Powder Metallurgy and Metal Ceramics最新文献

The structure and mechanical properties of rods produced from alloys in the Al–Fe–Si–V system, additionally doped with Cr, Ti, and Zr, were studied. In contrast to the creep-resistant Al–Fe–Si–V alloys, commonly known as FVS alloys and characterized by an optimal Fe/V ratio of ~5–11, the Fe content in the test alloys was reduced by adding Cr, ensuring that the (Fe + Cr)/V ratio remained within the ~5–11 range. Rods with a 9 mm diameter were produced from the test alloys by extruding degassed capsules filled with compressed water-atomized powders in the (–63+40) μm size fraction. The powder was consolidated through severe plastic deformation without sintering. The structure was examined using X-ray diffraction, transmission electron microscopy, and scanning electron microscopy with electron probe microanalysis. The phase composition and distribution of the doping elements were determined as a function of the alloy chemical composition. Mechanical properties were evaluated at 20, 190, and 300°C through tensile tests. Fracture of the test alloy rods followed a ‘cone–cup’ pattern at room temperature and 300°C. The fracture mechanism was dimple-like. The replacement of some iron by chromium in the base alloy resulted in a shift in the phase composition of the strengthening particles. Specifically, instead of the Al₁₃(FeV)₃Si intermetallics typical of Al–Fe–Si–V alloys, particles of the icosahedral quasicrystalline phase and Al₁₃Cr₂ intermetallics were observed. All studied alloys exhibited high strength at temperatures up to 300°C, surpassing the strength of established creep-resistant alloys such as FVS 0812. This enhanced strength was attributed to precipitation hardening effects induced by two distinct types of nanosized particles within the aluminum matrix, having a crystalline and icosahedral quasicrystalline structure. The Al₉₃Fe₂Cr₂V_0.5Si_1.5Ti_0.5Zr_0.5 alloy showed the highest mechanical properties at both elevated and room temperatures.

The robocasting method is a promising and innovative approach to the layer-by-layer manufacturing of complex-shaped products. Its prospects for printing MoSi₂ ceramics by extruding a paste with a high content of solid particles (ceramics, metals, fibers, etc.) and a plasticizer to build a product layer by layer were demonstrated. A 10 wt.% solution of rubber in gasoline was chosen as the plasticizer. A comprehensive process was developed for the full cycle of manufacturing samples of heating elements, ranging from the preparation of molybdenum disilicide powder pastes to the sintering of the product in a vacuum furnace and the determination of its physical, mechanical, and electrical properties. The influence of the scale factor (variation in the size of a single printed layer) on the features of printing with the robocasting method was studied. The relationship between nozzle diameter/layer thickness and paste composition (MoSi₂ powder and plasticizer) was established. The operating range of the plasticizer content for printing with nozzles having a diameter of 0.84–3 mm was found to be 12–17 wt.%. Analysis of the rate at which the plasticizer content reduced in the preparation and transportation of the paste, caused by the evaporation of volatile components, showed that the time for preparing the paste should not exceed 5 min. Samples produced by the robocasting method were heat-treated in a vacuum drying oven at 350°C for 2 h and consolidated in a vacuum furnace at 1900°C for 1 h. X-ray diffraction performed at all production stages revealed changes in the composition of the sintered samples, including the formation of up to 15 wt.% of the Mo₅Si₃ phase. The sintered samples were tested for electrical and mechanical properties. In the determination of current–voltage characteristics, the samples were heated to 90°C at a power of approximately 1 W. The Vickers hardness was 9.5 ± 1.4 GPa.

Mo₂FeB₂-based cermets exhibit promising industrial manufacturing applications due to their excellent mechanical properties, higher oxidation resistance, and thermal stability. In this study, ternary boride solid solution powders of Mo₂(Fe_x, Ni_1–x)B₂ were successfully prepared with a unique technique via employing B₄C powder as a boron source, Mo, Fe, and Ni powders as metal sources as well as Ca powder as the decarburization agent. The effect of the Fe/Ni ratio on the phase composition, morphological evolution and average grain size of powders was studied. The shift of diffraction peak in the XRD results and the homogeneous distributions of Mo, Fe, Ni, and B by the EDS energy spectrum validated the successful synthesis of ternary boride solid solution powders. The morphology of solid solution powders varied depending on the Fe/Ni ratio. For compositions with Fe/Ni ratios of 10 : 0, 7 : 3, and 5 : 5, the ternary solid solution powders exhibited pronounced spherical grains with average grain sizes of approximately 3, 1, and 1 μm, respectively. Conversely, when the Fe/Ni ratios were 3 : 7 and 0 : 10, the solid solution powders exhibited mixed morphologies of spherical (with diameters of approximately 1 μm) and prismatic grains (with lengths of about 8 μm and diameters of around 3 μm), corresponding respectively to the tetragonal and orthorhombic crystal structures of Mo₂NiB₂. Using ultrafine Mo powder as a raw material to boost reaction kinetics resulted in the product's stable phase being orthorhombic Mo₂NiB₂. Nonetheless, at a Fe/Ni ratio of 3 : 7, the product still consisted of orthorhombic and tetragonal Mo₂NiB₂ phases.

