Powder Metallurgy and Metal Ceramics最新文献

Nanocrystalline substitutional solid solutions of molybdenum dichalcogenides, 2D MoS_2–xSe_x (0 ≤ x ≤ 2), were synthesized by chemical vapor deposition. X-ray diffraction studies established that they had homogeneous chemical composition and a uniform layered structure (2H-MoS₂), consisted of nanostructures (2D, few-layer nanosheets), and did not contain impurities of foreign phases, including X-ray amorphous ones, and other nanostructures or microsized particles. The average sizes of anisotropic 2D MoS_2–xSe_x (x = 0, 0.25, 0.5, 1, 1.5, 1.75, and 2) nanoparticles were determined in the crystallographic [013] and [110] directions: d_[013] = 2.9(2)–60.5(4) nm and d_[110] = 10.4(6)–126(8) nm, respectively. Data on the averaged 2D MoS_2–xSe_x (0 ≤ x ≤ 2) atomic structure indicated that homogeneity existed over the entire composition range. The average sizes of 2D MoS_2–xSe_x (0 ≤ x ≤ 2) nanoparticles, lattice parameters a and c, and unit cell volumes V correlated with the chemical composition of the solid solutions with a statistical distribution of S and Se atoms. The parameters a, c, and V increased linearly with the Se content in 2D MoS_2–xSe_x (0 ≤ x ≤ 2) nanostructures according to Vegard’s rule. The electron microscopy results indicated that 2D MoS_2–xSe_x (0 ≤ x ≤ 2) nanoparticles had well-defined outlines (as triangles or hexagons). Their morphology qualitatively depended on the composition and, consequently, on the state of S–Se solution–melt and pressures of chalcogens in the vapor phase in chemical vapor deposition. The research findings can serve as a basis for developing competitive laboratory nanotechnologies for producing nanocrystalline (few-layer nanosheets) 2D MoS_2–xSe_x (0 ≤ x ≤ 2) substitutional solid solutions and studying their structural properties as components of interdisciplinary studies aimed at developing new multifunctional 2D nanomaterials.

This study investigates the effect of varying La-ion content on the structural, magnetic, dielectric, and adsorption isotherms of Co_0.5Mn_0.5Fe₂O₄ for industrial wastewater treatment. Nanoparticles of La_xCo_0.5–xMn_0.5Fe₂O₄ (x = 0, 0.005, 0.010, 0.015, and 0.020 wt.%) were successfully synthesized using the sol-gel auto-combustion method. XRD patterns confirmed the formation of a new singlephase cubic spinel structure. The surface microstructure of the composites was examined using field emission scanning electron microscopy (FE-SEM). EDS analysis confirmed the presence of expected chemical elements in the samples. Fourier transform infrared (FT-IR) spectroscopy is used to identify and quantify molecular vibrations of the samples. The magnetic properties, measured using a vibrating sample magnetometer (VSM), revealed that the saturation magnetization increased gradually from 16.328 emu/g to 66.247 emu/g with increasing La-doping. The dielectric properties of the samples, such as the dielectric constant (ε′) and dielectric loss factor (ε′′), were also studied. Additionally, the samples' heavy-metal adsorption capacity was evaluated, with the La = 0.02 wt.% sample exhibiting the highest Cr(VI) removal efficiency from wastewater.

A model was developed to describe the behavior of ‘matrix–inclusion’ powder composites, whose properties are sensitive to loading and deformation patterns, particularly under tension and compression. Stress–strain relationships were proposed with a new material parameter m, which characterizes the tendency of materials to exhibit different resistance in tension and compression. Building on the research findings of Kachanov et al., the physical meaning of this new parameter within modified elasticity theory was established, and its connection with structural defects in the composite was identified. The relationships between the effective elastic characteristics of the composites and the content of defects of various types arising from the powder-based origin of the material were analyzed, with particular consideration of inclusions and the degree of their bonding to the matrix. Primary attention was paid to materials where the defects were volumetric pores and two-dimensional cracks. The results were further used to study elastic wave propagation within the modified model of a powder composite with differential resistance. In general, contrastingly to classical elasticity theory, the propagation velocities of longitudinal and transverse waves in powder composites were not material constants but depended on the dynamic loading pattern, which can be described through the ratio of bulk to shear strains. The dependence of wave velocity on loading pattern may serve as a basis for assessing the degree of imperfection in materials, while the established relationship between the degree of differential resistance and the content of various defect types can be applied to evaluate the contribution of each defect to the service properties of the material.

