Search Results (1,559)

Binder Jetting 3D Printing (BJ3DP) offers an effective pathway for the rapid fabrication of complex high-entropy alloy (HEA) components. In this study, the macroscopic characteristics, microstructural evolution and mechanical properties of Al_0.5Cr_0.9FeNi_2.5V_0.2 HEA green parts prepared via BJ3DP were investigated under various sintering conditions. Results showed that the relative density of the sintered parts increased significantly with temperature, transitioning from a low density (<90%) at 1300–1330 °C to near-fully dense (~98%) at 1340–1350 °C. Consequently, the mechanical properties were remarkably improved. The yield strength (σ_0.2) increased from 300 MPa to 710 MPa (a 136% increase), and the ultimate tensile strength (σ_b) rose from 310 MPa to 780 MPa (a 148% increase) as sintering temperature rose from 1300 °C to 1350 °C. Microstructural analysis revealed that at lower sintering temperatures, the alloy exhibited high porosity and a non-coherent structure composed of an FCC matrix and Cr-rich BCC phase, with Al/Ni intermetallic compounds distributed around pores. Conversely, at the final sintering stage, pore closure was achieved, and a coherent structure consisting of an FCC matrix and scale-like L1₂ precipitates was formed. Optimal mechanical properties (tensile strength ≥ 700 MPa) were achieved when sintering at 1340 °C, primarily attributed to densification and precipitation strengthening. Full article

The present study investigates the morphology, chemical composition, and phase constitution of oxide scales formed on the Fe40Al5Cr0.2TiB intermetallic alloy after long-term oxidation at 700 °C for 2000 h in air and water vapor environments. The results demonstrate the formation of an extremely thin oxide scale (≈300 nm), composed predominantly of α-Al₂O₃, which provides effective protection against further oxidation. The oxide layer exhibits locally heterogeneous morphology, including whisker-like structures and fine crystallites. Due to the very limited thickness of the oxide scale, significant challenges arise in the interpretation of microanalytical data. It is shown that the accelerating voltage strongly influences the effective information depth in SEM-EDS analysis, leading to a substantial contribution from the substrate even at low voltages. Monte Carlo simulations were used to support the interpretation of electron–matter interactions and to explain the observed discrepancies in chemical analysis. The study demonstrates that reliable characterization of ultrathin oxide scales requires careful optimization of SEM parameters and the combined use of complementary techniques, including EDS/WDS, XRD, and EBSD. The findings highlight the importance of methodological considerations in the analysis of thin oxide layers and provide guidance for the correct interpretation of experimental data in similar systems. Full article

The combination of elevated temperature and tribo-corrosion leads to the accelerated degradation of structural components used in many extreme environments. Recently developed high-entropy alloys (HEAs) with multiple principal elements have the potential for superior degradation resistance compared with presently used structural alloys. Here, we demonstrate the microstructural stability, pitting resistance, and superior tribo-corrosion degradation resistance of the AlCoCrFeNi_2.1 eutectic HEA in comparison with duplex stainless steel 2205 in deionized water (controlled low-ionic-strength electrolyte) at 25 °C, 50 °C and 100 °C. The AlCoCrFeNi_2.1 HEA showed excellent microstructural stability and tribo-corrosion resistance at all three temperatures, an order-of-magnitude lower wear rate, and a lower coefficient of friction compared with duplex 2205 steel. The lowest wear volume loss and wear rate for both AlCoCrFeNi_2.1 and duplex steel were recorded at 50 °C, which was attributed to temperature-assisted passivation and formation of a comparatively stable tribological surface condition. These results suggest superior performance of eutectic HEAs in tribo-corrosion applications compared with currently used dual-phase steels and motivate future evaluation in ion-containing industrial water chemistries. Full article

