Powder Metallurgy and Metal Ceramics最新文献

The electrochemical properties of composite electrodes produced from ZrNi_1.2Mn_0.5Cr_0.2V_0.1 and ZrNi_1.2Mn_0.45Cr_0.2V_0.15 alloys with and without copper powder additions, pressed with alloy-to-copper weight ratios of 1 : 0.5 and 1 : 1, were studied under two discharge modes: discharge to a voltage of 0.85 and 0.7 V between the test electrode and the counter electrode. X-ray diffraction was employed to determine the phase composition of the alloys. An increase in vanadium content by ~1.3 wt.% led to a significant decrease in the amount of the Zr₇Ni₁₀ phase in the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 and ZrNi_1.2Mn_0.45Cr_0.2V_0.15 alloys (~17 and ~8 vol.%, respectively). The activation of the starting electrodes (without copper additions) depends on the amount of this phase with discharge to 0.85 V: the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy electrode, with a higher Zr₇Ni₁₀ content, activated faster. Composite electrodes from both alloys with 1 : 1 copper additions discharged to 0.7 V activated at the same rate within eight cycles, indicating that activation in these conditions does not depend on the Zr₇Ni₁₀ content. The substitution of manganese with vanadium slightly decreased the maximum discharge capacity of the electrodes (with and without copper powder additions) under both discharge modes. When discharged to 0.7 V relative to the Ni(OH)₂ electrode (or ~0.4 V relative to the Hg/HgO electrode), both alloy electrodes, with and without copper powder additions, preserved their cyclic stability and showed accelerated activation compared to discharge at 0.85 V. The maximum discharge capacity was achieved with 1 : 1 copper additions and discharge to 0.7 V: 385 mA · h/g for the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy and 400 mA · h/g for the ZrNi_1.2Mn_0.45Cr_0.2V_0.15 alloy (versus ~280 mA · h/g at 0.85 V). Thus, a lower manganese content, along with an accordingly higher vanadium content (~1.3 wt.%), only slightly reduced the maximum discharge capacity of the electrodes and slowed their activation in the absence of catalytic additions. The activation of the starting electrodes produced from both alloys depends on the Zr7Ni₁₀ content but does not depend on this phase in the case of 1 : 1 copper additions and discharge to 0.7 V.

The creep-resistant γ-TiAl-based Ti₄₆Al₄₉Nb₄Mo₁ alloy, with a composition close to that of the third- generation TNM alloy, was developed with the powder metallurgy method using titanium hydride and intermetallics as starting materials. The alloy had a duplex structure, with 20–25 μm grains, consisting of 22% α₂ phase and 78% γ phase. No additional phases were detected. Mechanical properties of the powder material at temperatures up to 850°C were studied by compression and bending tests. At a temperature of 20°C, the Ti₄₆Al₄₉Nb₄Mo₁ alloy exhibited a bending strength of 800 MPa and significant high-temperature strength, remaining at a level of 670 MPa at 850°C. The alloy also showed enhanced creep resistance in compression tests, attributed to its fine-grained duplex structure. At temperatures up to 800°C, the alloy demonstrated considerably higher yield stress and strengthened more rapidly than the three-component material. Creep testing of the Ti₄₆Al₄₉Nb₄Mo₁ alloy between 750 and 800°C indicated increased high-temperature creep resistance. The strain rate sensitivity remained unchanged at both 750°C and at 800°C under all applied loads, suggesting an invariant deformation mechanism. The calculated thermal activation parameters for creep were in good agreement with data for cast alloys of this class. The mechanical properties of the Ti₄₆Al₄₉Nb₄Mo₁ alloy indicate its potential for use at temperatures up to 800°C.

