Search Results (192)

The fabrication of WC-based cemented carbides faced challenges including inhomogeneous composition and grain coarsening. To solve these problems, WC–Co cemented carbides were fabricated via spark plasma sintering (SPS) using core–shell WC–Co powders prepared by an electroless plating method. The effects of sintering pressure and Co content on the microstructure and mechanical properties of the cemented carbides were investigated. The results showed that, with increasing sintering pressure, the relative density of the sintered samples was improved (98.4–99.6%) while the grains were coarsened (0.94–1.07 μm). The optimal properties (fracture toughness 11.11 MPa·m^1/2, and hardness 2100.3 HV30) were obtained when sintered with a pressure of 20 MPa. Grain coarsening at higher pressure (30 MPa) reduced the toughness of the cemented carbides. When the Co content was increased from 3 wt.% to 8 wt.%, fracture toughness was improved while the hardness of the cemented carbides was reduced, attributed to the intrinsic high toughness and low hardness of the Co phase. The WC–8 wt.% Co cemented carbides exhibited optimized synergic mechanical performance (hardness of 1874.2 HV30 and fracture toughness of 13.77 MPa·m^1/2). This work elucidated the relationship between the key sintering parameters (pressure and Co content) and the microstructure and mechanical properties of the cemented carbides. The achievements obtained provide a theoretical foundation for high-quality fabrication of the WC–Co cemented carbides. Full article

This article presents the wear characteristics of the working surface of WC-Co (Tungsten Carbide–Cobalt) tungsten carbide tools obtained using the innovative U-FAST (Upgraded Field-Assisted Sintering Technology) method for particleboard machining. Three groups of tools with a similar chemical composition but differing WC (Tungsten Carbide) grain sizes were tested. Milling tests were carried out on a CNC (Computer Numerical Control) machine tool with the following cutting parameters: spindle rotation at 15,000 rpm, a feed rate of 0.25 mm per tooth, and a feed rate of 3.75. The experimental results show that tools with submicron WC grit sizes of 0.4 µm and 0.8 µm have the longest tool life. Wear of the cutting edges occurred through the removal of the cobalt bond between the tungsten carbide grains, leading to fracture and mechanical removal of the grains from the cutting edge surface. The similarities in the relative wear characteristics of blades with submicron tungsten carbide grain sizes suggest that micro-abrasion and bond phase extrusion may be the main wear mechanisms under the experimental conditions. Nanometric WC grain size significantly influences tool wear through chipping and cracking. Full article

Laser-Directed Energy Deposition (L-DED) is an additive manufacturing technique used for producing and repairing components, mainly for coating applications, depositing metal matrix composites such as cemented carbides, composed of hard metal carbides and a metallic binder. In this sense, this study evaluated the preparation of a ready-to-press WC-25Co powder as a reliable feedstock for L-DED process. This powder required pre-heat treatment studies to prevent fragmentation during powder feeding, due to the absence of metallurgical bonding between WC and Co particles. In the current study, the Taguchi methodology was used, varying laser power, powder feed rate, and scanning speed to reach an optimised deposition window. The best bead morphology resulted from 2400 W laser power, 11 mm/s scanning speed, and 9 g/min feed rate. Moreover, defects such as porosity and cracking were mitigated by applying a remelting strategy of 2400 W and 9 mm/s. Therefore, a perfect deposition is obtained using the optimised processing parameters. Microstructural analysis of the optimised deposited line revealed a fine structure, comprising columnar and equiaxed dendrites of complex carbides. The average hardness of the deposited WC-25Co powder on a AISI 1045 steel was 854 ± 37 HV0.2. These results demonstrate the potential of L-DED for processing high-performance cemented carbide coatings. Full article

In the present work, the optimization of ceramic-based composite WC(Co,Ni) welds by laser cladding was carried out using response surface methodology based on finite element analysis. The heat distribution and temperature field of laser-melted WC(Co,Ni) ceramic coatings were simulated using ANSYS software, which allowed the computation of the distribution of residual stresses. The results show that the isotherms in the simulation of the temperature field are elliptical in shape, and that the isotherms in front of the moving heat source are dense with a larger temperature gradient, while the isotherms behind the heat source are sparse with a smaller temperature gradient. In addition, the observed microstructural evolution shows that the melting zone domains of WC(Co,Ni) are mainly composed of unmelted carbides. These carbides are dendritic, rod-like, leaf-like, or net-like, and are agglomerated into smaller groups. The W content of these unmelted carbides exceeds 80%, while the C content is around 1.5–3.0%. The grey areas are composed of WC, Co and Ni compounds. Based on the regression model, a quadratic model was successfully constructed. A three-dimensional profile model of the residual stress behaviour was further explored. The estimated values of the RSM-based FEA model for residual stress are very similar to the actual results, which shows that the model is effective in reducing residual stress by laser cladding. Full article

