Search Results (459)

Hydrogen trapping at carbide/matrix interfaces is important for improving the resistance of steels to hydrogen embrittlement. In this work, the segregation behavior of hydrogen at the coherent α-Fe/V₄C₃ interface was investigated by first-principles calculations. Representative hydrogen sites were considered systematically, including interstitial sites in the near-interface region, interfacial sites, and carbon-vacancy sites in V₄C₃. All of the sites examined are energetically favorable for hydrogen trapping, but the carbon vacancy inside V₄C₃ exhibits the strongest trapping tendency. Charge density, Bader charge, and density-of-states analyses indicate that hydrogen at this site gains more electrons and forms stronger interactions with neighboring V atoms, leading to enhanced stability. The behavior of H₂ at the internal carbon vacancy was also evaluated. After structural relaxation, the H₂ molecule dissociated into two separate H atoms, indicating that hydrogen is more stably trapped in atomic rather than molecular form. These findings reveal the crucial role of carbon vacancies in regulating hydrogen trapping at the α-Fe/V₄C₃ interface and provide atomic-scale insight into the hydrogen trapping mechanism of vanadium carbide precipitates in steels. Full article

Concentrated Solar Power (CSP) tower systems require receiver materials capable of operating above 1000 °C to meet the efficiency targets of third-generation technologies (25–30%). Hybrid solutions, combining ceramic coatings with metallic substrates, offer promising thermomechanical stability under severe thermal cycling. This study investigates the high-temperature behavior of silicon carbide (SiC) coatings deposited on Fe-C-Al-Mo alloys under concentrated solar flux. Substrates were pre-oxidized to form a continuous 1–2 µm α-Al₂O₃ interlayer, serving as a chemical and mechanical buffer. SiC coatings (10–24 µm thick) were deposited via High-Temperature Chemical Vapor Deposition (HT-CVD). Characterization using XRD, SEM, EDS, and optical spectrophotometry identified cubic 3C-SiC with a globular microstructure and high compressive residual stresses (−2000 to −2400 MPa), inducing microcracking. Stress relaxation was achieved by increasing coating thickness or post-deposition annealing. Controlled oxidation formed a thin silica layer, enhancing solar absorptivity to over 90%. Accelerated thermal cycling (up to ~900 kW/m², 1050–1200 °C) revealed that coating stability depends on SiC thickness, residual stress evolution, α-Al₂O₃ interlayer thickness, and cycling severity. Optimizing these parameters is essential for ensuring the long-term durability of hybrid CSP receivers. Full article

In this study, a brazed diamond micro-powder grinding wheel with Ni-based filler metal was fabricated, which achieved one-step grinding forming of YG-6 cemented carbide rods. The interfacial microstructure, elemental diffusion behavior, and interfacial phases of the brazed diamond micro-powder joint were systematically characterized. Furthermore, the machining performance of the brazed diamond micro-powder grinding wheel was comprehensively evaluated in combination with its service life and the surface roughness of the machined YG-6 cemented carbide rods. The results show that the Ni-based filler exhibits good wettability to diamond micro-powder particles, and the diamonds have a reasonable protrusion height in the filler layer, with no graphitization observed on the surface of the brazed diamonds. During the brazing process, the active element Cr continuously segregates toward the diamond surfaces and reacts progressively with dissolved C atoms on the diamond surfaces, eventually forming a lath-shaped Cr–C compound layer on the diamond surfaces. XRD results identify this compound as Cr₃C₂. Elemental diffusion occurs between the filler layer and the steel substrate, forming a Fe–Ni solid solution diffusion zone. Consequently, the Ni-based filler forms a reliable chemical metallurgical bond with both the diamond micro-powder particles and the steel substrate. The as-prepared brazed diamond micro-powder grinding wheel exhibits excellent service life: a single wheel can grind more than 1300 YG-6 cemented carbide rods on average before failure. The surface roughness (Ra) of the machined YG-6 cemented carbide workpieces remains below 1.6 μm throughout all processing stages, which satisfies the requirements for one-step precision grinding. Full article

The present study examined the interactions between the structure, microstructure and mechanical properties of CrMnFeCoNi, CrMnFeCoNiV_0.5 and CrMnFeCoNiMo_0.5 High-Entropy Alloys (HEAs). Starting from elemental powders, the HEAs were obtained by high-energy ball milling, followed by vacuum annealing at 1373 K for 1 h. After milling, a binary FCC-BCC solid solution was formed; the samples showed hardness values ranging from 800 to 973 HV. Evidence shows that annealing HEAs reduced the solubility of V and Mo in the alloys’ FCC structure. Additionally, the Cr content in the FCC phase also decreases. The carbon derived from the decomposition of the process control agent was trapped in the interstices of the HEA structure during mechanical alloying. This amount of carbon is sufficient to form carbides during annealing. The thermodynamic stability of the precursor elements in HEAs is a determining factor in M_xC_y-type formation. The hardness response of HEAs was associated with the HEAs’ structure, while the elastic modulus was affected by their microstructure. Full article

