Search Results (921)

cBN-reinforced particle Ti-based composite coatings were deposited by high-speed laser cladding technology to enhance the wear resistance of Ti alloy. In this work, the influence of Ag addition on the microstructure and tribological behavior was systematically investigated. The microstructure and phase composition of the coatings were characterized using SEM/EDS and XRD. And the microhardness and tribological performance of coatings with Ag addition were assessed from room temperature up to 500 °C. The results show that the solidification process evolves with different Ag content. At lower Ag concentrations, Ag dissolves in the Ti-based solid solution, whereas higher Ag concentrations lead to the precipitation of Ag and Ag-Ti intermetallic. Due to the solid-solution strengthening effect and the formation of high-hardness intermetallic phases, the hardness of the coating increases with increasing Ag content. However, excessive Ag addition (>2.5 wt.%) results in a decrease in hardness. Tribological tests reveal that the friction coefficient and wear volume at room temperature decrease with increasing Ag content. With 10 wt.% Ag added, the friction coefficient of the coating decreases by 15% to 0.56, and the wear volume reduces by 28%, with the wear mechanism evolving from adhesive and fatigue wear to oxidative wear. At elevated temperatures (300 °C–500 °C), the friction-reducing effect is further enhanced due to the “sweating” of Ag and the formation of an oxide film, leading to reductions in the friction coefficient of 18%, 13%, and 7% at 300 °C, 400 °C, and 500 °C, respectively, for coatings with 5 wt.% Ag compared to coatings without Ag. Moreover, the formation of hard phases improves the coating’s high-temperature softening resistance and wear resistance property, as evidenced by an 85% reduction in wear volume at 500 °C for coatings containing 5 wt.% Ag. Full article

To address the limitations in the corrosion resistance of 316L stainless steel, ceramic reinforcements are increasingly utilized in additive manufacturing. However, their influence on corrosion behavior varies significantly. Via laser powder bed fusion (LPBF), 316L stainless steel composites reinforced with, respectively, 1 wt.% ceramic particles (TiC, SiC, SiO₂, WC, Y₂O₃) were fabricated, and the comparing microstructure and corrosion performance was investigated in this work. The results indicated that ceramic particle addition increased porosity (0.24% to 1.40%) due to the thermal expansion coefficient mismatch between particles and matrix and defects from incompletely melted particles. Microstructural analysis revealed that LPBF-processed 316L exhibited cellular sub-grain boundaries with distinct melt pool boundaries. Ceramic particle addition refined sub-grain boundaries to varying degrees across composites, accompanied by increased sub-grain boundary density. Interfacial reactions and thermal stresses induced crack formation in SiC/316L and SiO₂/316L composites. Electrochemical testing demonstrated that Y₂O₃/316L exhibited the highest corrosion resistance, followed by TiC/316L and WC/316L. The corrosion resistance of the as-built L-BPF 316L matrix was inferior to that of these three composites. Conversely, SiC/316L and SiO₂/316L exhibited the poorest corrosion resistance. The optimized corrosion resistance of Y₂O₃/316L is hypothesized to result from pronounced grain refinement and the highest sub-grain boundary density, which provided abundant nucleation sites for passive film formation. Conversely, SiC/316L and SiO₂/316L showed lower corrosion resistance than the as-built L-BPF 316L matrix due to elevated defect density. Corrosion morphology analysis indicated preferential corrosion propagation along melt pool boundaries in 316L, TiC/316L, WC/316L, and Y₂O₃/316L. In contrast, pores and microcracks in SiC/316L and SiO₂/316L accelerated pit nucleation, indicating failure dominated by localized corrosion mechanisms. Full article

High-quality BaTiO₃ nanopowders were synthesized via a sol–gel method using butyl titanate and barium serving as precursors. This study systematically investigates the influence of calcination temperature (600–1000 °C) and gel aging time (2–10 h) on the phase evolution and microstructure of the nanoparticles. A pure tetragonal phase with a high tetragonality (c/a ratio of 1.0100) and an average particle size of 140 nm was achieved at 1000 °C. X-ray photoelectron spectroscopy and Ultraviolet–Visible diffuse reflectance spectroscopy analyses revealed that high-temperature calcination induced the formation of oxygen vacancies and Ti³⁺ defects, leading to a narrowing of the optical bandgap from 3.01 eV to 2.98 eV. An optimal aging time of 4 h yielded uniform nanoparticles with a high specific surface area, whereas prolonged aging (>6 h) resulted in the re-emergence of BaCO₃ impurities and severe agglomeration due to the formation of a rigid gel network. This work provides a precise processing window for fabricating high-purity, highly tetragonal BaTiO₃ nanopowders suitable for the next generation of miniaturized electronic devices. Full article