This study focuses on synthesizing and characterizing CaSnO₃:Bi²⁺ near-infrared (NIR) long persistent luminescent materials. NIR persistent luminescent materials enable safe and efficient imaging due to their deep tissue penetration and reduced phototoxicity compared to ultraviolet (UV) excited materials. The CaSnO₃:Bi²⁺ materials were synthesized using a high-temperature solid-state method. The effects of varying Bi²⁺ doping concentrations (1, 2, 5, 7, and 10%) on the material’s properties were systematically investigated. The synthesis process was confirmed by X-ray diffraction (XRD) analysis, revealing a perovskite structure for all samples. Scanning electron microscopy (SEM) analysis indicated uniform particle sizes of approximately 1 μm, successfully incorporating Bi²⁺ ions confirmed by energy-dispersive X-ray spectroscopy (EDS). The luminescent properties of the CaSnO₃:Bi²⁺ materials were characterized using fluorescence spectroscopy and thermoluminescence spectroscopy. The excitation and emission spectra showed peaks at 260, 620, and 680 nm, corresponding to the transitions of Bi²⁺ ions. The samples exhibited NIR persistent luminescence under 260 nm excitation, with the CaSnO₃:5% Bi²⁺ sample demonstrating the highest phosphorescence intensity and longest decay time. This optimal performance was attributed to the highest trap concentration, confirmed by thermoluminescence spectroscopy. The persistent NIR luminescence of the CaSnO₃:Bi²⁺ materials was attributed to trap level up-conversion, a phenomenon where NIR excitation leads to NIR emission without the involvement of up-conversion materials. This mechanism arises from the reverse carrier transition from deep traps (DTs) to shallow traps (STs). Thermoluminescence spectroscopy further confirmed the occurrence of trap level up-conversion in the CaSnO₃:5% Bi²⁺ sample. The successful synthesis and characterization of CaSnO₃:Bi²⁺NIR long persistent luminescent materials with trap level up-conversion mechanisms opens up new avenues for their application in various fields.

This paper examines the relative merits of integral and traditional segmented compaction concerning three key aspects: uniformity of relative density, distribution of low-density areas, and the influence of loading mode on relative density. Under the actual operational conditions and anticipated dimensions of the final product, the initial dimensions of the material and the surface pressure applied before compaction are calculated. The average relative density and relative density distribution of circular titanium electrode blocks with different diameters (450, 500, and 550 mm) and different compaction processes were analyzed in the densification process. The impact of lubrication on the relative density distribution was investigated by modifying the coefficient of friction from 0.7 to 0.5, 0.3, and 0.1. The findings indicate that the electrode block's diameter significantly influences the relative density distribution. When the diameter exceeds 500 mm, it is imperative to pay particular attention to the low-density area (less than 0.7), which exhibits a notable increase from 0.42 to 1.71% in unidirectional compaction and from 0.02 to 0.18% in bidirectional compaction when the integral method is employed. Accordingly, the reduction in slag volume resulting from this factor should be considered when using the integral compaction method. In the case of electrode blocks with a diameter of 800 mm, the percentage of relative density between 0.7 and 0.8 under bidirectional compaction is higher than that under unidirectional one. However, the results were contrary in the range of 0.8 to 0.9. Compared to the integral method, the segmented method exhibited a comparable trend, with a percentage of relative density between 0.7 and 0.8, reaching 86.03% and a percentage of less than 0.7, equaling 0%. Furthermore, the core density of the segmented method is also higher than that of the integral one and has a standard deviation of approximately half that of the integral method. It indicates that in the case of uniform mixing, the uniformity of the segmented compaction is superior, and segregation is not readily produced. The standard deviation of the relative density distribution decreased with a reduction in the coefficient of friction, suggesting that the lubricant addition is beneficial in enhancing the uniformity of the density.

The thermokinetics of recrystallization processes that occur during the heating of porous compacts, produced by cold pressing a mixture of ultrapure aluminum and iron powders in a 50: 50 ratio in a steel die, was experimentally studied. Over the 130–190°C temperature range, the aluminum component of the mixture undergoes relaxation, exhibiting wave-like behavior with a period of 0.2– 0.3 sec. Complete recrystallization occurs within the 165–235°C range. Subsequently, the relaxation process begins in the iron component of the mixture, with the initial stage characterized by nonlinear oscillations, transitioning to the next stage involving wave propagation of thermal energy. There are several periods of changes in wave propagation. The nonlinear wave-like rise in temperature during relaxation typically ends with another surge of energy release when the temperature rise period shortens, indicating more intense heat release. At its initial stage, the recrystallization process shows stationary linear behavior, which later transitions to the emergence of nonlinear waves. Changes in wave frequency are observed, along with intermittent wave behavior, suggesting the turbulence of thermal flows. Following this regime, the temperature increases up to the melting point of aluminum. However, complete melting does not occur because of crystallization within lower-temperature regions. All transitions marked by changes in thermokinetic paths at both relaxation and recrystallization stages are accompanied by bifurcation changes in the amplitude of the thermal waves.