This study explores how variations in mechanical alloying time and sintering temperature influence the microstructure, mechanical properties, and corrosion resistance of MnAlCuFeTi high-entropy alloys (HEAs). The MnAlCuFeTi alloy was produced by means of mechanical alloying for 5, 10, 15, and 20 h. Afterward, the alloy samples were sintered at two different temperatures: 550 °C and 650 °C. Structural properties were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Analysis of grain sizes, calculated using the Scherrer formula from SEM images, confirmed that grain size had decreased to the nanostructured regime and that microstructural homogeneity had improved. Corrosion behavior was evaluated using polarization curves, corrosion current density (I_corr), and corrosion rate measurements. The results show that increasing the mechanical alloying time reduces the alloy’s grain size, thereby improving its mechanical and corrosion resistance. At a sintering temperature of 550 °C, I_corr and corrosion rate decrease with increasing grinding time, whereas at 650 °C, although high temperatures accelerate diffusion processes and increase phase homogeneity, they weaken corrosion resistance. These findings emphasize the importance of balancing alloying time and sintering temperature to optimize performance in high-corrosion-resistant HEA applications. Full article

Hydrogen plasma heating, a unique method for heating and reducing iron ore, is distinguished by its high heat, rapid reduction, and high efficiency, making it a promising technique in the metallurgy field. In this study, a non-transferred arc plasma heating system was used with Ar-H₂ as the working gas and acidic pellets as the raw material. The microstructures and elemental distributions of the slag and iron phases during the reduction process were examined using electron microscopy and energy-dispersive X-ray. The variation patterns of Fe-containing phases in the reduction products were found using X-ray diffraction and full-spectrum fitting refinement. The conversion rate of the oxidized pellets and the deoxidation conversion rate per area were estimated for various gas flow rates and reduction times. A reaction kinetics model was also used to study the reaction controlling step. The results showed that during the reduction process, with an H₂ flow rate of 4.5 L min⁻¹ and a 40 min reduction, the conversion(α) reached 99.89% and the purity of the reduced metallic iron reached 99.9%, achieving the industrial-grade 3N standard. Si and Al in the melt bath generated fayalite (Fe₂SiO₄) and hercynite (FeAl₂O₄) with Fe_xO. The deoxidation conversion rate per unit area was 1.11 g (cm² min)⁻¹. A three-dimensional diffusion-controlled model was used to describe the reduction process, and the mechanism function was 2/3(1 + α)^3/2[(1 + α)^1/3]⁻¹. The values of the reduction reaction rate constant (K) were 12.6 × 10⁻² s⁻¹ and 12.8 × 10⁻² s⁻¹ when the flow rates of H₂ gas were 3 and 4.5 L min⁻¹, respectively. The apparent activation energy was 21.9 kJ mol⁻¹. The empirical equation for the specific reduction rate was calculated as ln r = −2637.5/T − 0.407. Full article

This study reports the synthesis of a high-entropy AlFeCuTiNi alloy via high-energy ball milling. The study investigates the effects of mechanical alloying time and sintering temperature on the microstructure, mechanical properties, wear, and corrosion behavior of the high-entropy AlFeCuTiNi alloy. XRD, SEM, and EDX analyses revealed that the mechanical alloying time and sintering temperature significantly affected the alloy’s homogeneity, phase structure, and oxide film stability. As the mechanical alloying time increases, the corrosion resistance of alloys sintered at 550 °C initially increases and then stabilizes. In samples sintered at 650 °C, corrosion resistance is generally higher. The highest corrosion resistance was achieved after 15 h of mechanical alloying and sintering at 650 °C. The study reveals that the best corrosion, wear, hardness, and wear density performance was observed in samples obtained at medium conditions, achieved after 20 h of mechanical alloying and sintering at 650 °C. These findings may contribute to optimizing production processes for sustainable material design. Moreover, this research highlights that high-entropy alloys and powder-metallurgy-based production methods enable industrial applications for energy-efficient, sustainable material design and contribute to sustainable production and circular-economy principles. Full article