The production of granulated nickel powders in size fractions of 20–45, 45–71, and 71–125 μm with specified chemical composition by hydrogen reduction of NiO for the fabrication of highly porous items was studied. Nickel carbonate powder was used as the starting material for preparing nickel oxide powder through thermal decomposition in air. Nickel oxide was reduced in hydrogen by two methods: in moving beds in a rotary furnace chamber and in stationary continuous tubular furnaces. The required chemical composition of the nickel powders was ensured by using high-purity nickel carbonate. The effect of temperature–time parameters of the reduction process was examined at 400, 475, 500, and 600°C for 1 and 2 h at a heating rate of 10°C/min. The nickel powders were separated into fractions by sifting through a set of calibrated sieves. The formation patterns and properties of the granulated nickel powders were established by comprehensive analysis involving X-ray diffraction, electron microscopy, and measurements of specific surface area and bulk density. The reduced granulated nickel powders were found to exhibit morphological features characterized by a hierarchical structure. The granule size in the reduced nickel powder depended on the NiO granule size, reduction temperature, and additional experimental conditions of reduction (fixed NiO powder bed in stationary mode, moving NiO powder bed in rotating mode, preliminary NiO powder granulation, and NiO powder granulation temperature). The nickel powders in the 45–71 μm and >71 μm fractions consisted of sintered granules formed from finer granules with an average size of ~11–12 μm. The <45 μm fraction consisted solely of granules with an average size of ~12 μm within the 10–20 μm range.

Among non-equilibrium processing methods, mechanical alloying is relatively simple to employ and leads to grain refinement, intermixing, solid-state interdiffusion, supersaturation beyond the equilibrium solubility limit, and chemical reactions, thereby forming metastable phases. To study the effect of Li addition in Al–Mg powders on steady-state-milling time, phase formation, high energy ball milling at different milling times was done to produce Al–5Mg (wt.%) and Al–5Mg–1.8Li (wt.%) alloy powders by using elemental powders as precursor materials and characterizations of the powders was done by X-ray diffraction (XRD), scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS), and transmission electron microscopy (TEM). According to SEM results, the milled particles exhibited a uniformly dispersed, equiaxed morphology, characteristic of the mechanical alloying process. As per XRD examination, an increasing trend in the lattice parameter up to 9 h of milling time for Al–5Mg–1.8Li and up to 6 h for Al–5Mg alloy powders shows the dissolution of Mg to Al, while a decreasing tendency indicates the completion of the Al(Mg) soluble particles/α-Al phases after 12 h and 9 h, respectively, of milling, at which point the particles reached steady-state. As indicated by XRD data, the 9 h milled Al–5Mg alloy powders completely transformed into Al(Mg) soluble particles, whereas the 12 h milled Al–5Mg–1.8Li alloy powders produced the Al₃Li phases, which are uniformly dispersed over the α-Al matrix, as confirmed by TEM analysis.