The influence of heat treatment temperature of the starting powders, ranging from 400 to 1450°C, on the consolidation of zirconia-toughened alumina (ZTA) composites was studied. In these composites, particles of a ZrO₂ (Y₂O₃, CeO₂) solid solution with high fracture toughness are dispersed in an Al₂O₃ matrix. The powders for developing the ZTA composites (wt.%)—90 Al₂O₃–10 (ZrO₂ (Y₂O₃,CeO₂) (90 AZK) and 70 Al₂O₃–30 (ZrO₂ (Y₂O₃,CeO₂) (70 AZK)—were produced using a combination of hydrothermal synthesis and mechanical mixing. Cold uniaxial pressing and sintering in air at 1600°C for 1.5 h were employed for the consolidation. The sintered materials were examined by X-ray diffraction and scanning electron microscopy. The compaction of the composites was associated with the brittle fracture of hard sintered agglomerates (for 90 AZK) and with the plastic deformation effect (for 70 AZK). The sintering of the 90 AZK and 70 AZK composites was accompanied with ZrO₂ phase transformations, abnormal growth of the Al₂O₃ grains, and zonal segregation effect. The Zener pinning effect in the 70 AZK composites inhibited the abnormal growth of Al₂O₃ grains. The increased porosity of the 90 AZK composites was due to the bimodal distribution of the starting powder agglomerates in accordance with the shape factor. The Vickers hardness of the 90 AZK samples varied from 6.4 to 4.4 GPa and that of the 70 AZK samples from 10.3 to 7.2 GPa. The decreased hardness of the 90 AZK composites was attributed to the formation of a two-scale porous microstructure. The topological memory of the ceramics was demonstrated to determine the conditions for microstructural design of advanced ZTA composites for tool, structural, and functional purposes with the required properties.

Powder metallurgy (PM) is a manufacturing approach that enables the production of complex shapes with minimal waste. This approach allows for creating intricate and readily deployable components, often surpassing the capabilities of traditional casting and metal forming techniques. The present study explores the feasibility of employing friction stir spot welding (FSSW) to join aluminum alloy 6061 (AA6061) components fabricated using the PM route. The research involves fabricating AA6061 samples employing the PM process. The sintering process involved induction heating at 530–550°C, followed by hot forging, ensuring optimal densification. FSSW was applied to both PM-processed and conventionally wrought AA6061 samples using three welding parameters. Comparative evaluations focused on the resulting welds’ microstructural characteristics and mechanical properties. Microstructural analysis revealed that PM-fabricated samples exhibited finer grain structures and superior hardness within the weld zones than their wrought counterparts. Furthermore, the thermomechanically affected zone (TMAZ) was narrower in PM-processed joints, indicating enhanced mechanical properties and a more uniform microstructure. The hardness values witnessed in the FSSW of the PM-processed Al 6061 point to the formation of superior-quality joints when compared to FSSW-welded sections of sheets produced through conventional means. This study highlights the potential of PM-fabricated AA6061 for advanced welding applications, demonstrating notable improvements in microstructural refinement and joint quality, integrating PM techniques with advanced welding processes to overcome traditional manufacturing limitations.