This paper presents a practical implementation of relative primary radiation thermometry (RPRT) together with MultiFixRadSoft, an open-source software package developed in accordance with the Mise-en-Pratique for the kelvin (MeP-K) for realization of the thermodynamic temperature scale and uncertainty evaluation under the new definition of the kelvin. The software enables realization of temperature scales using ITS-90 metal fixed points as well as metal–carbon and metal–carbide–carbon eutectic high-temperature fixed points (HTFPs) for both radiation thermometers and radiometers. It incorporates automated routines for melting plateau analysis, including determination of the point of inflection, liquidus point, and melting range, together with correction modules for size-of-source effect, detector nonlinearity, emissivity, and temperature drop. Validation is demonstrated through experimental realization using six fixed points (Cu, Fe–C, Co–C, Pd–C, Ru–C, and WC–C) and a linear radiation thermometer. The software also supports ITS-90 extrapolation procedures and flexible calibration schemes (n = 1 to n ≥ 3), with automated Sakuma–Hattori fitting and full uncertainty propagation compliant with MeP-K requirements. The results show excellent agreement with manual analyses and published data, confirming the correctness of the implemented algorithms. By integrating data processing, scale realization, and uncertainty analysis within a unified and transparent framework, MultiFixRadSoft provides a robust and accessible tool for traceable radiometric thermometry, supporting emerging NMIs and industrial laboratories while promoting the wider adoption of primary thermodynamic temperature realization methods. Full article

This study quantitatively evaluates the effect of solid-phase pre-reduction of chromite concentrate on the energy efficiency and techno-economic performance of high-carbon ferrochrome (HC FeCr) smelting. Laboratory pre-reduction experiments were conducted at 1200–1400 °C using Shubarkol coal, metallurgical coke, and special coke as carbonaceous reducing agents. Structural and phase transformations were characterized by X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). At 1200 °C, the degree of metallization remained low (<5%), whereas at 1400 °C it increased to 41.3% under laboratory conditions and up to 65% in pilot-scale tests due to the decomposition of the spinel matrix and the formation of metallic and carbide phases. The application of pre-reduced feedstock in a submerged arc furnace reduced specific electricity consumption by up to 33.5% compared with conventional smelting and increased chromium recovery to 89.71%. Industrial-scale extrapolation indicates the potential to decrease power consumption to approximately 3190 kWh/t of alloy. Techno-economic analysis demonstrates that the use of pre-reduced feedstock reduces the production cost by approximately 10–23%, depending on the type of carbonaceous reducing agent (Shubarkol coal, metallurgical coke, or special coke). Special coke provided the highest energy efficiency, whereas Shubarkol coal ensured the greatest direct economic benefit. The integrated microstructural, energetic, and economic assessment confirms the industrial applicability of the proposed pre-reduction approach. Full article

The objective of this article is to optimise the deposition modes and the content of exothermic additions (EAs) in the core filler in Fe-C-Cr-Ti with Cu additions hardfacing. To achieve this, JMatPro Release 7.0, Sente Software Ltd., 2016 material characterisation software was used to simulate and calculate the equilibrium phase structure and composition of the Fe-C-Cr-Ti-Cu alloy during the welding thermal cycle. A synergistic approach combining the Taguchi–Analysis of Variance (ANOVA)–Factorial design (FD) method with the standard hybrid Taguchi–ANOVA–Principal Component Analysis (PCA)–Grey Relational Analysis (GRA) is used and justified to optimise factors and develop mathematical models for parameters in the L9 orthogonal experimental design. The study examines how the transfers of deoxidisers depend on the content of exothermic additions in the cored wire filler (EA) and the contact tip-to-work distance (CTWD), while the behaviour of carbide formers is influenced by wire feed speed (WFS) and present arc voltage at the power source (U_set). The research specifically investigates the Fe-C-Cr-Ti-Cu system and the role of copper in stabilising austenite. Findings show that high Cu concentrations (7 wt.%) enhance hardenability by 13%, effectively suppressing pearlite transformation and expanding the bainite region. The desired chemical composition of the deposited metal is determined by the distribution of selected factors, as measured by the transfer coefficients of each element. Full article

