change due to neutron irradiation. Therefore, it is necessary to understand the effects of irradiation on magnetism. Helium irradiation was conducted as a simulated irradiation, and the effect of cavity formation on magnetic properties was thoroughly investigated. High-quality single-crystal Fe-x%Cr (x = 0, 10, 20) films, with a thickness of 180–200 nm, were fabricated through ultra-high vacuum evaporation. Subsequently, irradiation of 19 dpa with 30 keV He⁺ ions was conducted at room temperature. X-ray diffraction measurements and electron microscopy observations confirmed significant lattice expansion and the formation of high-density cavities after irradiation. The magnetization curve of pure iron remained unchanged, while magnetic hardening was noticed in iron–chromium alloys. This phenomenon is believed to be due to the combined effect of cavity formation and changes in the atomic arrangement of chromium. Full article

Wire arc additive manufacturing (WAAM) has attracted increasing interest in industry and academia due to its capability to produce large and complex metallic components at a high deposition rate. One of the basic tasks in WAAM is to determine appropriate process parameters, which will directly affect the morphology and quality of the weld bead. However, the selection of process parameters relies heavily on empirical data from trial-and-error experiments, which results in significant time and cost expenditures. This paper employed different machine learning models, including SVR, BPNN, and XGBoost, to predict process parameters for WAAM. Furthermore, the SVR model was optimized by the Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithms. A 3D laser scanner was employed to obtain the weld bead’s point cloud, and the weld bead size was extracted using the point cloud processing algorithm as the training data. The K-fold cross-validation strategy was applied to train and validate machine learning models. The comparison results showed that PSO–SVR predicted process parameters with the highest precision, with the RMSE, R², and MAE being 1.1670, 0.9879, and 0.8310, respectively. Based on the process parameters produced by PSO–SVR, an optimal process parameter combination was chosen by taking into comprehensive consideration the impacts of power consumption and efficiency. The effectiveness of the process parameter optimization method was proved through three groups of validation experiments, with the energy consumption of the first two groups decreasing by 10.68% and 11.47%, respectively. Full article

The work is focused on experimental research of deformation characteristics on three grades of hot-dip galvanized steels for the automotive industry. Deformation maps were obtained using the DIC (Digital Image Correlation) method. The map documents the development of longitudinal and transverse deformations under tensile stress. In addition to uniaxial tension, the investigated specimens were subjected to eccentric tension. The stable crack growth (SCG) was evaluated using a non-contact measurement technique on CT (compact tension) specimens. The deformation of steels, which affects the resistance to stable crack growth (confirmed by the Design of Experiments—DOE method), was manifested in the first stages of eccentric loading of specimens. The notch root radius varies considerably due to the blunting of the starting fatigue crack. The resistance to stable crack growth, which represents a safety reserve during a vehicle crash, was obtained. Full article

The effect of microwave treatment on the grinding and flotation performance of a typical copper–nickel sulfide ore was evaluated, based on the determination of its microwave absorption capability, grinding and flotation indexes such as crack percentage, mineral liberation degree, particle size distribution, relative work index (RWI), metal enrichment ratio and recovery. There were obvious differences between the microwave absorption capabilities of the main minerals in the ore, as demonstrated by their different microwave penetration depths. They also induced temperature differences between sulfide minerals and gangue minerals which could reach 418 °C after microwave treatment for 20 s. It was shown that microwave treatment could effectively improve the grindability of the ore, as proven by the increase in fine particles smaller than 0.074 mm and the decrease in RWI after grinding due to the higher crack percentage and mineral liberation degree. Moreover, microwave treatment affected the ore floatability because of the generation of cuprite, retgersite, and rozenite with poor floatability when the treatment time was extended. By microwave treatment for a proper time, 20 s, an optimal balance between the grindability and flotation performance could be achieved. Compared with the untreated ore, the RWI of the ore decreased by 11.5%. After flotation, the Cu and Ni enrichment ratios of the flotation concentrate increased by 0.3 and 0.2, respectively. Meanwhile, their corresponding recoveries increased by 4.2% and 3.1%. This study provides new insights for the treatment of copper–nickel sulfide ore to enhance the grinding and flotation process. Full article

This paper deals with the possibility of smelting quasi-high-entropy alloys (QHEAs) with the partial use of ferroalloys in the charge instead of pure metals. The Cantor alloy (CoCrFeMnNi) was used as the base alloy and the comparison sample, into which niobium was introduced in the amount of 14 to 18% by weight. The structure, hardness, strength, and tribological properties of prototypes were studied. The results obtained showed, on the one hand, the possibility of using ferroalloys as charge components in the smelting of QHEAs and, on the other hand, the positive effect of niobium in the amount of 14–17% on the strength and wear resistance of the alloy. Increasing the niobium content above 18% leads to its uneven distribution in the structure, consequently decreasing the strength and wear resistance of the alloy. The structure of the studied alloys is represented by a solid solution of FCC, which includes all metals, and the niobium content varies widely. In addition, the structure is represented by the phases of implementation: niobium carbide NbC 0.76–1.0, manganese carbide Mn₇C₃, and a CrNi intermetallic compound with a cubic lattice. Full article