To address the high-salinity and hyper-humid thermal environment of tropical oceans and meet industrial demands for high strength and lightweight, austenitic low-density steel was developed as a novel corrosion-resistant steel. A 3.5 wt.% NaCl solution was used to simulate the marine environment to study the effect of Si on the corrosion behavior of this steel. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were employed to characterize the microstructures and corrosion behaviors of two test steels, as well as the phase compositions and element distributions of corrosion products after polarization and cyclic immersion accelerated corrosion tests. The results show that a dense oxide film initially forms on the steel surface in 3.5 wt.% NaCl solution at the early corrosion stage. Si addition induces SiO₂ formation and promotes Al conversion to Al₂O₃, enhancing oxide film compactness and inhibiting matrix atom outward diffusion and Cl⁻ inward penetration. With prolonged corrosion, the oxide film is dissolved or broken, forming a dense rust layer dominated by Fe₃O₄, Fe₂O₃ and FeOOH. Si enriches in the inner rust layer adjacent to the matrix and pitting cavities, inhibiting pitting deepening and promoting γ-FeOOH to α-FeOOH transformation, thus improving the steel’s corrosion resistance. Full article

A Cu-containing FeCrMnNiAl multi-principal element alloy was processed by laser-based and electron beam-based powder bed fusion (PBF-LB/M and PBF-EB/M) to investigate processing–microstructure–property relationships. In focus were alloy variants with a relatively high Cu content. Two PBF-LB/M scan strategies, employing a Gaussian beam with and without a re-scan with a laser featuring a flat-top profile, were compared to PBF-EB/M processing, followed by heat-treatments between 300 °C and 1000 °C. The phase constitution, elemental partitioning and grain boundary characteristics were analyzed by X-ray diffraction, electron backscatter diffraction and energy-dispersive X-ray spectroscopy. Mechanical behavior was assessed by hardness and tensile testing. Both manufacturing routes promoted the evolution of stable multi-phase microstructures composed of face-centered-cubic (FCC)- and body-centered-cubic (BCC)-type phases across all heat-treatment conditions. PBF-LB/M processing resulted in finer, dendritic microstructures and suppressed formation of a Cu-rich FCC phase due to higher cooling rates, whereas PBF-EB/M promoted the evolution of Cu-rich FCC segregates and equiaxed grain morphologies. Heat-treatment above 700 °C led to recrystallization, accompanied by an increase of the FCC phase fraction, grain coarsening, and recovery. At lower heat-treatment temperatures, the changes in microstructure are different. Here, it is assumed that small, non-clustered Cu-rich precipitates formed at the grain and sub-grain boundaries, although this assumption is only based on the assessment of the mechanical properties. The size of these precipitates is below the resolution limit of the techniques applied for analysis in the present work. Additional structures seen within the Cu-rich areas of PBF-EB/M-manufactured samples treated at lower temperatures also seem to have an influence on the hardness and yield strength. All of the conditions investigated exhibited pronounced brittleness, limiting reliable tensile property evaluation and indicating the need for further optimization of processing strategies and microstructural control for high-Cu-fraction-containing multi-principal element alloys. Full article

Urban rail wheels endure prolonged exposure to frequent starts and stops, heavy cyclic loads, and complex track conditions, which often lead to premature failure modes such as wear, fatigue cracking, and corrosion in conventional wheel materials. These limitations restrict their ability to meet the evolving demands of modern rail systems for enhanced durability and performance. To address this, the present study uses laser cladding to deposit high-entropy alloy coatings with systematically varied aluminium content onto wheel substrates. The study compares phase composition, microstructure, and mechanical properties across the different coatings. Results show that increasing Al content transforms the coating microstructure from a single face-centred cubic (FCC) phase to a dual-phase structure of FCC and body-centred cubic (BCC) phases, accompanied by notable grain refinement. Among the variants, the CrMnFeCoNi(Al)₈ coating has the densest microstructure and the most favourable mechanical performance. It achieves a microhardness of 399.62 HV_0.5 in the as-clad state and 450 ± 5 HV_0.5 after heat treatment, representing an increase of approximately 12.6%. This coating also demonstrates improved corrosion resistance, with an open-circuit potential 0.07 V higher than the CL60 substrate. Multi-body dynamics simulations confirm that the clad wheels maintain excellent operational stability and safety under service conditions. Full article

