Powder Metallurgy and Metal Ceramics最新文献

Modern research findings for the interaction of two-dimensional molybdenum disulfide (primarily in the nanocrystalline state) with water and air moisture were analyzed. Studies focusing on water intercalation/deintercalation processes and mechanisms in nanocrystalline d-transition metal dichalcogenides (TMDs, mainly 2D MoS₂) are at their initial stage. Intercalated water was found to significantly influence the multifunctional properties of 2D MoS₂ nanostructures and microsized powders. The need for interdisciplinary studies of 2D TMD nanostructures intercalated with water through complex mechanisms was justified. In particular, the studies should include the development of intercalation/deintercalation nanotechnologies, establishment of interrelationships between the intercalation processes/mechanisms and the state of actual surfaces and features of actual nanostructures, determination of differences in intercalation processes and mechanisms for various semiconductor and metallic nanostructures, and design of multifunctional low-dimensional van der Waals nanomaterials with controllable properties based on nanosized 2D/nD heterostructures (n = = 0, 1, 2, 3) intercalated with water. Promising applications for 2D MoS₂ nanostructures intercalated with water are as follows: nanotechnologies of heterostructures with abnormal water properties, tribological characteristics of solid lubricants with moisture present, nanotechnologies using water or aqueous solutions, sorbents and photocatalysts for water purification, electro(photo, piezo)catalysts for the production of hydrogen and oxygen through water electrolysis, as well as hydrovoltaic effects, air humidity sensors, biosensors, and disinfection agents (COVID-19 pandemic).

The evolution of the stress-strain state and the relative density distribution throughout a porous workpiece in the two-stage hot forging process was studied. The primary stage involved hot deformation of a cylindrical preform with the application of force to its lateral surface to form an intermediate semi-finished product with a cross-section shaped as a truncated cone. Further deformation in the secondary stage involved hot forging of the conical workpiece into a prism. These process stages were simulated using the finite-element method with the DEFORM 2D/3D software package. The starting preform was a cylinder with uniformly distributed porosity throughout the volume. The simulation results revealed significant uneven strains ε_i across the workpiece following the primary process stage, leading to an area with increased strains ε_i concentrated near the upper punch. Conversely, the secondary process stage noticeably evened out the strain values across the forged workpiece. This occurred because the severe deformation area in the secondary process stage matched the stagnant area in the primary stage. The proposed two-stage deformation pattern achieved sufficiently high strains (1.3–1.7), allowing the production of forged materials with excellent mechanical properties.

TiAl intermediate compound is an important material for high-temperature applications due to its superior creep resistance and oxidation resistance. It is suitable for high-pressure compressors and low-pressure turbine blades of advanced military aircraft engines. TiAl intermediate compound is an excellent substitute for nickel-based superalloys, as it can decrease weight by 40% and greatly enhance aircraft thrust-to-weight ratio. In this paper, the microstructure evolution and the mechanical properties of Ti₂AlNb alloy with a 3.0 wt.% W and 0.1 wt.% Y addition obtained by blending elemental ultrafine powders was investigated by XRD, SEM-EDS, and mechanical testing device. The findings show that high relative density of 0.9945, and the excellent mechanical properties of Ti₂AlNb–3W–0.1Y alloy can be obtained through isothermal sintering for 3 hour in a furnace with controllable argon atmosphere flow of 200 mL/min at 1,500°C. The alloy’s tensile strength, yield strength, and elongation reach 1,030 MPa, 913 MPa, and 15.1% at 700°C, respectively. Meanwhile, the 3 wt.% of element W is added to the alloy to form (TiW)C as the second strengthening phase, which is uniformly distributed in the matrix of Ti₂AlNb. The addition of Y element at 0.1 wt.% into the alloy can act as an effective scavenger of oxygen and inhibit the unsatisfactory precipitation of the brittle α₂-phase in the Ti₂AlNb alloy. Compared to the alloy without additions, the Ti₂AlNb alloy with 3 wt.% W and 0.1 wt.% Y demonstrated 13.5% and 19.35% improvements in the fracture resistance at 25°C and 700°C, respectively. The alloy’s yield strength was increased as well. The evolution regularity of the main metallography is (Ti₂AlNb–TiAl–Ti₃Al) → (Ti₂AlNb–Ti₃Al) → (Ti₂AlNb–Ti₃Al–(TiW) C) during the isothermal sintering of Ti–22Al–25Nb–3W–0.1Y alloy at 1,500°C. This study provides technical guidance for the preparation of ultrafine TiAl-based alloy powder and high-temperature aerospace applications

