Search Results (114)

Fe-Cr-C-based coatings were fabricated on Q690 steel via ultrasonic vibration-assisted plasma cladding at varying ultrasonic powers (0–65 W) with a fixed frequency of 18.5 kHz. The coatings primarily consisted of martensite, retained austenite, and (Cr,Fe)₇C₃ carbides, along with (Cr,Fe,Mo)-B borides along grain boundaries. Increasing ultrasonic power promoted cavitation and acoustic streaming, which refined columnar dendrites, reduced elemental segregation (notably for B and Mo), and increased the fraction of fine equiaxed grains without altering phase composition. As a result, the average microhardness increased from 797.1 to 828.5 HV0.1. The friction coefficient decreased from 0.675 to 0.626, while the wear-track width, wear depth, and wear mass loss decreased from 4.0 mm to 2.5 mm, from 112.5 μm to 32.4 μm, and from 20.40 mg to 4.75 mg, respectively. The wear mechanism shifted from severe adhesive wear to mild abrasive wear. These results demonstrate that increasing ultrasonic vibration power effectively refines the solidification microstructure and significantly improves the hardness and wear resistance of plasma-clad Fe-Cr-C-based coatings. Full article

In this work, ternary Mo–Ni–X (X = Al, Co, Cr, Cu, Fe, W) thin films with nominal composition Mo₈₀Ni₁₀X₁₀ (at. %) were prepared by magnetron sputtering and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in alkaline media. The influence of alloy composition, substrate type, and deposition temperature on catalytic performance was systematically investigated. Electrochemical screening revealed a strong dependence of HER activity on both substrate conductivity and ternary alloying, with Al-, Cr-, and W-containing systems showing the best performance on glassy carbon substrates. This highlights the importance of interfacial charge-transfer efficiency in determining catalytic behavior. The Mo₈₀Ni₁₀Cr₁₀/GC system was selected for detailed analysis. Deposition temperatures ≥ 500 °C resulted in enhanced HER activity, reaching an overpotential of η₁₀ = −222 mV at j = −10 mA cm⁻². The improved performance is attributed to temperature-induced microstructural optimization and electrochemically driven surface reconstruction, leading to the formation of a Ni-enriched active interface. AFM analysis confirmed surface restructuring during operation, with roughness increasing from ~1 to ~3 nm, indicating the formation of additional electrochemically accessible active sites. XPS results suggest partial depletion of Mo during cycling, while Cr mainly contributes to structural stabilization of the evolving thin film. Overall, the results demonstrate that HER performance is governed by the coupled effects of alloy composition, substrate-dependent charge transport, and in situ surface reconstruction. This work highlights magnetron sputtering as a scalable approach for designing homogeneous noble-metal-free thin-film electrocatalysts with tunable activity. Full article

This study investigates the oxidation behavior and microstructural evolution of Sanicro 25 steel (X7NiCrWCuCoNb25-23-3-3-2) after long-term exposure to water vapor at 700 °C for 30,000 h. Particular attention was paid to the relationship between protective oxide-scale formation, chromium depletion in the near-surface region, and the possible changes in secondary-phase stability in the steel substrate. FIB-SEM tomography was applied to characterize the oxide scale and the underlying affected zone, enabling three-dimensional visualization of oxide morphology, interfacial voids, and microstructural reconstruction beneath the scale. Long-term exposure resulted in the formation of a continuous Cr-rich oxide scale with a thickness of approximately 2.6 µm and local Mn enrichment. The scale exhibited a complex multilayered morphology, consisting of outer Cr-rich oxide crystallites, fine-grained chromium oxides, and an inner heterogeneous Mn-enriched region, suggesting the possible formation of mixed spinel-type oxides. Si-enriched regions were observed near the oxide/metal interface; however, no continuous Si oxide layer was detected. Despite the presence of interfacial voids, no scale spallation was observed in the investigated regions. SEM-EDX analysis revealed a chromium-depleted subsurface zone extending to approximately 6.5 µm below the oxide scale. CALPHAD calculations suggest that local chromium depletion may reduce the thermodynamic stability of Cr-rich M₂₃C₆ carbides and the Nb–Cr–N-type Z phase. This possible reduction in phase stability may contribute to the formation of a precipitate-depleted region and local microstructural reconstruction beneath the oxide scale. In the bulk region, where oxidation effects were negligible, the microstructure consisted of an austenitic matrix containing M₂₃C₆ carbides, σ phase, Cr–Ni–Fe nitride with an A13-type structure, ε-Cu precipitates, Z phase, and W-rich Cu-containing TCP precipitates. The simulations further suggest that most secondary phases form during the early stage of annealing, whereas prolonged exposure is dominated by diffusion-controlled coarsening. Overall, Sanicro 25 shows good resistance to long-term steam oxidation at 700 °C due to the formation of a continuous Cr-rich protective scale. However, this protection is accompanied by chromium depletion and local near-surface microstructural changes, which should be considered when assessing the long-term stability and service performance of this steel under high-temperature steam conditions. Full article