The performance improvement of mechanical components often relies on heat treatment processes, but these processes inevitably result in oxidation burn-off. The repeated formation and spallation of Fe₂O₃ rich oxide scales lead to substantial iron depletion and surface deterioration. Consequently, environmentally sustainable and economically viable protective coatings are required to suppress oxidation induced burn off. In this work, a TiO₂-MgAl₂O₄ composite coating was synthesized from magnesium slag and applied to Q235 carbon steel to enhance its performance during prolonged high temperature heat treatment. Oxidation tests conducted at 900 °C for 60 min demonstrated that the coating markedly improved the oxidation resistance of carbon steel, with an enhancement of approximately 87% relative to the uncoated specimens. To elucidate the protective mechanism, SEM-EDS, XRD, TG-DSC, and XPS analyses were employed. Based on Wagner Theory, the formation of interfacial phases such as Mg_7.92Al_15.31Fe_0.66O₃₂, which effectively impeded oxygen ion diffusion and thereby enhanced the oxidation resistance during high-temperature exposure. Furthermore, the synergistic effect of aluminum-, magnesium-, and titanium-containing compounds in the coating contributed to suppressing the diffusion of oxygen and iron ions, thus further improving the protective performance. This study provides a systematic theoretical foundation and practical guidance for addressing material loss during high-temperature processing of mechanical components, as well as for promoting the resource utilization of magnesium slag. Full article

Cemented carbides are essential in applications requiring exceptional hardness and wear resistance. However, the reliance on cobalt as a binder raises concerns related to cost, supply security, and health. High-entropy alloys (HEAs) are promising cobalt-free binders offering favorable mechanical properties and potential grain-growth control. This work presents a new approach for the development of Co-free WC-based cemented carbide employing an HEA binder designed through CALPHAD-guided simulations. An optimized composition corresponding to Al5Cr5Cu10Fe35Mn10Ni35 (at%) alloy is predicted to be FCC-dominant with minimal σ-phase formation and good compatibility with WC. A preliminary batch of powder of the proposed binder was produced by blending elemental powders, arc remelting, and ultrasonic atomization, yielding predominantly spherical particles with a dendritic microstructure. WC–HEA composites (WC–12 wt% HEA) were then prepared by ball milling, pressing, vacuum sintering, and sinter-HIP for a first evaluation of the microstructure and achievable hardness. The microstructure exhibited residual porosity without significant WC grain coarsening. XRD analyses showed the dominant presence of WC, along with FCC and M₃W₃C phases (M mainly Fe and Mn), indicating thermal interaction between the binder and WC. Despite these effects, the composite achieved a hardness of 1913 HV and retained a fine WC grain size (0.86 μm). The proposed design approach allowed the definition of a promising Co-free binder composition based on HEA with the expected microstructure, which will need further evaluation, especially aimed at investigating toughness properties as a function of the WC content. Full article

As a new generation of structural materials, Fe-Mn-Al-C lightweight steels with low density, high strength, and excellent strength-toughness properties have shown significant application potential in fields such as transportation, aerospace, and energy equipment. In the present work, the effects of Mo alloying and annealing processes on the microstructural evolution and mechanical properties of Fe-18Mn-8Al-1C-3Cu lightweight steel are investigated. Due to the addition of Mo, the recrystallization temperature is significantly increased, and the recrystallization process is delayed. The fine and dispersed Mo₆C precipitated phases can effectively impede dislocation movements and pin the grain boundaries, hindering recrystallization and grain growth. After annealing at 900 °C, the yield and tensile strengths of the Mo-alloyed steel were enhanced, achieving 1181 MPa and 1345 MPa, respectively, while maintaining an elongation of 24%, thus exhibiting excellent comprehensive performance. Quantitative analysis of strengthening mechanisms confirmed that the strength enhancement primarily resulted from the synergistic contributions of grain refinement strengthening (~152 MPa), solid solution strengthening (44 MPa), dislocation strengthening (131.6 MPa), and Mo₆C precipitation strengthening (52.23 MPa). Through Mo alloying and annealing process optimization, a high-strength, ductile lightweight steel was successfully developed, providing theoretical foundations and technical pathways for its application in high-performance structural materials. Full article