The morphological and structural changes in a mixture of iron and aluminum powders after grinding in a planetary mill were examined. Work hardening caused the powder particles to acquire lamellar shapes. X-ray diffraction revealed a high number of deformation-induced defects. Work hardening was found to significantly complicate the densification process. Following cold pressing, the porosity remained at ~35–40%. A comparative analysis of phase and structural changes during heating and sintering of the ground powders was carried out. Differential scanning calorimetry showed that the self-propagating high-temperature synthesis of the Fe₂Al₅ intermetallic compound occurred predominantly in the solid phase, below the melting point of aluminum and produced onethird of the thermal effect observed for the unground powders. Dilatometric studies demonstrated that the ground powders swelled less during self-propagating high-temperature synthesis and exhibited much poorer densification and sintering behavior as the temperature increased up to 1450°C. Because of the insufficient density and poor quality of interparticle contacts, sintered samples produced from the ground powders showed substantially lower mechanical properties than those from the unground powders. Considerable attention was given to phase formation features in the temperature range typical of direct powder forging (600–1000°C). Analysis of phase and structural changes accounted for the effect of a sealed container, restricting volume changes in the sample in reactive synthesis. The presence of the container accelerated phase formation at the initial heating stage through deformation, which suppressed swelling. At higher heating temperatures, the container slightly slowed down phase transformations. After heating to 1000°C and holding for 20 min, the samples produced from both ground and unground powders transformed into the Fe₃Al phase with a disordered A2-type structure.

Alloys of hafnium with refractory platinum-group metals (in particular, rhodium and iridium) are of interest as high-temperature creep-resistant structural materials. The scientific basis for the design of new structural alloys with a tailored and controllable combination of properties is provided by phase diagrams of the respective multicomponent systems and related information on physicochemical interactions (crystal structure of solid phases and thermodynamic properties of solid and liquid phases). Information on phase equilibria in the Hf–Rh–Ir system was unavailable at the beginning of our research. Based on experimental findings, the solidus and liquidus surfaces, melting diagram, and Scheil diagram were constructed for the first time. The complexity of the phase equilibria required more detailed understanding of alloy formation processes. Therefore, vertical sections of the phase diagram were presented to illustrate phase transformations during alloy crystallization. Sixteen alloy compositions were prepared from iodide-refined hafnium (99.98%), rhodium wire (99.97%), and iridium powder (99.97%) by electric-arc melting. The alloys were annealed at subsolidus temperatures (20–50°C below the solidus). In as-cast and annealed states, the alloys were studied by microstructural analysis, differential thermal analysis, electron probe microanalysis, X-ray diffraction, and the Pirani–Alterthum technique. The experimental results were used to construct, for the first time, vertical sections of the ternary Hf–Rh–Ir phase diagram along the Ir : Rh = 1 : 1 line at the 15 at.% Ir, 10 and 42.5 at.% Rh, and 30, 33, and 62.5 at.% Hf isopleths. These sections demonstrate characteristic features of the phase equilibria in the system, particularly the alloy crystallization ranges and the nature of phase transformations.

Gadolinium zirconate Gd₂Zr₂O₇ (GZ₂) has excellent thermal stability up to 1530°C, low thermal conductivity (1.1 W ∙ m^–1 ∙ K^–1), a low sintering rate, and a higher coefficient of thermal expansion (CTE) (10.4 ∙ 10^–6 K^–1, 293–1373 K) compared with LZ₂. Therefore, GZ₂ is a very promising candidate for new thermal barrier coatings (TBCs). However, the relatively low fracture toughness of GZ₂, which promotes crack propagation, limits its application as a TBC. In addition, GZ₂ tends to react with aluminum oxide to form the porous GdAlO₃ phase. For this reason, the implementation of the two-layer coating concept will retain the advantageous properties of GZ₂ and mitigate its weaknesses. Analysis of published sources on the production and properties of two- and multilayer GZ₂/YSZ TBCs shows that two-layer GZ₂/YSZ coatings can be successfully applied employing all established techniques: atmospheric plasma spraying (APS), electron-beam physical vapor deposition (EB–PVD), plasma spray–physical vapor deposition (PS–PVD), solution precursor plasma spray (SPPS), and suspension plasma spray (SPS). Such coatings endure a greater number of thermal cycles than the single-layer 8YSZ coating at 1550°C. Two-layer GZ₂/YSZ TBCs are capable of increasing the operating temperature up to 1400°C and have a longer service life than similar LZ₂/YSZ TBCs. Nevertheless, the CTE mismatch between the layers and the low fracture toughness remain a serious problem for such coatings. The interaction between the GZ₂ and YSZ layers does not critically affect the TBC properties. Reduction in Young’s modulus of TBCs appears promising to achieve excellent characteristics. Multilayer TBCs demonstrate significantly longer thermal shock lives at both 1100 and 1200°C. Doping the GZ₂ topcoat with Yb₂O₃ increases the thermal cyclic life and CTEs of two-layer TBCs. At 1050°C, GZ₂-based coatings are more thermally and chemically stable than YSZ and show better hot corrosion resistance. The key factors that influence the properties of the GZ₂ layer in the two-layer APS GZ₂/YSZ coatings include the specific microstructure of the GZ₂ topcoats, particularly a higher density of defects and a higher proportion of unmelted particles compared with conventional YSZ coatings. In the post-sprayed state, the roughness of GZ₂ coatings is lower than that of YSZ coatings with the same porosity. The GZ₂ layers examined do not show higher resistance to sintering at 1100°C.