Worn roller mill roll shafts made of Steel 45 require cost-effective surface restoration; plasma transferred arc (PTA) deposition of Ni–Cr–B–Si + WC composite coatings is a promising approach, yet the effect of arc current on coating quality remains insufficiently characterised for this substrate. Six coatings were deposited from PS-12NVK-01 powder (65 wt.% PG-10N-01 + 35 wt.% WC) at arc currents of 50–100 A on Steel 45 substrates using a ZTW3501DC PTA system; coatings were characterised by SEM, EDS mapping, XRD (HighScore Plus, PDF-2), Vickers microhardness profiling, and ball-on-flat tribological testing. EDS analysis revealed that compositional dilution increases from 18.1% at 60 A to 46.6% at 100 A; XRD identified WC + Cr₃C₂ + Ni₃B + Ni₂B + (Fe,Ni)γ at 50 A, transitioning through Cr₇C₃ + W₂C dominance at 80 A to an Fe₀.₆₄Ni₀.₃₆ matrix at 100 A; and coating thickness peaked at 2.70 mm at 80 A. The 60 A coating yielded the highest surface hardness (887 ± 76 HV, >4× the substrate), the lowest specific wear rate (4.00 × 10⁻⁶ mm³/(N·m), ~22× lower than uncoated Steel 45), and minimum dilution (18.1%), identifying 60 A as the most favourable deposition current for the restoration of roller mill roll shafts under the process parameters employed. Full article

Annealing is a critical step in the fabrication of soft magnetic composites (SMCs), and precise coordination of annealing atmosphere and temperature is essential for optimizing their performance. In this study, FeSiCr SMCs were annealed under three different atmospheres (air, nitrogen, and argon) across a range of temperatures, and the effects of the annealing atmosphere on their microstructure and soft magnetic properties were systematically investigated. The results demonstrate that annealing in an inert atmosphere, particularly argon, within the temperature range of 450–750 °C, yields superior magnetic properties compared with air annealing. After annealing under argon at 550 °C, the effective magnetic permeability (μ_e) reached 47.5, and the power loss (P_cv) was 1457.3 kW/m³ at 1000 kHz and 30 mT. These improvements are primarily attributed to effective stress relaxation and the substantial retention of the polyvinyl butyral (PVB) insulating layer. With further increases in annealing temperature, the magnetic properties deteriorate rapidly due to the complete decomposition of PVB and the formation of conductive chromium carbides. Under such conditions, air annealing exhibits distinct advantages. Selective oxidation of FeSiCr occurs, leading to the formation of a dense chromium oxide insulating layer that enhances magnetic performance (after annealing at 850 °C, μ_e = 47.9, P_cv = 1632.0 kW/m³). Moreover, the mechanical properties were significantly improved, with the radial crush strength increasing from 22.36 N in the unannealed state to 330 N after annealing. These results indicate that the comprehensive performance of SMCs can be effectively tailored through the appropriate selection of annealing atmosphere and temperature, providing valuable guidance for the design and optimization of high-performance SMCs. Full article

Ruthenium (Ru) and its alloys exhibit high corrosion resistance in acidic environments; however, their corrosion behavior in supercritical acidic fluids remains unclear. In this study, the corrosion resistance of Ru–Mo–W and Ru–Mo–Fe–Cr alloy systems in supercritical nitric acid was evaluated using a combinatorial approach. Alloy thin-film libraries with a thickness of approximately 300 nm were fabricated on (001) sapphire substrates by multi-target magnetron sputtering. Composition and thickness were evaluated by X-ray fluorescence (XRF) before and after corrosion testing. The composition-dependent corrosion behavior was compared in a 0.2 M nitric acid solution at 400 °C and 30 MPa. In the Ru–Mo–W system, most Ru-rich compositions exhibited corrosion rates below 0.2 mm/y, and at comparable Ru contents, Mo addition provided higher corrosion resistance than W addition. In the Ru–Mo–Fe–Cr system, significant dissolution and film delamination were observed on the low-Ru side. These results demonstrate that the combination of combinatorial thin-film libraries and XRF-based thickness evaluation is an effective first-stage approach for identifying promising alloy composition regions in supercritical acidic environments. 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