Catalytic materials are central to the advancement of hydrogen generation technologies, playing a pivotal role in enabling sustainable, carbon-neutral energy systems. Hydrogen can be produced via electrochemical water splitting, thermochemical reforming, or photocatalysis—each imposing unique performance requirements on catalysts in terms of activity, selectivity, stability, and efficiency. While traditional noble metals (e.g., platinum, ruthenium, iridium) provide benchmark catalytic activity, their widespread use is hindered by scarcity, high cost, and limited long-term durability. Consequently, researchers have increasingly focused on earth-abundant alternatives such as transition metals (Ni, Co, Fe, Mo), alloys, metal oxides, carbides, sulfides, nitrides, and carbon-based systems. Among these, two-dimensional materials, particularly the MXene family, have attracted significant attention due to their metallic conductivity, layered structure, and tunable surface chemistry. These features enable rapid charge transfer and abundant active sites, making MXenes and related nanostructured catalysts promising for both the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) across a wide range of electrochemical conditions. Parallel efforts have integrated novel semiconductors, plasmonic nanomaterials, and hybrid heterostructures to improve the efficiency of solar-to-hydrogen energy conversion. This paper reviews the main types of catalytic materials used in hydrogen production, explains their design strategies and structure–performance relationships, and discusses key engineering challenges such as integrating renewable energy sources, scaling up manufacturing, and ensuring long-term durability in real-world systems. Future research goals are also highlighted, including the development of affordable non-noble catalysts, enhancing catalyst stability through surface and defect engineering, and coupling hydrogen production with circular economy principles, all of which are essential to making hydrogen generation more efficient, scalable, and cost-effective as the world transitions to clean and sustainable energy. Full article

This study investigated the properties of a composite NiCrFeSiB coating with fine-dispersed WC additives, deposited by the HVOF method. The NiCrFeSiB powder alloy with WC additives was applied to a steel substrate. The WC content in the coating was 10, 15, and 20% by weight. The particle size distribution of the mixture ranged from 3 to 10 µm. The WC used was the WC8 alloy (92% WC, 8% Co). The levels of stress, phase composition, hardness, wear resistance, and coating structure were investigated. The studies revealed that the structure was primarily composed of the γ-Ni-Fe solid solution phase, with secondary phases including Ni₃B, Fe₃B, (Cr,)₂B, and carbides of the W₂C, WC, M₇C₃ type. A small amount of the initial WC particles was also present. The use of a fine-dispersed NiCrFeSiB powder mixture with WC particles resulted in a nearly twofold increase in hardness and wear resistance compared to the same parameters of the coating without WC. The coating with 20% WC exhibited the highest hardness. However, its wear resistance was lower than that of the coating with 15% WC. This fact could be explained by a slight difference in the phase composition and an increase in the proportion of the unsolidified WC phase in the structure. This led to the spalling of fine particles and a reduction in wear resistance. The study demonstrated the feasibility of using a fine-dispersed NiCrFeSiB coating with WC additives without additional remelting. Similar hardness and wear resistance results were achieved immediately after HVOF spraying when using a fine-dispersed NiCrFeSiB + 15% WC/Co mixture with a 92/8 composition. This simplification of the technology reduced the coating application process time. It also lowered production costs by eliminating the remelting stage. Full article

By optimizing the carburizing heat treatment process, the grain size of the carburized layer of M50NiL steel was successfully refined to the sub-micron level. The mechanism for the generation of a large number of sub-micron crystal regions (SMCR) is that dislocations are entangled and linked due to the pinning effect of nanometer-sized carbides. In this study, a stacking fault energy (SFE) model for austenite in M50NiL steel was established. First-principles calculations were employed to investigate the effects of alloying elements, as well as the position and quantity of carbon (C) atoms, on the generalized stacking fault energy (GSFE). The variations in SFE were further analyzed in combination with differential charge density calculations. The simulation results revealed that the addition of alloying elements excluding nickel led to a reduction in the unstable stacking fault energy. Differential charge density analysis indicated that this decrease was associated with the weakening of Fe–Fe bonds in the L0 layer, where stacking faults occurred. When C atoms are interstitially dissolved near the L0 layer, the Fe–Fe bonds near the L0 layer are enhanced, and the unstable stacking fault energy is correspondingly increased. Compared with the pure iron system, the combined effect of alloying elements and C atoms in M50NiL steel maintained a relatively low level of both the unstable stacking fault energy and the stacking fault formation barrier, provided that C atoms were not dissolved in the L1 layer. This condition was favorable for dislocation slip. Meanwhile, the stable stacking fault energy significantly increased, enhancing the stability of austenite. Based on these simulation results, the relationship between the GSFE of austenite in M50NiL steel and the formation of subgrains and twins within the submicron crystalline regions of the carburized layer was discussed. Full article