In this study, an accumulative press bonding process (APB) is used to manufacture an AA1100/Al₂O₃ composite. Initially, Al/Al₂O₃ composites were manufactured via powder metallurgy, followed by warm roll bonding in four steps. To obtain the composites, the starting components were ground in a stainless steel ball mill in nitrogen at a pressure of 0.7 MPa for 24 hours at a speed of 450 rpm. During grinding, Al₂O₃ was mixed with Al 1100 alloy powder obtained by atomization. After milling, the resulting mixture was cold-pressed to form compact samples. The compaction was performed using a steel die at 750 MPa. Subsequently, the compacts were extruded at 550°C for 50 min. Al/Al₂O₃ samples produced by hot extrusion were preheated to 250°C for 10 min and pressed with a 50% reduction in thickness. A 100-ton press was used for pressing. This cycle was repeated four times. The corrosion resistance of the samples was measured using electrochemical impedance spectroscopy and potential dynamic polarization tests. The corrosion current density (J_corr), corrosion potential (E_corr), polarization resistance (R_p), and corrosion rate (C.Rat, mm/year; V_corr, μm/year) are investigated. A considerable improvement in the main electrochemical parameters was achieved for composites fabricated with higher press bonding steps. It was found that the APB process had a positive effect on the corrosion improvement of composite samples. Additionally, the electrochemical experiments demonstrated the positive influence of the APB process on the corrosion behavior.

The evolution of rheological parameters of chitosan hydrogel/silicon nitride paste was studied during and after the application of mechanical shear at different rates using a Rheotest RN 4.1 rotational viscometer. The paste composition for 3D printing by robocasting included chitosan, food-grade gelatin, Si₃N₄ nanopowder, distilled water, and a 9% acetic acid solution. At a shear rate of 800 sec^–1 (the maximum value for Rheotest RN 4.1), the paste exhibited a sharp decrease in dynamic viscosity: about 99% relative to the initial value. After cessation of shear, the paste recovered 25–35% of its viscosity within a period referred to by the authors as ‘viscosity stabilization time’. Based on practical observations, this viscosity stabilization time was determined to be 18–19 sec. According to the authors, the pronounced decrease in dynamic viscosity and thixotropic behavior of the paste can be attributed to the inherent properties of gelatin. They also suggest that the abrupt change in viscosity proceeds through a threshold mechanism. Printed samples were produced using a Zmorph 2.0SX Full Set (FDM) 3D printer equipped with a direct piston extruder developed by the authors. It was experimentally established that, even at a shear rate of 200 sec^–1, the paste had 7000 mPa · sec viscosity, which is sufficient for printing. Analysis of the drying process for the printed samples indicated the need for careful humidity control in the room or within the drying chamber. Examination of the material’s structure demonstrated the benefits of using (or adding) nanosized components, primarily intended to reduce pore sizes in the products and facilitate the penetration of biomaterials during subsequent biomedical use.