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

Previous research indicates that WC-12Co contents above 60 wt.% in feedstock powders for cermet coatings impair adhesion and wear resistance. This study characterizes NiCrFeSiAlBC coatings—unreinforced or reinforced with 65 wt.% or 85 wt.% WC-12Co—applied via high-velocity oxy-fuel (HVOF) spraying onto stainless steel substrates under controlled parameters. It quantifies the influence of high carbide volume fractions within the NiCrFeSiAlBC matrix on microstructure and tribomechanical performance. Microstructural analysis revealed uniformly distributed cermet layers featuring dissolved reinforcements and WC hard phase formation, with minimal W₂C crystallization. Elevated WC-12Co incorporation promoted densification and reduced porosity. Vickers microhardness tests (HV 0.3) demonstrated increased hardness upon WC-12Co addition, attributable to finer particle sizes, lower porosity, and the presence of WC phases alongside crystallographic refinements. Under dry reciprocating sliding conditions, friction coefficients and wear volumes decreased markedly. Consequently, the coating with 85 wt.% WC exhibited the best mechanical and tribological properties. Full article

The design of ladle furnace (LF) refining pathways for weathering steels requires precise control of multi-component steel/slag reactions governed simultaneously by thermodynamics and interfacial mass transfer kinetics. An EERZ-based kinetic modeling strategy was employed using the Thermo-Calc^® (version 2022a) Process Metallurgy Module and the CALPHAD TCOX11 database to develop LF refining schedules capable of upgrading conventional S355J2R steel to weathering steel grades: S355J2W and S355J2WP. First, the sensitivity of predicted compositions to key kinetic inputs was quantified. The validated model was then used to simulate deoxidation and desulfurization sequences, predicting the evolution of liquid–steel and slag compositions, slag basicity, and FeO activity throughout the LF cycle. Subsequently, Cr- and P-ferroalloys were introduced to design tap-to-tap schedules that meet the EN 10025-5 chemical specifications for S355J2W and S355J2WP. To correlate simulation outcomes with material performance, plates produced following the modeled schedules were evaluated through a 1000 h accelerated salt spray test. Steel density and steel phase mass transfer coefficients were found to produce the highest prediction sensitivity (up to 7.5 wt.% variation in C and S), whereas slag phase parameters exhibited a lower impact. The predicted steel compositions showed strong agreement with industrial values obtained during plant trials. SEM-EDS analyses confirmed the development of a Cr-enriched protective patina and validated model-based alloying strategies. Full article

High-entropy alloys (HEAs) are a class of multi-principal element materials composed of five or more elements in near-equimolar ratios. This unique compositional design generates high configurational entropy, which stabilizes simple solid solution phases and reduces the tendency for intermetallic compound formation. Unlike conventional alloys, HEAs exhibit a combination of properties that are often mutually exclusive, such as high strength and ductility, excellent thermal stability, superior corrosion and oxidation resistance. The exceptional mechanical performance of HEAs is attributed to mechanisms including lattice distortion strengthening, sluggish diffusion, and multiple active deformation pathways such as dislocation slip, twinning, and phase transformation. Advanced characterization techniques such as transmission electron microscopy (TEM), atom probe tomography (APT), and in situ mechanical testing have revealed the complex interplay between microstructure and properties. Computational approaches, including CALPHAD modeling, density functional theory (DFT), and machine learning, have significantly accelerated HEA design, allowing prediction of phase stability, mechanical behavior, and environmental resistance. Representative examples include the FCC-structured CoCrFeMnNi alloy, known for its exceptional cryogenic toughness, Al-containing dual-phase HEAs, such as AlCoCrFeNi, which exhibit high hardness and moderate ductility and refractory HEAs, such as NbMoTaW, which maintain ultra-high strength at temperatures above 1200 °C. Despite these advances, challenges remain in controlling microstructural homogeneity, understanding long-term environmental stability, and developing cost-effective manufacturing routes. This review provides a comprehensive and analytical study of recent progress in HEA research (focusing on literature from 2022–2025), covering thermodynamic fundamentals, design strategies, processing techniques, mechanical and chemical properties, and emerging applications, through highlighting opportunities and directions for future research. In summary, the review’s unique contribution lies in offering an up-to-date, mechanistically grounded, and computationally informed study on the HEAs research-linking composition, processing, structure, and properties to guide the next phase of alloy design and application. Full article

To prepare a high-performance Fe-based laser cladding coating, herein, various Fe60/WC/Y₂O₃ coatings are deposited on the surface of 42CrMo steel plate via a laser cladding technique. The WC dosage is fixed as 10 wt%, while the dosage of Y₂O₃ ranges from 0 to 7.5 wt%. The influences of Y₂O₃ dosage on the coating hardness, wear resistance, and corrosion resistance are investigated. With the addition of Y₂O₃, the feature peak of WC disappears, and the peaks of M₂₃C₆ gradually weaken, indicating that Y₂O₃ promotes the decomposition of WC and suppresses the formation of new metal carbides. When the dosage of Y₂O₃ is 2.5 wt%, a grid-like structure is formed on the coating surface, suggesting uniform distribution of decomposed W within the Fe matrix. When the Y₂O₃ dosage exceeds 5 wt%, a large amount of CO₂ gas is released, leading to an increase in surface pores. Through a comparison, the optimal dosage of Y₂O₃ is 2.5 wt%, and the resulting 3# coating has the highest hardness of 861.97 HV. Moreover, the 3# coating also shows the minimum friction coefficient and the minimum wear volume, reflecting its superior wear resistance. The polished coating serves as a working electrode, and the corrosion resistance is tested in 3.5% NaCl solution. The sample containing 2.5 wt% Y₂O₃ has the highest corrosion potential and the lowest corrosion current density, indicating excellent corrosion resistance. The enhanced performance is ascribed to the improved surface quality and the formation of a W-reinforced grid structure. The high-performance coating has promising application potential in material and component repair. Full article