15 Cr ferritic oxide dispersion strengthened (ODS) steels are considered prime fuel cladding materials in nuclear reactors due to their excellent creep, swelling, and oxidation resistance. In the present study, the nominal compositions Fe–15Cr–2W–xY₂O₃ (x = 0, 0.3, 0.7, and 1.0) of ferritic ODS steels were prepared by mechanical alloying followed by spark plasma sintering. The sintered samples were annealed at different temperatures of 950, 1100, and 1250°C with a holding time of 60 min at respective temperatures. Further, the samples were also annealed at 1100°C for various durations of 0, 60, and 120 min. The role of varying yttria dispersoids and annealing temperatures on the grain growth kinetics, as well as their mechanical properties (hardness and compressive strength), were analyzed. The compressive strength of the sintered samples with varying yttria contents and at elevated temperatures of 600 and 700°C was determined. Modeling of compressive yield strength at room and elevated temperatures, as well as a correlation with the experimental values, were established for all the compositions. The grain growth exponent (n) and activation energy (Q) rose with the increase in yttria content and were estimated to be 11.52 and 612.91 kJ/mol, respectively, with 1.0 wt.% yttria. The grain size was nearly stable at the annealing temperature of 1100°C. A significant rise in compressive strength at room temperature and elevated temperatures was observed with a yttria reinforcement content of 0.7 wt.%. According to the strength model at different conditions, the role of ultrafine grains and dispersoids seemed to be predominant at room temperature and high temperatures, respectively.

The detonation spraying of coatings from fine composite materials is analyzed in the paper. The use of detonation coatings was found to improve the properties of machines and mechanisms and extend their life, while their functional performances are maintained over long-term operation. The structural features, strength, and fracture toughness of the coatings produced by multichamber detonation spraying from 75 wt.% Cr₃C₂ + 25 wt.% NiCr and Ni–Cr–Fe–B–Si (77–81.5 wt.% Ni, 10–14 wt.% Cr, 5–7 wt.% Fe, 2.0–2.3 wt.% B, 2.0–3.2 wt.% Si, 0.5 wt.% C) powder materials were examined. Changes in the detonation spraying parameters were proved to significantly influence the structure of the coatings: microhardness, phase composition, volume content of lamellae, sizes of grains and subgrains, phase formation, and dislocation density. The structural and phase state of the coatings was studied at all structural levels using a comprehensive approach, involving light and scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The prospects of the multichamber detonation spraying method, ensuring the necessary combination of structural and phase parameters of the coating material with a simultaneous increase in their physical, mechanical, and operational properties, were demonstrated. A high level of strengthening and fracture toughness of the coatings was promoted by optimal structural and phase constituents: fine grain and subgrain structure, uniform distribution of nanosized strengthening particles, and uniform dislocation density. The improved fracture toughness of the coatings is due to the absence of extended structural areas of dislocation clusters. The gradient-free distribution of dislocation density prevents the formation of local internal stress concentrators in the resulting coatings.

The powders produced by plasma-arc wire atomization in an argon atmosphere or air were studied for their use in 3D printing of complex-shaped metal parts and in granular metallurgy. The dependence of the morphology, structure, phase composition, and microhardness of the powders on the current and atomization conditions was established. In all studied operating modes of the plasma torch (180, 220, and 270 A), the atomized particles are predominantly spherical. The number of nonspherical particles increases with particle size. The powders atomized in an argon atmosphere exhibit a stable phase composition. The main component is iron aluminide Fe₃Al (or a mixture of Fe₃Al and AlFe). The α-Fe, Fe₃O₄, and Fe₂O₃ phases were also found. At currents of 220 and 270 A, the powder in –200+100 μm fraction contains the highest amount of aluminides, 83.88 and 86.30 wt.%, and the lowest content of oxides, 6.61–10.18 wt.%. In fine powders (–100+75 μm), the content of aluminides is 70.38– 28.3 wt.%), but the amount of oxides increases to 23.32–29.62 wt.%. The microhardness of oxide particles (5320–8150 MPa) is higher than that of metal particles (3070–4590 MPa). In atomization in air, the key components are Fe₂O₃, Fe₃O₄, FeO, and Al₃O₄. The total amount of oxides reaches 57.19–90.34%. The percentage of iron aluminides decreases significantly, and their maximum content (28.3 wt.%) is shown by the –315+200 μm powder at a plasma torch current of 270 A. In the finest powder fraction of –100+75 μm, the content of aluminides ranges from 6.2 to 15.36 wt.%. The average microhardness of metal particles is much lower (2750–4940 MPa) than that of oxide particles (4500–7460 MPa). It was found that the best material in terms of phase composition, structure, hardness, and shape factor was produced by atomization of a flux-cored wire in an argon atmosphere. In atomization in air, intense oxidation processes occur.