Powder Metallurgy and Metal Ceramics最新文献

The effect of sintering-activating Y₂O₃ and SiO₂–Y₂O₃ additives on the mechanical and dielectric properties of Si₃N₄ and Si₃N₄–BN ceramics consolidated by spark plasma sintering was examined. The heating rate and applied pressure were maintained at 50°C/min and 35 MPa, respectively. The holding time at a sintering temperature of 1800°C varied depending on the composition of the oxide additives. The Si₃N₄–BN ceramics with Y₂O₃–SiO₂ additives exhibited a 30% reduction in mechanical properties (hardness and fracture toughness) compared to Si₃N₄–Y₂O₃ or Si₃N₄–Y₂O₃–SiO₂ ceramics. The Si₃N₄ ceramics demonstrated resistance to deformation at temperatures ranging from 20 to 900°C. Specifically, Si₃N₄ ceramics with Y₂O₃ or Y₂O₃–SiO₂ additives showed average strengths of approximately 950 and 820 MPa, whereas Si₃N₄–BN ceramics demonstrated a strength of 490 MPa. An increase in temperature from 1000 to 1400°C for all ceramics studied resulted in a gradual decrease in bending strength to approximately 200 MPa. The strength at room and elevated temperatures, Vickers hardness of approximately 4 GPa and 15.5 GPa, and fracture toughness of about 7.7 MPa · m^1/2 meet the current requirements for this type of ceramics. Radiofrequency measurements showed that dense Si₃N₄-based ceramics had a dielectric constant of 8. When 10 wt.% BN was added, the dielectric constant of the composite decreased by approximately 8%. Additionally, residual porosity of about 10% further decreased the dielectric constant of the Si₃N₄–BN composite by around 13% (ε ~ 6.3). This reduction in the dielectric constant had a positive effect on radio transparency. The dielectric loss tangent of the test ceramics did not exceed 2 · 10^–3.

The thermokinetics of recrystallization and interaction processes in the heating of porous compacts produced from a mixture of ultrapure aluminum and iron in a 20 : 80 ratio after cold pressing in a steel die was studied using direct thermal analysis. Recrystallization of the aluminum component and relaxation of the iron component were observed in the temperature range 170–265°C. The iron relaxation and recrystallization exhibited a wavelike behavior. The iron component recrystallized completely in the temperature range 500–700°C. The interaction between aluminum and iron initiated with a reduction reaction through a small amount of surface iron oxides. The reduction of surface iron oxides, involving insignificant heat release, occurred in two stages, reflecting the existence of several iron oxides. Active interaction commenced at the melting point of aluminum. A cascade of exothermic effects, attributed to the interaction of intermetallic compounds with lower stoichiometries, was revealed. In this case, temperature exceeded the existence of the intermetallics, leading to their decomposition and subsequent cooling through the endothermic effect. The cooling rate during the decomposition of intermetallics closely resembled the rate of reaction synthesis. When the nonequilibrium solid solution cooled within the temperature range 500–600°C, the ironbased solid solution decomposed and the intermetallic compound synthesized. Thermokinetic oscillations emerge and gradually subside. At all stages of transitions from stationary states to temperature surges or drops, thermokinetic oscillations with varying frequencies and amplitudes were observed.

90W–7Ni–3Fe refractory alloy with high density and excellent corrosion resistance was obtained for the first time by hot oscillating pressure (HOP) under different oscillating amplitudes (5, 10, and 15 MPa) at low temperatures (1000°C). As the amplitude increased, the 15 MPa sintered sample reached the maximum density of 99.4% with an average grain size of 3.41 μm by min-grain growth rate (about two-thirds of 5 MPa sintered sample), and the max-Vickers hardness reached 462.3 HV_0.5. The sintering curve was changed gently and presented full density at the end of the isothermal holding period. More importantly, the corrosion current density i_corr was reduced by nearly 1.07 times, and the corrosion resistance of 15 MPa samples was better than that of 5 MPa and 10 MPa samples and similar materials ever reported. The results show that the increase of amplitude is beneficial to the densification of refractory tungsten alloy and has a positive effect on improving the density, hardness, corrosion resistance and inhibiting the growth of grain size (the retention of the fine-grained microstructure) at low temperatures.

