Powder Metallurgy and Metal Ceramics最新文献

Rotary furnaces are used as reactors to intensify chemical processes between the powder and gas atmosphere around it. The furnace rotation leads to relative motion and dilation of the powder layers, facilitating gas access. The paper is devoted to the modeling of nickel oxide powder behavior in a rotary furnace to estimate the contribution of furnace rotation speed to gas permeability when the nickel oxide granules are reduced in a hydrogen atmosphere. Discrete element modeling of powder granules in a rotary furnace was conducted employing Altair EDEM commercial software to estimate the powder gas permeability at different stages. The powder bed in a horizontal cylindrical rotary furnace was modeled as a packing of identical spherical granules with diameters equal to those of the nickel oxide granules. The furnace rotation led to periodic oscillations of the powder along the furnace wall with an amplitude that gradually diminished to some steady value. Gas permeability of the powder bed was evaluated through the porosity function, derived from the Carman permeability equations. Greater gas permeability resulting from significant powder dilation was observed only in active shear zones on the powder bed surface and in the contact area between the powder and the furnace wall. Sizes of the shear zones depended on the furnace rotation speed but never exceeded several granule diameters for all rotation speeds. The efficiency of a rotary furnace as a chemical reactor was shown to be determined not only by the powder dilation but also by the regeneration rate for the powder bed surface. The regeneration rate can be calculated and changes nonlinearly with the furnace rotation speed.

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

Ultrahigh-temperature ceramics (UHTC) have a wide range of applications, particularly in supersonic aircraft vehicles. However, the production of UHTCs with predetermined mechanical parameters is relevant. The paper analyzes the structurization trends and their influence on the properties of film coatings from transition metal nitrides and borides synthesized by ion-plasma and magnetron sputtering methods. Under optimal deposition energy conditions, the films show general regularities in their formation, such as the presence of a columnar (fibrous) structure and growth texture. The average grain size varies from 18–20 nm to 60–80 nm, depending on the deposition parameters and method. The films demonstrate excellent mechanical properties, including hardness, elastic modulus, recoverable elastic indicators under load, etc. Growth directions <111> and <100> are observed for transition metal carbide and nitride coatings, while growth in direction <0001> is typical of transition metal diborides. The identified trends will allow realistic computer modeling of the film formation process, using predetermined film properties and optimal sputtering parameters to promote excellent mechanical characteristics of the surface. A thermodynamic model describing the formation of nuclei for a typical film in the environment of atoms randomly deposited onto the substrate is proposed. The critical radius for nucleus growth and, accordingly, for film crystallization is analytically estimated. The influence of Gibbs energy changes on the crystallization process is discussed within the model.

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.

The distribution of doping elements and impurities between the external surfaces and internal volumes of typical fine particles in samples of gas-atomized commercial additive powders of hightemperature creep-resistant (Inconel 939, ZhS32) and high-temperature oxidation-resistant (Inconel 625, Hastelloy C22) nickel superalloys was examined employing energy-dispersive X-ray analysis (EDX). Significant concentration gradients were observed between the surfaces and internal volumes of powder particles for doping elements reaching 4–5 wt.%: Re, Mo Ta, and Nb in the high-temperature creep-resistant alloys and Al, Nb, Co, Fe, V, and Mn in the Inconel 625 hightemperature oxidation-resistant alloy. Besides doping elements, concentration gradients of O, N, S, P, and Si impurities were found in the near-surface layers of the additive powders. The EDX findings and data from the reduction–extraction method were used to calculate the amounts of oxygen and nitrogen in the internal volumes and the near-surface layer of typical fine powder particles and the thickness of this layer corresponding to the increased content of impurities. The surface layer of typical fine particles was shown to increase the total weight-average content of impurities in the samples of commercial additive powders: oxygen up to 2.5 times and nitrogen up to 1.8 times. To assess the influence of impurity amounts of oxygen <0.16 wt.% and nitrogen <0.13 wt.% on the welding process properties of the atomized additive powders, additional samples of hightemperature oxidation-resistant (ChS40) and high-temperature creep-resistant (ZhS6U, ZhS32, Renè 80) nickel superalloys were tested to ascertain their suitability for microplasma powder deposition at a welding current of up to 15 A. It was found that the suitability of the additive powder for lowamperage deposition was mainly determined by the limited oxygen impurity content: weight-average content up to 0.025 wt.% and content in the 1–3 μm thick near-surface layer of a typical fine particle up to 0.1 wt.%.