The present study focuses on redesigning the composition of the conventional M50 steel grade, which is widely used for high-temperature bearings. Through thermodynamic calculations, a new steel variant was developed in the laboratory with the aim of refining carbides and improving hardness. After undergoing quenching at 1070 °C and triple tempering at 540 °C, the hardness reached 66 HRC, which is 7.57% higher than that of M50 steel (61 HRC). Meanwhile, the hardness at 400 °C reached 60 HRC. In addition to the typical M₂C and M₆C carbides found in M50 steel, the presence of Fe and Cr-rich M₂₃C₆ carbides was detected in the redesigned steel after triple tempering. These carbides play a significant role in enhancing hardness. Furthermore, the heat treatment process effectively eliminated the uneven and coarse carbides. The average size of primary carbides is 4.6 ± 0.6 μm, which represents a 27.0% reduction compared to M50 steel (6.3 ± 0.1 μm). The detrimental V-rich MC carbides commonly found in M50 were eliminated. 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

Wear of crushing and grinding equipment components causes frequent maintenance and downtime; therefore, effective repair hardfacing routes are required to extend service life. This study investigates plasma transferred arc (PTA) surfacing of 35L cast steel using a high-chromium Fe–Cr–C powder (PG-S27) and clarifies how the welding current (40–120 A) governs layer geometry, microstructure, phase constitution, hardness, and dry-sliding tribological behavior. All deposits exhibited a dendritic–eutectic structure; increasing current led to dendrite coarsening, wider interdendritic regions, and deeper penetration/dilution. X-ray diffraction indicated an α-Fe matrix with chromium carbide phases (Cr₇C₃/Cr₂₃C₆), while the carbide-related signal decreased with higher current, consistent with enhanced dilution. The coatings showed a strong hardening effect compared with the substrate (~190 HV), reaching ~625–650 HV at 40–80 A and decreasing to ~556–589 HV at 100–120 A. In dry ball-on-flat sliding, the steady-state friction coefficient was nearly unchanged (μ ≈ 0.50–0.55) across all regimes; however, wear resistance depended strongly on current: the lowest wear was achieved at low-to-moderate currents (40–80 A), whereas higher currents (100–120 A) resulted in substantially increased material loss, approaching the substrate level. These results identify 40–80 A as the most favorable current window for obtaining wear-resistant PTA layers from PG-S27 on 35L steel. Full article

Linear α-olefins (LAOs) from CO/H₂ represent an attractive non-petroleum route, yet their selective formation over Fe catalysts is often limited by CO₂ formation via water–gas shift (WGS) reaction and by secondary hydrogenation that consumes terminal olefins. In this work, we demonstrate that these competing pathways can be regulated on carbon-nanotube (CNT) supported Fe catalysts by controlling the CNT interfacial oxygen environment through NO treatment or high-temperature annealing and by adjusting the Mn incorporation protocol between co-impregnation and stepwise addition. Under identical reaction conditions at 280 °C and 3.0 MPa with an H₂-to-CO ratio of 1, high-temperature treated CNTs improve olefin preservation and LAO retention compared with NO-treated CNTs. Mn promotion further shifts selectivity toward α-olefins and lowers CO₂ selectivity. At the same Fe-to-Mn ratio, the Mn introduction sequence produces distinct reducibility and CO-binding behaviors that lead to different steady-state oxide and carbide phases. XPS, H₂-TPR, and CO-TPD collectively suggest that CNT pretreatment and the Mn protocol modulate near-surface oxygen speciation, reduction kinetics, and CO adsorption strength. Mössbauer spectroscopy confirms a predominantly χ-Fe₅C₂ population and indicates the presence of ε-Fe₂C in selected samples together with residual oxide and superparamagnetic Fe species. These results highlight the importance of controlling the CNT–metal interface and Mn–Fe proximity to enhance LAO retention under high-temperature CO hydrogenation. Full article

This study analyses the effect of electrolytic plasma treatment on improving the wear resistance of 30CrMnSi steel used under conditions of high abrasive and impact-abrasive loads. The samples were processed using various technological regimes, namely electrolytic plasma quenching, nitriding, nitrocarburising, and carburising. A range of analytical methods were employed to comprehensively characterise the structure, phase composition, and mechanical properties, including SEM/EDS, XRD, and microhardness testing. The tribological properties of the materials were evaluated using a TRB³ tribometer, and abrasive and impact-abrasive wear tests were performed in accordance with GOST 23.208–79 and GOST 23.207–79 standards. The results show that electrolytic plasma treatment leads to the formation of diffusion layers with a thickness of 50–150 μm, accompanied by the formation of carbide, nitride, and carbonitride phases (Fe₄C, Fe₇C₃, Fe₄N, Fe₂N, Fe₃(CN)). This process results in a significant increase in surface hardness (up to 610–930 HV) and improved wear resistance. The study indicates that electrolytic plasma nitrocarburising provides a favourable combination of hardness and tribological behaviour, leading to a low friction coefficient (0.25–0.35) and enhanced resistance to abrasive and impact-abrasive wear. The obtained results demonstrate the potential of this technology for improving the performance of components made of 30CrMnSi steel operating under severe wear conditions. Full article