The microstructure, phase composition, and microhardness of the cast high-entropy VNb₂TaCrMoW alloy with the addition of titanium diboride were studied. The initial VNb₂TaCrMoW alloy consisted of two bcc solid solutions, slightly differing in lattice parameters (a = 0.3139 nm and 0.3200 nm). The addition of boron as titanium diboride and repeated remelting led to a bcc solid solution with a larger lattice parameter (a = 0.3217 nm) and a boride with W_3.5Fe_2.5B₄ structure (a = 0.6054 nm and c = 0.3256 nm). The bcc solid solution was the first to crystallize, and the boride was part of the eutectic grains and precipitated from the last melt portions, forming a closed network. The resulting alloy was applied to a carbon steel substrate as a coating using electrospark deposition employing an Elitron-24A installation with varying electrical pulse energy. Higher pulse energy during coating deposition increased the layer thickness and surface roughness but did not influence the phase composition. The microstructure of the coatings was more uniform compared to the cast alloys, and X-ray diffraction showed that the coatings contained bcc solid solutions, Fe₇W₆ intermetallic compound, and a small amount of TaO₂ oxide. The coatings had a hardness of about 10 GPa and were 11–15 μm and 16–20 μm thick at discharge energies of 0.52 and 1.1 J, respectively. A comparative analysis of the phase composition, hardness, and microstructure of the cast alloy and associated coatings was carried out. The coatings deposited at a discharge energy of 0.52 J were subjected to laser processing. Laser processing of the coatings resulted in a thermally affected zone, while the surface layer hardness hardly changed. The wear resistance of the coatings deposited at a discharge energy of 0.52 J was analyzed. Wear resistance testing was conducted for three counterface materials (VK6, Al₂O₃, and Si₃N₄) in quasistatic and dynamic loading modes. Laser processing of the electrospark coatings changed the wear mechanism and significantly increased the wear resistance regardless of the counterface material and loading mode.

An experimental technique was developed for the production of tableted nanostructured fibrous enterosorbent for medical applications using a nanostructured activated carbon fiber material of solid-phase pyrolytic origin, created by our research team. The properties of the main active ingredient in the pills, as an effective adsorbing component, were studied. The porous structure parameters were examined with the desiccator method based on the absorption of benzene vapors, while the specific surface area was analyzed with the Brunauer–Emmett–Teller (BET) method. Spectrophotometric methods were employed to determine the concentration of the sorbate in solutions. The microstructure of the samples was studied using a scanning electron microscope (Superprobe-733 X-ray microanalyzer, JEOL, Japan). Energy-dispersive X-ray analysis provided data on the chemical composition and biocompatibility of the samples, serving as an integral indicator. Conditions for the key stages in the enterosorbent production process were experimentally tested. The influence of different types of binders on the process properties of the tablet charge and on the characteristics of test enterosorbent pills was analyzed. The novelty of the developed process was the use of material with special characteristics, promoted by bound carbon nanoforms present in its structure, for enterosorbent production. Improvements in the process operations were proposed, such as decreasing the compaction speed and simultaneously increasing the time the tablet charge was kept under pressure, leading to the redistribution of strains. It was proposed that the compaction process be conducted using punches with a flat surface of purity class 10 to prevent sticking. Therefore, our research team developed tableted enterosorbent with typical features of its main component—nanostructured activated fibrous carbon material—as an effective adsorbent for a relatively wide range of different compounds.

The features peculiar to the solid-state synthesis of MoSi₂ through vacuum heat treatment of a powder mixture of molybdenum and silicon nitride, as a precursor, in the temperature range 1000–1400°C were examined. X-ray diffraction established that the solid-state interaction began at 1100°C and progressed through the reaction diffusion of highly active silicon, resulting from the decomposition of Si₃N₄, into molybdenum to form lower Mo₃Si and Mo₅Si₃ silicide phases. In the temperature range 1100–1300°C, the redistribution of phases occurred: the contents of the starting molybdenum and β-Si₃N₄ components in the reaction mixtures gradually decreased, while the contents of lower molybdenum silicides increased. Molybdenum disilicide formed in situ at 1400°C via successive development of lower silicide phases. The final product contained Mo₅Si₃. This was attributed to a deficiency of silicon as it evaporated at a temperature above 1200°C. This led to the conclusion that the addition of 20 wt.% excess silicon nitride was necessary to produce a homogeneous MoSi₂ phase and up to 40 wt.% excess silicon nitride to produce a two-phase MoSi₂–Si₃N₄ composite powder. The elevated temperature in the synthesis of MoSi₂ compared to conventional synthesis from simple elements was explained by the slow formation of active silicon in the Si₃N₄ dissociation process. Based on the features observed in the solid-state vacuum interaction within the powder mixture of molybdenum and silicon nitride, as a precursor, a method was proposed for producing MoSi₂–Si₃N₄ composite powders, involving the introduction of 30 and 40 wt.% excess Si₃N₄ powder. The synthesis resulted in agglomerated composite powders with a homogeneous distribution of the MoSi₂ and β -Si₃N₄ phases. The MoSi₂ phase exhibited a capsular structure with a smooth surface. The synthesized composite powders are intended for the fabrication of components and parts with high oxidation resistance and corrosion resistance at elevated temperatures.