The development and detailed characterization of mesoporous ternary nanocomposite Ag/Ce/N/ZnO were meticulously undertaken using a hydrothermal technique. The elemental composition was authenticated through energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS), confirming the constituents of the developed samples. Surface and pore structure analyses, conducted via the Brunauer–Emmett–Teller (BET) method, revealed the mesoporous characteristics of the materials, evidenced by class IV hysteresis loops, highlighting an enhanced surface area to 59.01 m²/g due to mesoporosity. Ultraviolet-visible (UV-Vis) spectroscopy results indicated a reduction in the optical band gap from 3.094 to 2.501 eV, associated with increased Ag-dopant concentration to 6%. The structural integrity, maintained as a hexagonal wurzite configuration, was verified by X-ray diffraction (XRD), which also showed a slight increase in crystallite dimensions from 21 to 23 nm with higher doping levels. Scanning electron microscopy (SEM) analyses depicted the synthesized entities' agglomeration tendencies and distinct morphological features. Photoluminescence (PL) studies suggested decreased electron-hole recombination rates for samples with elevated doping ratios. Moreover, these enhanced materials showcased augmented photocatalytic performance in the degradation of methylene blue and Congo red dyes after 90 min of contact, indicating their promising applications for water purification.

The electromagnetic characteristics, particularly the real ε_r′ and imaginary ε_r″ parts of the dielectric constant, of new AlN-based composites with additions of powdered diamond, soot, and diamond with 3–5 wt.% molybdenum, synthesized by hot pressing, were studied at frequencies ranging from 12.4 to 18 GHz. Structural features and key phases of the composites—AlN, C (graphite), Al₃(O, N)₄, Al, and Mo₂C (in the AlN–Y₂O₃–C (diamond)–Mo system)—were determined by X-ray diffraction. Scanning electron microscopy with energy-dispersive X-ray analysis for determining the quantitative elemental composition of the key phases revealed a low oxygen content in the AlN lattice. Measurements of the electromagnetic characteristics showed that the new composites with graphite phase inclusions had stable dielectric characteristics over the entire frequency range (ε_r′ = 12.38–33.03 and tgδ = 0.009–0.214). The introduction of 3% diamond powder to the AlN-based charge hardly increased the ε_r′ and tgδ values (12.3 and 0.009, respectively). When a 5% : 5% mixture of diamond and molybdenum powders was added, the dielectric constant ε_r′ reached 17.04 and tgδ was 0.067. Composites with 5% soot demonstrated the highest dielectric constant (33.03) and dielectric losses (0.214). Thus, the dielectric constant was found to be increased through specific phase composition of the materials and dispersed distribution of conductive phases (C, Mo₂C) within the composites with minimal contacts between them.

Solid oxide fuel cells (SOFCs) are among the most promising energy-generating devices, offering high efficiency, environmental friendliness, and flexibility to use a wide range of fuels. The main components of an SOFC are an electrolyte, an anode, a cathode, and a connector (interconnect). The operating principle of SOFCs is as follows. Oxygen is supplied to the cathode, where it is reduced. Oxygen ions move through a dense ceramic electrolyte (ionic conductor) from the cathode to the anode. Meanwhile, hydrogen is supplied to the anode, where a catalyst (metallic nickel) promotes its dissociation into atoms. When hydrogen is oxidized, it releases electrons into the external electric circuit, forming water in the process. The water formation reaction is exothermic. As a result, a constant electric current flows through the external electric circuit, enabling the direct conversion of chemical energy into electrical energy. The interconnect is a component that connects individual fuel cells into a power system — an SOFC stack. A brief overview of materials for ceramic fuel cell connectors (interconnects) and areas for improving their properties are provided. The classification of ceramic (lanthanum chromite LaCrO₃) and metallic (chromium-based alloys, nickel–chromium alloys, and ferritic stainless steels) interconnect materials is presented. Ceramic interconnects are commonly used for high-temperature SOFCs (~1000°C). The disadvantages of these materials include the difficulty of manufacturing interconnects with complex shapes and their high cost, resulting from the use of rare-earth elements. Among metallic materials, ferritic stainless steels with high chromium content (Crofer 22 APU and Crofer 22) are the most promising in terms of key performance indicators. The main shortcomings of modern chromium-based steel materials for interconnects in SOFC energy systems and the principles for changing the development paradigm for advanced lightweight materials with improved properties are outlined. The replacement of chromium steels with promising titanium-based composites is proposed.