To address the challenges of zwitterionic dissociation and steric hindrance in the esterification of α-aromatic amino acids, this study prepared the solid superacid catalyst SO₄²⁻/TiO₂/HZSM-5 (STH) and its plasma-modified derivative SO₄²⁻/TiO₂/HZSM-5 (STH-RF) via an aging-impregnation method. Systematic characterization revealed that plasma modification optimizes the crystal morphology and particle dispersion of the catalyst, while also achieving pore clearance and an increase in the specific surface area. Furthermore, it gradationally enhances acidic properties by increasing the abundance of strong acid and Lewis acid sites, and promotes uniform loading and stable bonding of the SO₄²⁻ active component. Performance evaluation using the synthesis of L-phenylalanine methyl ester as a model reaction demonstrated that STH-RF exhibits optimal catalytic activity, affording a product yield of 85.7%, which is significantly higher than that of unmodified STH (19%) and the homogeneous catalyst H₂SO₄ (63%). This superior performance originates from a “structure–acidity” synergistic effect, combining the thermodynamic advantage of a lower energy barrier for the rate-determining step (12.6 Kcal·mol⁻¹) with efficient kinetics under optimal process conditions (1.0 MPa, 2000 rpm, 170 °C). Moreover, STH-RF maintained a yield above 80% after four consecutive reaction cycles, indicating excellent stability. This work provides a novel catalytic system for the green and efficient synthesis of highly hindered α-amino acid derivatives, holding significant theoretical and practical implications. Full article

TiO₂ nanoparticles were synthesized by a simple sol–gel route followed by high-temperature calcination at 800 °C, aiming to obtain an anatase-dominant reference photocatalyst with enhanced structural stability after severe thermal treatment. Raman spectroscopy and X-ray diffraction confirmed that anatase is the major crystalline phase, with only a minor rutile contribution after calcination at 800 °C. Nitrogen adsorption–desorption measurements revealed a narrow mesoporous contribution arising from interparticle voids and a relatively high specific surface area (108 m² g⁻¹) despite the severe thermal treatment, while electron microscopy showed nanometric primary particles assembled into compact agglomerates. Surface hydroxyl groups were identified by Fourier-transform infrared spectroscopy, consistent with sol–gel-derived TiO₂ systems. Diffuse reflectance UV–Vis spectroscopy combined with Kubelka–Munk and Tauc analysis yielded an optical band gap of 3.12 eV, typical of anatase TiO₂. Methylene blue (MB) was used as a probe molecule to evaluate photocatalytic activity under ultraviolet and visible light irradiation. Under UV illumination, degradation kinetics were governed by band-gap excitation and reactive oxygen species generation, whereas a slower but reproducible reference behavior under visible light was predominantly associated with surface-related effects and dye sensitization rather than intrinsic visible-light absorption. Overall, the results establish this anatase-dominant TiO₂ as a reliable high-temperature reference photocatalyst, retaining measurable activity after calcination at 800 °C and exhibiting UV-driven behavior as the dominant contribution. Full article

Laser powder bead fusion (LPBF) allows for the fabrication of highly accurate components from metal powders, which is difficult to achieve using traditional methods. LPBF-produced components can be characterized by their porosity and unfavorable microstructure, making further processing difficult. Therefore, appropriate post-printing methods are crucial, as they reduce porosity, reduce residual stresses, and stabilize the microstructure. The aim of this paper was to determine the effect of post-printing methods on the microhardness and microstructure of Ti6Al4V titanium alloy samples fabricated using the LPBF process in different orientations. Hot isostatic pressing (HIP) at various temperatures (910 °C, 1150 °C, 1250 °C), annealing at 1020 °C, and twist channel angular pressing using a 90° channel ending with a helical exit were considered postprocessing methods for LPBF-produced samples. Printing orientation significantly determined the effectiveness of HIP and the heat treatment processes. Higher microhardness was observed on the cross-section oriented perpendicular to the 3D printing direction. Annealing under appropriately selected conditions favors the precipitation of fine particles of the α phase in the β phase, leading to a strengthening effect by precipitation. Based on the microhardness measurements, clear differences were observed in the mean values, statistical ranges, and result distributions depending on the printing plane, HIP process parameters, and the use of an additional heat treatment. The HIP process leads to a more pronounced homogenization of microstructure and defect reduction, with the morphology of the microstructure and microhardness distribution dependent on the HIP process temperature. Full article