To investigate the effect of liquid-phase laser ablation on the hardness of WC-Co cemented carbide, this study performed hardness testing, elemental distribution analysis, and XRD phase analysis. The influence of ablation times on the hardness, elemental distribution, and phase composition of WC-Co cemented carbide was examined, and a model describing the hardness evolution mechanism under liquid-phase laser ablation was proposed. The results demonstrated that the hardness of WC-Co cemented carbide increased with the number of ablations. After 14 ablation times, the maximum hardness reached 2800 HV, representing an increase of 51%–56% compared to the matrix hardness. As the number of ablations increased, the content of ditungsten carbide (W₂C) and tungsten carbide (WC) in the cemented carbide increased, the WC grain size decreased, the dislocation density increased, and the distribution became more uniform. The refinement of WC grains and the elevated dislocation density facilitated stronger intergranular bonding, thereby significantly enhancing the material’s hardness. This study provides theoretical guidance for improving the surface mechanical properties of WC-Co cemented carbide tools through liquid-phase laser ablation. Full article

Many components in industry are subjected to high loads during operation and therefore often do not reach their intended service life. Conventional steels frequently do not provide sufficient protection against wear and corrosion. One solution is to coat these components using methods like thermal spraying to apply cermet coatings such as Cr₃C₂-NiCr or WC-Co-Cr. In light of increasingly strict environmental regulations, more eco-friendly alternatives are needed, especially ones that use little or no Cr, Ni, Co, or W. Another alternative is the recycling of powder materials, which is the focus of this research project. This study investigated whether filter dust from an HVOF system could be used to develop a new coating suitable for use in applications requiring resistance to wear and corrosion. This is challenging as the filter dusts have heterogeneous compositions and irregular particle sizes. Nevertheless, this recycled material, referred to as “Green Cermets” (GCs), offers previously untapped potential that may also be of ecological interest. An established WC-Co-Cr coating served as a reference. In addition to friction wear and corrosion resistance, the study also examined particle size distribution, hardness, microstructure, and susceptibility to crack formation at the interface and inside the coating. Even though the results revealed a diminished performance of the GC coatings relative to the conventional WC-CoCr, they may still be applicable in various industrial applications. Full article

Portland cement production is one of the main global sources of CO₂ emissions, driving the search for sustainable solutions to reduce its environmental footprint. This study evaluated the use of biochar derived from sugarcane bagasse as a partial cement replacement in cementitious composites, aiming to investigate its effects on mechanical and microstructural properties. Composites were prepared with 0, 2, and 5 (% w w⁻¹) biochar at two water-to-cement (w/c) ratios: 0.28 and 0.35. It was hypothesized that the porous structure and carbon-rich composition of biochar could enhance the microstructure of the cementitious matrix and contribute to strength development. Characterization of the biochar indicated compliance with the European Biochar Certificate (EBC) standard, high thermal stability, and notable water retention capacity. Mechanical testing revealed that incorporating 5% w w⁻¹ biochar increased compressive strength by up to 48% in the 0.35 w/c formulation compared to the control. Microstructural analyses (SEM/EDS) showed good interaction between the biochar and the cementitious matrix, with the formation of hydration products at the interfaces. The results confirm the potential of sugarcane bagasse biochar as a supplementary cementitious material, promoting more sustainable composites with improved mechanical performance and reduced environmental impact. Full article

In this study, graded cemented carbide layers were fabricated using Laser Powder-Directed Energy Deposition (LP-DED) to investigate the effects of laser input energy and WC content on crack formation, compositional distribution, and hardness. Two-layer structures were formed, with the first layer containing either 30.5 wt.% or 42.9 wt.% WC and the second layer containing 63.7 wt.% WC. Crack formation was evaluated in situ using acoustic emission (AE) sensors, and elemental composition and Vickers hardness were measured across the cross-section of the deposited layers. The results showed that crack formation increased with higher laser power and higher WC content in the first layer. Elemental analysis revealed that higher laser input led to greater Co enrichment and reduced W content near the surface. Additionally, the formation of brittle structures was observed under high-energy conditions, contributing to increased hardness but decreased toughness. These findings indicate that both WC content and laser energy strongly influence the microstructural evolution and mechanical properties of graded cemented carbide layers. Optimizing the balance between WC content and laser parameters is essential for improving the crack resistance and performance of cemented carbide layers in additive manufacturing applications. Full article