The evolution of phase composition and thermal oxidation behavior of high-entropy AlCrFeCoNiMn_x alloys (x = 0.5 and 1) during long-term oxidation at 900°C were studied. A single- phase ordered (B2) bcc alloy formed in the starting as-cast state regardless of manganese content. The scale phase composition varied with exposure time and manganese content. After 10 h of oxidation, high-entropy spinel-type MeMn₂O₄, as well as Mn₃O₄ and Al₂O₃, formed on the AlCrFeCoNiMn alloy, while only Mn₃O₄ and Al₂O₃ oxides emerged on the AlCrFeCoNiMn_0.5 alloy. Increase in the oxidation time for the equiatomic alloy up to 25 h led to spinel NiMn₂O₄ and bixbyite FeMnO₃ in the oxide scale; Mn₃O₄ and Al₂O₃ were also present. The phase composition of the oxidized layer on the AlCrFeCoNiMn_0.5 alloy did not change. After 50 h, the structure of the oxide scale was similar for both alloys and consisted of NiMn₂O₄, FeMnO₃, Mn₃O₄, and Al₂O₃ in different ratios. The oxidation kinetics of the alloys naturally depended on the manganese content: the higher the manganese content, the higher the oxidation rate. A continuous layer of the fcc solid solution rich in chromium, iron, and cobalt was observed under the scale in both alloys. An internal oxidation area was also found in the subscale layer of the AlCrFeCoNiMn alloy. Long-term (more than 50 h) oxidation at 900°C substantially changed the phase composition of the alloy matrices: the bcc (B2) solid solution underwent spinodal decomposition to form bcc and fcc phases and tetragonal σ phase. Analyses of the alloy matrices showed a sharp increase in their microhardness after annealing. This can be attributed to the formation of a significant amount of the σ phase.

The method of reactive ball milling was used to synthesize MgH₂-based composites adding nanoparticles of complex oxides RTO₃ (R-rare earth and T-transition metals) as catalysts and graphite. All composites contain 5 wt.% of complex oxides Dy_0.5Nd_0.5FeO₃ and TbFe_0.5Cr_0.5O₃ synthesized by the sol-gel method, and some of them additionally contain 3 wt.% of graphite. The oxides have an orthorhombic perovskite structure (GdFeO₃ type) and are characterized by an average particle size of 80–300 nm. The effect of perovskites on the hydrogenation of magnesium during the milling process and the improvement of hydrogen sorption-desorption kinetics is demonstrated. The Mg–Dy_0.5Nd_0.5FeO₃ and Mg–TbFe_0.5Cr_0.5O₃ composites absorbed 6.7 and 6.2 wt.% of hydrogen, respectively. X-ray powder diffraction after ball milling did not reveal any new compounds, except magnesium hydride. Thermal desorption from these composites occurs in two stages at temperatures above 300°C. The activation energy (E_a) of hydrogen desorption was determined by the Kissinger method. For the composite with TbFe_0.5Cr_0.5O₃, E_a is 123 kJ/mol, and for the composite with Dy_0.5Nd_0.5FeO₃ E_a = 147 kJ/mol. These composites were also tested as materials for hydrogen generation by hydrolysis in pure water and MgCl₂ water solutions. In pure water, the hydrogen yield during hydrolysis ranged from 320 to 350 ml per gram. The conversion degree was significantly improved by the addition of MgCl₂. It reached 90% (~1400 ml/g) after 30 min of hydrolysis for the MgH₂–nano-TbFe_0.5Cr_0.5O₃. These characteristics show that the synthesized MgH₂–nano-RTO₃ composites can be used in hydrogen generation systems.

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.