Improving the thermal utilisation of organic production waste to generate energy is integral to solving one of the most pressing issues of our time: transitioning away from fossil fuels. In this context, the thermal utilisation of organic waste, particularly sewage sludge (SS) and lignin-containing by-products from the biochemical industry, is of considerable scientific and practical interest. This study provides a thorough analysis of the co-combustion processes involving SS, lignin-based pellets and briquettes, and their mixtures with various component ratios. The aim of the work is to evaluate the fuel properties, thermokinetic characteristics, and potential for synergistic interactions during joint fuel combustion, considering the mechanical impact on lignin during granulation. The aim is to optimise conditions for the thermal utilisation of industrial waste. The study employed standard analytical methods: the thermophysical properties of the fuels were determined; morphological analysis of the particle surface was conducted using scanning electron microscopy; and X-ray fluorescence analysis was performed to identify the inorganic oxide phase. It has been established that lignin briquettes have the highest lower heating value, exceeding that of lignin pellets and sewage sludge by 7% and 27%, respectively. Thermogravimetric analysis (TGA) in an oxidising atmosphere (air, heating rate of 10 °C/min) made it possible to determine the following key combustion parameters: the ignition temperature of the coke residue (T_i); the temperature at which oxidation is complete (T_b); the maximum combustion rate (R_max); and the combustion efficiency index (Q). The ignition temperature of the coke residue was 262.1 °C for SS, 291.8 °C for lignin pellets, and 290.0 °C for lignin briquettes. Analysis of co-combustion revealed non-linear behaviour in the thermograms, indicating synergistic effects, which are manifested by a decrease in the maximum combustion rate compared to the additive prediction, particularly in mixtures with a moderate lignin content (25–50%). It was established that the main synergistic interactions between the mixture components occurred during moisture evaporation and the combustion of coke residue. These results are valuable for designing and operating power plants that focus on co-combusting industrial organic waste, and they contribute to the development of thermal utilisation technologies within closed production cycles. Full article

Al₂O₃-TiC/6061Al composites were fabricated via in situ powder metallurgy using 6061 Al, TiO₂, and graphite powders as starting materials. The effects of sintering temperature and ceramic particle content on the microstructure and mechanical properties of the composites were investigated. The wear performance of composites sintered at 1200 °C with varying ceramic particle content was also examined. The results indicate that the microstructure of the composite varied with the sintering temperature. At 1000 °C and 1100 °C, the microstructure primarily consisted of Al₃Ti, Al₂O₃, and TiC phases. At 1200 °C and 1250 °C, the microstructure was predominantly composed of Al₂O₃ and TiC phases. The 6061 Al-12% (TiO₂ + C) composite sintered at 1200 °C exhibited a tensile strength of 246 MPa, an elongation of 12.7%, and a microhardness of 104.2 HV_0.1. Regarding wear performance, the wear behavior of the composites under different loads at 1200 °C was studied. Under a 30 N load, the 6061 Al-12% (TiO₂ + C) composite demonstrated the lowest friction coefficient and wear rate, measured at 0.253 and 0.396 mm³·N⁻¹·m⁻¹, respectively. Analysis of the worn surface morphology under a 30 N load indicates that the dominant wear mechanism for the 6061 aluminum alloy is delamination wear, whereas for the 6061 Al-12% (TiO₂ + C) composite, it is primarily abrasive wear. Full article