In this study, hydroxyapatite (HA) was used as a bioceramic on a TiNi shape memory alloy. Butanol and tri-ethanolamine were used as suspensions with HA particles. The electrophoretic deposition (EPD) process was performed at 20, 30, and 40 V for 1–5 min on the cathode. Samples were left at room temperature for 24 hours to obtain slow drying after deposition. Weight and layer thickness were then measured. Sintering was conducted in an Ar atmosphere at 800°C for 2 h. The phases and surface morphologies were examined using XRD and SEM. The results showed that a uniform, homogeneous, crack-free coating layer can be achieved at a voltage of 30 V and low sintering temperatures. Also, longer deposition times increased the coatings' weight and thickness. Compared to other deposition methods, such as sol-gel and plasma coating, the method presented in this research can be used as an alternative method for bioactive coatings. The hardness of the undecorated HA coatings obtained at 15 and 30 V EPD voltage reached 0.2245 ± 0.036 GPa and 0.0661 ± 0.008 GPa, respectively.

Three layered materials from technically pure iron sheets with varying degrees of interlayer bonding were produced by hot and cold pseudovacuum rolling methods. The elastic, damping, and high-cycle fatigue characteristics of the materials were determined through resonant vibration testing of flat samples under bending conditions. Known fatigue damage dependences based on the cyclic strength energy density model for structural materials under low-cycle fatigue were considered. Using the studied materials as an example, the feasibility of extending this energy-based approach to the high-cycle fatigue and nondestructive loading regions was demonstrated. The elastic and inelastic components of the strain energy density were calculated from experimental fatigue curves for rolled layered materials over a range of 105 to 107 load cycles and from dependences of the vibration decrement on the cyclic loading amplitude varying from low to destructive strains. Thus, the strain energy density model was extended to the nondestructive cyclic (operational) loading region. In this case, the density of the elastic component of cyclic strain energy was found to be 1.92 times more sensitive to load amplitude than the destructive fatigue curve stresses, while the reliability coefficient for the total cyclic strain energy density was significantly higher than that for the inelastic strain energy density. The decrement of vibrations as a function of cyclic load amplitude and, accordingly, the inelastic component of the strain energy density were shown to be sensitive to the interlayer bonding strength, while the fatigue resistance (endurance limit) was sensitive to the degree of cold rolling applied to the layered materials.

Establishing the relationship between atomized particle sizes and atomization process parameters is important both theoretically and technologically. However, the large number of process parameters complicates this task. A potential solution is to establish simple dependences on the main (defining) parameters (or functional dependences). Determining the mass median particle diameter of a powder batch is particularly difficult, so this study incorporates data from other authors in addition to personal research findings. This study used personal research findings and calculations of the mass median particle diameter of the powders produced at the pilot plant of the Frantsevich Institute for Problems of Materials Science by high-pressure (0.05 to 200 MPa) water atomization of the Al-40.1 Cu-16.9 Fe melt. A series of experiments were performed on the Al-40.1 Cu-16.9 Fe alloy to produce powders by varying the atomization pressure and melt temperature. The dataset included the size distributions of water-atomized powders of pure metals: lead, zinc, copper, stainless and high-speed steels, and copper-phosphorus and ferrosilicon alloys. For comparison, mass median diameters of lead, aluminum, and copper powder particles produced by compressed air atomization at 0.4 to 2.8 MPa were also used. Based on these data, the relationship between the ratio of the mass median particle diameter to the gravitational melt jet diameter, d₅₀/D (inverse degree of atomization), and the Weber number (We) was plotted in logarithmic coordinates. The correlation between the inverse degree of water and gas atomization for liquid metals and alloys and the Weber number followed a linear dependence: (text{lg}left({d}_{50}/Dright)=2.0-0.5times text{lg}left(text{We}right)).