This study examines the effect of vanadium addition on the microstructure and mechanical properties of low-cost powder metallurgy Ti-4Al-2Fe-3Cu alloys. Alloys with and without 6 wt.% V were fabricated by hot extrusion of blended elemental powders followed by vacuum heat treatment. Microstructural analysis revealed that the base alloy exhibits a coarse lamellar α/β structure, while vanadium addition promotes a refined basketweave morphology with a significantly higher β-phase fraction, increasing from 28.1% to 46.2%. Energy-dispersive spectroscopy confirmed preferential partitioning of Fe, Cu, and V into the β phase. Mechanical testing showed that the addition of 6 wt.% V markedly enhances strength, increasing yield strength and ultimate tensile strength from 1122 MPa and 1214 MPa to 1291 MPa and 1349 MPa, respectively, while maintaining comparable tensile ductility (~3.5%). The strength improvement is attributed to α-plate refinement, increased β-phase fraction, and solid-solution strengthening of the β phase. These results demonstrate that vanadium addition is an effective approach for improving the strength of low-cost PM titanium alloys without compromising ductility. Full article

To address the challenge of controlling Fe impurity content during the recycling of aluminum alloys, this study utilized commercial 5083 aluminum alloy as a matrix to prepare alloy samples with four different Fe contents via smelting. The effects of Fe content on the microstructure, mechanical properties, and corrosion resistance of the as-cast 5083 aluminum alloy were systematically investigated. The results indicate that increasing the Fe content induces a significant morphological evolution of the Fe-rich phases, transitioning from compact Chinese-script α-Al(Fe,Mn)Si phases at low Fe levels to coarse needle-like β-AlFeSi phases. Concurrently, both the quantity and size of the second phases increase significantly. Mechanical testing reveals that the hardness of the alloy gradually rises from 67 HV to 72 HV due to second-phase strengthening. The tensile strength shows a trend of initially increasing and then decreasing, peaking at 0.45 wt.% Fe; however, excessive Fe leads to the formation of needle-like phases that cause stress concentration, resulting in a decline in tensile strength. The elongation decreases gradually with increasing Fe content, with a maximum reduction of 19.7%. Electrochemical tests show that higher Fe content increases the self-corrosion current density and decreases the capacitive loop radius, indicating a significant degradation in the alloy’s corrosion resistance. This work provides an experimental basis for the tolerance control of Fe impurities and the performance optimization of recycled 5083 aluminum alloys. Full article

The 2011 Fukushima accident highlighted the vulnerability of traditional Zr alloy fuel cladding under loss-of-coolant accident (LOCA) conditions, prompting the development of accident-tolerant fuel (ATF) systems. A promising near-term solution involves depositing protective coatings on existing Zr alloy cladding. Among various deposition techniques, cold spray technology has emerged as one of the leading methods due to its solid-state, low-temperature process, which minimises thermal degradation and allows for the deposition of a wide range of high-performance materials. This review provides a comprehensive examination of recent advances in cold-sprayed coatings for ATF cladding, beginning with an overview of the fundamentals of cold spray technology and its specific advantages for nuclear applications. The core of the review critically analyses three primary coating systems: Cr, FeCrAl alloys, and MAX phase composites, with a particular focus on Cr coatings, as they have been more extensively studied compared to the other two material systems. Key coating properties, including microstructure of the coating-substrate interface, mechanical properties, thermal conductivity, oxidation resistance, irradiation tolerance, and performance under normal operation and simulated LOCA conditions, are discussed in detail, with particular emphasis on the potential of cold-sprayed Cr coatings to enhance Zr alloy cladding. Cr coatings demonstrate significant improvements in oxidation resistance and irradiation stability, but also face challenges such as high-temperature interfacial reactions. To address these issues, promising solutions, such as diffusion-barrier bilayer systems, are being explored. Additionally, the review discusses FeCrAl and MAX phase composite coatings, highlighting their promising long-term performance under extreme conditions. The review concludes with recommendations for further research to optimise cold spray processes and ensure the robustness of coatings in operational reactor environments. Full article