Cementitious materials prepared by the ice-templating method appear to have difficulty simultaneously possessing good mechanical properties and an oriented microstructure with microchannels. Surface micro-ceramicization of TiB₂ and the decomposed products of cement hydrates at high temperatures can be regarded as in situ solid–solid reactions involving oxygen, thereby enhancing mechanical properties. This study investigates the mechanical property changes in cement paste with different water-to-cement ratios containing 25% TiB₂ micron powder before and after high-temperature treatment. Cementitious samples are prepared using both freeze-casting (F-CAST) and regular casting (R-CAST) methods with and without the heating post-treatment. The average compressive strength of samples with a W/C of 0.65 prepared by the freeze-casting method at −60 °C with a heating post-treatment is much larger than that of samples prepared by the regular casting method with and without the same heating process. The freeze-casting process for preparing cementitious composites with TiB₂ not only reorders the distribution of water molecules but also redistributes the concentrations of the TiB₂ particles and the main hydrates in the frozen samples. Due to the concentration increase near ice crystal channels within the samples, led by the freeze concentration effect, the new products are formed and cover the channel surfaces after high-temperature treatment. This enhances both the overall and internal properties of the cement-based TiB₂ composite material. The variation in TiB₂ content within the specimens is of paramount importance. Full article

The stability of nanoparticles (NPs) in ODS steel is an important factor affecting their long-term service behavior. In the current work, the 9Cr-ODS steel samples were irradiated using 3.5 MeV Fe¹³⁺ ion irradiation up to 20 dpa at 350–650 °C, and the microstructure stability was studied using the transmission electron microscope. The correlation between the particle coarsening rate and the irradiation depth has been investigated. The results show that fine Y-Ti-O NPs undergo coarsening under irradiation at 350 and 500 °C, and the coarsening rate shows a trend of first increasing and then decreasing with the increase in depth. NP coarsening reached its peak at a certain depth, and the peak depth increased with the increase in irradiation temperature. While the coarsening was inhibited at 650 °C, almost no changes in particle size were observed, only slightly coarsening at the end of the irradiation layer. In addition, b = 1/2<111> type dislocation loops were dominant at 350 °C, and the formation of b = <100> type dislocation loops was confirmed at 500 °C. Dislocation lines were formed at 650 °C. Additionally, the segregation of Cr, O, C, Y, and Ti toward the surface in the irradiated layer was observed due to the surface effect. The stability of NPs with irradiation temperature is discussed. Full article

This study reports the fabrication of copper-based metal matrix composites reinforced with a combination of micro- and nano-sized titanium carbide (TiC) particles using the powder metallurgy route. The micro-TiC content was maintained at 5 wt.%, while the nano-TiC addition was systematically varied between 1 and 3 wt.% in increments of 1 wt.%. The consolidation of the blends was achieved by uniaxial compaction at 500 MPa, followed by sintering in a nitrogen atmosphere at 750–900 °C for 2 h. Tribological assessment under dry sliding conditions was performed using a pin-on-disk apparatus. Structural and microstructural examinations using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) confirmed a uniform incorporation of the reinforcements within the Cu matrix. The incorporation of nano-TiC up to 2 wt.% significantly enhanced density, hardness, and wear resistance, after which a marginal decline was observed. SEM analysis of worn surfaces revealed that adhesive wear, abrasion, and delamination were the primary wear mechanisms. To better understand the relationship between processing conditions and material responses, response surface methodology (RSM) was employed. The developed models for density, hardness, and wear loss showed good agreement with the experimental results, with confirmatory tests yielding errors of 1.59%, 2.06%, and 2%, respectively, thereby validating the approach’s reliability. Full article

Titanium compounds are an integral component for paint pigments, food additives (E171), catalysts, precursors for resistant structural materials, medicine, and water, and air purification and disinfection processes. A new and rather promising trend for titanium dioxide production is obtaining it from minerals with magnesium titanium structure. Magnesium titanates obtained by pyrometallurgical processing of quartz–leucoxene concentrate (oil sandstones). It was found that the optimal pyrometallurgical processing conditions were 4 h and a temperature of 1425–1450 °C, with TiO₂ → Mg_XTi_YO_Z conversion exceeding 95%, and that sulfation of the magnesium titanate mixture with 60–70% H₂SO₄ for 150–210 min allows a 95% extraction of titanium compounds into solution. Investigation of the mechanism of titanium compound precipitation from Mg-Ti-containing sulfuric acid solutions revealed that in the pH range from 3 to 6, only titanium compounds were extracted from solution, while coprecipitation of magnesium compounds begins only at pH above 6.5. The product obtained by precipitation is titanium dioxide with an anatase structure, with particle distribution ranging from 0.8 to 5.0 µm and a developed surface area over 250 m²/g with mesopores characteristic of sorption materials. Full article