The anodic stability of tungsten carbide (WC) and iron oxide with a spinel structure (Fe₃O₄) were compared against similar data for nanostructured, boron-doped diamond (BDD), and the benchmark Vulcan XC72 carbon, in view of their eventual application as alternative supports for the anion exchange membrane electrolyzer anode. To this end, metal oxide composites were prepared by the in situ autocombustion (ISAC) method, and the anodic behavior of materials (composites as well as supports alone) was investigated in 1 M NaOH electrolyte by the rotating ring–disc electrode method, which enables the separation oxygen evolution reaction and materials’ degradation currents. Among all supports, BDD has proven to be the most stable, while Vulcan XC72 is the least stable under the anodic polarization, with Fe₃O₄ and WC demonstrating intermediate behavior. The Co₃O₄-BDD, -Fe₃O₄, -WC, and -Vulcan composites prepared by the ISAC method were then tested as catalysts of the oxygen evolution reaction. The Co₃O₄-BDD and Co₃O₄-Fe₃O₄ composites appear to be competitive electrocatalysts for the OER in alkaline medium, showing activity comparable to the literature and higher support stability towards oxidation, either in cyclic voltammetry or chronoamperometry stability tests. On the contrary, WC- and Vulcan-based composites are prone to degradation. Full article

This study develops novel superhydrophobic UHMWPE/PTFE/PVA composites via hot-pressing sintering to achieve ultra-low friction and enhanced wear resistance. The ternary system synergistically combines UHMWPE’s mechanical stability, PTFE’s lubricity, and PVA’s dispersion/binding capability. Results show PTFE disrupts UHMWPE crystallization, reducing melting temperature by 2.77 °C and enabling energy dissipation. All composites exhibit hydrophobicity, with optimal formulations (UPP3/UPP4) reaching superhydrophobicity. Tribological testing under varied loads and frequencies reveals low friction, where UPP1 achieves a COF of 0.043 and wear rate below 1.5 × 10⁻⁵ mm³/(N·m) under low-load conditions. UHMWPE oxidative degradation forming carboxylic acids at the interface (C=O at 289 eV, C–O at 286 eV). Formation of tungsten oxides (WO₃/WO₂), carbides (WC), and transfer films on steel counterparts. A four-step tribochemical reaction pathway is established. PVA promotes uniform transfer films, while PTFE lamellar peeling and UHMWPE chain stability enable sustained lubrication. Carbon-rich stratified accumulations under high-load/speed increase COF via abrasive effects. The composites demonstrate exceptional biocompatibility and provide a scalable solution for biomedical and industrial tribological applications. Full article

Conventional WC-Co hard metals have proven to be difficult to manufacture by means of laser powder bed fusion (PBF-LB), resulting in residual pores, crack formation, foreign phase formation, and the inhomogeneous growth of the carbide phase. Alternative compositions such as the W-C-Ti system presented in this study need to be investigated. Through the employment of a high-throughput screening approach, 11 alloy compositions were investigated to determine the influence of the carbon content and tungsten–titanium ratios on microstructure formation and basic mechanical properties. Two screenings were conducted, with one varying the carbon content (10–35 at.%) and the other adjusting the W/Ti ratios (10:90 to 60:40 at.%). Microstructural analyses using scanning electron microscopy (SEM), X-ray diffraction (XRD), and hardness measurements provided insights into phase formation, grain distribution, and mechanical properties. The results showed that increasing the carbon content significantly enhanced the hardness (from 681 HV (10 at.% C) to 1898 HV (35 at.% C)) due to higher δ-(Ti,W)C_1−x carbide phase fractions. Alloys with a higher tungsten content exhibited finer microstructures and an improved crack resistance while maintaining a high hardness (1900–2100 HV). This study identified an alloy with 32.5 at.% W, 32.5 at.% Ti, and 35 at.% C as a promising candidate for further investigation, with properties similar to those of a conventional WC-Co hard metal. Full article

The CO₂ capture from flue gas using biomass-derived porous carbons presents an environmentally friendly and sustainable strategy for mitigating carbon emissions. However, the conventional fabrication of porous carbons often relies on highly corrosive activating agents like KOH and ZnCl₂, posing environmental and safety concerns. To address this challenge, in the present work sodium metaborate tetrahydrate (NaBO₂·4H₂O) has been utilized as an alternative, eco-friendly activating agent for the first time. Moreover, a water chestnut shell (WCS) is used as a sustainable precursor for boron-doped porous carbons with varied microporosity and boron concentration. It was found out that pyrolysis temperature significantly determines the textural features, elemental composition, and CO₂ adsorption capacity. With a narrow micropore volume of 0.27 cm³/g and a boron concentration of 0.79 at.% the representative adsorbent presents the maximum CO₂ adsorption (2.51 mmol/g at 25 °C, 1 bar) and a CO₂/N₂ selectivity of 18 in a 10:90 (v/v) ratio. Last but not least, the as-prepared B-doped carbon adsorbent possesses a remarkable cyclic stability over five cycles, fast kinetics (95% equilibrium in 6.5 min), a modest isosteric heat of adsorption (22–39 kJ/mol), and a dynamic capacity of 0.80 mmol/g under simulated flue gas conditions. This study serves as a valuable reference for the fabrication of B-doped carbons using an environmentally benign activating agent for CO₂ adsorption application. Full article