Bioreduction is an effective method to reduce Cr(VI) for bioremediation. In this study, a hexavalent chromium-reducing bacterium with salt tolerant abilities, Acinetobacter ZQ-1, was isolated, which could efficiently reduce Cr(VI) under a wide range of pH (6.0–9.0), temperatures (28–42 °C) and coexisting heavy metals (Mn²⁺, Pb²⁺ and Fe³⁺). It is worth mentioning that the strain ZQ-1 could reduce Cr(VI) containing 15% (w/v) NaCl, showing strong salt tolerance. Under optimal culture conditions, strain ZQ-1 was able to completely reduce 50 mg/L of Cr(VI) in 24 h. The metabolic data of ZQ-1 showed that salt stress significantly altered the composition of metabolites, in which the accumulation of compatible solutes such as Arginine, Leucine, Lysine and Proline contributed to the alleviation of high salt stress for strain ZQ-1. Meanwhile, the increased content of alginate and betaine also helped to maintain the normal function of strain ZQ-1 in a high-salt environment. This is of great significance for the development, utilization and mechanism of action of salt-tolerant hexavalent chromium-reducing bacteria in the future. Full article

In order to enhance the performance of 20# steel, this study successfully fabricated AlCoCrFeNi high-entropy alloy coatings with different WC contents (x = 0, 10, 20, 30 wt%) on its surface using plasma cladding technology. The effects of WC content on the microstructure, mechanical properties, and corrosion resistance of the coatings were systematically investigated. The results indicate that without WC addition, the coating consists of a dual-phase structure comprising BCC and FCC phases. With the incorporation of WC, the FCC phase disappears, and the coating evolves into a composite structure based on the BCC matrix, embedded with multiple carbide phases such as W₂C, M₇C₃, M_xC_γ, and Co₆W₆C. These carbides are predominantly distributed along grain boundaries. As the WC content increases, significant grain refinement occurs and the volume fraction of carbides rises. The coating exhibits a mixed microstructure of equiaxed and columnar crystals, with excellent metallurgical bonding to the substrate. The microhardness of the coating increases markedly with higher WC content; however, the rate of enhancement slows when WC exceeds 20 wt%. The hardness of 1066.36 HV is achieved at 30 wt% WC. Wear test results show that both the friction coefficient and wear rate first decrease and then increase with increasing WC content. The optimal wear resistance is observed at 20 wt% WC, with a friction coefficient of 0.549 and a wear mass loss of only 0.25 mg, representing an approximately 40% reduction compared to the WC-free coating. Electrochemical tests demonstrate that the coating with 20 wt% WC facilitates the formation of a dense and stable passive film in NaCl solution, effectively inhibiting Cl⁻ ion penetration. This coating exhibits the best corrosion resistance, characterized by the lowest corrosion current density of 1.349 × 10⁻⁶ A·cm⁻² and the highest passive film resistance of 2764 Ω·cm². Full article

This study presents an effective route for producing functionally graded metal matrix composites with enhanced abrasion wear resistance by incorporating ex situ Fe–WC preforms into austenitic stainless-steel castings. The preforms, produced by cold-pressing mixed WC and Fe powders, were positioned in the desired locations in sand molds and reacted in situ with the molten steel during casting. This process generated a metallurgically bonded reinforcement zone with a continuous microstructural and compositional gradient, characteristic of a Functionally Graded Material (FGM). Near the surface, the microstructure consisted of a martensitic matrix with WC particles and (W,Fe,Cr)₆C carbides, while towards the base metal, it transitioned to austenitic dendrites with an interdendritic network of Cr- and W-rich carbides, including (W,Fe,Cr)₆C, (Fe,Cr,W)₇C₃, and (Fe,Cr,W)₂₃C₆. Vickers hardness measurements revealed surface-adjacent values (969 ± 72 HV 30) approximately six times higher than those of the base alloy, and micro-abrasion tests demonstrated a 70% reduction in micro-abrasion wear rate in the reinforced zones. These findings show that WC dissolution during casting enables tailored hardness and abrasion wear performance, offering an accessible manufacturing solution for high-demand mechanical environments. Full article