WC-based cermet coatings with a CoCrNiAlTi binder were fabricated on 04Cr13Ni5Mo stainless steel substrates using the atmospheric high-velocity air–fuel (HVAF) spraying process. The influence of the air-to-fuel ratio (AFR) on the microstructure, mechanical properties, and wear resistance of the WC-CoCrNiAlTi coatings was systematically investigated. The results indicate that the WC-CoCrNiAlTi coatings primarily consisted of WC, (Co, Ni)₃W₃C and a face-centered cubic (FCC) binder phase. As the AFR increased, the formation of the (Co, Ni)₃W₃C phase gradually decreased. Concurrently, the coating density improved, which was attributed to the enhanced particle melting state and increased flight velocity, leading to better flattening upon impact. The average microhardness of the WC-CoCrNiAlTi coatings gradually increased with an increasing AFR. The coating produced at an AFR of 1.130 exhibited the highest microhardness of 1355.68 HV_0.2. Both the friction coefficient and the wear rate of the coatings decreased progressively as the AFR increased. At the optimal AFR of 1.130, the coating demonstrated the lowest friction coefficient (0.6435) and wear rate (1.15 × 10⁻⁶ mm³·N⁻¹·m⁻¹), indicating a wear resistance 34.85 times that of the stainless steel substrate. Furthermore, the slurry erosion weight loss rate of the WC-CoCrNiAlTi coatings decreased gradually with increasing AFR. The coating sprayed at an AFR of 1.130 showed the minimum erosion rate (1.70 × 10⁻⁶ g·cm⁻²·min⁻¹), which was 24.04 times lower than that of the substrate. The erosion mechanism of the WC-CoCrNiAlTi coatings was identified as the fatigue-induced removal of WC particles under alternating stress. The ductile high-entropy alloy (HEA) binder effectively protects the brittle WC phase through adaptive deformation, thereby significantly mitigating coating damage. Full article

The main goal of this research is the preparation of mechanically and mechanochemically activated Ti/B₄C/(±Ni) composite powders, which will constitute the source of reinforcement formation in the titanium powder matrix. For this purpose, two composite powders of the Ti/B₄C/(±Ni) type were obtained in the molar ratio Ti:B₄C = 5:1 and Ti:B₄C:Ni = 6:1:1, respectively, by mechanical milling (MM) in a high-energy planetary ball mill for up to 7 h. The morphological and structural characteristics of composite powders were determined by laser particle size analysis, scanning electron microscopy with energy-dispersive X-ray spectrometry, X-ray diffraction, and differential thermal analysis. By milling for up to 7 h, a good homogenization of B₄C in the Ti matrix occurs. Also, the addition of Ni leads to new phases of formation: NiTi and TiB₂. Full article

Investment casting of aluminum alloys is widely used in the aeronautical and automotive sectors for manufacturing complex components. However, conventional alloys lack sufficient mechanical strength and high-temperature resistance, prompting the need for enhanced materials. This study investigated the addition of submicron TiC particles, introduced via stir casting process, to an AlSi7Mg0.3 alloy for investment casting. Chemical analysis confirmed the incorporation of up to 0.1 wt.% TiC, but no significant improvement in tensile properties was observed. High Resolution Scanning Electron Microscopy (HRSEM) and Transmission Electron Microscopy (TEM) revealed a complex microstructure with few TiC particles and needle-shaped intermetallic phases containing titanium, iron, silicon, or aluminum. The high mold temperature (700 °C) and slow solidification rate likely caused partial TiC dissolution and intermetallic precipitation, which may have offset strengthening mechanisms like the Hall–Petch effect. Notably, the partial dissolution of TiC particles in investment casting has not been previously reported in similar alloys. These findings highlight the challenges of using particle-reinforced alloys in this process and emphasize the need for further research into process–microstructure relationships. Full article