The long-term post-fire recovery phase is a critical stage for forest ecosystems to progress toward regeneration and mature succession. During this process, soil bacteria exhibit greater environmental adaptability, rapidly driving nutrient cycling and facilitating vegetation restoration. This study investigated the community structure and diversity of soil bacteria during long-term recovery after forest fires in the cold temperate zone, focusing on soils from the 2000 fires in Daxing’anling. Soil samples were classified into Low (L), Moderate (M), and High (H) fire damage intensity, with bacterial community composition and diversity analyzed using Illumina sequencing technology. After long-term fire recovery, the contents of soil organic carbon, black carbon, total nitrogen, alkaline nitrogen, available phosphorus, and available potassium were significantly higher elevated (p < 0.05), and water content was significantly lower, compared with that in the control check (CK) group. Soil urease, fluorescein diacetate, soil acid phosphatase, and soil dehydrogenase activities were significantly higher, and soil sucrase activity was significantly lower in H. There was a significant difference in the Alpha diversity index among the groups. Compared with CK, the Shannon index was significantly increased (p < 0.05) in L, while both Chao1 and Shannon indices were significantly decreased (p < 0.05) in M and significantly higher in H than CK. The results of the PCoA showed that there was a significant difference in the Beta diversity of the bacterial community among the groups (R² = 0.60 p = 0.001). The dominant bacteria groups were Proteobacteria and Acidobacteriota, while Actinobacteria became the new dominant group during the long-term post-fire recovery. AP, WC, DOC, MBC, S-DHA, and S-SC were significantly and positively correlated with soil bacterial diversity (p < 0.05). The results of the co-occurrence network analysis showed that all groups were dominated by symbiotic relationships, with M having the highest network complexity and strongest competitive effects. This study found that the physicochemical properties of soils recovered over a long period of time after fire returned to or exceeded the unfired forest condition. The Actinobacteria phylum became a new dominant bacterial group, with stronger network complexity and competition, in the process of forest recovery after moderate fire. Full article

This paper presents a comprehensive analysis of recent advancements in the application of thermal spraying techniques to enhance the durability and wear resistance of agricultural machinery components, with a particular focus on disc harrow assemblies. Given the harsh conditions under which tillage tools operate—characterized by abrasive wear, impact stresses, and chemical exposure from various soil types—thermal sprayed coatings have emerged as a viable solution to extend the service life of these components. The study discusses various deposition methods, particularly Atmospheric Plasma Spraying (APS), and evaluates their effectiveness in creating high-performance surface layers that resist wear, corrosion, and mechanical degradation. The review also summarizes experimental and field test results for coatings based on materials such as NiCrBSi, WC-Co-Cr, TiO₂, Al₂O₃, Cr₂O_3, and ceramic–metal composites, highlighting their significant improvements in hardness, friction reduction, and resistance to delamination and oxidation. The paper highlights research using thermal spraying techniques, especially APS for agricultural applications, with emphasis mostly on components intended for soil processing and requiring good resistance to abrasive wear. Full article

This work demonstrates the possibility of creating effective composite coatings with a complex structure and phase composition on carbon steel C45 via electrospark deposition (ESD) with multicomponent electrodes with a bonding mass composition of Co-Ni-Cr-B-Si semi-self-fluxing alloys and superhard compounds WC, B₄C and TiB₂. The variation in the roughness, thickness, composition, structure, microhardness and wear at the friction of the coatings as a function of the ratios between the bonding mass and the high-hardness components in the composition of the electrode and of the pulse energy for ESD has been studied. It has been established that with a content of the bonding mass in the electrode of 25–35%, coatings with improved adhesion and simultaneously higher hardness and toughness are obtained. Suitable electrode compositions and optimal pulse energy have been defined, which provide dense and uniform coatings with an increased amount of crystalline-amorphous structures, as well as intermetallic and wear-resistant phases, with thickness, roughness and microhardness that can be changed by the ESD modes in the ranges of δ = 8–65 µm, Ra = 1.5–7 µm, and HV 8.5–15.0 GPa, respectively, and minimal wear of the coated surfaces that is up to 5 times lower than that of the substrate and up to 1.5 times lower than that obtained with conventional WC-Co electrodes. Full article