In this study, forming limit diagrams (FLDs), fracture toughness (FT), and mechanical, magnetic, and electro-physical properties of Al/Fe₂O₃ composites have been investigated experimentally. Accumulative roll bonding (ARB) was used to manufacture composite samples. Then, Al/Fe₂O₃ composites were produced at 300°C for up to eight ARB passes. Also, magnetic composites have been fabricated with 0, 5, and 10 wt.% of Fe₂O₃ particles. The interlayer bonding quality was improved at higher passes. By studying the SEM rapture morphology, it was shown that the rapture mode changed to shear ductile for samples with more passes. For composite samples fabricated at higher passes and compared to annealed samples, elongated dimples were turned into shallow ones. FLDs area as the main forming criterion dropped severely after passing one and then began to improve at higher passes. The fracture test results showed that after the 8^th pass, the value of FT gradually enhanced to the maximum value of 34.3 MPa ⋅ m^1/2. It is also shown that the distribution of Fe₂O₃ particles in the aluminum matrix becomes more and more homogeneous with an increase in the number of rolling cycles, significantly affecting the uniformity of the magnetic capacity. The hysteresis curves improve after more passes due to the higher Fe₂O₃ content, indicating increased coercive force H_c and residual magnetization M_R.

The first part of this review addresses mechanical, physical, and some chemical methods (thermal decomposition, dynamic method, solution combustion synthesis, and sonochemical synthesis) for producing nanocrystalline and fine-grained ZrO₂-based powders. Mechanical methods (high-energy grinding in planetary and ball mills in dry and liquid environments) are used in the synthesis of ZrO₂ powders and analysis of ZrO₂ phase transformations, in the hydrothermal synthesis of ZrO₂ powders in acidic and alkaline environments, and for the deagglomeration of powders produced by other methods. Physical methods (plasma processing, reactive magnetron sputtering, and chemical vapor deposition) are employed when the requirements for powders are prioritized over production costs. They are used in the development of catalysts, sorbents, and coatings. Chemical methods provide control over the formation of primary particles with specific morphology, size, and surface area. Thermal decomposition produces primary particles shaped as spheres, nanorods, and hollow ZrO₂ microspheres with customizable shell structures. Dynamic methods, involving the detonation of high-energy materials or explosives, are promising for the synthesis of nanosized ceramic oxide powders with narrow particle size distributions. Solution combustion synthesis is based on the propagation of self-sustaining exothermic reactions in aqueous or sol–gel environments. Sonochemical synthesis relies on acoustic cavitation. The synthesized powders are applied in the design of photocatalysts, optical materials, forensic materials for fingerprint detection, sensors, biological markers, etc. There is no universal synthesis method that would meet the diverse requirements for all ZrO₂-based materials. The selection of a method to synthesize the starting powders depends on the requirements for properties of the resulting composites.

Experimental studies were conducted to examine the drag forces in the finishing of ferromagnetic and paramagnetic samples shaped as bars with square and equilateral triangular cross-sections, having a side length of 16 mm. Variations in the total drag forces exerted by the magnetic abrasive tool (MAT), composed of magnetic abrasive powders of various types and particle sizes, on the movement of samples within large ring-shaped working gaps were analyzed to determine the percentage contributions of the drag force components. The drag forces most significantly depended on the midship section of the parts and were determined by the magnetic forces and the degree of powder compaction between the side surfaces of the samples and the pole tips. The drag forces associated with the midship section during magnetic abrasive finishing (MAF) constituted up to 60–65% of the total drag forces from the MAT side for ferromagnetic samples and 80–85% for paramagnetic samples. The contribution of friction forces unrelated to the action of magnetic forces did not exceed 10–15%. A significant share of the drag forces on the MAT side, reaching 25%, was attributed to the magnetic pressing of powder particle groups against the surfaces of ferromagnetic samples near the pole tips within the working area. The features peculiar to the movement of MAT particles in the finishing of ferromagnetic and paramagnetic parts were established. These features define the prevailing friction mechanisms in the finished surface–MAT contact areas, occurring between the side surfaces of the parts and the pole tips. Thus, sliding friction forces prevail in the finishing of ferromagnetic parts, whereas rolling forces dominate for paramagnetic parts, determining the conditions for forming finished surfaces through predominant microcutting or microplastic deformation.

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.

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 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.

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.